is time travel two words

A beginner's guide to time travel

Learn exactly how Einstein's theory of relativity works, and discover how there's nothing in science that says time travel is impossible.

Everyone can travel in time . You do it whether you want to or not, at a steady rate of one second per second. You may think there's no similarity to traveling in one of the three spatial dimensions at, say, one foot per second. But according to Einstein 's theory of relativity , we live in a four-dimensional continuum — space-time — in which space and time are interchangeable.

Einstein found that the faster you move through space, the slower you move through time — you age more slowly, in other words. One of the key ideas in relativity is that nothing can travel faster than the speed of light — about 186,000 miles per second (300,000 kilometers per second), or one light-year per year). But you can get very close to it. If a spaceship were to fly at 99% of the speed of light, you'd see it travel a light-year of distance in just over a year of time. 

That's obvious enough, but now comes the weird part. For astronauts onboard that spaceship, the journey would take a mere seven weeks. It's a consequence of relativity called time dilation , and in effect, it means the astronauts have jumped about 10 months into the future. 

Traveling at high speed isn't the only way to produce time dilation. Einstein showed that gravitational fields produce a similar effect — even the relatively weak field here on the surface of Earth . We don't notice it, because we spend all our lives here, but more than 12,400 miles (20,000 kilometers) higher up gravity is measurably weaker— and time passes more quickly, by about 45 microseconds per day. That's more significant than you might think, because it's the altitude at which GPS satellites orbit Earth, and their clocks need to be precisely synchronized with ground-based ones for the system to work properly. 

The satellites have to compensate for time dilation effects due both to their higher altitude and their faster speed. So whenever you use the GPS feature on your smartphone or your car's satnav, there's a tiny element of time travel involved. You and the satellites are traveling into the future at very slightly different rates.

But for more dramatic effects, we need to look at much stronger gravitational fields, such as those around black holes , which can distort space-time so much that it folds back on itself. The result is a so-called wormhole, a concept that's familiar from sci-fi movies, but actually originates in Einstein's theory of relativity. In effect, a wormhole is a shortcut from one point in space-time to another. You enter one black hole, and emerge from another one somewhere else. Unfortunately, it's not as practical a means of transport as Hollywood makes it look. That's because the black hole's gravity would tear you to pieces as you approached it, but it really is possible in theory. And because we're talking about space-time, not just space, the wormhole's exit could be at an earlier time than its entrance; that means you would end up in the past rather than the future.

Trajectories in space-time that loop back into the past are given the technical name "closed timelike curves." If you search through serious academic journals, you'll find plenty of references to them — far more than you'll find to "time travel." But in effect, that's exactly what closed timelike curves are all about — time travel

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There's another way to produce a closed timelike curve that doesn't involve anything quite so exotic as a black hole or wormhole: You just need a simple rotating cylinder made of super-dense material. This so-called Tipler cylinder is the closest that real-world physics can get to an actual, genuine time machine. But it will likely never be built in the real world, so like a wormhole, it's more of an academic curiosity than a viable engineering design.

Yet as far-fetched as these things are in practical terms, there's no fundamental scientific reason — that we currently know of — that says they are impossible. That's a thought-provoking situation, because as the physicist Michio Kaku is fond of saying, "Everything not forbidden is compulsory" (borrowed from T.H. White's novel, "The Once And Future King"). He doesn't mean time travel has to happen everywhere all the time, but Kaku is suggesting that the universe is so vast it ought to happen somewhere at least occasionally. Maybe some super-advanced civilization in another galaxy knows how to build a working time machine, or perhaps closed timelike curves can even occur naturally under certain rare conditions.

This raises problems of a different kind — not in science or engineering, but in basic logic. If time travel is allowed by the laws of physics, then it's possible to envision a whole range of paradoxical scenarios . Some of these appear so illogical that it's difficult to imagine that they could ever occur. But if they can't, what's stopping them? 

Thoughts like these prompted Stephen Hawking , who was always skeptical about the idea of time travel into the past, to come up with his "chronology protection conjecture" — the notion that some as-yet-unknown law of physics prevents closed timelike curves from happening. But that conjecture is only an educated guess, and until it is supported by hard evidence, we can come to only one conclusion: Time travel is possible.

A party for time travelers 

Hawking was skeptical about the feasibility of time travel into the past, not because he had disproved it, but because he was bothered by the logical paradoxes it created. In his chronology protection conjecture, he surmised that physicists would eventually discover a flaw in the theory of closed timelike curves that made them impossible. 

In 2009, he came up with an amusing way to test this conjecture. Hawking held a champagne party (shown in his Discovery Channel program), but he only advertised it after it had happened. His reasoning was that, if time machines eventually become practical, someone in the future might read about the party and travel back to attend it. But no one did — Hawking sat through the whole evening on his own. This doesn't prove time travel is impossible, but it does suggest that it never becomes a commonplace occurrence here on Earth.

The arrow of time 

One of the distinctive things about time is that it has a direction — from past to future. A cup of hot coffee left at room temperature always cools down; it never heats up. Your cellphone loses battery charge when you use it; it never gains charge. These are examples of entropy , essentially a measure of the amount of "useless" as opposed to "useful" energy. The entropy of a closed system always increases, and it's the key factor determining the arrow of time.

It turns out that entropy is the only thing that makes a distinction between past and future. In other branches of physics, like relativity or quantum theory, time doesn't have a preferred direction. No one knows where time's arrow comes from. It may be that it only applies to large, complex systems, in which case subatomic particles may not experience the arrow of time.

Time travel paradox 

If it's possible to travel back into the past — even theoretically — it raises a number of brain-twisting paradoxes — such as the grandfather paradox — that even scientists and philosophers find extremely perplexing.

Killing Hitler

A time traveler might decide to go back and kill him in his infancy. If they succeeded, future history books wouldn't even mention Hitler — so what motivation would the time traveler have for going back in time and killing him?

Killing your grandfather

Instead of killing a young Hitler, you might, by accident, kill one of your own ancestors when they were very young. But then you would never be born, so you couldn't travel back in time to kill them, so you would be born after all, and so on … 

A closed loop

Suppose the plans for a time machine suddenly appear from thin air on your desk. You spend a few days building it, then use it to send the plans back to your earlier self. But where did those plans originate? Nowhere — they are just looping round and round in time.

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Andrew May holds a Ph.D. in astrophysics from Manchester University, U.K. For 30 years, he worked in the academic, government and private sectors, before becoming a science writer where he has written for Fortean Times, How It Works, All About Space, BBC Science Focus, among others. He has also written a selection of books including Cosmic Impact and Astrobiology: The Search for Life Elsewhere in the Universe, published by Icon Books.

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Is Time Travel Possible?

We all travel in time! We travel one year in time between birthdays, for example. And we are all traveling in time at approximately the same speed: 1 second per second.

We typically experience time at one second per second. Credit: NASA/JPL-Caltech

NASA's space telescopes also give us a way to look back in time. Telescopes help us see stars and galaxies that are very far away . It takes a long time for the light from faraway galaxies to reach us. So, when we look into the sky with a telescope, we are seeing what those stars and galaxies looked like a very long time ago.

However, when we think of the phrase "time travel," we are usually thinking of traveling faster than 1 second per second. That kind of time travel sounds like something you'd only see in movies or science fiction books. Could it be real? Science says yes!

This image from the Hubble Space Telescope shows galaxies that are very far away as they existed a very long time ago. Credit: NASA, ESA and R. Thompson (Univ. Arizona)

How do we know that time travel is possible?

More than 100 years ago, a famous scientist named Albert Einstein came up with an idea about how time works. He called it relativity. This theory says that time and space are linked together. Einstein also said our universe has a speed limit: nothing can travel faster than the speed of light (186,000 miles per second).

Einstein's theory of relativity says that space and time are linked together. Credit: NASA/JPL-Caltech

What does this mean for time travel? Well, according to this theory, the faster you travel, the slower you experience time. Scientists have done some experiments to show that this is true.

For example, there was an experiment that used two clocks set to the exact same time. One clock stayed on Earth, while the other flew in an airplane (going in the same direction Earth rotates).

After the airplane flew around the world, scientists compared the two clocks. The clock on the fast-moving airplane was slightly behind the clock on the ground. So, the clock on the airplane was traveling slightly slower in time than 1 second per second.

Credit: NASA/JPL-Caltech

Can we use time travel in everyday life?

We can't use a time machine to travel hundreds of years into the past or future. That kind of time travel only happens in books and movies. But the math of time travel does affect the things we use every day.

For example, we use GPS satellites to help us figure out how to get to new places. (Check out our video about how GPS satellites work .) NASA scientists also use a high-accuracy version of GPS to keep track of where satellites are in space. But did you know that GPS relies on time-travel calculations to help you get around town?

GPS satellites orbit around Earth very quickly at about 8,700 miles (14,000 kilometers) per hour. This slows down GPS satellite clocks by a small fraction of a second (similar to the airplane example above).

GPS satellites orbit around Earth at about 8,700 miles (14,000 kilometers) per hour. Credit: GPS.gov

However, the satellites are also orbiting Earth about 12,550 miles (20,200 km) above the surface. This actually speeds up GPS satellite clocks by a slighter larger fraction of a second.

Here's how: Einstein's theory also says that gravity curves space and time, causing the passage of time to slow down. High up where the satellites orbit, Earth's gravity is much weaker. This causes the clocks on GPS satellites to run faster than clocks on the ground.

The combined result is that the clocks on GPS satellites experience time at a rate slightly faster than 1 second per second. Luckily, scientists can use math to correct these differences in time.

If scientists didn't correct the GPS clocks, there would be big problems. GPS satellites wouldn't be able to correctly calculate their position or yours. The errors would add up to a few miles each day, which is a big deal. GPS maps might think your home is nowhere near where it actually is!

In Summary:

Yes, time travel is indeed a real thing. But it's not quite what you've probably seen in the movies. Under certain conditions, it is possible to experience time passing at a different rate than 1 second per second. And there are important reasons why we need to understand this real-world form of time travel.

If you liked this, you may like:

Time travel could be possible, but only with parallel timelines

Assistant Professor, Physics, Brock University

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Barak Shoshany does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

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Have you ever made a mistake that you wish you could undo? Correcting past mistakes is one of the reasons we find the concept of time travel so fascinating. As often portrayed in science fiction, with a time machine, nothing is permanent anymore — you can always go back and change it. But is time travel really possible in our universe , or is it just science fiction?

Read more: Curious Kids: is time travel possible for humans?

Our modern understanding of time and causality comes from general relativity . Theoretical physicist Albert Einstein’s theory combines space and time into a single entity — “spacetime” — and provides a remarkably intricate explanation of how they both work, at a level unmatched by any other established theory. This theory has existed for more than 100 years, and has been experimentally verified to extremely high precision, so physicists are fairly certain it provides an accurate description of the causal structure of our universe.

For decades, physicists have been trying to use general relativity to figure out if time travel is possible . It turns out that you can write down equations that describe time travel and are fully compatible and consistent with relativity. But physics is not mathematics, and equations are meaningless if they do not correspond to anything in reality.

Arguments against time travel

There are two main issues which make us think these equations may be unrealistic. The first issue is a practical one: building a time machine seems to require exotic matter , which is matter with negative energy. All the matter we see in our daily lives has positive energy — matter with negative energy is not something you can just find lying around. From quantum mechanics, we know that such matter can theoretically be created, but in too small quantities and for too short times .

However, there is no proof that it is impossible to create exotic matter in sufficient quantities. Furthermore, other equations may be discovered that allow time travel without requiring exotic matter. Therefore, this issue may just be a limitation of our current technology or understanding of quantum mechanics.

The other main issue is less practical, but more significant: it is the observation that time travel seems to contradict logic, in the form of time travel paradoxes . There are several types of such paradoxes, but the most problematic are consistency paradoxes .

A popular trope in science fiction, consistency paradoxes happen whenever there is a certain event that leads to changing the past, but the change itself prevents this event from happening in the first place.

For example, consider a scenario where I enter my time machine, use it to go back in time five minutes, and destroy the machine as soon as I get to the past. Now that I destroyed the time machine, it would be impossible for me to use it five minutes later.

But if I cannot use the time machine, then I cannot go back in time and destroy it. Therefore, it is not destroyed, so I can go back in time and destroy it. In other words, the time machine is destroyed if and only if it is not destroyed. Since it cannot be both destroyed and not destroyed simultaneously, this scenario is inconsistent and paradoxical.

Eliminating the paradoxes

There’s a common misconception in science fiction that paradoxes can be “created.” Time travellers are usually warned not to make significant changes to the past and to avoid meeting their past selves for this exact reason. Examples of this may be found in many time travel movies, such as the Back to the Future trilogy.

But in physics, a paradox is not an event that can actually happen — it is a purely theoretical concept that points towards an inconsistency in the theory itself. In other words, consistency paradoxes don’t merely imply time travel is a dangerous endeavour, they imply it simply cannot be possible.

This was one of the motivations for theoretical physicist Stephen Hawking to formulate his chronology protection conjecture , which states that time travel should be impossible. However, this conjecture so far remains unproven. Furthermore, the universe would be a much more interesting place if instead of eliminating time travel due to paradoxes, we could just eliminate the paradoxes themselves.

One attempt at resolving time travel paradoxes is theoretical physicist Igor Dmitriyevich Novikov’s self-consistency conjecture , which essentially states that you can travel to the past, but you cannot change it.

According to Novikov, if I tried to destroy my time machine five minutes in the past, I would find that it is impossible to do so. The laws of physics would somehow conspire to preserve consistency.

Introducing multiple histories

But what’s the point of going back in time if you cannot change the past? My recent work, together with my students Jacob Hauser and Jared Wogan, shows that there are time travel paradoxes that Novikov’s conjecture cannot resolve. This takes us back to square one, since if even just one paradox cannot be eliminated, time travel remains logically impossible.

So, is this the final nail in the coffin of time travel? Not quite. We showed that allowing for multiple histories (or in more familiar terms, parallel timelines) can resolve the paradoxes that Novikov’s conjecture cannot. In fact, it can resolve any paradox you throw at it.

The idea is very simple. When I exit the time machine, I exit into a different timeline. In that timeline, I can do whatever I want, including destroying the time machine, without changing anything in the original timeline I came from. Since I cannot destroy the time machine in the original timeline, which is the one I actually used to travel back in time, there is no paradox.

After working on time travel paradoxes for the last three years , I have become increasingly convinced that time travel could be possible, but only if our universe can allow multiple histories to coexist. So, can it?

Quantum mechanics certainly seems to imply so, at least if you subscribe to Everett’s “many-worlds” interpretation , where one history can “split” into multiple histories, one for each possible measurement outcome – for example, whether Schrödinger’s cat is alive or dead, or whether or not I arrived in the past.

But these are just speculations. My students and I are currently working on finding a concrete theory of time travel with multiple histories that is fully compatible with general relativity. Of course, even if we manage to find such a theory, this would not be sufficient to prove that time travel is possible, but it would at least mean that time travel is not ruled out by consistency paradoxes.

Time travel and parallel timelines almost always go hand-in-hand in science fiction, but now we have proof that they must go hand-in-hand in real science as well. General relativity and quantum mechanics tell us that time travel might be possible, but if it is, then multiple histories must also be possible.

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April 26, 2023

Is Time Travel Possible?

The laws of physics allow time travel. So why haven’t people become chronological hoppers?

By Sarah Scoles

yuanyuan yan/Getty Images

In the movies, time travelers typically step inside a machine and—poof—disappear. They then reappear instantaneously among cowboys, knights or dinosaurs. What these films show is basically time teleportation .

Scientists don’t think this conception is likely in the real world, but they also don’t relegate time travel to the crackpot realm. In fact, the laws of physics might allow chronological hopping, but the devil is in the details.

Time traveling to the near future is easy: you’re doing it right now at a rate of one second per second, and physicists say that rate can change. According to Einstein’s special theory of relativity, time’s flow depends on how fast you’re moving. The quicker you travel, the slower seconds pass. And according to Einstein’s general theory of relativity , gravity also affects clocks: the more forceful the gravity nearby, the slower time goes.

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“Near massive bodies—near the surface of neutron stars or even at the surface of the Earth, although it’s a tiny effect—time runs slower than it does far away,” says Dave Goldberg, a cosmologist at Drexel University.

If a person were to hang out near the edge of a black hole , where gravity is prodigious, Goldberg says, only a few hours might pass for them while 1,000 years went by for someone on Earth. If the person who was near the black hole returned to this planet, they would have effectively traveled to the future. “That is a real effect,” he says. “That is completely uncontroversial.”

Going backward in time gets thorny, though (thornier than getting ripped to shreds inside a black hole). Scientists have come up with a few ways it might be possible, and they have been aware of time travel paradoxes in general relativity for decades. Fabio Costa, a physicist at the Nordic Institute for Theoretical Physics, notes that an early solution with time travel began with a scenario written in the 1920s. That idea involved massive long cylinder that spun fast in the manner of straw rolled between your palms and that twisted spacetime along with it. The understanding that this object could act as a time machine allowing one to travel to the past only happened in the 1970s, a few decades after scientists had discovered a phenomenon called “closed timelike curves.”

“A closed timelike curve describes the trajectory of a hypothetical observer that, while always traveling forward in time from their own perspective, at some point finds themselves at the same place and time where they started, creating a loop,” Costa says. “This is possible in a region of spacetime that, warped by gravity, loops into itself.”

“Einstein read [about closed timelike curves] and was very disturbed by this idea,” he adds. The phenomenon nevertheless spurred later research.

Science began to take time travel seriously in the 1980s. In 1990, for instance, Russian physicist Igor Novikov and American physicist Kip Thorne collaborated on a research paper about closed time-like curves. “They started to study not only how one could try to build a time machine but also how it would work,” Costa says.

