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May 14, 2020

Time travel into the future is totally possible

by Paul M. Sutter, Universe Today

Believe it or not, time travel is possible.

In fact, you're doing it right now. Every single second of every single day, you are advancing into your own future. You are literally moving through time, the same way you would move through space. It may seem pedantic, but it's a very important point. Movement through time is still movement, and you are reaching your own future (whether you like it or not).

And what's even cooler is that you can skip forward in time if you feel like it.

Well, let me be clear, you need to do a little bit of engineering first.

We know through the physics of Einstein's special theory of relativity that you can trade motion in space for motion in time. If you're standing perfectly still, you're moving through the dimension of time at a particular speed (the speed of light , for those of you who are curious). As soon as you start moving through space, however, you slow down your rate of moving through time.

In other words, the faster you move in space , the slower you move in time.

This means that moving objects, like a clock on a rocket, run a little bit slow. One second for someone in a moving spaceship lasts a little bit longer than a second for someone staying still.

The trick is that in order for this to have any sort of noticeable impact, you have to get close to the speed of light, which is really hard to do—to give you some perspective, astronauts that orbit the Earth at tens of thousands of miles per hour are off by only a microsecond or so from our clocks on the ground.

Our fastest human spacecraft don't even crack a tenth of a percent of the speed of light. But if you could somehow spend a good amount of time hugging close to that ultimate speed limit in the universe, the slower your clock will run. You will travel through time into the future. Nothing will feel different for you, but after a couple of years' journey you would return to the Earth to find our clocks advanced by thousands or even tens of thousands of years, depending on how fast you go.

So the future is yours, and you get to choose how quickly you reach it.

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Time travel: five ways that we could do it

Cathal O’Connell

Cathal O'Connell is a science writer based in Melbourne.

In 2009 the British physicist Stephen Hawking held a party for time travellers – the twist was he sent out the invites a year later (No guests showed up). Time travel is probably impossible. Even if it were possible, Hawking and others have argued that you could never travel back before the moment your time machine was built.

But travel to the future? That’s a different story.

Of course, we are all time travellers as we are swept along in the current of time, from past to future, at a rate of one hour per hour.

But, as with a river, the current flows at different speeds in different places. Science as we know it allows for several methods to take the fast-track into the future. Here’s a rundown.

1. Time travel via speed

This is the easiest and most practical way to time travel into the far future – go really fast.

According to Einstein’s theory of special relativity, when you travel at speeds approaching the speed of light, time slows down for you relative to the outside world.

This is not a just a conjecture or thought experiment – it’s been measured. Using twin atomic clocks (one flown in a jet aircraft, the other stationary on Earth) physicists have shown that a flying clock ticks slower, because of its speed.

In the case of the aircraft, the effect is minuscule. But If you were in a spaceship travelling at 90% of the speed of light, you’d experience time passing about 2.6 times slower than it was back on Earth.

And the closer you get to the speed of light, the more extreme the time-travel.

Computer solves a major time travel problem

The highest speeds achieved through any human technology are probably the protons whizzing around the Large Hadron Collider at 99.9999991% of the speed of light. Using special relativity we can calculate one second for the proton is equivalent to 27,777,778 seconds, or about 11 months , for us.

Amazingly, particle physicists have to take this time dilation into account when they are dealing with particles that decay. In the lab, muon particles typically decay in 2.2 microseconds. But fast moving muons, such as those created when cosmic rays strike the upper atmosphere, take 10 times longer to disintegrate.

2. Time travel via gravity

The next method of time travel is also inspired by Einstein. According to his theory of general relativity, the stronger the gravity you feel, the slower time moves.

As you get closer to the centre of the Earth, for example, the strength of gravity increases. Time runs slower for your feet than your head.

Again, this effect has been measured. In 2010, physicists at the US National Institute of Standards and Technology (NIST) placed two atomic clocks on shelves, one 33 centimetres above the other, and measured the difference in their rate of ticking. The lower one ticked slower because it feels a slightly stronger gravity.

To travel to the far future, all we need is a region of extremely strong gravity, such as a black hole. The closer you get to the event horizon, the slower time moves – but it’s risky business, cross the boundary and you can never escape.

And anyway, the effect is not that strong so it’s probably not worth the trip.

Assuming you had the technology to travel the vast distances to reach a black hole (the nearest is about 3,000 light years away), the time dilation through travelling would be far greater than any time dilation through orbiting the black hole itself.

(The situation described in the movie Interstellar , where one hour on a planet near a black hole is the equivalent of seven years back on Earth, is so extreme as to be impossible in our Universe, according to Kip Thorne, the movie’s scientific advisor.)

The most mindblowing thing, perhaps, is that GPS systems have to account for time dilation effects (due to both the speed of the satellites and gravity they feel) in order to work. Without these corrections, your phones GPS capability wouldn’t be able to pinpoint your location on Earth to within even a few kilometres.

3. Time travel via suspended animation

Another way to time travel to the future may be to slow your perception of time by slowing down, or stopping, your bodily processes and then restarting them later.

Bacterial spores can live for millions of years in a state of suspended animation, until the right conditions of temperature, moisture, food kick start their metabolisms again. Some mammals, such as bears and squirrels, can slow down their metabolism during hibernation, dramatically reducing their cells’ requirement for food and oxygen.

Could humans ever do the same?

Though completely stopping your metabolism is probably far beyond our current technology, some scientists are working towards achieving inducing a short-term hibernation state lasting at least a few hours. This might be just enough time to get a person through a medical emergency, such as a cardiac arrest, before they can reach the hospital.