Just as importantly, though, they investigated the problems with time travel. What if, for instance, you tossed a billiard ball into a time machine, and it traveled to the past and then collided with its past self in a way that meant its present self could never enter the time machine? “That looks like a paradox,” Costa says.

Since the 1990s, he says, there’s been on-and-off interest in the topic yet no big breakthrough. The field isn’t very active today, in part because every proposed model of a time machine has problems. “It has some attractive features, possibly some potential, but then when one starts to sort of unravel the details, there ends up being some kind of a roadblock,” says Gaurav Khanna of the University of Rhode Island.

For instance, most time travel models require negative mass —and hence negative energy because, as Albert Einstein revealed when he discovered E = mc 2 , mass and energy are one and the same. In theory, at least, just as an electric charge can be positive or negative, so can mass—though no one’s ever found an example of negative mass. Why does time travel depend on such exotic matter? In many cases, it is needed to hold open a wormhole—a tunnel in spacetime predicted by general relativity that connects one point in the cosmos to another.

Without negative mass, gravity would cause this tunnel to collapse. “You can think of it as counteracting the positive mass or energy that wants to traverse the wormhole,” Goldberg says.

Khanna and Goldberg concur that it’s unlikely matter with negative mass even exists, although Khanna notes that some quantum phenomena show promise, for instance, for negative energy on very small scales. But that would be “nowhere close to the scale that would be needed” for a realistic time machine, he says.

These challenges explain why Khanna initially discouraged Caroline Mallary, then his graduate student at the University of Massachusetts Dartmouth, from doing a time travel project. Mallary and Khanna went forward anyway and came up with a theoretical time machine that didn’t require negative mass. In its simplistic form, Mallary’s idea involves two parallel cars, each made of regular matter. If you leave one parked and zoom the other with extreme acceleration, a closed timelike curve will form between them.

Easy, right? But while Mallary’s model gets rid of the need for negative matter, it adds another hurdle: it requires infinite density inside the cars for them to affect spacetime in a way that would be useful for time travel. Infinite density can be found inside a black hole, where gravity is so intense that it squishes matter into a mind-bogglingly small space called a singularity. In the model, each of the cars needs to contain such a singularity. “One of the reasons that there's not a lot of active research on this sort of thing is because of these constraints,” Mallary says.

Other researchers have created models of time travel that involve a wormhole, or a tunnel in spacetime from one point in the cosmos to another. “It's sort of a shortcut through the universe,” Goldberg says. Imagine accelerating one end of the wormhole to near the speed of light and then sending it back to where it came from. “Those two sides are no longer synced,” he says. “One is in the past; one is in the future.” Walk between them, and you’re time traveling.

You could accomplish something similar by moving one end of the wormhole near a big gravitational field—such as a black hole—while keeping the other end near a smaller gravitational force. In that way, time would slow down on the big gravity side, essentially allowing a particle or some other chunk of mass to reside in the past relative to the other side of the wormhole.

Making a wormhole requires pesky negative mass and energy, however. A wormhole created from normal mass would collapse because of gravity. “Most designs tend to have some similar sorts of issues,” Goldberg says. They’re theoretically possible, but there’s currently no feasible way to make them, kind of like a good-tasting pizza with no calories.

And maybe the problem is not just that we don’t know how to make time travel machines but also that it’s not possible to do so except on microscopic scales—a belief held by the late physicist Stephen Hawking. He proposed the chronology protection conjecture: The universe doesn’t allow time travel because it doesn’t allow alterations to the past. “It seems there is a chronology protection agency, which prevents the appearance of closed timelike curves and so makes the universe safe for historians,” Hawking wrote in a 1992 paper in Physical Review D .

Part of his reasoning involved the paradoxes time travel would create such as the aforementioned situation with a billiard ball and its more famous counterpart, the grandfather paradox : If you go back in time and kill your grandfather before he has children, you can’t be born, and therefore you can’t time travel, and therefore you couldn’t have killed your grandfather. And yet there you are.

Those complications are what interests Massachusetts Institute of Technology philosopher Agustin Rayo, however, because the paradoxes don’t just call causality and chronology into question. They also make free will seem suspect. If physics says you can go back in time, then why can’t you kill your grandfather? “What stops you?” he says. Are you not free?

Rayo suspects that time travel is consistent with free will, though. “What’s past is past,” he says. “So if, in fact, my grandfather survived long enough to have children, traveling back in time isn’t going to change that. Why will I fail if I try? I don’t know because I don’t have enough information about the past. What I do know is that I’ll fail somehow.”

If you went to kill your grandfather, in other words, you’d perhaps slip on a banana en route or miss the bus. “It's not like you would find some special force compelling you not to do it,” Costa says. “You would fail to do it for perfectly mundane reasons.”

In 2020 Costa worked with Germain Tobar, then his undergraduate student at the University of Queensland in Australia, on the math that would underlie a similar idea: that time travel is possible without paradoxes and with freedom of choice.

Goldberg agrees with them in a way. “I definitely fall into the category of [thinking that] if there is time travel, it will be constructed in such a way that it produces one self-consistent view of history,” he says. “Because that seems to be the way that all the rest of our physical laws are constructed.”

No one knows what the future of time travel to the past will hold. And so far, no time travelers have come to tell us about it.

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From millennium-skipping Victorians to phone booth-hopping time traveler teenagers, the term time travel often summons our most fantastic visions of what it means to move through the fourth dimension. But of course you don't need a time machine or a fancy wormhole to jaunt through the years.

As you've probably noticed, we're all constantly engaged in the act of time travel. At its most basic level, time is the rate of change in the universe -- and like it or not, we are constantly undergoing change. We age, the planets move around the sun, and things fall apart.

We measure the passage of time in seconds, minutes, hours and years, but this doesn't mean time flows at a constant rate. In fact Einstein's theory of relativity determines that time is not universal. Just as the water in a river rushes or slows depending on the size of the channel, time flows at different rates in different places. In other words, time is relative.

But what causes this fluctuation along our one-way trek from the cradle to the grave? It all comes down to the relationship between time and space. Human beings frolic about in the three spatial dimensions of length, width and depth. Time joins the party as that most crucial fourth dimension . Time can't exist without space, and space can't exist without time. The two exist as one: the space time continuum . Any event that occurs in the universe has to involve both space and time.

In this article, we'll look at the real-life, everyday methods of time travel in our universe, as well as some of the more far-fetched methods of dancing through the fourth dimension.

Did you know your GPS devices rely on time-travel calculations to help you navigate around town? It's true! GPS satellite clocks are about 3 8 seconds longer per day than a clock closer to earth due to the gravitational frequency shift. They make up for this discrepancy by using time travel calculations or they could be way off from your current location and time.

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Time Travel

There is an extensive literature on time travel in both philosophy and physics. Part of the great interest of the topic stems from the fact that reasons have been given both for thinking that time travel is physically possible—and for thinking that it is logically impossible! This entry deals primarily with philosophical issues; issues related to the physics of time travel are covered in the separate entries on time travel and modern physics and time machines . We begin with the definitional question: what is time travel? We then turn to the major objection to the possibility of backwards time travel: the Grandfather paradox. Next, issues concerning causation are discussed—and then, issues in the metaphysics of time and change. We end with a discussion of the question why, if backwards time travel will ever occur, we have not been visited by time travellers from the future.

1.1 Time Discrepancy

1.2 changing the past, 2.1 can and cannot, 2.2 improbable coincidences, 2.3 inexplicable occurrences, 3.1 backwards causation, 3.2 causal loops, 4.1 time travel and time, 4.2 time travel and change, 5. where are the time travellers, other internet resources, related entries, 1. what is time travel.

There is a number of rather different scenarios which would seem, intuitively, to count as ‘time travel’—and a number of scenarios which, while sharing certain features with some of the time travel cases, seem nevertheless not to count as genuine time travel: [ 1 ]

Time travel Doctor . Doctor Who steps into a machine in 2024. Observers outside the machine see it disappear. Inside the machine, time seems to Doctor Who to pass for ten minutes. Observers in 1984 (or 3072) see the machine appear out of nowhere. Doctor Who steps out. [ 2 ] Leap . The time traveller takes hold of a special device (or steps into a machine) and suddenly disappears; she appears at an earlier (or later) time. Unlike in Doctor , the time traveller experiences no lapse of time between her departure and arrival: from her point of view, she instantaneously appears at the destination time. [ 3 ] Putnam . Oscar Smith steps into a machine in 2024. From his point of view, things proceed much as in Doctor : time seems to Oscar Smith to pass for a while; then he steps out in 1984. For observers outside the machine, things proceed differently. Observers of Oscar’s arrival in the past see a time machine suddenly appear out of nowhere and immediately divide into two copies of itself: Oscar Smith steps out of one; and (through the window) they see inside the other something that looks just like what they would see if a film of Oscar Smith were played backwards (his hair gets shorter; food comes out of his mouth and goes back into his lunch box in a pristine, uneaten state; etc.). Observers of Oscar’s departure from the future do not simply see his time machine disappear after he gets into it: they see it collide with the apparently backwards-running machine just described, in such a way that both are simultaneously annihilated. [ 4 ] Gödel . The time traveller steps into an ordinary rocket ship (not a special time machine) and flies off on a certain course. At no point does she disappear (as in Leap ) or ‘turn back in time’ (as in Putnam )—yet thanks to the overall structure of spacetime (as conceived in the General Theory of Relativity), the traveller arrives at a point in the past (or future) of her departure. (Compare the way in which someone can travel continuously westwards, and arrive to the east of her departure point, thanks to the overall curved structure of the surface of the earth.) [ 5 ] Einstein . The time traveller steps into an ordinary rocket ship and flies off at high speed on a round trip. When he returns to Earth, thanks to certain effects predicted by the Special Theory of Relativity, only a very small amount of time has elapsed for him—he has aged only a few months—while a great deal of time has passed on Earth: it is now hundreds of years in the future of his time of departure. [ 6 ] Not time travel Sleep . One is very tired, and falls into a deep sleep. When one awakes twelve hours later, it seems from one’s own point of view that hardly any time has passed. Coma . One is in a coma for a number of years and then awakes, at which point it seems from one’s own point of view that hardly any time has passed. Cryogenics . One is cryogenically frozen for hundreds of years. Upon being woken, it seems from one’s own point of view that hardly any time has passed. Virtual . One enters a highly realistic, interactive virtual reality simulator in which some past era has been recreated down to the finest detail. Crystal . One looks into a crystal ball and sees what happened at some past time, or will happen at some future time. (Imagine that the crystal ball really works—like a closed-circuit security monitor, except that the vision genuinely comes from some past or future time. Even so, the person looking at the crystal ball is not thereby a time traveller.) Waiting . One enters one’s closet and stays there for seven hours. When one emerges, one has ‘arrived’ seven hours in the future of one’s ‘departure’. Dateline . One departs at 8pm on Monday, flies for fourteen hours, and arrives at 10pm on Monday.

A satisfactory definition of time travel would, at least, need to classify the cases in the right way. There might be some surprises—perhaps, on the best definition of ‘time travel’, Cryogenics turns out to be time travel after all—but it should certainly be the case, for example, that Gödel counts as time travel and that Sleep and Waiting do not. [ 7 ]

In fact there is no entirely satisfactory definition of ‘time travel’ in the literature. The most popular definition is the one given by Lewis (1976, 145–6):

What is time travel? Inevitably, it involves a discrepancy between time and time. Any traveller departs and then arrives at his destination; the time elapsed from departure to arrival…is the duration of the journey. But if he is a time traveller, the separation in time between departure and arrival does not equal the duration of his journey.…How can it be that the same two events, his departure and his arrival, are separated by two unequal amounts of time?…I reply by distinguishing time itself, external time as I shall also call it, from the personal time of a particular time traveller: roughly, that which is measured by his wristwatch. His journey takes an hour of his personal time, let us say…But the arrival is more than an hour after the departure in external time, if he travels toward the future; or the arrival is before the departure in external time…if he travels toward the past.

This correctly excludes Waiting —where the length of the ‘journey’ precisely matches the separation between ‘arrival’ and ‘departure’—and Crystal , where there is no journey at all—and it includes Doctor . It has trouble with Gödel , however—because when the overall structure of spacetime is as twisted as it is in the sort of case Gödel imagined, the notion of external time (“time itself”) loses its grip.

Another definition of time travel that one sometimes encounters in the literature (Arntzenius, 2006, 602) (Smeenk and Wüthrich, 2011, 5, 26) equates time travel with the existence of CTC’s: closed timelike curves. A curve in this context is a line in spacetime; it is timelike if it could represent the career of a material object; and it is closed if it returns to its starting point (i.e. in spacetime—not merely in space). This now includes Gödel —but it excludes Einstein .

The lack of an adequate definition of ‘time travel’ does not matter for our purposes here. [ 8 ] It suffices that we have clear cases of (what would count as) time travel—and that these cases give rise to all the problems that we shall wish to discuss.

Some authors (in philosophy, physics and science fiction) consider ‘time travel’ scenarios in which there are two temporal dimensions (e.g. Meiland (1974)), and others consider scenarios in which there are multiple ‘parallel’ universes—each one with its own four-dimensional spacetime (e.g. Deutsch and Lockwood (1994)). There is a question whether travelling to another version of 2001 (i.e. not the very same version one experienced in the past)—a version at a different point on the second time dimension, or in a different parallel universe—is really time travel, or whether it is more akin to Virtual . In any case, this kind of scenario does not give rise to many of the problems thrown up by the idea of travelling to the very same past one experienced in one’s younger days. It is these problems that form the primary focus of the present entry, and so we shall not have much to say about other kinds of ‘time travel’ scenario in what follows.

One objection to the possibility of time travel flows directly from attempts to define it in anything like Lewis’s way. The worry is that because time travel involves “a discrepancy between time and time”, time travel scenarios are simply incoherent. The time traveller traverses thirty years in one year; she is 51 years old 21 years after her birth; she dies at the age of 100, 200 years before her birth; and so on. The objection is that these are straightforward contradictions: the basic description of what time travel involves is inconsistent; therefore time travel is logically impossible. [ 9 ]

There must be something wrong with this objection, because it would show Einstein to be logically impossible—whereas this sort of future-directed time travel has actually been observed (albeit on a much smaller scale—but that does not affect the present point) (Hafele and Keating, 1972b,a). The most common response to the objection is that there is no contradiction because the interval of time traversed by the time traveller and the duration of her journey are measured with respect to different frames of reference: there is thus no reason why they should coincide. A similar point applies to the discrepancy between the time elapsed since the time traveller’s birth and her age upon arrival. There is no more of a contradiction here than in the fact that Melbourne is both 800 kilometres away from Sydney—along the main highway—and 1200 kilometres away—along the coast road. [ 10 ]

Before leaving the question ‘What is time travel?’ we should note the crucial distinction between changing the past and participating in (aka affecting or influencing) the past. [ 11 ] In the popular imagination, backwards time travel would allow one to change the past: to right the wrongs of history, to prevent one’s younger self doing things one later regretted, and so on. In a model with a single past, however, this idea is incoherent: the very description of the case involves a contradiction (e.g. the time traveller burns all her diaries at midnight on her fortieth birthday in 1976, and does not burn all her diaries at midnight on her fortieth birthday in 1976). It is not as if there are two versions of the past: the original one, without the time traveller present, and then a second version, with the time traveller playing a role. There is just one past—and two perspectives on it: the perspective of the younger self, and the perspective of the older time travelling self. If these perspectives are inconsistent (e.g. an event occurs in one but not the other) then the time travel scenario is incoherent.

This means that time travellers can do less than we might have hoped: they cannot right the wrongs of history; they cannot even stir a speck of dust on a certain day in the past if, on that day, the speck was in fact unmoved. But this does not mean that time travellers must be entirely powerless in the past: while they cannot do anything that did not actually happen, they can (in principle) do anything that did happen. Time travellers cannot change the past: they cannot make it different from the way it was—but they can participate in it: they can be amongst the people who did make the past the way it was. [ 12 ]

What about models involving two temporal dimensions, or parallel universes—do they allow for coherent scenarios in which the past is changed? [ 13 ] There is certainly no contradiction in saying that the time traveller burns all her diaries at midnight on her fortieth birthday in 1976 in universe 1 (or at hypertime A ), and does not burn all her diaries at midnight on her fortieth birthday in 1976 in universe 2 (or at hypertime B ). The question is whether this kind of story involves changing the past in the sense originally envisaged: righting the wrongs of history, preventing subsequently regretted actions, and so on. Goddu (2003) and van Inwagen (2010) argue that it does (in the context of particular hypertime models), while Smith (1997, 365–6; 2015) argues that it does not: that it involves avoiding the past—leaving it untouched while travelling to a different version of the past in which things proceed differently.

2. The Grandfather Paradox

The most important objection to the logical possibility of backwards time travel is the so-called Grandfather paradox. This paradox has actually convinced many people that backwards time travel is impossible:

The dead giveaway that true time-travel is flatly impossible arises from the well-known “paradoxes” it entails. The classic example is “What if you go back into the past and kill your grandfather when he was still a little boy?”…So complex and hopeless are the paradoxes…that the easiest way out of the irrational chaos that results is to suppose that true time-travel is, and forever will be, impossible. (Asimov 1995 [2003, 276–7]) travel into one’s past…would seem to give rise to all sorts of logical problems, if you were able to change history. For example, what would happen if you killed your parents before you were born. It might be that one could avoid such paradoxes by some modification of the concept of free will. But this will not be necessary if what I call the chronology protection conjecture is correct: The laws of physics prevent closed timelike curves from appearing . (Hawking, 1992, 604) [ 14 ]

The paradox comes in different forms. Here’s one version:

If time travel was logically possible then the time traveller could return to the past and in a suicidal rage destroy his time machine before it was completed and murder his younger self. But if this was so a necessary condition for the time trip to have occurred at all is removed, and we should then conclude that the time trip did not occur. Hence if the time trip did occur, then it did not occur. Hence it did not occur, and it is necessary that it did not occur. To reply, as it is standardly done, that our time traveller cannot change the past in this way, is a petitio principii . Why is it that the time traveller is constrained in this way? What mysterious force stills his sudden suicidal rage? (Smith, 1985, 58)

The idea is that backwards time travel is impossible because if it occurred, time travellers would attempt to do things such as kill their younger selves (or their grandfathers etc.). We know that doing these things—indeed, changing the past in any way—is impossible. But were there time travel, there would then be nothing left to stop these things happening. If we let things get to the stage where the time traveller is facing Grandfather with a loaded weapon, then there is nothing left to prevent the impossible from occurring. So we must draw the line earlier: it must be impossible for someone to get into this situation at all; that is, backwards time travel must be impossible.

In order to defend the possibility of time travel in the face of this argument we need to show that time travel is not a sure route to doing the impossible. So, given that a time traveller has gone to the past and is facing Grandfather, what could stop her killing Grandfather? Some science fiction authors resort to the idea of chaperones or time guardians who prevent time travellers from changing the past—or to mysterious forces of logic. But it is hard to take these ideas seriously—and more importantly, it is hard to make them work in detail when we remember that changing the past is impossible. (The chaperone is acting to ensure that the past remains as it was—but the only reason it ever was that way is because of his very actions.) [ 15 ] Fortunately there is a better response—also to be found in the science fiction literature, and brought to the attention of philosophers by Lewis (1976). What would stop the time traveller doing the impossible? She would fail “for some commonplace reason”, as Lewis (1976, 150) puts it. Her gun might jam, a noise might distract her, she might slip on a banana peel, etc. Nothing more than such ordinary occurrences is required to stop the time traveller killing Grandfather. Hence backwards time travel does not entail the occurrence of impossible events—and so the above objection is defused.

A problem remains. Suppose Tim, a time-traveller, is facing his grandfather with a loaded gun. Can Tim kill Grandfather? On the one hand, yes he can. He is an excellent shot; there is no chaperone to stop him; the laws of logic will not magically stay his hand; he hates Grandfather and will not hesitate to pull the trigger; etc. On the other hand, no he can’t. To kill Grandfather would be to change the past, and no-one can do that (not to mention the fact that if Grandfather died, then Tim would not have been born). So we have a contradiction: Tim can kill Grandfather and Tim cannot kill Grandfather. Time travel thus leads to a contradiction: so it is impossible.

Note the difference between this version of the Grandfather paradox and the version considered above. In the earlier version, the contradiction happens if Tim kills Grandfather. The solution was to say that Tim can go into the past without killing Grandfather—hence time travel does not entail a contradiction. In the new version, the contradiction happens as soon as Tim gets to the past. Of course Tim does not kill Grandfather—but we still have a contradiction anyway: for he both can do it, and cannot do it. As Lewis puts it:

Could a time traveler change the past? It seems not: the events of a past moment could no more change than numbers could. Yet it seems that he would be as able as anyone to do things that would change the past if he did them. If a time traveler visiting the past both could and couldn’t do something that would change it, then there cannot possibly be such a time traveler. (Lewis, 1976, 149)

Lewis’s own solution to this problem has been widely accepted. [ 16 ] It turns on the idea that to say that something can happen is to say that its occurrence is compossible with certain facts, where context determines (more or less) which facts are the relevant ones. Tim’s killing Grandfather in 1921 is compossible with the facts about his weapon, training, state of mind, and so on. It is not compossible with further facts, such as the fact that Grandfather did not die in 1921. Thus ‘Tim can kill Grandfather’ is true in one sense (relative to one set of facts) and false in another sense (relative to another set of facts)—but there is no single sense in which it is both true and false. So there is no contradiction here—merely an equivocation.

Another response is that of Vihvelin (1996), who argues that there is no contradiction here because ‘Tim can kill Grandfather’ is simply false (i.e. contra Lewis, there is no legitimate sense in which it is true). According to Vihvelin, for ‘Tim can kill Grandfather’ to be true, there must be at least some occasions on which ‘If Tim had tried to kill Grandfather, he would or at least might have succeeded’ is true—but, Vihvelin argues, at any world remotely like ours, the latter counterfactual is always false. [ 17 ]

Return to the original version of the Grandfather paradox and Lewis’s ‘commonplace reasons’ response to it. This response engenders a new objection—due to Horwich (1987)—not to the possibility but to the probability of backwards time travel.

Think about correlated events in general. Whenever we see two things frequently occurring together, this is because one of them causes the other, or some third thing causes both. Horwich calls this the Principle of V-Correlation:

if events of type A and B are associated with one another, then either there is always a chain of events between them…or else we find an earlier event of type C that links up with A and B by two such chains of events. What we do not see is…an inverse fork—in which A and B are connected only with a characteristic subsequent event, but no preceding one. (Horwich, 1987, 97–8)

For example, suppose that two students turn up to class wearing the same outfits. That could just be a coincidence (i.e. there is no common cause, and no direct causal link between the two events). If it happens every week for the whole semester, it is possible that it is a coincidence, but this is extremely unlikely . Normally, we see this sort of extensive correlation only if either there is a common cause (e.g. both students have product endorsement deals with the same clothing company, or both slavishly copy the same influencer) or a direct causal link (e.g. one student is copying the other).

Now consider the time traveller setting off to kill her younger self. As discussed, no contradiction need ensue—this is prevented not by chaperones or mysterious forces, but by a run of ordinary occurrences in which the trigger falls off the time traveller’s gun, a gust of wind pushes her bullet off course, she slips on a banana peel, and so on. But now consider this run of ordinary occurrences. Whenever the time traveller contemplates auto-infanticide, someone nearby will drop a banana peel ready for her to slip on, or a bird will begin to fly so that it will be in the path of the time traveller’s bullet by the time she fires, and so on. In general, there will be a correlation between auto-infanticide attempts and foiling occurrences such as the presence of banana peels—and this correlation will be of the type that does not involve a direct causal connection between the correlated events or a common cause of both. But extensive correlations of this sort are, as we saw, extremely rare—so backwards time travel will happen about as often as you will see two people wear the same outfits to class every day of semester, without there being any causal connection between what one wears and what the other wears.

We can set out Horwich’s argument this way:

• If time travel were ever to occur, we should see extensive uncaused correlations.
• It is extremely unlikely that we should ever see extensive uncaused correlations.
• Therefore time travel is extremely unlikely to occur.

The conclusion is not that time travel is impossible, but that we should treat it the way we treat the possibility of, say, tossing a fair coin and getting heads one thousand times in a row. As Price (1996, 278 n.7) puts it—in the context of endorsing Horwich’s conclusion: “the hypothesis of time travel can be made to imply propositions of arbitrarily low probability. This is not a classical reductio, but it is as close as science ever gets.”

Smith (1997) attacks both premisses of Horwich’s argument. Against the first premise, he argues that backwards time travel, in itself, does not entail extensive uncaused correlations. Rather, when we look more closely, we see that time travel scenarios involving extensive uncaused correlations always build in prior coincidences which are themselves highly unlikely. Against the second premise, he argues that, from the fact that we have never seen extensive uncaused correlations, it does not follow that we never shall. This is not inductive scepticism: let us assume (contra the inductive sceptic) that in the absence of any specific reason for thinking things should be different in the future, we are entitled to assume they will continue being the same; still we cannot dismiss a specific reason for thinking the future will be a certain way simply on the basis that things have never been that way in the past. You might reassure an anxious friend that the sun will certainly rise tomorrow because it always has in the past—but you cannot similarly refute an astronomer who claims to have discovered a specific reason for thinking that the earth will stop rotating overnight.

Sider (2002, 119–20) endorses Smith’s second objection. Dowe (2003) criticises Smith’s first objection, but agrees with the second, concluding overall that time travel has not been shown to be improbable. Ismael (2003) reaches a similar conclusion. Goddu (2007) criticises Smith’s first objection to Horwich. Further contributions to the debate include Arntzenius (2006), Smeenk and Wüthrich (2011, §2.2) and Elliott (2018). For other arguments to the same conclusion as Horwich’s—that time travel is improbable—see Ney (2000) and Effingham (2020).

Return again to the original version of the Grandfather paradox and Lewis’s ‘commonplace reasons’ response to it. This response engenders a further objection. The autoinfanticidal time traveller is attempting to do something impossible (render herself permanently dead from an age younger than her age at the time of the attempts). Suppose we accept that she will not succeed and that what will stop her is a succession of commonplace occurrences. The previous objection was that such a succession is improbable . The new objection is that the exclusion of the time traveler from successfully committing auto-infanticide is mysteriously inexplicable . The worry is as follows. Each particular event that foils the time traveller is explicable in a perfectly ordinary way; but the inevitable combination of these events amounts to a ring-fencing of the forbidden zone of autoinfanticide—and this ring-fencing is mystifying. It’s like a grand conspiracy to stop the time traveler from doing what she wants to do—and yet there are no conspirators: no time lords, no magical forces of logic. This is profoundly perplexing. Riggs (1997, 52) writes: “Lewis’s account may do for a once only attempt, but is untenable as a general explanation of Tim’s continual lack of success if he keeps on trying.” Ismael (2003, 308) writes: “Considered individually, there will be nothing anomalous in the explanations…It is almost irresistible to suppose, however, that there is something anomalous in the cases considered collectively, i.e., in our unfailing lack of success.” See also Gorovitz (1964, 366–7), Horwich (1987, 119–21) and Carroll (2010, 86).

There have been two different kinds of defense of time travel against the objection that it involves mysteriously inexplicable occurrences. Baron and Colyvan (2016, 70) agree with the objectors that a purely causal explanation of failure—e.g. Tim fails to kill Grandfather because first he slips on a banana peel, then his gun jams, and so on—is insufficient. However they argue that, in addition, Lewis offers a non-causal—a logical —explanation of failure: “What explains Tim’s failure to kill his grandfather, then, is something about logic; specifically: Tim fails to kill his grandfather because the law of non-contradiction holds.” Smith (2017) argues that the appearance of inexplicability is illusory. There are no scenarios satisfying the description ‘a time traveller commits autoinfanticide’ (or changes the past in any other way) because the description is self-contradictory (e.g. it involves the time traveller permanently dying at 20 and also being alive at 40). So whatever happens it will not be ‘that’. There is literally no way for the time traveller not to fail. Hence there is no need for—or even possibility of—a substantive explanation of why failure invariably occurs, and such failure is not perplexing.

3. Causation

Backwards time travel scenarios give rise to interesting issues concerning causation. In this section we examine two such issues.

Earlier we distinguished changing the past and affecting the past, and argued that while the former is impossible, backwards time travel need involve only the latter. Affecting the past would be an example of backwards causation (i.e. causation where the effect precedes its cause)—and it has been argued that this too is impossible, or at least problematic. [ 18 ] The classic argument against backwards causation is the bilking argument . [ 19 ] Faced with the claim that some event A causes an earlier event B , the proponent of the bilking objection recommends an attempt to decorrelate A and B —that is, to bring about A in cases in which B has not occurred, and to prevent A in cases in which B has occurred. If the attempt is successful, then B often occurs despite the subsequent nonoccurrence of A , and A often occurs without B occurring, and so A cannot be the cause of B . If, on the other hand, the attempt is unsuccessful—if, that is, A cannot be prevented when B has occurred, nor brought about when B has not occurred—then, it is argued, it must be B that is the cause of A , rather than vice versa.

The bilking procedure requires repeated manipulation of event A . Thus, it cannot get under way in cases in which A is either unrepeatable or unmanipulable. Furthermore, the procedure requires us to know whether or not B has occurred, prior to manipulating A —and thus, it cannot get under way in cases in which it cannot be known whether or not B has occurred until after the occurrence or nonoccurrence of A (Dummett, 1964). These three loopholes allow room for many claims of backwards causation that cannot be touched by the bilking argument, because the bilking procedure cannot be performed at all. But what about those cases in which it can be performed? If the procedure succeeds—that is, A and B are decorrelated—then the claim that A causes B is refuted, or at least weakened (depending upon the details of the case). But if the bilking attempt fails, it does not follow that it must be B that is the cause of A , rather than vice versa. Depending upon the situation, that B causes A might become a viable alternative to the hypothesis that A causes B —but there is no reason to think that this alternative must always be the superior one. For example, suppose that I see a photo of you in a paper dated well before your birth, accompanied by a report of your arrival from the future. I now try to bilk your upcoming time trip—but I slip on a banana peel while rushing to push you away from your time machine, my time travel horror stories only inspire you further, and so on. Or again, suppose that I know that you were not in Sydney yesterday. I now try to get you to go there in your time machine—but first I am struck by lightning, then I fall down a manhole, and so on. What does all this prove? Surely not that your arrival in the past causes your departure from the future. Depending upon the details of the case, it seems that we might well be entitled to describe it as involving backwards time travel and backwards causation. At least, if we are not so entitled, this must be because of other facts about the case: it would not follow simply from the repeated coincidental failures of my bilking attempts.

Backwards time travel would apparently allow for the possibility of causal loops, in which things come from nowhere. The things in question might be objects—imagine a time traveller who steals a time machine from the local museum in order to make his time trip and then donates the time machine to the same museum at the end of the trip (i.e. in the past). In this case the machine itself is never built by anyone—it simply exists. The things in question might be information—imagine a time traveller who explains the theory behind time travel to her younger self: theory that she herself knows only because it was explained to her in her youth by her time travelling older self. The things in question might be actions. Imagine a time traveller who visits his younger self. When he encounters his younger self, he suddenly has a vivid memory of being punched on the nose by a strange visitor. He realises that this is that very encounter—and resignedly proceeds to punch his younger self. Why did he do it? Because he knew that it would happen and so felt that he had to do it—but he only knew it would happen because he in fact did it. [ 20 ]

One might think that causal loops are impossible—and hence that insofar as backwards time travel entails such loops, it too is impossible. [ 21 ] There are two issues to consider here. First, does backwards time travel entail causal loops? Lewis (1976, 148) raises the question whether there must be causal loops whenever there is backwards causation; in response to the question, he says simply “I am not sure.” Mellor (1998, 131) appears to claim a positive answer to the question. [ 22 ] Hanley (2004, 130) defends a negative answer by telling a time travel story in which there is backwards time travel and backwards causation, but no causal loops. [ 23 ] Monton (2009) criticises Hanley’s counterexample, but also defends a negative answer via different counterexamples. Effingham (2020) too argues for a negative answer.

Second, are causal loops impossible, or in some other way objectionable? One objection is that causal loops are inexplicable . There have been two main kinds of response to this objection. One is to agree but deny that this is a problem. Lewis (1976, 149) accepts that a loop (as a whole) would be inexplicable—but thinks that this inexplicability (like that of the Big Bang or the decay of a tritium atom) is merely strange, not impossible. In a similar vein, Meyer (2012, 263) argues that if someone asked for an explanation of a loop (as a whole), “the blame would fall on the person asking the question, not on our inability to answer it.” The second kind of response (Hanley, 2004, §5) is to deny that (all) causal loops are inexplicable. A second objection to causal loops, due to Mellor (1998, ch.12), is that in such loops the chances of events would fail to be related to their frequencies in accordance with the law of large numbers. Berkovitz (2001) and Dowe (2001) both argue that Mellor’s objection fails to establish the impossibility of causal loops. [ 24 ] Effingham (2020) considers—and rebuts—some additional objections to the possibility of causal loops.

4. Time and Change

Gödel (1949a [1990a])—in which Gödel presents models of Einstein’s General Theory of Relativity in which there exist CTC’s—can well be regarded as initiating the modern academic literature on time travel, in both philosophy and physics. In a companion paper, Gödel discusses the significance of his results for more general issues in the philosophy of time (Gödel 1949b [1990b]). For the succeeding half century, the time travel literature focussed predominantly on objections to the possibility (or probability) of time travel. More recently, however, there has been renewed interest in the connections between time travel and more general issues in the metaphysics of time and change. We examine some of these in the present section. [ 25 ]

The first thing that we need to do is set up the various metaphysical positions whose relationships with time travel will then be discussed. Consider two metaphysical questions:

• Are the past, present and future equally real?
• Is there an objective flow or passage of time, and an objective now?

We can label some views on the first question as follows. Eternalism is the view that past and future times, objects and events are just as real as the present time and present events and objects. Nowism is the view that only the present time and present events and objects exist. Now-and-then-ism is the view that the past and present exist but the future does not. We can also label some views on the second question. The A-theory answers in the affirmative: the flow of time and division of events into past (before now), present (now) and future (after now) are objective features of reality (as opposed to mere features of our experience). Furthermore, they are linked: the objective flow of time arises from the movement, through time, of the objective now (from the past towards the future). The B-theory answers in the negative: while we certainly experience now as special, and time as flowing, the B-theory denies that what is going on here is that we are detecting objective features of reality in a way that corresponds transparently to how those features are in themselves. The flow of time and the now are not objective features of reality; they are merely features of our experience. By combining answers to our first and second questions we arrive at positions on the metaphysics of time such as: [ 26 ]

• the block universe view: eternalism + B-theory
• the moving spotlight view: eternalism + A-theory
• the presentist view: nowism + A-theory
• the growing block view: now-and-then-ism + A-theory.