In 2005, American scientists demonstrated a way to slow the metabolism of mice (which do not hibernate) by exposing them to minute doses of hydrogen sulphide, which binds to the same cell receptors as oxygen. The core body temperature of the mice dropped to 13 °C and metabolism decreased 10-fold. After six hours the mice could be reanimated without ill effects.

Unfortunately, similar experiments on sheep and pigs were not successful, suggesting the method might not work for larger animals.

Another method, which induces a hypothermic hibernation by replacing the blood with a cold saline solution, has worked on pigs and is currently undergoing human clinical trials in Pittsburgh.

4. Time travel via wormholes

General relativity also allows for the possibility for shortcuts through spacetime, known as wormholes, which might be able to bridge distances of a billion light years or more, or different points in time.

Many physicists, including Stephen Hawking, believe wormholes are constantly popping in and out of existence at the quantum scale, far smaller than atoms. The trick would be to capture one, and inflate it to human scales – a feat that would require a huge amount of energy, but which might just be possible, in theory.

Attempts to prove this either way have failed, ultimately because of the incompatibility between general relativity and quantum mechanics.

5. Time travel using light

Another time travel idea, put forward by the American physicist Ron Mallet, is to use a rotating cylinder of light to twist spacetime. Anything dropped inside the swirling cylinder could theoretically be dragged around in space and in time, in a similar way to how a bubble runs around on top your coffee after you swirl it with a spoon.

According to Mallet, the right geometry could lead to time travel into either the past and the future.

Since publishing his theory in 2000, Mallet has been trying to raise the funds to pay for a proof of concept experiment, which involves dropping neutrons through a circular arrangement of spinning lasers.

His ideas have not grabbed the rest of the physics community however, with others arguing that one of the assumptions of his basic model is plagued by a singularity, which is physics-speak for “it’s impossible”.

The Royal Institution of Australia has an Education resource based on this article. You can access it here .

Related Reading: Computer solves a major time travel problem

Originally published by Cosmos as Time travel: five ways that we could do it

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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:

Is time travel possible? Why one scientist says we 'cannot ignore the possibility.'

A common theme in science-fiction media , time travel is captivating. It’s defined by the late philosopher David Lewis in his essay “The Paradoxes of Time Travel” as “[involving] a discrepancy between time and space time. Any traveler departs and then arrives at his destination; the time elapsed from departure to arrival … is the duration of the journey.”

Time travel is usually understood by most as going back to a bygone era or jumping forward to a point far in the future . But how much of the idea is based in reality? Is it possible to travel through time? 

Is time travel possible?

According to NASA, time travel is possible , just not in the way you might expect. Albert Einstein’s theory of relativity says time and motion are relative to each other, and nothing can go faster than the speed of light , which is 186,000 miles per second. Time travel happens through what’s called “time dilation.”

Time dilation , according to Live Science, is how one’s perception of time is different to another's, depending on their motion or where they are. Hence, time being relative. 

Learn more: Best travel insurance

Dr. Ana Alonso-Serrano, a postdoctoral researcher at the Max Planck Institute for Gravitational Physics in Germany, explained the possibility of time travel and how researchers test theories. 

Space and time are not absolute values, Alonso-Serrano said. And what makes this all more complex is that you are able to carve space-time .

“In the moment that you carve the space-time, you can play with that curvature to make the time come in a circle and make a time machine,” Alonso-Serrano told USA TODAY. 

She explained how, theoretically, time travel is possible. The mathematics behind creating curvature of space-time are solid, but trying to re-create the strict physical conditions needed to prove these theories can be challenging. 

“The tricky point of that is if you can find a physical, realistic, way to do it,” she said. 

Alonso-Serrano said wormholes and warp drives are tools that are used to create this curvature. The matter needed to achieve curving space-time via a wormhole is exotic matter , which hasn’t been done successfully. Researchers don’t even know if this type of matter exists, she said.

“It's something that we work on because it's theoretically possible, and because it's a very nice way to test our theory, to look for possible paradoxes,” Alonso-Serrano added.

“I could not say that nothing is possible, but I cannot ignore the possibility,” she said. 

She also mentioned the anecdote of  Stephen Hawking’s Champagne party for time travelers . Hawking had a GPS-specific location for the party. He didn’t send out invites until the party had already happened, so only people who could travel to the past would be able to attend. No one showed up, and Hawking referred to this event as "experimental evidence" that time travel wasn't possible.

What did Albert Einstein invent?: Discoveries that changed the world

Just Curious for more? We've got you covered

USA TODAY is exploring the questions you and others ask every day. From "How to watch the Marvel movies in order" to "Why is Pluto not a planet?" to "What to do if your dog eats weed?" – we're striving to find answers to the most common questions you ask every day. Head to our Just Curious section to see what else we can answer for you. 

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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Paradox-Free Time Travel Is Theoretically Possible, Researchers Say

Matthew S. Schwartz

A dog dressed as Marty McFly from Back to the Future attends the Tompkins Square Halloween Dog Parade in 2015. New research says time travel might be possible without the problems McFly encountered. Timothy A. Clary/AFP via Getty Images hide caption

A dog dressed as Marty McFly from Back to the Future attends the Tompkins Square Halloween Dog Parade in 2015. New research says time travel might be possible without the problems McFly encountered.

"The past is obdurate," Stephen King wrote in his book about a man who goes back in time to prevent the Kennedy assassination. "It doesn't want to be changed."

Turns out, King might have been on to something.

Countless science fiction tales have explored the paradox of what would happen if you went back in time and did something in the past that endangered the future. Perhaps one of the most famous pop culture examples is in Back to the Future , when Marty McFly goes back in time and accidentally stops his parents from meeting, putting his own existence in jeopardy.

But maybe McFly wasn't in much danger after all. According a new paper from researchers at the University of Queensland, even if time travel were possible, the paradox couldn't actually exist.