So much for positions on time itself. Now for some views on temporal objects: objects that exist in (and, in general, change over) time. Three-dimensionalism is the view that persons, tables and other temporal objects are three-dimensional entities. On this view, what you see in the mirror is a whole person. [ 27 ] Tomorrow, when you look again, you will see the whole person again. On this view, persons and other temporal objects are wholly present at every time at which they exist. Four-dimensionalism is the view that persons, tables and other temporal objects are four-dimensional entities, extending through three dimensions of space and one dimension of time. On this view, what you see in the mirror is not a whole person: it is just a three-dimensional temporal part of a person. Tomorrow, when you look again, you will see a different such temporal part. Say that an object persists through time if it is around at some time and still around at a later time. Three- and four-dimensionalists agree that (some) objects persist, but they differ over how objects persist. According to three-dimensionalists, objects persist by enduring : an object persists from t 1 to t 2 by being wholly present at t 1 and t 2 and every instant in between. According to four-dimensionalists, objects persist by perduring : an object persists from t 1 to t 2 by having temporal parts at t 1 and t 2 and every instant in between. Perduring can be usefully compared with being extended in space: a road extends from Melbourne to Sydney not by being wholly located at every point in between, but by having a spatial part at every point in between.

It is natural to combine three-dimensionalism with presentism and four-dimensionalism with the block universe view—but other combinations of views are certainly possible.

Gödel (1949b [1990b]) argues from the possibility of time travel (more precisely, from the existence of solutions to the field equations of General Relativity in which there exist CTC’s) to the B-theory: that is, to the conclusion that there is no objective flow or passage of time and no objective now. Gödel begins by reviewing an argument from Special Relativity to the B-theory: because the notion of simultaneity becomes a relative one in Special Relativity, there is no room for the idea of an objective succession of “nows”. He then notes that this argument is disrupted in the context of General Relativity, because in models of the latter theory to date, the presence of matter does allow recovery of an objectively distinguished series of “nows”. Gödel then proposes a new model (Gödel 1949a [1990a]) in which no such recovery is possible. (This is the model that contains CTC’s.) Finally, he addresses the issue of how one can infer anything about the nonexistence of an objective flow of time in our universe from the existence of a merely possible universe in which there is no objectively distinguished series of “nows”. His main response is that while it would not be straightforwardly contradictory to suppose that the existence of an objective flow of time depends on the particular, contingent arrangement and motion of matter in the world, this would nevertheless be unsatisfactory. Responses to Gödel have been of two main kinds. Some have objected to the claim that there is no objective flow of time in his model universe (e.g. Savitt (2005); see also Savitt (1994)). Others have objected to the attempt to transfer conclusions about that model universe to our own universe (e.g. Earman (1995, 197–200); for a partial response to Earman see Belot (2005, §3.4)). [ 28 ]

Earlier we posed two questions:

Gödel’s argument is related to the second question. Let’s turn now to the first question. Godfrey-Smith (1980, 72) writes “The metaphysical picture which underlies time travel talk is that of the block universe [i.e. eternalism, in the terminology of the present entry], in which the world is conceived as extended in time as it is in space.” In his report on the Analysis problem to which Godfrey-Smith’s paper is a response, Harrison (1980, 67) replies that he would like an argument in support of this assertion. Here is an argument: [ 29 ]

A fundamental requirement for the possibility of time travel is the existence of the destination of the journey. That is, a journey into the past or the future would have to presuppose that the past or future were somehow real. (Grey, 1999, 56)

Dowe (2000, 442–5) responds that the destination does not have to exist at the time of departure: it only has to exist at the time of arrival—and this is quite compatible with non-eternalist views. And Keller and Nelson (2001, 338) argue that time travel is compatible with presentism:

There is four-dimensional [i.e. eternalist, in the terminology of the present entry] time-travel if the appropriate sorts of events occur at the appropriate sorts of times; events like people hopping into time-machines and disappearing, people reappearing with the right sorts of memories, and so on. But the presentist can have just the same patterns of events happening at just the same times. Or at least, it can be the case on the presentist model that the right sorts of events will happen, or did happen, or are happening, at the rights sorts of times. If it suffices for four-dimensionalist time-travel that Jennifer disappears in 2054 and appears in 1985 with the right sorts of memories, then why shouldn’t it suffice for presentist time-travel that Jennifer will disappear in 2054, and that she did appear in 1985 with the right sorts of memories?

Sider (2005) responds that there is still a problem reconciling presentism with time travel conceived in Lewis’s way: that conception of time travel requires that personal time is similar to external time—but presentists have trouble allowing this. Further contributions to the debate whether presentism—and other versions of the A-theory—are compatible with time travel include Monton (2003), Daniels (2012), Hall (2014) and Wasserman (2018) on the side of compatibility, and Miller (2005), Slater (2005), Miller (2008), Hales (2010) and Markosian (2020) on the side of incompatibility.

Leibniz’s Law says that if x = y (i.e. x and y are identical—one and the same entity) then x and y have exactly the same properties. There is a superficial conflict between this principle of logic and the fact that things change. If Bill is at one time thin and at another time not so—and yet it is the very same person both times—it looks as though the very same entity (Bill) both possesses and fails to possess the property of being thin. Three-dimensionalists and four-dimensionalists respond to this problem in different ways. According to the four-dimensionalist, what is thin is not Bill (who is a four-dimensional entity) but certain temporal parts of Bill; and what is not thin are other temporal parts of Bill. So there is no single entity that both possesses and fails to possess the property of being thin. Three-dimensionalists have several options. One is to deny that there are such properties as ‘thin’ (simpliciter): there are only temporally relativised properties such as ‘thin at time t ’. In that case, while Bill at t 1 and Bill at t 2 are the very same entity—Bill is wholly present at each time—there is no single property that this one entity both possesses and fails to possess: Bill possesses the property ‘thin at t 1 ’ and lacks the property ‘thin at t 2 ’. [ 30 ]

Now consider the case of a time traveller Ben who encounters his younger self at time t . Suppose that the younger self is thin and the older self not so. The four-dimensionalist can accommodate this scenario easily. Just as before, what we have are two different three-dimensional parts of the same four-dimensional entity, one of which possesses the property ‘thin’ and the other of which does not. The three-dimensionalist, however, faces a problem. Even if we relativise properties to times, we still get the contradiction that Ben possesses the property ‘thin at t ’ and also lacks that very same property. [ 31 ] There are several possible options for the three-dimensionalist here. One is to relativise properties not to external times but to personal times (Horwich, 1975, 434–5); another is to relativise properties to spatial locations as well as to times (or simply to spacetime points). Sider (2001, 101–6) criticises both options (and others besides), concluding that time travel is incompatible with three-dimensionalism. Markosian (2004) responds to Sider’s argument; [ 32 ] Miller (2006) also responds to Sider and argues for the compatibility of time travel and endurantism; Gilmore (2007) seeks to weaken the case against endurantism by constructing analogous arguments against perdurantism. Simon (2005) finds problems with Sider’s arguments, but presents different arguments for the same conclusion; Effingham and Robson (2007) and Benovsky (2011) also offer new arguments for this conclusion. For further discussion see Wasserman (2018) and Effingham (2020). [ 33 ]

We have seen arguments to the conclusions that time travel is impossible, improbable and inexplicable. Here’s an argument to the conclusion that backwards time travel simply will not occur. If backwards time travel is ever going to occur, we would already have seen the time travellers—but we have seen none such. [ 34 ] The argument is a weak one. [ 35 ] For a start, it is perhaps conceivable that time travellers have already visited the Earth [ 36 ] —but even granting that they have not, this is still compatible with the future actuality of backwards time travel. First, it may be that time travel is very expensive, difficult or dangerous—or for some other reason quite rare—and that by the time it is available, our present period of history is insufficiently high on the list of interesting destinations. Second, it may be—and indeed existing proposals in the physics literature have this feature—that backwards time travel works by creating a CTC that lies entirely in the future: in this case, backwards time travel becomes possible after the creation of the CTC, but travel to a time earlier than the time at which the CTC is created is not possible. [ 37 ]

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causation: backward | free will: divine foreknowledge and | identity: over time | location and mereology | temporal parts | time | time machines | time travel: and modern physics

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Give Merriam Webster the Year You Were Born and They’ll Give You the Hot New Words From Then

Merriam-Webster is giving us all one more way to judge just how much we’ve aged with a new “time traveler” engine on the dictionary brand’s website. Just plug in your birth year, and they’ll show you all the words that were first used in print that year. It’s worth noting that the “First Known Use Date” that they’re going with doesn’t, of course, take into account how long a word was already accepted as part of the spoken vernacular. Rather, it’s based on when it was first published in a print story, journal, article or similar.

All dictionary word entries have notes identifying their origins; many of our words date back to the Old English or Middle English periods. But we’re now in the Modern English period, which goes back to 1500. And thanks to Merriam-Webster’s impressively-organized time traveling engine, we can identify the exact evolution of language year to year.

Most Popular from TIME

While it’s fun to see just what was popping up in language when you were born — “bestie” in 1991, anyone? — it’s also interesting to jump back even further to track our English development. For instance, at the turn of the 20th century words like “tote bag,” “never-never land” and “milk chocolate” entered the dictionary. Move up to 1950 and “Big Brotherism,” “mug shot” and “multimedia” enter the conversation. More recent years have far fewer entries; the only addition to our vocabulary in 2015 was apparently “ aquafaba ,” the liquid that results when beans are cooked in water.

Their portal goes back to the 13th century and before, so you can also check out plenty of older entries.

Merriam-Webster’s latest tool has caught the attention of the internet, where people are eager to share the results of their own birth year word discoveries. Language often influences the way we perceive our world, after all; it’s worth paying attention to the ways our views were shaped by the verbal era we entered.

"website" WOW MERRIAM WEBSTER I HAVE NEVER FELT OLDER. https://t.co/dAlCst8P04 — Eric Stern (@EricWStern) October 25, 2018

good year @MerriamWebster pic.twitter.com/caYlSqTuMe — the slunch (@PenisWright) October 26, 2018

Enjoying this selection of words from my birth year on the @MerriamWebster Time Traveler... "air quotes" https://t.co/YnJtkndLyg pic.twitter.com/jEAexCNURR — Imogen Ruth (@ImogenRH) October 26, 2018

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Time-Travelling with Merriam-Webster’s Dictionary

By Elif Batuman

I like to think that I know a lot of words, but I definitely don’t know all of them. The other day I came across a new one, on page 2 of Michael Robbins’s new book, “ Equipment for Living ,” in a quote from the critic Kenneth Burke: “Surely the most highly alembicated and sophisticated work of art, arising in complex civilizations, could be considered as designed to organize and command the army of one’s thoughts and images.” I did not feel, at first, that I had to look up “alembicated,” because it was clear from the context that the word basically meant “sophisticated,” and also because I knew that an alembic was some kind of glassware, and this seemed, at the time, like enough knowledge. But then I came to a second instance: “I assume that what Burke says about poetry applies, mutatis mutandis, to the songs of Def Leppard, though they are hardly alembicated at all.” This usage sounded somehow more specific than the first, and it made me realize that I didn’t know the lyrics to even one Def Leppard song. Now I felt inadequate, and had to Google something.

I thought for a while about which to investigate, Def Leppard or “alembicated,” and decided on the latter. Indeed, it basically meant “sophisticated,” like something boiled for a long time in an alembic, or, to quote Merriam-Webster , “overrefined as if by excessive distillation.” Then, just as I was about to leave the dictionary’s Web site, I noticed something new: next to the earliest known year that a word appears in print—for “alembicated,” 1786—Merriam-Webster now offers a link to a list of all the other words that were first used in the same year. The feature is called Time Traveler, and it has indeed enabled me to travel in time, because once I start looking at it I find that hours have passed. What could be more bewitching than to see, under a given year , all the words that it birthed, like a squirming litter of word-kittens? In an effort to save the public some of the time I myself have lost in this fashion, I will endeavor to summarize my findings.

The year-by-year lists start with 1500, the rich vintage that gave us “backside,” “brownie,” “cadaver,” “civil law,” and “haircloth.” The fifteenth, fourteenth, thirteenth, and twelfth centuries each have their own lists, as does the catchall “before 12th century,” notable for its outmoded Anglo-Saxon administrative vocabulary—“ wapentake ,” “ witenagemot ”—and for a charming, antiquated term for vocabulary itself: “word-hoard.” Time Traveler comes to a stop in the arids of 2010, a year with only two entries: “Arab Spring” and “gamification.”

One pleasure of searching the lists, I discovered, is to look for apparent anachronisms. I took a childish delight in seeing that “outgoing,” “marshmallow,” and “weird” predate the twelfth century, and that “hamster” and “housecat” both date to 1607. (This fine Shakespearean year also gives us “Banquo,” “flotsam,” “large-hearted,” “Machiavellianism,” “marmot,” and “melancholia.”) “Quixotic” and “Shakespeareana” don’t appear until 1718, in conjunction with “American,” “Franklin stove,” “Hobbesian,” “joint-stock company,” “pukka,” and “unelected”: one feels one is in the age of expansion and imperialism. The first year of the American Revolution, 1775, brings “anti-American,” “free speech,” “Indian grass,” “insurgent,” and “liberalize.” Then, in 1776, a premonitory alphabetic run: “shotgun,” “slaveholder,” “slough of despond.”

In 1790, the year after the French Revolution, “guillotine,” “exterminatory,” “furore,” “sansculotte,” and, ominously, “ lamppost ” enter the fray. The Civil War years see into print “anthrax,” “anti-draft,” “mortarman,” “Old Glory,” and “rebel yell,” as well as “vibrator” and “Wiener schnitzel,” because every era is too complex to allow easy generalization. In 1887, we get “trench warfare” and “department store,” “helicopter” and “mujahideen,” “screwy” and “Statue of Liberty”; 1914 ushers in, all at once, “atomic bomb,” “bad guy,” “Bolshevik,” “gas gangrene,” and “newsreel,” but also “pillow talk” and “raw bar”—life, for some, goes on.

By 1937 (“blitzkrieg,” “scorched earth,” “show trial”), I found myself obsessively combing the lists for strings of found poetry:

boo-boo, borscht belt, B picture, bubble gum, bubkes hydroponics, hyperrealism, ice-cream headache tsk, Turing machine, twinset washateria, widow’s walk, women’s room, yeti

The nineteen-sixties roll around with “after-party,” “diazepam,” and “funny farm.” Every time, it seems, was always the best of times and the worst of times—the time of “Jack Russell terrier” and “Kalashnikov,” “roach clip” and “sudden infant death syndrome,” “self-destruct” and “shell steak.”

Browsing the seventies, I was struck by how the vocabulary of modernity seemed to striate into recurring categories with characteristic voices. Cuisine and geopolitics were cosmopolitan and knowing (“carpaccio,” “chai,” “gulag,” “Moonie”), finance affected to be straight-shooting and square-jawed (“direct deposit,” “junk bond,” “sweat equity”), and fashion invoked comparisons to things that were practical or military (“cargo pocket,” “string bikini”). Workplace lingo was relentlessly jocular (“gotcha,” “wake-up call,” “wimp out”).

I was born in the year of “parachute pants” and “stepparenting,” “bad cholesterol” and “exercise bike,” “brewskis” and “Ebola.” Is it because I was a child then that the lists of the eighties seem to evoke whole worlds? An abridged alphabet of 1982: “ AIDS ,” “barista,” “ couch potato ,” “escape key,” “G-spot,” “immersion blender,” “metalhead,” “phone sex,” “Shiba Inu,” “Valley girl,” “zone out.”

I graduated from college in the year of “bling” and “blog,” “chillax” and “clickbait.” I wrote a dissertation in the year of “bucket list” and “mumblecore,” and finished my Ph.D. in time for “listicles,” “tweeps,” and “sharing economy.” Each of these more recent years gets only a handful of words: 2008 is just “Bitcoin,” “exome,” and “photobomb.” The record, it seems, is still being compiled. ( New entries that don’t yet appear in the dictionary but have been suggested by users in the past few months include “ nothing burger ,” “negging,” “po-po,” and “heteronegativity.”)

Closing the Time Traveler tabs one by one, I found myself back where I started, in 1786, filled with new admiration for the language that, in this solitary year, found time to notice and to name so many creatures great and small—from the “hartebeest” to the “Hessian fly,” from the “millionaire” to the “poverty-stricken,” from the “priapic” to the “pigeon-toed,” from the “lance corporal” to the “niminy-piminy.” I returned to that Burke quote—“Surely the most highly alembicated and sophisticated work of art, arising in complex civilizations, could be considered as designed to organize and command the army of one’s thoughts and images”—and thought it was a fine description of the dictionary.

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By Michael Agger

By Jamie Lauren Keiles

1000-Word Philosophy: An Introductory Anthology

Philosophy, One Thousand Words at a Time

Time Travel

Author: Taylor W. Cyr Category: Metaphysics Word Count: 1000

Time travel is familiar from science fiction and is interesting to philosophers because of the metaphysical issues it raises: the nature of time, causation, personal identity, and freedom, among others. [1]

It’s widely accepted that time travel to the future is possible, but the possibility of backward time travel remains hotly debated. [2] This article will sketch some models of backward time travel (hereafter simply “time travel”) before addressing the main objections to its possibility. [3]

1. Models of Time Travel

According to the standard model of time travel, time is linear so a time traveler’s journey may be depicted along a single timeline, with some events that occur earlier in the timeline’s being experienced as later by the traveler: [4]

On another model, time travel results in the creation of a new universe that branches out from the same trunk (shared past) as the original:

A third model of time travel maintains that there is a second temporal dimension, and so, in addition to times, there are “hyper-times.” [5] On this model, time is more like a plane than like a line, and a time traveler may, in returning to an earlier time, reach that time at a later hyper-time, with the result that the aforementioned time bears different properties at the different hyper-times: [6]

2. Changing the Past

It is natural to suppose that time travel would change the past, which many believe is impossible. Changing the past would require that the past have a certain property at one “time” and then lack that property at another “time.” This is incoherent on the standard model of time travel, which maintains that time is linear (there is no “second time around”), so the standard model precludes changing the past.

But time travel doesn’t require changing the past. We may distinguish changing the past from affecting the past, where the latter requires only that the time traveler’s travels have effects in the past. [7] For example, suppose a time traveler finds her younger self and attempts to convince herself not to time travel. [8] Assuming the standard model of time travel, she will fail to prevent herself from time traveling, but the attempt will affect how the past was “all along,” so to speak. From the outside, the scene will look like an ordinary conversation between two people, but, assuming the time traveler remembers the scene, she will remember an older version of herself trying to convince her not to time travel. [9]

Moreover, according to the other two models of time travel, one and the same time may exist in two different universes or hyper-times, and so it isn’t obviously incoherent to state that some past time may have a property at one “time” (either in one universe, or at one hyper-time) that it lacks at another “time” (in another universe, or at another hyper-time). [10]

3. Causal Loops

Consider some events from the television show Lost . [11] At one point, Richard gives a compass to Locke, telling him to return it the next time they meet. Locke then travels back in time, sees a younger Richard, and returns the compass, which Richard keeps until he gives it to Locke in the aforementioned meeting.

The Lost compass is strange. It was not created in the usual way—in fact, it has no creator! It appeared (with Locke) at time t1 (when it was given to Richard), remained with Richard at a later time t2, and then was given to Locke at t3, when Locke set out for t1, resulting in a “causal loop.” At each time t1-t3, there is a causal explanation for the compass’s presence by reference to the prior stage in the loop. But no explanation can be given for the loop itself. (Where did the compass come from to begin with? There is no answer.)

Now, if such cases are impossible, this might cast doubt on the possibility of time travel. As David Lewis says in response, however, such cases “are not too different from inexplicabilities we are already inured to” such as “God, or the Big Bang, or the decay of a tritium atom,” all of which are “uncaused and inexplicable” (1976: 149).

Note that this objection assumes the standard model of time travel, since these strange loops do not necessarily result from time travel on the other models. Moreover, it may be possible for there to be cases of time travel that don’t generate causal loops even assuming the standard model. [12]

4. Time Travelers’ Abilities

Suppose Tim time travels and attempts to kill his Grandfather before his parents are conceived. Assuming Tim has a gun, is a good shot, etc., it would seem that Tim can kill Grandfather. But Tim can’t kill Grandfather, for doing so would preclude his own existence. Tim both can and can’t kill Grandfather: that’s a contradiction, so we should give up the assumption that led to it, namely that time travel is possible.

This is the Grandfather Paradox, and it is the main objection to the possibility of time travel. Here are two responses, both of which assume the standard model of time travel. [13]

First, one might understand “can” claims like “Tim can kill Grandfather” as claims about what is possible in view of certain facts—and which facts are held fixed is determined by the context of utterance. [14] For example, in view of Tim’s possession of a gun, his reliable aim, etc., it is true that Tim can kill Grandfather. But if we also hold fixed the fact that Grandfather lives , then Tim’s killing Grandfather isn’t possible, and thus he can’t kill Grandfather. So, there is no contradiction; it is true that Tim can kill Grandfather holding certain facts fixed, and it is false holding more fixed, but the claim is not both true and false in the same context. [15]

A second approach denies that Tim can kill Grandfather. [16] This denial follows from certain independently motivated views of agents’ abilities, and it avoids the Paradox by restricting the freedom of time travelers.

5. Conclusion

Perhaps time travel is (metaphysically) possible, but it doesn’t follow that it’s technologically feasible, or that it will ever actually occur. Only time will tell.

[1]   While not the first philosophical discussion of time travel, David Lewis’s classic 1976 essay “The Paradoxes of Time Travel” popularized the subject in metaphysics. For a recent philosophical discussion of time travel—an excellent summary of several facets of the debate, as well as some new developments—see Wasserman (2018).

[2]   By “possibility” I mean metaphysical possibility—consistency with the laws of metaphysics, such as the laws of causation, identity, etc. For more on the discussion of the various senses of possibility we might be asking about in connection with time travel, see Wasserman (2018, chapter 1), and see the rest of the same book for a summary of the debate about the metaphysical possibility of backward time travel.

[3]   There are other objections, but there isn’t space to consider all of them here. One objection concerns its likelihood rather than its possibility . As we will see below, there are certain things that it would seem time travelers cannot do, and so if time travelers attempted the impossible, something would prevent them from succeeding (perhaps the time traveler would have a change of heart, or perhaps she would slip on a banana peel, or…). Horwich (1987) argues that since backward time travel would result in such improbable events, this casts doubt on the likelihood of time travel. See Smith (1997) for discussion and a response to Horwich.

[4]   See the first figure. Reprinted from Wasserman (2018, chapter 3) with permission of Ryan Wasserman and Oxford University Press.

[5]   For developments of the hyper-time model, see Meiland (1974), Goddu (2003), and van Inwagen (2010).

[6]   If we graphed the two dimensions of time on a plane, with the temporal dimension along the x- axis and the hyper-temporal dimension along the y -axis, as in the third figure, time travel would amount to moving leftward (back in time) and upward (forward in hyper-time).

[7]   As Brier explains, “One cannot change the past or undo what has been done. Rather, what is at issue is whether one can affect the past; that is, by a present action cause something to have happened which would not have happened otherwise” (1973: 361).

[8]   For a simple example of this from science-fiction, see the film Interstellar . After leaving Earth, Cooper is able to send messages back in time, and he uses his first message to try to get his daughter to make him stay on Earth, as seen here .

[9]   For another example of affecting (but not changing) the past, see J. K. Rowling’s Harry Potter and the Prisoner of Azkaban . An especially excellent case of time travel occurs toward the end of the book when Hermione takes Harry back in time, allowing him to save himself from Dementors. In the film version, we see Harry attacked by (but saved from) Dementors here , and then we see Hermione take Harry back in time here , and finally, we see Harry save himself here .

[10]   It is contentious whether these models of time travel really allow for changing the past. See Smith (1997, 2015) and Baron (2017) for arguments against, and see Law (Forthcoming) for a response.

[11]   The first of these occurs in the third episode of season five, “Jughead,” from 39:44-41:19,  and the second scene occurs in the first episode of season five, “Because You Left,” from 29:30-34:34.

[12]   For example, suppose I travel back in time by twenty seconds but set my machine to a destination on the other side of the planet. Presumably, my appearance in the past will not have any causal consequences across the globe, despite its occurring twenty seconds earlier than my departure, and thus no causal loop will be generated. For a similar example, see Hanley (2004: 130).

[13]   On the other models, there is no reason to think that Tim can’t kill Grandfather, for doing so would preclude Tim’s future birth in the new timeline (the new branch or hyper-time), but Grandfather would not have been killed in the original, and thus Tim is still born in that timeline.

[14] See Kratzer (1977).

[15]   While Lewis’s (1776: 149-152) influential response to the Paradox also relies on the Kratzer semantics for “can,” his proposed resolution is slightly different, for he sees the fact that Grandfather lives as one that it would be illegitimate to hold fixed. Holding it fixed, he thinks, amounts to “fatalist trickery,” as such a fact “is an irrelevant fact about the future masquerading as a relevant fact about the past” (1976: 151).

[16]   See Vihvelin (1996).

Baron, Sam (2017). “Back to the Unchanging Past,” Pacific Philosophical Quarterly 98: 129–147.

Brier, Bob (1973). “Magicians, Alarm Clocks, and Backward Causation,” Southern Journal of Philosophy 11: 359-364.

Goddu, G. C. (2003). “Time Travel and Changing the Past (or How to Kill Yourself and Live to Tell the Tale),” Ratio 16: 16-32.

Hanley, Richard (2004). “No End in Sight: Causal Loops in Philosophy, Physics, and Fiction,” Synthese 141: 123-152.

Horwich, Paul (1997). Asymmetries In Time: Problems In the Philosophy of Science . Cambridge, MA: MIT Press.

Kratzer, Angelika (1977). “What ‘Must’ and ‘Can’ Must and Can Mean,” Linguistics and Philosophy 1: 337-355.

Law, Andrew (Forthcoming). “The Puzzle of Hyper-Change,” Ratio .

Lewis, David (1976). “The Paradoxes of Time Travel,” American Philosophical Quarterly 13: 145-152.

Meiland, Jack (1974). “A Two-Dimensional Passage Model of Time for Time Travel,” Philosophical Studies 26: 152-173.

Smith, Nicholas J. J. (1997). “Bananas Enough for Time Travel?” The British Journal for the Philosophy of Science 48: 363-389.

Smith, Nicholas J. J. (2015). “Why Time Travellers (Still) Cannot Change the Past,” Revista Portuguesa de Filosofia 71: 677–694.

van Inwagen, Peter (2010). “Changing the Past,” in D. Zimmerman, ed., Oxford Studies in Metaphysics , vol. 5. Oxford: Oxford University Press.

Vihvelin, Kadri (1996). “What Time Travelers Cannot Do,” Philosophical Studies 81: 315-330.

Wasserman, Ryan (2018). Paradoxes of Time Travel . New York: Oxford University Press.

Related Essays

Philosophy of Space and Time: Are  the  Past and Future Real ?  by Dan Peterson

Personal Identity by Chad Vance

Free Will and Free Choice  by Jonah Nagashima

Translation

This essay has been translated into Italian for the Italian cultural magazine  L’Indiscreto .

About the Author

Taylor W. Cyr is an Assistant Professor of Philosophy at Samford University. His main research interests lie at the intersection of ethics and metaphysics, including such topics as free will, moral responsibility, death, and time. His work has appeared in such journals as Ethics , Philosophical Studies , Philosophical Quarterly , and Erkenntnis . TaylorWCyr.com

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Synonyms of travel

• as in to trek
• as in to traverse
• as in to fly
• as in to associate
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Thesaurus Definition of travel

 (Entry 1 of 2)

Synonyms & Similar Words

• peregrinate
• road - trip
• knock (about)
• perambulate
• pass (over)
• cut (across)
• proceed (along)
• get a move on
• make tracks
• shake a leg
• hotfoot (it)
• fast - forward

Antonyms & Near Antonyms

• hang (around or out)
• slow (down or up)
• collaborate
• take up with
• keep company (with)
• rub shoulders (with)
• fall in with
• pal (around)
• rub elbows (with)
• mess around
• be friends with
• interrelate
• confederate
• cold - shoulder

Thesaurus Definition of travel  (Entry 2 of 2)

• peregrination
• commutation

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“Travel.” Merriam-Webster.com Thesaurus , Merriam-Webster, https://www.merriam-webster.com/thesaurus/travel. Accessed 10 May. 2024.

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Time Travel Words

Words related to time travel.

Below is a massive list of time travel words - that is, words related to time travel. The top 4 are: time , space , science fiction and spacetime . You can get the definition(s) of a word in the list below by tapping the question-mark icon next to it. The words at the top of the list are the ones most associated with time travel, and as you go down the relatedness becomes more slight. By default, the words are sorted by relevance/relatedness, but you can also get the most common time travel terms by using the menu below, and there's also the option to sort the words alphabetically so you can get time travel words starting with a particular letter. You can also filter the word list so it only shows words that are also related to another word of your choosing. So for example, you could enter "time" and click "filter", and it'd give you words that are related to time travel and time.

You can highlight the terms by the frequency with which they occur in the written English language using the menu below. The frequency data is extracted from the English Wikipedia corpus, and updated regularly. If you just care about the words' direct semantic similarity to time travel, then there's probably no need for this.

There are already a bunch of websites on the net that help you find synonyms for various words, but only a handful that help you find related , or even loosely associated words. So although you might see some synonyms of time travel in the list below, many of the words below will have other relationships with time travel - you could see a word with the exact opposite meaning in the word list, for example. So it's the sort of list that would be useful for helping you build a time travel vocabulary list, or just a general time travel word list for whatever purpose, but it's not necessarily going to be useful if you're looking for words that mean the same thing as time travel (though it still might be handy for that).

If you're looking for names related to time travel (e.g. business names, or pet names), this page might help you come up with ideas. The results below obviously aren't all going to be applicable for the actual name of your pet/blog/startup/etc., but hopefully they get your mind working and help you see the links between various concepts. If your pet/blog/etc. has something to do with time travel, then it's obviously a good idea to use concepts or words to do with time travel.

If you don't find what you're looking for in the list below, or if there's some sort of bug and it's not displaying time travel related words, please send me feedback using this page. Thanks for using the site - I hope it is useful to you! 🐾

• science fiction
• theory of relativity
• time machine
• novikov self-consistency principle
• h. g. wells
• special relativity
• inertial frame of reference
• general relativity
• arrow of time
• time dilation
• fourth dimension
• the time machine
• time interval
• buy souvenir
• frank tipler
• robert forward
• chronological
• chronograph
• railway time
• time standard
• speed of light
• specious present
• clock watcher
• chronology protection conjecture
• plesiosauria
• exotic matter
• the clock that went backward
• twin paradox
• faster-than-light neutrino anomaly
• half century
• cosmic string
• compossibility
• synchronous
• simultaneity
• time of arrival
• time of departure
• amsterdam time
• morningtide
• crunch time
• between time
• greenwich mean time
• time horizon
• compile time
• time of day
• absolute time
• geological time
• spring break
• new york minute
• time measure
• standard time
• round trip ticket
• time measurement
• supper hour
• time signal
• visit other country
• canonical hour
• time keeper
• quantum mechanics
• mahabharata
• relativity of simultaneity
• mahākāśyapa
• quantum field theory
• einstein field equations
• philosophy of space and time
• gödel metric
• time travel in fiction
• quantum mechanics of time travel
• theoretical physics
• gautama buddha
• urashima tarō
• nihon shoki
• honi ha-m'agel
• louis-sébastien mercier
• washington irving
• rip van winkle
• circumnavigation
• the sleeper awakes
• samuel madden
• memoirs of the twentieth century
• guardian angel
• hypertravel
• alexander veltman
• peregrination
• peregrinate
• alexander the great
• anachronism
• cybertravel
• august derleth
• anonymous author
• simultaneously
• newcastle upon tyne
• synchronization
• charles dickens
• simultaneous
• theretofore
• a christmas carol
• pierre boitard
• edward everett hale
• alternate history
• edward page mitchell
• enrique gaspar y rimbau
• andrew sawyer
• safe-conduct
• closed timelike curve
• timewasting
• chronostratigraphy
• proper time
• interference
• quantum entanglement
• grandfather paradox
• stephen hawking
• fermi paradox
• semiclassical gravity
• experience different culture
• lose something
• see new place
• quantum gravity
• faster than light
• choose destination
• book holiday
• spacetime interval
• go to airport
• reverse commuter
• postulates of special relativity
• hand luggage
• motion sickness
• minkowski diagram
• plane ticket
• tachyonic antitelephone
• father time
• closed time-like curve
• hibernation
• vehicle propulsion
• one-way light time
• round-trip light time
• time weight
• back to the future
• launch window
• time period
• casimir effect
• energy condition
• matt visser
• tipler cylinder
• willem jacob van stockum
• cauchy horizon
• thermoregulation
• delayed choice quantum eraser
• alcubierre drive
• four-dimensionalism
• marlan scully
• fourier analysis
• double-slit experiment
• günter nimtz
• new scientist
• quantum tunneling
• ronald mallett
• university of toronto
• shengwang du
• photonic crystal
• relativistic speed
• time traveler convention
• albert einstein
• frame of reference
• gravity well
• global positioning system
• extraterrestrial life
• miles per hour
• seasonableness
• timekeeping
• go back home
• united states
• kornel lanczos
• weak energy condition
• magnetic field
• university of koblenz
• daylight save time
• st patrick's day

That's about all the time travel related words we've got! I hope this list of time travel terms was useful to you in some way or another. The words down here at the bottom of the list will be in some way associated with time travel, but perhaps tenuously (if you've currenly got it sorted by relevance, that is). If you have any feedback for the site, please share it here , but please note this is only a hobby project, so I may not be able to make regular updates to the site. Have a nice day! 🐓

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Why We Love Time Travel Stories

Time is an instrument of power, an object of faith, and an influence on our history. But in our fictions, it’s more than just a cerebral quagmire—it gets at our unanswerable questions and our deepest longings.

Near the beginning of Kaliane Bradley’s The Ministry of Time , a charmingly clever time-travel romance, the unnamed narrator articulates the standard take on such stories: “Anyone who has ever watched a film with time-travel, or read a book with time-travel, or dissociated on a delayed public transport vehicle by considering the concept of time-travel, will know that the moment you start to think about the physics of it, you are in a crock of shit.”

The organization that gives the novel its title tests the effects of time travel by extracting people from “historical war zones, natural disasters, and epidemics” who “would have died in their own timelines anyway.” The narrator acts as a “bridge” for the “expats” of history, aiding their acclimation. About the mental conundrums that invariably arise, she assures us: “Don’t worry about it.” Logic, after all, goes out the window in stories about, as Mark Twain called it, “the transposition of epochs—and bodies.” Time travel, in other words, is too intellectually challenging for our limited brains.

Time-travel stories repeatedly tell us this. “The technology’s all in the folders in front of you,” the president’s chief of staff tells a table of senators in Timecop . “You won’t understand it any better than I can.” In terms of narrative efficiency, this is an understandable approach to what would ultimately amount to superfluous exposition. For whatever reason, time travel is the fictional technology that movies and novels spend the most time justifying, which leads to shit like this: In the comic The Man Who F*%@ed Up Time , an inventor explains the final ingredient that made his machine work: “that neutrino manifold to stabilize the oscillation frequency of the tachyon harmonics.” Oh, of course ! Why hadn’t I thought of that?

Nowadays, we are all now conscious of and even comfortable with the paradoxes and illogic that stem from time travel. We can casually cite the grandfather and bootstrap paradoxes; we know that matter can’t be in two places at once and that any changes made to the past will have disproportionate (butterfly) effects on the present. As a culture, we’ve grown savvy to (and thus bored of) the perfunctory use of thorny abstractions to legitimize plot points, which is why Bradley’s preemptive dismissal quoted above has become the more common move in contemporary time-travel stories.