Researchers ran the numbers and determined that even if you made a change in the past, the timeline would essentially self-correct, ensuring that whatever happened to send you back in time would still happen.

"Say you traveled in time in an attempt to stop COVID-19's patient zero from being exposed to the virus," University of Queensland scientist Fabio Costa told the university's news service .

"However, if you stopped that individual from becoming infected, that would eliminate the motivation for you to go back and stop the pandemic in the first place," said Costa, who co-authored the paper with honors undergraduate student Germain Tobar.

"This is a paradox — an inconsistency that often leads people to think that time travel cannot occur in our universe."

A variation is known as the "grandfather paradox" — in which a time traveler kills their own grandfather, in the process preventing the time traveler's birth.

The logical paradox has given researchers a headache, in part because according to Einstein's theory of general relativity, "closed timelike curves" are possible, theoretically allowing an observer to travel back in time and interact with their past self — potentially endangering their own existence.

But these researchers say that such a paradox wouldn't necessarily exist, because events would adjust themselves.

Take the coronavirus patient zero example. "You might try and stop patient zero from becoming infected, but in doing so, you would catch the virus and become patient zero, or someone else would," Tobar told the university's news service.

In other words, a time traveler could make changes, but the original outcome would still find a way to happen — maybe not the same way it happened in the first timeline but close enough so that the time traveler would still exist and would still be motivated to go back in time.

"No matter what you did, the salient events would just recalibrate around you," Tobar said.

The paper, "Reversible dynamics with closed time-like curves and freedom of choice," was published last week in the peer-reviewed journal Classical and Quantum Gravity . The findings seem consistent with another time travel study published this summer in the peer-reviewed journal Physical Review Letters. That study found that changes made in the past won't drastically alter the future.

Bestselling science fiction author Blake Crouch, who has written extensively about time travel, said the new study seems to support what certain time travel tropes have posited all along.

"The universe is deterministic and attempts to alter Past Event X are destined to be the forces which bring Past Event X into being," Crouch told NPR via email. "So the future can affect the past. Or maybe time is just an illusion. But I guess it's cool that the math checks out."

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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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Time Travel: Dream or Possible Reality?

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Time travel is a favorite plot device in science fiction stories and movies. Perhaps the most famous recent series is Dr. Who , with its traveling Time Lords who whisk throughout time as if traveling by jet. In other stories, the time travel is due to unexplainable circumstances such as a too-close approach to a very massive object like a black hole. In Star Trek: The Voyage Home , the plot device was a trip around the Sun that hurled Kirk and Spock back to 20th century Earth. In the popular movie series Back to the Future , the characters traveled both backward and forward in time. However it is described in stories, traveling through time seems to pique people's interest and ignite their imaginations. But, is such a thing possible? 

The Nature of Time

It's important to remember that we are always traveling into the future. That's the nature of space-time. This is why we remember the past (instead of "remembering" the future). The future is largely unpredictable because it hasn't happened yet, but everyone is headed into it all the time.

To speed up the process, to peer further into the future, to experience events more quickly than those around us, what would or could anyone do to make it happen? It's a good question without a definitive answer. Right now, no one has built a working time machine to travel temporally.

Traveling into the Future

While it's not possible (yet) to travel to the future fast than the rate at which we're doing it now, it is possible to speed up the passage of time. But, it only happens in small increments of time. And, it has only happened (so far) to very few people who have traveled off Earth's surface. For them, time moves at an infinitesimally different rate. Could it happen over longer time spans? 

It might, theoretically. According to Einstein's theory of special relativity , the passage of time is relative to an object's speed. The more quickly an object moves through space, the more slowly time passes for it compared to an observer traveling at a slower pace. 

The classic example of traveling into the future is the twin paradox . It works like this: take a pair of twins, each 20 years old. They live on Earth. One takes off on a spaceship on a five-year journey traveling at nearly the speed of light . The traveling twin ages five years while on the journey and returns to Earth at the age of 25. However, the twin who stayed behind is 95 years old! The twin on the ship experienced only five years of time passing, but returns to an Earth that is much farther into the future.

Using Gravity as a Means of Time Travel

In much the same way that traveling at speeds close to the speed of light can slow down perceived time, intense gravitational fields can have the same effect.

Gravity only affects the movement of space, but also the flow of time. Time passes more slowly for an observer inside a massive object's gravitational well. The stronger the gravity, the more it affects the flow of time. 

Astronauts on the  International Space Station experience a combination of these effects, though on a much smaller scale. Since they are traveling quite quickly and orbiting around Earth (a massive body with significant gravity), time slows down for them compared to people on Earth. The difference is much less than a second over the course of their time in space. But, it is measurable.

Could We Ever Travel into the Future?

Until we can figure out a way to approach the speed of light (and warp drive doesn't count , not that we know how to do that at this point, either), or travel near black holes (or travel to black holes for that matter) without falling in, we won't be able to do time travel any significant way into the future. 

Travel into the Past

Moving into the past is also impossible given our current technology. If it were possible, some peculiar effects could occur. These include the famous "go back in time and kill your grandfather" paradox. If you did do it, you couldn't do it, because you already killed him, so therefore you don't exist and can't go back in time to do the dastardly deed. Confusing, isn't it? 

Key Takeaways

• Time travel is a science fiction trope that may possibly be technically possible. But, no one has achieved it.
• We do travel into the future all our lives, at a second per second. To do it faster requires technology we don't have.
• Travel to the past is also impossible at the present time.
• Is Time Travel Possible?| Explore , www.physics.org/article-questions.asp?id=131.
• NASA , NASA, spaceplace.nasa.gov/review/dr-marc-space/time-travel.html.
• “Time Travel.”  TV Tropes , tvtropes.org/pmwiki/pmwiki.php/Main/TimeTravel.