For writers, though, time travel is a clusterfuck of narrative assembly. As Dean Craig Pelton weepily laments in an episode of Community , it’s “ really hard to write about.”

Ironically, the device of having characters journey to the past or future resolves more complexities than it pretends to create. Our human longings to make different choices or live beyond the capacities of our bodies, not to mention the endless array of unanswerable questions that constitute our imaginations—it is the impossibility of such yearnings and such inquiries that make us us . In time-travel stories, these are made manifest, the questions answerable, our longings requited. And in doing so, the allure of mystery is replaced by the banality of fact.

Reading The Ministry of Time , it’s difficult not to contemplate the more recent tropes of the genre it playfully skewers but also neatly encapsulates—temporal bureaucracy, fish-out-of-water anachronism, an elaborate vocabulary of techno-jargon—and wonder how the conventions have changed over time. Moreover, Bradley’s novel reminds us how time-travel stories fail to address the many ways time itself—our understanding of it, cultural paradigms about it, its use by powerful entities—determines so much about our lives, our history, and the very foundations of our society. The conceit that time travel is so complicated as to require explicatory condescension from authors belies the truly complex issues revolving around time, sans any fantastical feats. Not only will the great problems at the heart of existence not be fixed by time travel, but such stories rarely even take on those problems, nor the very real dangers and surprisingly wide influence of the construct whose rules they’re ostensibly violating.

So let’s put the two up against each other—time travel versus time—to show that the former is a kind of devil’s advocacy, while the latter is multipronged, with numerous iterations and contradictory attributes. But if we can rethink our reflexive grasp of time, in this life, now, it can do more for us than a novel’s thought experiment—hell, it could do more for us than if time travel actually existed.

The plots of time-travel stories, rather than the theoretical concept of moving through time, are what truly bewilder us—with their doubling and tripling of characters, their narrative contradictions, their constant juggle of story and twist. Watching a brilliantly constructed show like Dark challenges our ability to retain complex developments—characters depicted at various ages, in numerous periods, as well as their parents and children, who, by a miracle of casting, look remarkably similar to the actors playing their kin, making the show feel more realistic but also more confounding.

Confusing us with convoluted plots, though, is different from doing so with the theories from which they derive. In practical reality, the quagmires of time travel run their course rather quickly. Storytellers, on the other hand, push beyond the nonsensical repercussions in search of a way to explain away, incorporate, or ignore the inevitable contradictions and dramatic dead ends. Their dedication to the intricacies of plot can be impressive, to be sure, but it’s nothing more than an elaborate construction festooned with quantum accoutrement. The claims of physics disabuse us of explanations based on our common sense, but they leave nothing to replace them other than a series of vague terms like “branes” and “strings” and “foam” and “blurring.” Physics—like all sciences—aims to discover the laws that govern the universe, but in the eyes of ordinary people, it seems merely to disprove ideas to which we’ve only just grown accustomed. The scientific method operates on the premise that our search is never over, that our assumptions don’t necessarily hold, and that new and better ideas are always on the horizon. Existence in all its naked glory has yet to be completely understood.

Stories, conversely, seek fundamental truths in the messy, incomplete pile of the ways things are. They rummage through what’s there—regardless of its value—and sift out something resembling meaning and purpose. Time travel, then, provides writers with additional mounds of life to contrast with the one belonging to the character’s own period. In Mark Twain’s early take on the genre, A Connecticut Yankee in King Arthur’s Court , a man from the 1880s tries to introduce his era’s ethos to medieval England. In H.G. Wells’s seminal The Time Machine , it’s the economically segregated future that brings relief to the societal ills of the traveler’s present. The Ministry of Time jettisons a Victorian sea commander into near-future England, and what’s wonderful about Bradley’s approach is the leisure it allows itself in tracing the commander’s acclimation to his new temporal circumstances. Bradley has a lot of fun with this setup, giving Commander Gore some hilarious moments, as in the chapter where he returns to his “bridge” (his future-time handler) and asks her, “Some charming young women—out on the heath—addressed me quite boisterously—what is a ‘dilf’?”

Such fish-out-of-water antics are the bread and butter of time-travel narratives, certainly, but they’re also the meeting point of science and literature: The circumstances are brought about by scientific ideas but examined by literary principles. In the years after Wells published The Time Machine , James Gleick writes in his indispensable Time Travel: A History , philosophers scrutinized his concept, despite the fact that Wells “never meant to promulgate a new theory of physics” and would later disappoint admirers with his curt dismissal of time travel’s viability. Gleick quotes Wells from the late 1930s: “The reader got a fine confused sense of immense and different things. The effect of reality is easily produced. One jerks in one or two little unexpected gadgets or so, and the trick is done. It is a trick.”

For Wells’s contemporaries, Gleick notes, “technology had a special persuasive power.” For us, now a quarter of the way through the 21st century, things have grown complicated. Technology governs everything we do, but rather than enhancing our lives, our gadgets seem to exploit us, isolate us, box us in. Moreover, the technology itself has moved beyond our understanding, leaving us dependent on the two or three corporate entities producing it. The World of Tomorrow never arrived; no matter how much technology has progressed, it is still frustratingly Today.

Instead of holding out for a future that will solve our problems, contemporary readers now look into the past to address the wrongs inflicted on the less powerful, so what makes a convincing time-travel story in the 21st century isn’t the verisimilitude of the science but rather the morality of the characters’ intentions. In her book on ’80s movies, Life Moves Pretty Fast , Hadley Freeman notes that in Back to the Future , “Marty’s meddling in the past results in his parents living in a nice house, with chicer furnishings, posher breakfast dishes, and even domestic help in the form of Biff Tannen in 1985. Marty’s triumph is to lift his family up to middle-class status.” If Hollywood rebooted the franchise today, Freeman writes, “Marty’s challenge would be to save the world.” I still think a remake would keep Marty’s adventures confined to his personal bubble; it’s just that instead of reuniting his parents to ensure his existence, his mission would instruct him to meddle in his parents’ past because, down the line, this will save the world. Nowadays, to exploit time travel for personal gain—and indeed to tell a story in which such actions are uncritically celebrated—is unacceptable, as is returning to our discriminatory, segregated, slavery-filled history without seriously grappling with those realities. It’s no longer technology but rather moral conviction that now has a special persuasive power on us.

Not all time-travel stories involve a person literally moving through time. Peggy Sue doesn’t actually go back to high school in Peggy Sue Got Married ; rather, she dreams it (although there is, in another trope, an inexplicable trace of her journey left in the form of a book dedication). In Marge Piercy’s novel A Woman on the Edge of Time , Connie, the Chicano protagonist, is a “catcher” whose “mind and nervous system are open, receptive, to an unusual extent” and can receive messages from “senders” in the future. A similar idea is explored in the film Frequency , in which a son in the late ’90s talks with his dead father in 1969 through a ham radio. Washington Irving’s Rip Van Winkle unwittingly sleeps for 20 years and thus experientially travels through time, but he’s no more jumping ahead than any of us are.

One of the most insightful works on the subject is Ted Chiang’s novella “Story of Your Life” (and Denis Villeneuve’s film adaptation, Arrival) . In both versions, aliens touch down on Earth; as the story unfolds, scientists learn the nuances of their language, which differs from human languages because the aliens experience time non-causally, so they can see the past, present, and future simultaneously. In the film, the purpose of their visit is to help humanity, because they know that in three millennia, they will need our help. What’s fascinating about both versions is how learning the language of the aliens changes the human characters’ fundamental perception of time, freeing them from the limitations of cause and effect. This is, in the film, the gift the aliens traveled across galaxies to give us—language not as a tool that describes how we understand reality, but one that determines how reality appears to us. Moreover, with her newfound time-language, the main character can learn from the future—essentially, time travel as a personal premonition.

The Ministry of Time also explores the relationship between language and time. The ministry hypothesizes that because “language informs experience,” the more an expat assimilates linguistically, “the more likely they would temporally adjust.” In her role as a bridge to Commander Gore, the narrator assiduously updates his vocabulary. She recognizes the appeal of a language-generated reality: “At its heart,” she says, “the theory promised that the raw stuff of the universe could be carved into a clausal household, populated by an extended family of concepts.” When, finally, she stands in the presence of the ministry’s time machine, language abandons her: “Words flex and disperse when I think about it,” she says. “It had a mouth, I think. About it, color was not. About it, space was not.” The ominous object “belched its belly-deep cosmos outward” and “fired time as a rifle fires bullets.” Its shelling “radiated” antagonism and “appeared both constructed and grown.”

A protracted moment of awestruck speechlessness in the face of a time-travel device is actually a staple of the genre, but the narrator’s loss for words is not due to reverence but rather timelessness. If language determines our perception of time, then without time, there is no language.

Just as the term “time travel” includes so many varieties as to render it almost meaningless, the very concept of time is one of the strangest and most mind-boggling precisely because time relates to all things, micro and macro. Bradley isn’t the first writer to menacingly anthropomorphize time. Time is definitely a villain—just not the way we typically think.

The British author J.B. Priestley was a writer haunted by time. (He was also one of the aforementioned fans to be disappointed by Wells.) Born near the end of the Victorian era, Priestley witnessed the final stages of the world’s adoption of standard time just as Einsteinian relativity upended its validity as a concept. Although he channeled much of his wariness onto the stage via his Time Plays—which explored various theories and themes of the subject not through science fiction but human drama—he seems to have saved up a good deal of his anguished energy for his nonfiction work Man and Time , published in 1964. Describing the undertaking as “the hardest task I ever set myself,” Priestley embarks on a personal, passionate, and vigorous examination of society’s relationship to time. He recounts with striking vividness the grandfather clocks of his childhood some six decades earlier. These ominous and ornate contraptions appeared to young Priestley as “half human, half mechanical” beings who “cleared their throats” every hour, kept watch over the children, and introduced the boy to the concept of death when “their gravely deliberate tick-tock, tick-tock … made us wonder what it was that was being tick-tocked away.”

In Priestley’s adolescent view, time is a merciless villain gobbling up the hours until we are no more. The grown-up Priestley takes it further: He imagines a future of “machine-men” who manage to keep pace with the robot overlords. What truly frightens Priestley are “not the machines but these men who were no longer on our side , so convinced they were that it was only a matter of time before machines would be much better than men.” The phrasing here is purposeful:

And a matter of time it really is. For if we really are completely contained within passing time, not able to escape from it with any part of our being, then machines that work faster, are more dependable, and last much longer, may indeed be better than men. But that will only be when we have completely forgotten what men really are, when we have disinherited ourselves perhaps for ever.

He compares the belief in an ever-marching time with conquest, living as if “bulldozing our way to a receding glorious future.”

This criticism recalls one of the charges Friedrich Nietzsche levied against Christianity, with its emphasis on the rewards (or punishments) of the afterlife in exchange for living in a way that goes against nature. Denis Villeneuve’s Dune: Part Two voices the same insight regarding the prophecy of Paul Atreides’s messianic destiny: “You want to control people?” Chani (Zendaya) asks. “Tell them a messiah will come. They’ll wait for centuries.” She’s rightfully dubious: The prophecy does turn out to be a fabrication by a powerful religious cabal planning to prove the prediction true by orchestrating its claims—but Chani’s point would be accurate even if no premonitions came “true.” Prophecies, she tells her fellow Fremen, are tools the powerful use to enslave the powerless. Time can be weaponized.

.css-f6drgc:before{margin:-0.99rem auto 0 -1.33rem;left:50%;width:2.1875rem;border:0.3125rem solid #FF3A30;height:2.1875rem;content:'';display:block;position:absolute;border-radius:100%;} .css-1aglugu{font-family:Lausanne,Lausanne-fallback,Lausanne-roboto,Lausanne-local,Arial,sans-serif;font-size:1.625rem;line-height:1.2;margin:0rem;}@media(max-width: 48rem){.css-1aglugu{font-size:1.75rem;line-height:1.2;}}@media(min-width: 64rem){.css-1aglugu{font-size:2.375rem;line-height:1.2;}}.css-1aglugu b,.css-1aglugu strong{font-family:inherit;font-weight:bold;}.css-1aglugu em,.css-1aglugu i{font-style:italic;font-family:inherit;}.css-1aglugu:before{content:'＂';display:block;padding:0.3125rem 0.875rem 0 0;font-size:3.5rem;line-height:0.8;font-style:italic;font-family:Lausanne,Lausanne-fallback,Lausanne-styleitalic-roboto,Lausanne-styleitalic-local,Arial,sans-serif;} How you see time, what you believe about it, is a major factor in your circumstances.

The literary theorist Mikhail Bakhtin borrowed a metaphor from Einstein in his term “chronotope” (“literally, ‘time space’”), which describes “the intrinsic connectedness” of time and space in fiction. Bakhtin points out something he calls “historical inversion”: a view of time that “locates such categories as purpose, ideal, justice, perfection, the harmonious condition of man and society and the like in the past .” It’s basically Golden Age thinking, and as a result, “the present and even more the past are enriched at the expense of the future.” This is due, Bakhtin argues, to the present and the past containing, in our limited perception, “the force and persuasiveness of reality,” a stirring and convincing characterization of our tendency to privilege the immediacy of now and then —or, as Bakhtin puts it, “the ‘is’ and the ‘was’”—in our understanding of time.

Whether you’re a Fremen looking forward, waiting for salvation, or, conversely, Gil Pender from Midnight in Paris looking backward—traveling to what he considers the greatest era, Paris in the 1920s, only to meet Adriana, who claims the Belle Epoque period was truly the best—in either case, how you see time, what you believe about it, is a major factor in your circumstances.

Consider the ancient Greeks, who believed in a linear time conceived by Aristotle. Their development of concepts like reason and written history, Leonard Shlain argues in his book Art & Physics , “could have taken place only in a civilization that adhered to linear time.”

Or consider Thomas Jefferson, who was, in the words of Christopher Hitchens, “a revolutionary who believed above all in order.” Although he remained “opaque” about his religious beliefs, Jefferson is often attributed “an indeterminate deism, which accepted that the natural order seemed to require a designer but did not necessitate the belief that the said designer actually intervened in human affairs.” The perfect metaphor for deistic rationalism that Jefferson used was the same one William Paley famously used: the watchmaker analogy. This wasn’t merely an Enlightenment notion that Jefferson just happened to agree with; for him, it was the central metaphor for his life. He wrote, in his later years, that he was “an old watch, with a pinion worn here, and a wheel there, until it can go no longer.” Jefferson looked to time as a means to explain the universe, but he also saw in the timepiece a paragon of order that can operate indefinitely without further assistance from its creator—something he wanted to ensure for the new country he helped establish. America, then, is what it is in part because of philosophical views about time.

The same is true of our culture as a whole, defined and regulated as it is by temporal units. This fact relates, yes, to one person’s (incomplete) ideas about time: Isaac Newton.

The end of the 19th century and the beginning of the 20th witnessed a clash between two theories about time that might seem to differ only by degree. In truncated form: Isaac Newton believed there was an absolute time that chugs along independently; Einstein, as James Gleick puts it, proved that time “can be defined, but not absolutely .” Newton’s enormous influence can be seen in the ways the industrial revolution made clockwork of our days, measuring with infinitesimal exactitude what before had been abstract. Einstein’s monumental theories dispelled Newtonian time in favor of a relative spacetime, upending two centuries of thought. But instead of taking us back to the pre-industrial timekeeping of shadows and seasons, relativity thrust us into an uncertain new world in which space can bend and time can slow down. As Bertrand Russell put it in his Einstein guidebook The ABC of Relativity , “What is demanded is a change in our imaginative picture of the world,” a demand that is “always difficult, especially when we are no longer young.”

We still live our lives by clocks, schedules, dates, the varying flotsam of measured time—now, we just know it’s mostly an illusion (lunchtime doubly so), or at least we’re aware that the unceasing momentum of the calendar is more a methodology for productivity than an absolute truth of existence. Time, as it turns out, comes in endless flavors. There is “apparent” time and “mean” time—the former adjusts to the noon sun, while the latter is, per Michael O’Malley in his book Keeping Watch: A History of American Time , “an average of the sun’s daily variation.” Because there is no absolute time, the time that we as localized entities use for measurements is known as “proper” time. There’s “deep time,” a term coined by John McPhee to describe the unimaginable spans of time that geological change requires. On the micro side of things, Planck time is the minimum unit of measurable time before any concept of time ceases to matter.

Stories are organized around causality, and this makes us think that life is, too.

The human scale is measured in seconds, minutes, hours, years, because those are the durations we feel we experience, whereas nanoseconds, on one end, and millennia, on the other, exist only as abstractions to us. But nothing in reality says that our extremely limited and personalized perception of time ought to be the privileged one on which we base our claims about the nature of things way beyond our scope. No time is the time, which means there is no time, only times . The word “time” is how we name our inability to see these dimensions of existence.

These are not the kinds of ideas within the jurisdictions of the Time Enforcement Commission or the Ministry of Time. Of course they aren’t; stories about such dense and unsatisfying notions would be boring, frustrating, emotionally removed. But you can see why it’s funny how, for all their posturing about being complicated, time-travel stories not only fail to live up to the intricacies of time itself, but they usually reaffirm Newtonian time in the guise of destiny or fate. Conclusions are meant to be preordained or paradoxically instigated by future versions of the unwitting participants, because narrative needs the arrow moving in one direction. Stories are organized around causality, and this makes us think that life is, too.