Edited by Carolyn Collins Petersen .

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• What Is the Twin Paradox? Real Time Travel
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• Is Warp Drive From 'Star Trek' Possible?
• An Introduction to Black Holes
• Closed Timelike Curve
• Amazing Astronomy Facts
• The Science of Star Trek
• Cosmic Rays
• An Introduction to Gravitational Lensing
• Cosmos Episode 4 Viewing Worksheet
• Einstein's Theory of Relativity
• Learn about the Doppler Effect

February 1, 2006

How to Build a Time Machine

It wouldn't be easy, but it might be possible

By Paul Davies

Time travel has been a popular science-fiction theme since H. G. Wells wrote his celebrated novel The Time Machine in 1895. But can it really be done? Is it possible to build a machine that would transport a human being into the past or future?

For decades, time travel lay beyond the fringe of respectable science. In recent years, however, the topic has become something of a cottage industry among theoretical physicists. The motivation has been partly recreational--time travel is fun to think about. But this research has a serious side, too. Understanding the relation between cause and effect is a key part of attempts to construct a unified theory of physics. If unrestricted time travel were possible, even in principle, the nature of such a unified theory could be drastically affected.

Our best understanding of time comes from Einstein's theories of relativity. Prior to these theories, time was widely regarded as absolute and universal, the same for everyone no matter what their physical circumstances were. In his special theory of relativity, Einstein proposed that the measured interval between two events depends on how the observer is moving. Crucially, two observers who move differently will experience different durations between the same two events.

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The effect is often described using the twin paradox. Suppose that Sally and Sam are twins. Sally boards a rocket ship and travels at high speed to a nearby star, turns around and flies back to Earth, while Sam stays at home. For Sally the duration of the journey might be, say, one year, but when she returns and steps out of the spaceship, she finds that 10 years have elapsed on Earth. Her brother is now nine years older than she is. Sally and Sam are no longer the same age, despite the fact that they were born on the same day. This example illustrates a limited type of time travel. In effect, Sally has leaped nine years into Earth's future.

THE EFFECT, KNOWN AS time dilation, occurs whenever two observers move relative to each other. In daily life we don't notice weird time warps, because the effect becomes dramatic only when the motion occurs at close to the speed of light. Even at aircraft speeds, the time dilation in a typical journey amounts to just a few nanoseconds--hardly an adventure of Wellsian proportions. Nevertheless, atomic clocks are accurate enough to record the shift and confirm that time really is stretched by motion. So travel into the future is a proved fact, even if it has so far been in rather unexciting amounts.

To observe really dramatic time warps, one has to look beyond the realm of ordinary experience. Subatomic particles can be propelled at nearly the speed of light in large accelerator machines. Some of these particles, such as muons, have a built-in clock because they decay with a definite half-life; in accordance with Einstein's theory, fast-moving muons inside accelerators are observed to decay in slow motion. Some cosmic rays also experience spectacular time warps. These particles move so close to the speed of light that, from their point of view, they cross the galaxy in minutes, even though in Viewed from such a star, events here would resemble a fast-forwarded video. A black hole represents the ultimate time warp; at the surface of the hole, time stands still relative to Earth. This means that if you fell into a black hole from nearby, in the brief interval it took you to reach the surface, all of eternity would pass by in the wider universe. The region within the black hole is therefore beyond the end of time, as far as the outside universe is concerned. If an astronaut could zoom very close to a black hole and return unscathed--admittedly a fanciful, not to mention foolhardy, prospect--he could leap far into the future.

My Head Is Spinning

SO FAR I HAVE DISCUSSED travel forward in time. What about going backward? This is much more problematic. In 1948 Kurt Gdel of the Institute for Advanced Study in Princeton, N.J., produced a solution of Einstein's gravitational field equations that described a rotating universe. In this universe, an astronaut could travel through space so as to reach his own past. This comes about because of the way gravity affects light. The rotation of the universe would drag light (and thus the causal relations between objects) around with it, enabling a material object to travel in a closed loop in space that is also a closed loop in time, without at any stage exceeding the speed of light in the immediate neighborhood of the particle. Gdel's solution was shrugged aside as a mathematical curiosity--after all, observations show no sign that the universe as a whole is spinning. His result served nonetheless to demonstrate that going back in time was not forbidden by the theory of relativity. Indeed, Einstein confessed that he was troubled by the thought that his theory might permit travel into the past under some circumstances.

Other scenarios have been found to permit travel into the past. For example, in 1974 Frank J. Tipler of Tulane University calculated that a massive, infinitely long cylinder spinning on its axis at near the speed of light could let astronauts visit their own past, again by dragging light around the cylinder into a loop. In 1991 J. Richard Gott of Princeton University predicted that cosmic strings--structures that cosmologists think were created in the early stages of the big bang--could produce similar results. But in the mid-1980s the most realistic scenario for a time machine emerged, based on the concept of a wormhole.

In science fiction, wormholes are sometimes called stargates; they offer a shortcut between two widely separated points in space. Jump through a hypothetical wormhole, and you might come out moments later on the other side of the galaxy. Wormholes naturally fit into the general theory of relativity, whereby gravity warps not only time but also space. The theory allows the analogue of alternative road and tunnel routes connecting two points in space. Mathematicians refer to such a space as multiply connected. Just as a tunnel passing under a hill can be shorter than the surface street, a wormhole may be shorter than the usual route through ordinary space.

The wormhole was used as a fictional device by Carl Sagan in his 1985 novel Contact . Prompted by Sagan, Kip S. Thorne and his co-workers at the California Institute of Technology set out to find whether wormholes were consistent with known physics. Their starting point was that a wormhole would resemble a black hole in being an object with fearsome gravity. But unlike a black hole, which offers a oneway journey to nowhere, a wormhole would have an exit as well as an entrance.

In the Loop

FOR THE WORMHOLE to be traversable, it must contain what Thorne termed exotic matter. In effect, this is something that will generate antigravity to combat the natural tendency of a massive system to implode into a black hole under its intense weight. Antigravity, or gravitational repulsion, can be generated by negative energy or pressure. Negative- energy states are known to exist in certain quantum systems, which suggests that Thorne's exotic matter is not ruled out by the laws of physics, although it is unclear whether enough antigravitating stuff can be assembled to stabilize a wormhole [see Negative Energy, Wormholes and Warp Drive, by Law rence H. Ford and Thomas A. Roman; SCIENTIFIC AMERICAN, January 2000].

Soon Thorne and his colleagues realized that if a stable worm hole could be created, then it could readily be turned into a time machine. An astronaut who passed through one might come out not only somewhere else in the universe but somewhen else, too--in either the future or the past.

To adapt the wormhole for time travel, one of its mouths could be towed to a neutron star and placed close to its surface. The gravity of the star would slow time near that wormhole mouth, so that a time difference between the ends of the wormhole would gradually accumulate. If both mouths were then parked at a convenient place in space, this time difference would remain frozen in.

Suppose the difference were 10 years. An astronaut passing through the wormhole in one direction would jump 10 years into the future, whereas an astronaut passing in the other direction would jump 10 years into the past. By returning to his starting point at high speed across ordinary space, the second astronaut might get back home before he left. In other words, a closed loop in space could become a loop in time as well. The one restriction is that the astronaut could not return to a time before the wormhole was first built.

A formidable problem that stands in the way of making a wormhole time machine is the creation of the wormhole in the first place. Possibly space is threaded with such structures naturally--relics of the big bang. If so, a supercivilization might commandeer one. Alternatively, wormholes might naturally come into existence on tiny scales, the so-called Planck length, about 20 factors of 10 as small as an atomic nucleus. In principle, such a minute wormhole could be stabilized by a pulse of energy and then somehow inflated to usable dimensions.

ASSUMING THAT the engineering problems could be overcome, the production of a time machine could open up a Pandora's box of causal paradoxes. Consider, for example, the time traveler who visits the past and murders his mother when she was a young girl. How do we make sense of this? If the girl dies, she cannot become the time traveler's mother. But if the time traveler was never born, he could not go back and murder his mother.

Paradoxes of this kind arise when the time traveler tries to change the past, which is obviously impossible. But that does not prevent someone from being a part of the past. Suppose the time traveler goes back and rescues a young girl from murder, and this girl grows up to become his mother. The causal loop is now self-consistent and no longer paradoxical. Causal consistency might impose restrictions on what a time traveler is able to do, but it does not rule out time travel per se.

The bizarre consequences of time travel have led some scientists to reject the notion outright. Stephen W. Hawking of the University of Cambridge has proposed a chronology protection conjecture, which would outlaw causal loops. Because the theory of relativity is known to permit causal loops, chronology protection would require some other factor to intercede to prevent travel into the past. What might this factor be? One suggestion is that quantum processes will come to the rescue. The existence of a time machine would allow particles to loop into their own past. Calculations hint that the ensuing disturbance would become self-reinforcing, creating a runaway surge of energy that would wreck the wormhole.

Chronology protection is still just a conjecture, so time travel remains a possibility. A final resolution of the matter may have to await the successful union of quantum mechanics and gravitation, perhaps through a theory such as string theory or its extension, so-called M-theory. It is even conceivable that the next generation of particle accelerators will be able to create subatomic wormholes that survive long enough for nearby particles to execute fleeting causal loops. This would be a far cry from Wells's vision of a time machine, but it would forever change our picture of physical reality.

PAUL DAVIES is a theoretical physicist and professor of natural philosophy at Macquarie University's Australian Center for Astrobiology in Sydney. He is one of the most prolific writers of popular-level books in physics. His scientific research interests include black holes, quantum field theory, the origin of the universe, the nature of consciousness and the origin of life.

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Jason Statham's Highest-Rated Movie Proves Two Harsh Truths About His 26-Year Career

Beetlejuice 2 is reviving my excitement for tim burton's movies that i lost after his $245 million box office bomb, the iron claw’s bts detail gives more meaning to zac efron’s emotional final scene.

How does time travel work in iconic 1980s classic  Back To The Future , and does the concept bear any relation whatsoever to real science? Released in 1985,  Back To The Future  wasn't Hollywood's first dalliance with traveling through time, and certainly hasn't been the last. More than three decades later, however, it's still the movie everyone inevitably comes back to when discussing matters of a temporal nature.  Back To The Future is also regularly dubbed "the perfect film," and it's not hard to see why. With vibrant characters, fascinating settings and one of the leanest big screen plots you'll find,  Marty McFly 's story is somehow both quintessentially 1980s,  and utterly timeless.

Fun and adventure might be  Back To The Future 's mission statement, but the franchise makes no concessions with its sci-fi elements. Robert Zemeckis and Bob Gale developed a tightly woven set of rules for traveling through time, and despite Michael J. Fox's constant meddling, the timeline shenanigans hold up, generally honoring the script's own logic.  Back To The Future might be a light-hearted 1980s romp, but to paraphrase Doc Brown, the film's time travel is some serious sh...