In his essay “Tomorrow Rarely Knows,” Chuck Klosterman observes that although the temptation to travel backward in time would be “electrifying and rational,” it’s ultimately “a desire of weakness.” He writes, “At its nucleus, this is a fantasy about never having to learn anything.” Who, after all, has the authority to decide what should be altered? Even the worst tragedies can, in time, lead to wonderful things. This is why in Avengers: Endgame , when they bring back the billions dusted in the Blip, Tony Stark urges, “Don’t change anything from the last five years.” In the brief aftermath of losing half the population of the universe, humanity found things it didn’t want to let go of.

Time travel is the realm of the desperate, the selfish, the “people who want to solve life’s mysteries without having to do the work,” as Klosterman puts it. If you want to make the world a better place, a quick trip back in time seems much easier than trying to be a better person, or working to help others, or contributing to the beauty that makes time tolerable.

People often assume that peace is only an absence of conflict, rather than a complex state that must be painstakingly forged . Time travel isn’t the right solution because a better world—free of violence, oppression, suffering—is too complex to be achieved with minor adjustments. What’s needed, like Bertrand Russell said, is a change in our imaginative picture of the world. But now, it’s not about us grasping relativity or quantum physics; rather, it’s about recognizing how often our knee-jerk attitude toward time can deprive us of the thing in life we know to be real and true: our present moment. It’s about the lesson that Marcel Proust spends a million words and four-thousand pages learning in the greatest time-travel story ever told, In Search of Lost Time —namely, what he calls “embodied time, of past years not being separated from us.” It’s about seeing as best we can the grand Aristotelian triad— was, is, will be —not as three discrete entities but as one fluid, fluxing plane that bends and breaks and folds and crumples and stretches and rips and whatever else. It’s about learning the language of Ted Chiang’s aliens so that we might, in some way, learn from the future as well as the past. It’s about no longer being satisfied with thought experiments about how to improve existence, and instead demanding and forging changes in the boring, slow, old-fashioned way of traveling through time: living.

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How Fiction Became Edible

The Napkin Project (Love Stories Edition)

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The Napkin Project: Curtis Sittenfeld

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The Napkin Project: Jess Walter

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TIME TRAVEL DESCRIBE WORDS

Found 820 words to describe [time travel] . You can click on each words to see its definition.

• High Season
• Trafficking
• Expenditure
• Documentation
• Single Track
• Aeronautics
• Displacement
• Intercourse
• Move Around
• Package Holiday
• Package Tour
• Perambulate
• Peregrination
• Pullman Car
• Reservation
• Return Ticket
• Thoroughfare
• Transportation
• Travel Along
• Accelerating
• Acceleration
• Anachronism
• Apodiform Bird
• Astronomical Year
• Bill Of Health
• Carry Forward
• Channelling
• Christening
• Chronograph
• Chronometer
• Circulation
• Controlling
• Cytoskeleton
• Double Quick
• Flying Start
• Forestalling
• Get Through
• Giant Slalom
• Instantaneous
• Intercalation
• Neutralized
• Neutron Flux
• Periodicity
• Persistence
• Planetesimal
• Pollen Count
• Prerecorded
• Progression
• Pronunciation
• Quarantined
• Quick March

Adjectives For Time Travel

[time travel] implies to hypothetical or fictional travel at will to the past or the future, typically by means of a machine (a time machine) or a wormhole.

As you can see in the list above, top common adjectives for time travel are: Journey, Traveling, Trip, Voyage, Continue, Holiday, Log, Mak, Make, Speed. Based on our algorithm, there are 820 words to decribe time travel. I hope list of words to describe time travel could help you in improving your vocabulary and enhance your writing skills.

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Netflix’s Time Patrol Bon is a sci-fi anime odyssey about the value of human life

The smallest of actions beget the most profound of consequences

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Most time travel stories are either stories of intervention or preservation; following protagonists attempting to either alter the past to correct for something in the future, or doing everything in their power to return to their own time period without drastically altering the past. Time Patrol Bon sits squarely in the middle, which is exactly what makes it a beloved cult classic manga — and a surprisingly prescient adaptation from Netflix.

Based on the manga by Fujiko Fujio, the comic book-writing duo known for creating the beloved Japanese pop culture icon Doraemon , Time Patrol Bon (stylized on Netflix as T.P Bon ) follows Bon Namihira, an ordinary junior school student living in present-day Japan. He inadvertently crosses paths with a time-traveler named Ream from the future and learns of the existence of Time Patrol, a technologically advanced organization that travels through time and space rescuing innocent lives while maintaining the course of history.

It’s only after discovering Bon plays a pivotal role in the history of humanity that they choose not to erase him from history to protect the secret of Time Patrol’s existence; instead they offer him an opportunity to join their cause. Accompanied by Buyoyon, a sassy, ghost-like extra-dimensional creature, Bon joins Ream as her apprentice as they travel across history saving lives while growing into his new responsibilities as a Time Patrol agent.

It’s a fascinating premise, one that naturally begs a question that’s not all that dissimilar from what multiverse stories often broach: What is the value of a single life in the totality of existence? And who, if anyone, should have the authority to decide that? In the case of Time Patrol Bon , that authority is the Time Patrol Research Office, who are dedicated to finding and saving the lives of individuals who will not impact the course of history. In emphasizing the value of good, but otherwise unhistoric people whose lives were cut short on account of tragic accidents, misunderstandings, or overt malice, T.P Bon makes a case for the abiding value of all life in and of itself, as well as the importance of human relationships.

Take the anime’s eighth episode, wherein Bon and Ream are assigned to save one — and only one — kamikaze pilot during the Battle of Okinawa. Torn between his compassion for all human life and his obligation to uphold Time Patrol’s parameters lest he compromise the organization’s mission and very existence, Bon ultimately resolves that saving any life, even if only one life, is a worthwhile and noble endeavor if it can be done. It’s a really profound moment that nails home both Bon maturing into his responsibilities as a member of a Time Patrol, but also the series’ overall humanistic message. To put it another way: Not everything that is faced can be changed, but that’s not an excuse to do nothing. Even the smallest of actions is worth doing if it contributes to lessening the sum of human suffering.

By his own admission, Bon is an average everyday teenager. He doesn’t have any special powers, isn’t especially physically gifted or academically accomplished, and isn’t even all that popular at his school. From a glance, he barely registers as a footnote in the history of humanity, let alone the grand scheme of existence. If someone like Bon can go on to impact the future of humanity, aside from his role as a member of Time Patrol, then anyone can.

It helps that T.P Bon is helmed by respected animator Masahiro Ando, known for his work as a key animator on 1995’s End of Evangelion and Ghost in the Shell , as well as his own 2007 anime film Sword of the Stranger . Such a resume helps the show be all it wants to be: T.P Bon is an excellent blend of whimsical sci-fi spectacle, drama, and occasional edutainment, with stories featuring Bon and Ream rescuing sailors lost at sea, thwarting prehistoric poachers in the Jurassic period, and even inadvertently inspiring the 16th century legend of Journey to the West. In creating a series that strikes the balance between light-hearted adventure and existential meditation, Ando and studio Bones have delivered not only a faithful and worthy adaptation of Fujiko Fujio’s original manga, but one for the ages.

T.P Bon season 1 is available to stream on Netflix.

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Jared Leto on 'emotional time travel' of singing Thirty Seconds to Mars hits on new tour

Leto said the band is bringing "a new energy and passion" to nostalgic songs.

For Jared Leto , touring the world with his brother Shannon in their band Thirty Seconds to Mars is "one of the great gifts of a lifetime."

The Academy Award-winning actor and frontman spoke to "Good Morning America" from Poland -- which he said he's dubbed "Pierogi Central" -- ahead of the band's first stop on the European leg of its Seasons World Tour and discussed life on the road, his take on nostalgia and the art of the music video.

Though the tour is in support of the band's latest album, "It's the End of the World but It's a Beautiful Day," released in September, Leto said he's looking forward to performing some of their older hits.

"A funny thing happens sometimes when you kind of walk down a different path and you come back to your roots," he said. "We're playing a lot of old songs on the tour and it's almost like they're brand new songs."

Leto said songs like "Attack," "The Kill," "From Yesterday" and the titular track off the band's 2005 album "A Beautiful Lie" are making a comeback alongside new songs like "Stuck" and "Seasons."

"There's an energy around it. You kind of interpret the song differently," he explained of revisiting the classics. "We kind of exhausted them a bit so we needed to set them aside. But now we've come back with a new energy and passion and a new respect for the songs as well."

Leto told "GMA" that leaning into the nostalgic aspect of Thirty Seconds to Mars, which the brothers formed in 1998, is something he views as a "beautiful thing."

"I love nostalgia. Music is a chance to almost time travel in a way. It's like emotional time travel," he said. "I think music's really powerful in that way. It transports us."

The art of the music video

A recent post on the band's social media marked the 18th anniversary of the music video for "The Kill," their biggest hit to date. Leto described the music video as an "homage to 'The Shining'" and a something that changed his and his brother's lives forever.

The forthcoming "Tron: Ares" star said music videos are "kind of a dying art" but represent "one of the few places that you can really do whatever the hell you want to do."

"It's also a chance to kind of either interpret the song or reinterpret the song or change the way that people might think about a certain song," he explained. "For me, the identities of the songs are so tied to the videos of the song."

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Leto said each music video brings back a specific memory. For "A Beautiful Lie" it's the Arctic, while "From Yesterday" is all about China. Of "Stuck," the lead single off their latest album, Leto spoke of shooting the music video in France as "kind of my love letter to Paris and these photographers that influenced me so much."

Time to reintroduce themselves

Leto announced Thirty Seconds to Mars' Seasons World Tour in November in an unexpected way: climbing New York City's famous Empire State Building .

Reflecting on the headline-making feat, the rocker said it was his way of "put[ting] a little showmanship into something that would normally be a press release."

"It's like, why can't we dream a little bit bigger?" he added.

Following their dates in Europe, Thirty Seconds to Mars will head back home to the United States later this summer -- the first time they've toured in the U.S. in six years.

The band's Seasons World Tour is part of Live Nation's Concert Week program, which runs through May 14 and gives fans access to $25 tickets to over 5,000 shows from hundreds of artists, happening all year long. Tickets for select shows are available while supplies last.

"It's been a long time and we're excited to kind of get back out there and, you know, reintroduce ourselves," Leto said. "We're still here."

"It's incredible to be able to do this -- and especially share it with my brother Shannon for this long and to tour the world," he added. "We feel super, super, super lucky. So grateful to be able to do this."

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Client Flyer: Understanding Travel Risks for DACA Holders

AILA provides a client flyer on the travel risks that exist for DACA recipients. There is a generic PDF version and a customizable Word version. Please share widely with your networks. There are two easy ways to use this handout:

• The first and easiest way is to share directly with your clients. To send a client flyer, please download the PDF or personalize the Word document and share with your network.
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Market for 2-time all-pro could heat up in coming days.

• May 9, 2024
• David Latham, Managing Editor

The free agent wide receiver market is heating up, and two-time All-Pro Michael Thomas could find a new team before long. The former second-round pick is a shell of his former self, as age and injuries have prevented him from recapturing his early career magic. With that disclaimer out of the way, the 2023 season proved he can still play at an NFL level. Appearing in 13 games while making 10 starts, the Ohio State product finished the season with 39 receptions for 448 yards and one touchdown on 64 targets.

This isn’t game-changing production by any stretch of the imagination, but it’s similar to what Odell Beckham did with the Baltimore Ravens . The former first-round pick recently signed a modest one-year deal with the Miami Dolphins, and Thomas should secure a similar contract. The only question is which teams make the most sense for Michael Thomas as a free agent.

5 Teams Who Could Sign Free Agent Michael Thomas

Odell Beckham didn’t justify his massive one-year deal during his lone season in Baltimore, but the former first-round pick did his job as the veteran third option in the offense. Now that the wideout is in Miami, somebody else must fill that role. Perhaps Rashod Bateman can bounce back from his disappointing 2023, but Michael Thomas makes plenty of sense as a free agent. The former Saints legend may not be the player he once was, but he can still be a plug-and-play starter behind Mark Andrews and Zay Flowers.

The NFL has yet to suspend wide receiver Rashee Rice, but it’s safe to assume we won’t see him for a while . With the former second-round pick out of the picture, Kansas City’s wide receiver depth chart is headlined by Marquise Brown, a first-year Chief, and rookie Xavier Worthy. While those two both possess plenty of upside, the Chiefs could use a safe, low-risk free agent signing like Michael Thomas. The wideout isn’t capable of another 100-catch season, but he’s considerably better than Skyy Moore and Kadarius Toney.

The Pittsburgh Steelers wanted Courtland Sutton or DK Metcalf, and right now, they’re settling for Scotty Miller. Miller is a fine deep threat who can battle with Quez Watkins for a depth role, but this team still needs a short and intermediate threat capable of moving the chains. Micahel Thomas is the best one left on the free agent market and should be a welcome addition to Russell Wilson’s offense.

After losing Keenan Allen and Mike Williams during the offseason, Los Angeles is bringing in just about every wide receiver with a pulse. The team selected three receivers during the 2024 NFL Draft, signed DJ Chark shortly thereafter, and brought in Marquez Valdes-Scantling for a free agent visit. While Chark and Valdes-Scantling are deep threats who could take Josh Palmer’s job , the Chargers could use an intermediate threat to replace Keenan Allen. In theory, Ladd McConkey could fill this void, but Michael Thomas is a safe free agent signing in case the Georgia product needs time to adjust to the NFL.

CeeDee Lamb is a superstar, but somebody else must step up in this offense. With age catching up to Brandin Cooks and Michael Gallup on the Raiders , quarterback Dak Prescott could use another reliable option in the passing game. Seeing as Jerry Jones seems unwilling to spend big money, Michael Thomas could be the best cost-effective free agent signing left.

Main Photo: Marc Lebryk – USA Today Sports

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Travel advisory: president biden visiting seattle later this week – plan ahead and expect travel delays.

Blog stats: 400 words | 2-minute read

At-a-glance:

• President Joe Biden is scheduled to visit Seattle later this week.
• We expect significant travel delays and detours in the greater Seattle area in the coming days.
• Continue to check traffic conditions before you leave, and give yourself plenty of extra travel time.
• To stay informed, check King County Metro’s service advisories and sign up for transit alerts . You can also follow tweets from King County Metro , SDOT Traffic , and WSDOT Traffic .
• Thank you for your patience and cooperation during this Presidential visit to our region.

During President Biden’s visit, the U.S. Secret Service has the authority to provide security, including requiring intermittent closures of freeways and streets. The flow of buses and cars in downtown Seattle and around the region will be affected.

While the president’s exact travel route and timing are not published in advance, travelers can still plan ahead by anticipating delays and temporary road closures., what to expect and how to get around.

You can check media reports and the websites of local jurisdictions and transit agencies before you leave, so you have the latest information about travel conditions. Remember to give yourself plenty of extra time to reach your destination.

If you can, please consider options to get around without driving. Riding transit and biking can be good ways to avoid traffic, but please note that some bus routes may also be affected by temporary traffic closures or detours, including short-term re-routes.

Our Seattle Department of Transportation (SDOT) engineers can adjust traffic signal timing within the city of Seattle based on expected closures and any necessary re-routing. We may also post messages on dynamic message signs when needed.

How to stay informed

King County Metro publishes service advisories online and sends transit alerts to riders notifying them of bus re-routes and travel changes. You can see if your route is affected by visiting Metro’s service advisories page .

We also encourage you to sign up for Metro’s transit alerts and to monitor local news reports and social media updates.

• Sign up for King County Metro transit alerts
• Follow tweets from King County Metro , SDOT Traffic , and WSDOT Traffic .

Thank you again for your patience and cooperation during this Presidential visit.

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Kendrick Lamar vs. Drake Beef Goes Nuclear: What to Know

The two rappers had circled one another for more than a decade, but their attacks turned relentless and very personal in a slew of tracks released over the weekend.

By Joe Coscarelli

The long-building and increasingly testy rap beef between Kendrick Lamar and Drake exploded into full-bore acrimony and unverifiable accusations over the weekend. Both artists rapid-fire released multiple songs littered with attacks regarding race, appropriation, sexual and physical abuse, body image, misogyny, hypocrisy, generational trauma and more.

Most relentless was Lamar, a Pulitzer Prize winner from Compton, Calif., who tends toward the isolated and considered but has now released four verbose and conceptual diss tracks — totaling more than 20 minutes of new music — targeting Drake in the last week, including three since Friday.

Each racked up millions of streams and the three that were made available commercially — “Euphoria,” “Meet the Grahams” and “Not Like Us” — are expected to land near the top of next week’s Billboard singles chart, while seeming to, at least momentarily, shift the public perception of Drake, long a maestro of the online public arena and meme ecosystem .

In between, on Friday night, Drake released his own broadside against Lamar — plus a smattering of other recent challengers — in a teasing Instagram interlude plus a three-part track and elaborate music video titled “Family Matters,” in which he referred to his rival as a fake activist and attempted to expose friction and alleged abuse in Lamar’s romantic relationship.

But that song was followed within half an hour by Lamar’s “Meet the Grahams,” an ominous extended address to the parents and young son of Drake, born Aubrey Graham, in which Lamar refers to his rival rapper as a liar and “pervert” who “should die” in order to make the world safer for women.

Lamar also seemed to assert that Drake had more than a decade ago fathered a secret daughter — echoing the big reveal of his son from Drake’s last headline rap beef — a claim Drake quickly denied on Instagram before hitting back in another song on Sunday. (Neither man has addressed the full array of rapped allegations directly.)

On Tuesday, a security guard was shot and seriously injured outside of Drake’s Toronto home, which appeared on the cover art for Lamar’s “Not Like Us.” Authorities said they could not yet speak to a motive in the shooting, but the investigation was ongoing. Representatives for Drake and Lamar did not immediately comment.

How did two of the most famous artists in the world decide to take the gloves off and bring real-life venom into an extended sparring match for rap supremacy? It was weeks, months and years in the making, with a sudden, breakneck escalation into hip-hop infamy. Here’s a breakdown.