Related:  Why Back to the Future Recast Elisabeth Shue As Marty's Girlfriend

Throughout  Back To The Future and its two worthy sequels, Doc Brown and Marty McFly learn the mechanics of time travel on the job and, more pertinently, find out the consequences of disrupting the past. The audience, meanwhile, discover how Back To The Future 's time-bending gimmick compares to other works of fiction. Here's the full breakdown of  Back To The Future 's time travel rules, which perhaps aren't as unrealistic as you might assume ( DeLorean not withstanding).

How Time Travel Works In Back To The Future, Explained

In Back To The Future 's opening act, Doc Brown helpfully explains the requirements for mankind to breach the time barrier - his miraculous new scientific breakthrough. Inside the DeLorean are a set of time circuits and three readouts displaying the current date, the intended destination, and the most recent trip made (a helpful plot device for later). The most important device, however, is Doc Brown's flux capacitor invention, powered by 1.21 gigawatts of electricity. Brown begins  Back To The Future by powering the DeLorean with plutonium, but he later turns to alternative sources - a lightning strike, trash in a fusion reactor, and steam, all of which are more environmentally-friendly and less likely to upset Libyan terrorists. Taking the DeLorean to the magic speed of 88mph completes the cocktail of ingredients needed for time travel in  Back To The Future 's world.

Side effects of traversing the time-space continuum include the famous fiery tire tracks, and the car turning ice-cold for a brief time. Doc Brown also suggests the DeLorean's steel casing is vital for dispersing the flux capacitor's energy. Were a lesser substitute used, the flux particles might not wrap around the entire vehicle effectively enough to send it through the time barrier.

In  Back To The Future 's rule book, there's no difference between venturing into the past and rocketing ahead into the future. Both require the same process, and all Marty needs to do is alter the date on the time circuits. As Doc Brown's initial experiment with Einstein the dog proves, trips in both directions are instantaneous - the mutt is sent one minute into the future with a digital clock, and when he materializes 60 seconds later, the readout is exactly a minute slower than it should be. Furthermore, the traveler never moves in space. When the DeLorean hops through the years, it lands in exactly the same physical location from which it departed.

Related:  Why Back To The Future Was Almost Called Space Man From Pluto

Broadly speaking, there are three interpretations of time travel 's effects in fiction. The "what happened, happened" hypothesis posits that altering history is impossible, and any attempt to do so might even  cause whatever the traveler is trying to avoid. Examples of this can be found in  Lost and  Terminator , where John Connor sends his best friend back in time to impregnate his mother. The second variant is the "multiple timelines" idea. Visiting the past and changing history creates a breakaway reality, separate from the original, where any alterations play out. Thanks to  Avengers: Endgame , we know the MCU  utilizes this format. The last model, and the one  Back To The Future subscribes to, is the single, changeable timeline. There are no multiple branch realities, and changing the past has a corresponding effect on the present day.

This is perfectly demonstrated by Back To The Future 's "Twin Pines Mall" sign. As you've no doubt noticed already, the sign alters to "Lone Pine Mall" after Marty visits 1955 and knocks over a tree in Doc Brown's DeLorean. If "what happened, happened" were true, then the sign would've read "Lone Pine" from the start. In the MCU, meanwhile, two signs would exist in different timelines - the original "Twin Pines" and the new "Lone Pine". The shifting sign proves the malleable nature of  Marty 's world in  Back To The Future , but Robert Zemeckis doesn't go so far as to employ the Butterfly Effect. According to the Butterfly Effect theory, even the slightest change to the past would lead to an unrecognizable future via chain reaction.  Back To The Future 's time travel rules are far more localized and specific - i.e. knocking down the tree changes the mall sign, but everything else remains the the same.

How Scientifically Accurate Back To The Future's Time Travel Is

Sorry to be the bearer of bad news but time travel is, at the time of writing, not possible. Fortunately, that hasn't deterred more scientifically-minded folk from pondering the possible and plausible of crossing the quantum wake. One hurdle  Back To The Future (among many other time travel tales) must overcome is the laws of physics. If a person were to travel faster than the speed of light, they could theoretically move into the future, but the principle doesn't work in reverse, which would rule out traveling into the past entirely. As  New Scientist   duly points out, wormholes could provide the answer. According to Kip Thorne (physicist, smarter than us), if one side of a wormhole travels at light speed and the other side remains fixed, time begins to dilate, creating a "past" and "future" on either side of the tunnel. Though Thorne's theory is hotly debated, it lends a certain amount of credibility to the DeLorean 's two-way time travel in  Back To The Future .

Before etching Robert Zemeckis' name on that Nobel prize, it's worth considering that scientists generally believe the "multiple realities" version of time travel is the most theoretically sound - that when someone changes the past, they're creating an alternate timeline. String Theory has also been used to corroborate the idea of parallel realities, albeit not due to interference from time-meddlers. In  Back To The Future , Marty and Doc Brown seem to be going over the same single timeline, erasing and amending history as they see fit (the Lone Pine, Biff's sports almanac, Marty disappearing). This would mean  Back To The Future 's time travel perhaps isn't as realistic as it could be - amazing for a film in which every McFly male looks like Michael J. Fox.

Related:  Back To The Future: How Old Doc Brown Is In Each Movie

More recently, Germain Tobar of the University of Queensland poured cold water on  Back To The Future 's time travel, coming out in support of the "what happened, happened" theory. In layman's terms, Tobar purports that if an attempt to change history were made, the universe would " recalibrate " around the event. To return to  Back To The Future 's "Twin Pines Mall" example, Marty would knock down the tree in 1955, and old man Peabody would plant another, hence the sign remains the same, and altering the past is a futile endeavor. Again, the (theoretical) science contradicts  Back To The Future ... but does it actually matter?

Although various figures from the scientific community have offered their thoughts on the mechanics of time travel in a real-world scenario, their explanations are deeply speculative, and only cover specific elements of the overall concept (how to reach the past, changing history). As much as scientists might disagree with him, Robert Zemeckis' interpretation of time travel is just as valid as anyone else's until that first trip is made. Any time travel story requires its own fictional set of laws and limitations - something science cannot yet offer. For movies, the priority shouldn't be adhering to reality, but keeping consistent to whatever rules are established, and  Back To The Future   is, more or less, a success in this regard.

More:  Back To The Future: All Three Movies, Ranked Worst To Best

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Time travel for travelers? It’s tricky.

Scientific theories suggest it’s possible to travel through time. But the reality isn’t so clear.

Time travel has fascinated scientists and writers for at least 125 years. The concept feels especially intriguing now, when physical travel is limited. Here, a photo illustration of Tokyo’s Robot Restaurant captures the idea of speeding through time.

I’m stuck at home, you’re stuck at home, we’re all stuck at home. Jetting off to some fun-filled destination like we used to might not be in the cards for a little while yet. But what about travelling through time? And not just the boring way, where we wait for the future to arrive one second at a time. What if you could zip through time at will, travelling forward to the future or backward to the past as easily as pushing buttons on the dashboard of a souped-up DeLorean, just like in the movie Back to the Future ?

Time travel has been a fantasy for at least 125 years. H.G. Wells penned his groundbreaking novel, The Time Machine , in 1895, and it’s something that physicists and philosophers have been writing serious papers about for almost a century.

What really kick-started scientific investigations into time travel was the notion, dating to the closing years of the 19th century, that time could be envisioned as a dimension, just like space. We can move easily enough through space, so why not time?

At the end of the 19th century, scientists thought of time as a dimension like space, where travelers can go anywhere they want. This photo illustration of Tokyu Plaza in Tokyo’s Omotesando Harajuku evokes the feeling of visiting endless destinations.

“In space, you can go wherever you want, so maybe in time you can similarly go anywhere you want,” says Nikk Effingham, a philosopher at the University of Birmingham in the United Kingdom . “From there, it’s a short step to time machines.”

( Why are people obsessed with time travel? Best-selling author James Gleick has some ideas .)

Dueling theories

Wells was a novelist, not a physicist, but physics would soon catch up. In 1905, Albert Einstein published the first part of his relativity theory, known as special relativity . In it, space and time are malleable; measurements of both space and time depend on the relative speed of the person doing the measuring.

A few years later, the German mathematician Hermann Minkowski showed that, in Einstein’s theory, space and time could be thought of as two aspects of a single four-dimensional entity known as space-time . Then, in 1915, Einstein came up with the second part of his theory, known as general relativity . General relativity renders gravity in a new light: Instead of thinking of it as a force, general relativity describes gravity as a bending or warping of space-time.

But special relativity is enough to get us started in terms of moving through time. The theory “establishes that time is much more similar to space than we had previously thought,” says Clifford Johnson, a physicist at the University of Southern California. “So maybe everything we can do with space, we can do with time.”

Well, almost everything. Special relativity doesn’t give us a way of going back in time, but it does give us a way of going forward— and at a rate that you can actually control. In fact, thanks to special relativity, you can end up with two twins having different ages, the famous “twin paradox.”

Suppose you head off to the Alpha Centauri star system in your spaceship at a really high speed (something close to the speed of light), while your twin remains on Earth. When you come back home, you’ll find you’re now much younger than your twin. It’s counterintuitive, to say the least, but the physics, after more than a century, is rock solid.

“It is absolutely provable in special relativity that the astronaut who makes the journey, if they travel at very nearly the speed of light, will be much younger than their twin when they come back,” says Janna Levin, a physicist at Barnard College in New York . Interestingly, time appears to pass just as it always does for both twins; it’s only when they’re reunited that the difference reveals itself.

Maybe you were both in your 20s when the voyage began. When you come back, you look just a few years older than when you left, while your twin is perhaps now a grandparent. “My experience of the passage of time is utterly normal for me. My clocks tick at the normal rate, I age normally, movies run at the right pace,” says Levin. “I’m no further into my future than normal. But I’ve travelled into my twin’s future.”

( To study aging, scientist are looking to outer space .)

With general relativity, things really start to get interesting. In this theory, a massive object warps or distorts space and time. Perhaps you’ve seen diagrams or videos comparing this to the way a ball distorts a rubber sheet . One result is that, just as travelling at a high speed affects the rate at which time passes, simply being near a really heavy object—like a black hole —will affect one’s experience of time. (This trick was central to the plot of the 2014 film, Interstellar , in which Matthew McConaughey’s character spends time in the vicinity of a massive black hole. When he returns home, he finds that his young daughter is now elderly.)

To get around the “grandfather paradox,” some scientists theorize there could be multiple timelines. In these images of Nakagin Capsule Tower in Tokyo, Japan, time seems to pass at different rates.

But black holes are just the beginning. Physicists have also speculated about the implications of a much more exotic structure known as a wormhole . Wormholes, if they exist, could connect one location in space-time with another. An astronaut who enters a wormhole in the Andromeda Galaxy in the year 3000 might find herself emerging from the other end in our own galaxy, in the year 2000. But there’s a catch: While we have overwhelming evidence that black holes exist in nature—astronomers even photographed one last year—wormholes are far more speculative.

“You can imagine building a bridge from one region of space-time to another region of space-time,” explains Levin, “but it would require kinds of mass and energy that we don’t really know exist in reality, things like negative energy.” She says it’s “mathematically conceivable” that structures such as wormholes could exist, but they may not be part of physical reality.