Since late March, the much-anticipated head-to-head seemed inevitable. Following years of “will they or won’t they?” lyrical feints, Lamar hit directly on record first this year during a surprise appearance on the song “Like That” by the Atlanta rapper Future and the producer Metro Boomin, both formerly frequent Drake collaborators.

With audible disgust, Lamar invoked the track “First Person Shooter” from last year’s Drake album, “For All the Dogs,” in which a guest verse from J. Cole referred to himself, Drake and Lamar as “the big three” of modern MCs.

Lamar took exception to the grouping, declaring that there was no big three, “just big me.” He also called himself the Prince to Drake’s Michael Jackson — a deeper, more complex artist versus a troubled, pop-oriented hitmaker.

“Like That” spent three weeks at No. 1 on the Billboard Hot 100, as Future and Metro Boomin released two chart-topping albums — “We Don’t Trust You” and “We Still Don’t Trust You” — that were anchored by a parade of Drake’s past associates, each of whom seemed to share a simmering distaste toward the rapper, who later called the ambush a “20 v. 1” fight.

In early April, J. Cole fought back momentarily , releasing the song “7 Minute Drill,” in which he called Lamar overrated, before backtracking, apologizing and having the song removed from streaming services. But Drake soon picked up the baton, releasing a wide-ranging diss track called “Push Ups” less than a week later that addressed the field, with a special focus on Lamar’s height, shoe size and supposedly disadvantageous business dealings.

Less than a week later, Drake mocked Lamar’s lack of a response on “Taylor Made Freestyle,” a track released only on social media. It featured Drake taunting Lamar for being scared to release music at the same time as Taylor Swift and using A.I. voice filters to mimic Tupac and Snoop Dogg imploring Lamar to battle for the good of the West Coast.

“Since ‘Like That,’ your tone changed a little, you not as enthused,” Drake rapped in an abbreviated third verse, as himself. “How are you not in the booth? It feel like you kinda removed.” (“Taylor Made Freestyle” was later removed from the internet at the request of the Tupac Estate.)

But it was a seemingly tossed-off line from the earlier “Push Ups” that included the name of Lamar’s longtime romantic partner — “I be with some bodyguards like Whitney” — that Lamar would later allude to as a red line crossed, making all subject matter fair game in the songs to come. (It was this same alleged faux pas that may have triggered an intensification of Drake’s beef with Pusha T in 2018.)

How We Got Here

Even with Drake-dissing cameos from Future, Ye (formerly Kanye West), Rick Ross, the Weeknd and ASAP Rocky, the main event was always going to be between Drake, 37, and Lamar, 36, who have spent more than a decade subtly antagonizing one another in songs while maintaining an icy frenemy rapport in public.

In 2011, when Drake introduced Lamar to mainstream audiences with a dedicated showcase on his second album, “Take Care,” and an opening slot on the subsequent arena tour, the tone was one of side-eying competition. “He said that he was the same age as myself/and it didn’t help ’cause it made me even more rude and impatient,” Lamar rapped on “Buried Alive Interlude” of his earliest encounter with a more-famous Drake. (On his Instagram on Friday, Drake released a parody of the track, citing Lamar’s jealousy since then.)

The pair went on to appear together on “Poetic Justice,” a single from Lamar’s debut album, “Good Kid, M.A.A.D City,” in 2012, as well as “___ Problems” by ASAP Rocky the same year.

But their collaborations ceased as Drake became his generation’s premier hitmaker across styles in hip-hop and beyond, while Lamar burrowed deeper into his own psyche on knotty concept albums that brought wide critical acclaim alongside less constant commercial success.

When asked, the two rappers tended to profess admiration for one another’s skill, but seemed to trade subtle digs in verses over the years, always with plausible deniability and in the spirit of competition, leading to something of a hip-hop cold war.

The Week It Went Nuclear

Lamar’s first targeted response, “Euphoria,” was more than six minutes long and released last Tuesday morning. In three sections that raised the temperature as they built, he warned Drake about proceeding and insisted, somewhat facetiously, that things were still friendly. “Know you a master manipulator and habitual liar too,” Lamar rapped. “But don’t tell no lie about me and I won’t tell truths ’bout you.”

He accused the biracial Drake, who was born and raised in Toronto, of imitating Black American heritage and insulting him subliminally. “I hate the way that you walk, the way that you talk, I hate the way that you dress,” Lamar said. “I hate the way that you sneak diss, if I catch flight, it’s gon’ be direct.” And he called Drake’s standing as a father into question: “Teachin’ him morals, integrity, discipline/listen, man, you don’t know nothin’ ’bout that.”

Days later, Lamar doubled down with an Instagram-only track called “6:16 in LA,” borrowing both Drake’s “Back to Back” diss tactic from his 2015 beef with Meek Mill and a song title structure lifted from what is known as Drake’s time-stamp series of raps. Opting for psychological warfare on a beat produced in part by Jack Antonoff, Swift’s chief collaborator, Lamar hinted that he had a mole in Drake’s operation and was aware of his opponent’s opposition research.

“Fake bully, I hate bullies, you must be a terrible person,” he rapped. “Everyone inside your team is whispering that you deserve it.”

That night, Drake’s “Family Matters” started with its own justification for getting personal — “You mentioned my seed, now deal with his dad/I gotta go bad, I gotta go bad” — before taking on Lamar’s fatherhood and standing as a man in excruciating detail. “They hired a crisis management team to clean up the fact that you beat on your queen,” Drake rapped. “The picture you painted ain’t what it seem/you’re dead.”

Yet in a chess move that seemed to anticipate Drake’s familial line of attack, Lamar’s “Meet the Grahams” was released almost immediately. “This supposed to be a good exhibition within the game,” Lamar said, noting that Drake had erred “the moment you called out my family’s name.” Instead of a rap battle, Lamar concluded after another six minutes of psychological dissection, “this a long life battle with yourself.”

He wasn’t done yet. Dispensing with subtlety, Lamar followed up again less than 24 hours later with “Not Like Us,” a bouncy club record in a Los Angeles style that delighted in more traditional rap beef territory, like juvenile insults, proudly unsubstantiated claims of sexual preferences and threats of violence.

Lamar, however, didn’t leave it at that, throwing one more shot at Drake’s authenticity as a rapper, calling him a greedy and artificial user as a collaborator — “not a colleague,” but a “colonizer.”

On Sunday evening, Drake responded yet again. On “The Heart Part 6,” a title taken from Lamar’s career-spanning series, Drake denied the accusation that he preyed on young women, indicated that he had planted the bad information about his fake daughter and seemed to sigh away the fight as “some good exercise.”

“It’s good to get out, get the pen working,” Drake said in an exhausted outro. “You would be a worthy competitor if I was really a predator.” He added, “You know, at least your fans are getting some raps out of you. I’m happy I could motivate you.”

Joe Coscarelli is a culture reporter with a focus on popular music, and the author of “Rap Capital: An Atlanta Story.” More about Joe Coscarelli

Explore the World of Hip-Hop

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Gaza latest: Israel's use of weapons provided by US likely violated international law, report by Biden govt finds

The Biden administration says Israel likely violated international law with US-provided weapons. Earlier, Israel's ambassador to the UN used a paper shredder to shred the UN charter on stage at the UN General Assembly.

Saturday 11 May 2024 01:43, UK

• Israel-Hamas war

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• US report says Israel's use of arms likely violated international law
• Israeli ambassador to United Nations shreds 'copy of UN charter'
• UN General Assembly backs Palestinian bid for full membership
• Mark Stone analysis: Who voted with Israel at the UN and why were most Pacific Island nations?
• Netanyahu says Israelis will fight with 'fingernails' after Biden weapons warning - but Rafah decision unclear
• Israeli war cabinet 'approves expanded Rafah operation'
• Alistair Bunkall analysis: Biden's reputation is on the line if Netanyahu defies him
• Listen to the Daily above and tap here to follow wherever you get your podcasts
• Live reporting by Lauren Russell and (earlier) Richard Williams

Firefighters are battling a large blaze in Kiryat Shmona, a city in northern Israel, after 35 rockets were fired by Lebanon's Hezbollah, according to The Times of Israel.

The news site cited the Israel Fire and Rescue Services as saying 10 firefighting teams were at the scene.

Video posted on social media appeared to show the fire on what looked like the side of a hill.

No casualties or injuries have been reported. 

A report by the US government has said that Israel's use of US-provided weapons in Gaza likely violated international humanitarian law.

In the findings of a state department report - known as the national security memorandum - the Biden administration said it has found "reasonable" evidence to conclude that its ally had breached international law.

But it added it was unable to link specific US weapons to individual Israeli strikes. 

The report said: "Given Israel's significant reliance on US-made defence articles, it is reasonable to assess that defence articles have been used by Israeli security forces since 7 October in instances inconsistent with its international humanitarian law obligations or with established best practices for mitigating civilian harm."

It added that while Israel has the knowledge, experience and tools to implement the "best practices for mitigating civilian harm in its military operations" evidence from the ground - including high levels of civilian casualties - raise "substantial questions whether the IDF is using them effectively in all cases".

Turning to the issue of aid getting into Gaza, the US government report said it does not currently assess that the Israeli government is prohibiting or restricting the transport or delivery of aid. 

Crucially, the report stops short of saying that Israel has violated the terms under which it is able to use US weapons to carry out its offensive in Gaza.

By Mark Stone , US correspondent 

A huge majority of the world's nations voted with the Palestinians at the United Nations today.

But who were the nine countries that voted against the Palestinian quest for membership, rights and privileges at the UN, and why?

The current Israeli government is firmly against a Palestinian state in every sense.

Different iterations of Israeli governments over the years have oscillated on 'two states', but after the 7 October Hamas attacks the Israeli position cemented - no two states, no Palestinian state.

Broadly, they do not distinguish between the extremism of Hamas and the moderate nature of other Palestinian political factions like the Fatah-run Palestinian Authority in the West Bank. It's the crux of deadlock.

So who else? 

The United States

They stand behind Israel despite significant tension now between President Joe Biden and Prime Minister Benjamin Netanyahu. 

America is committed to a two-state solution but argues that it begins with a ceasefire and that the formation of a Palestinian state comes much further down the line.

Speaking after the vote, White House spokesman John Kirby said: "We continue to believe in the promise of a two-state solution and an independent state for the Palestinian people. 

"That's something that President Biden remains fully and firmly committed to. We also believe that the best way to do that is through direct negotiations with the parties and not through a vote at the UN of this kind, so that's why we voted no."

As always with geopolitics, relationships are so often symbiotic; they are all about mutual benefit even when, ostensibly, the relationship might seem incongruous.

The eastern-European EU member voted with Israel and against the Palestinians.

Don't assume that hard-right Hungarian Prime Minister Orban's hatred of Hungarian-born Jewish-US billionaire George Soros is a reflection of his views on Israel despite the anti-Soros narrative often being seen as antisemitic.

Antisemitism has haunted the right of politics in Hungary since the Second World War when half a million Jewish Hungarians were murdered. Yet Orban and Netanyahu have a close, longstanding relationship.

Israel and Hungary are aligned by mutual interests. 

Orban admires the way Netanyahu's ethos of building strength out of a small nation-state and the two leaders found mutual interest in standing up to liberal democratic headwinds.

Orban's fallout with the EU has aligned with Netanyahu's assessment that Europe is increasingly anti-Israel.

The Soros-hatred also aligns with Netanyahu in that the conspiracy is that Soros is somehow seeking to 'Islamise' Judeo-Christian Europe with his pro-immigration stance.

Argentina's vote is driven by new populist President Javier Milei who has pledged unwavering support for Netanyahu and has vowed to move Argentina's embassy to Jerusalem. 

Milei has said he plans to convert to Judaism.

Czech Republic

The Czech Republic also voted with Israel in line with a strongly pro-Israel stance underlined repeatedly since 7 October.

There is a strong historical bond between Czech leaders and the Zionist movement which helped cement the Jewish State which strengthened after the fall of Communism in 1989. 

As a new democracy, the Czech Republic bonded with a young democracy in Israel. In recent years, economic ties have flourished.

Pacific Island Nations

The rest, curiously maybe, are all Pacific Island nations: Micronesia, Papua New Guinea, Nauru and Palau.

The reason for their support is simple: straightforward soft power.

The small developing nations all enjoy generous Israeli aid from the government and from Israeli charities. 

The understanding is that, in return, they will always support Israel at international bodies of which they are members.

Israel insists that its motivation is predominantly humanitarian, but officials are up front to that it's also about positioning Israel in a better light.

Israel uses its considerable expertise in many arenas deftly.

At natural disasters, for example, Israeli rescue crews are often among the first on the ground. 

This targeted soft power diplomacy has helped Israel to secure votes, but also abstentions in its favour among many other nations too.

On this vote though, on Palestine, global opinion was overwhelmingly against Israel.

Israel's entry for Eurovision 2024, Eden Golan, has become one of the favourites among bookies to win this year's contest.

The 20-year-old singer climbed to second favourite from ninth after the semi-final, according to Eurovision World, a website that compiles betting odds from 15 of Europe's biggest bookmakers. 

It said Israel is seen as having a 22% chance of winning, behind Croatia's Baby Lasagna who was seen having a 41% chance.

It comes despite more than 10,000 people gathering in the host Swedish city of Malmo to stage a non-violent protest against Israel's participation in Saturday's final.

While the results of the two semi-finals are decided by viewers, in the final, audience votes will make up only half of the result, while juries of five music professionals in each participating country will make up the other half.

Earlier, the Israeli ambassador to the United Nations appeared on stage at a meeting of the UN General Assembly.

Whilst on stage in New York he shredded "a copy of the UN charter" - which was, in reality, three pieces of paper.

His actions came moments before the 193-member world body approved a resolution, giving Palestine new "rights and privileges" within the agency. 

Watch the full moment below. 

A first of its kind report by the US government is expected to conclude that Israel has not violated the terms of its use of US weapons, according to sources cited by the Associated Press. 

The report - known as the national security memorandum - was pushed by President Joe Biden's Democrats in Congress.

When agreed to back in February, defence and state departments were tasked to conduct "an assessment of any credible reports or allegations that such defence articles and, defence services, have been used in a manner not consistent with international law, including international humanitarian law".

They were also obliged to tell Congress if they thought Israel has acted to "arbitrarily to deny, restrict, or otherwise impede, directly or indirectly," delivery of any US-supported humanitarian aid into Gaza for starving civilians there.

It follows the US pausing a shipment of 3,500 bombs heading for Israel over concern they would be used in an offensive on Rafah.

The conclusions of the memorandum are expected to be sharply critical of Israel, but will not state that Israel violated terms of weapons agreements between the two countries. 

A senior Biden administration official said the full report is expected to be released later today, but declined to comment on its conclusions.

Palestinians in Rafah are still preparing to evacuate the eastern parts of the city amid the threat of an Israeli ground offensive. 

The United Nations estimates around 110,000 Palestinians have already fled in search of safety. 

In the latest pictures from the city, a tent camp where people are currently living is seen. 

In one of the images, people appear to have started to make piles of their belongings as they get ready to evacuate. 

South Africa has asked the International Court of Justice (ICJ) to order additional emergency measures against Israel over its attacks on the city of Rafah, the United Nations top court has said. 

It is part of the ongoing case brought by South Africa in January which accuses Israel of acts of genocide against Palestinians . 

The court - which is located in The Hague in the Netherlands - ordered Israel at the beginning of the year to take all measures within its power to prevent genocide.

South Africa wanted the ICJ to implement provisional measures on Israel which would "immediately suspend military operations in and against Gaza" - but the ICJ stopped short of that.

Any decision to impose provisional measures will be "hugely problematic" for the Israeli offensive, which Prime Minister Benjamin Netanyahu has vowed will continue until all hostages are returned and Hamas is destroyed.

Within the last few hours, the United Nations General Assembly has backed a bid put forward by Palestine for it to become a full agency member.

The vote passed by 143 votes to nine but 25 countries - including the UK - abstained.

In a post on X, the UK at the UN explained why it took the decision to abstain. 

"We are abstaining on this resolution because we believe that the first step towards achieving this goal is resolving the immediate crisis in Gaza," it said.

It said the fastest way to end the conflict is to secure a deal which releases all hostages and allows for a pause in fighting. 

The statement added that the UK remains firmly committed to a two-state solution and recognising a Palestinian state, including in the UN, and should be part of the process to achieving a sustainable ceasefire. 

The US ambassador to the UN Robert Wood gave similar reasons as to why America voted against the bid, saying its vote does not reflect opposition to Palestinian statehood.

"Instead, it is an acknowledgement that statehood will only come from a process that involves direct negotiations between the parties," he said.

What happens next?

For Palestine to become a full UN member, the 15-member UN Security Council will have to vote, and pass, the application.

At the last security council vote in March - which demanded a ceasefire in Gaza during the holy month of Ramadan - the US abstained.

The 14 other council members - including Russia, China and the UK - voted in favour.

For now, it remains unclear if or when the security council will vote on Palestine's membership bid.

Hamas has said it will hold talks with leaders of what it called "Palestinian resistance factions" to reconsider its negotiation strategy. 

It said the discussions need to be held due to Benjamin Netanyahu's behaviour, Israeli attacks on places in Rafah and the occupation of the city's border crossing with Egypt.

"Netanyahu and his government are using the negotiations as a cover to attack Rafah and occupy the crossing, and continue the war of extermination against our people, and they bear full responsibility for obstructing reaching an agreement," the statement said. 

Earlier this week, Hamas said they expressed agreement over a ceasefire deal following a phone call with Qatar's prime minister and Egypt's intelligence minister.

Israel later put an end to this, saying it would not accept the deal in its current form, a decision Hamas said today had brought things "back to square one". 

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