There’s also the troubling question of what happens to our notions of cause and effect if backward time travel were possible. The most famous of these conundrums is the so-called “ grandfather paradox .” Suppose you travel back in time to when your grandfather was a young man. You kill him (perhaps by accident), which means your parent won’t be born, which means you won’t be born. Therefore, you won’t be able to travel through time and kill your grandfather.

Multiple timelines?

Over the years, physicists and philosophers have pondered various resolutions to the grandfather paradox. One possibility is that the paradox simply proves that no such journeys are possible; the laws of physics, somehow, must prevent backward time travel. This was the view of the late physicist Stephen Hawking , who called this rule the “ chronology protection conjecture .” (Mind you, he never specified the actual physics behind such a rule.)

But there are also other, more intriguing, solutions. Maybe backward time travel is possible, and yet time travelers can’t change the past, no matter how hard they try. Effingham, whose book Time Travel: Probability and Impossibility was published earlier this year, puts it this way: “You might shoot the wrong person, or you might change your mind. Or, you might shoot the person you think is your grandfather, but it turns out your grandmother had an affair with the milkman, and that’s who your grandfather was all along; you just didn’t know it.”

Which also means the much-discussed fantasy of killing Hitler before the outbreak of World War II is a non-starter. “It’s impossible because it didn’t happen,” says Fabio Costa, a theoretical physicist at the University of Queensland in Australia . “It’s not even a question. We know how history developed. There is no re-do.”

In fact, suggests Effingham, if you can’t change the past, then a time traveler probably can’t do anything . Your mere existence at a time in which you never existed would be a contradiction. “The universe doesn’t care whether the thing you’ve changed is that you’ve killed Hitler, or that you moved an atom from position A to position B,” Effingham says.

But all is not lost. The scenarios Effingham and Costa are imagining involve a single universe with a single “timeline.” But some physicists speculate that our universe is just one among many . If that’s the case, then perhaps time travelers who visit the past can do as they please, which would shed new light on the grandfather paradox.

( The Big Bang could have led to the creation of multiple universes, scientists say .)

“Maybe, for whatever reason, you decide to go back and commit this crime [of killing your grandfather], and so the world ‘branches off’ into two different realities,” says Levin. As a result, “even though you seem to be altering your past, you’re not really altering it; you’re creating a new history.” (This idea of multiple timelines lies at the heart of the Back to the Future movie trilogy. In contrast, in the movie 12 Monkeys , Bruce Willis’s character makes multiple journeys through time, but everything plays out along a single timeline.)

More work to be done

What everyone seems to agree on is that no one is building a time-travelling DeLorean or engineering a custom-built wormhole anytime soon. Instead, physicists are focusing on completing the work that Einstein began a century ago.

After more than 100 years, no one has figured out how to reconcile general relativity with the other great pillar of 20th century physics: quantum mechanics . Some physicists believe that a long-sought unified theory known as quantum gravity will yield new insight into the nature of time. At the very least, says Levin, it seems likely “that we need to go beyond just general relativity to understand time.”

Meanwhile, it’s no surprise that, like H.G. Wells, we continue to daydream about having the freedom to move through time just as we move through space. “Time is embedded in everything we do,” says Johnson. “It looms large in how we perceive the world. So being able to mess with time—I’m not surprised we’re obsessed with that, and fantasize about it.”

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How Back To The Future's Time Travel Works

If you read the words “time travel” on a site like CinemaBlend, you can almost be assured that one thing will instantly come to mind. With the smell of burnt rubber and a familiar twinkle of well-worn musical notes, you can bet that the Back to the Future trilogy is one of those things that almost immediately presents itself in the pop culture consciousness. But we’re not here to talk about whether or not Robert Zemeckis and Bob Gale’s landmark sci-fi trilogy is good, we already know the original is one of the best sci-fi movies of all time. No, we’re here to talk about something much more important: how the time travel in the world of Doc Brown and Marty McFly actually works.

Better still, this academic exercise in temporal studies will open the door to even more examinations in how time travel works at the movies. Just as we’ve previously discussed with Avengers: Endgame , the subject of traveling through the past, present, and future of any given timeline is going to be something we’re going to invest a lot of time into. So if you like what you see here, there’s a great big beautiful tomorrow and/or yesterday waiting for you after! For now though, let’s go back… to the past, present, and future of Hill Valley, California!

The Time Travel In Back To The Future

Now, you can stop me if you’ve heard this story before, as Back to the Future itself has turned 35 this very year. However, a refresher is always a good idea when it comes to the moving pieces that you’ll see moving through the story of Robert Zemeckis and Bob Gale’s legendary sci-fi trilogy. So here’s a quick and basic rundown of what happened throughout the Back to the Future saga:

Who's Time Traveling

Throughout the course of three movies, we see Einstein the Dog, Marty McFly (Sr), Doctor Emmett L. Brown, Jennifer Parker, Biff Tannen, and Clara Clayton all zoom back and forth through time. Oh, don’t forget Jules and Verne, Doc and Clara’s kids. This concerns them too, though just barely.

From When To When

For the intents and purposes of the Back to the Future series, “the present day” is 1985. From that particular point on the timeline, the Back to the Future trilogy’s time travel adventures span between the final film’s trip to 1885 to the then far flung future of 2015 . Two stops in 1955 and a trip to alternate 1985 also take place, because who would have thought time travel was such a dangerous, life altering thing?

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The Purpose Of Their Trip

It all started with a science experiment in Back to the Future , which saw Doc Brown testing his time machine to see if it’d work. But then, Marty McFly accidentally goes back to 1955, and has to correct the mistake of throwing off his parent’s first meeting and falling in love. That’s a simple enough beginning, but then Marty has a double shot of intentional time travel adventures, as Back to the Future Part II starts with Doc bringing Marty and Jennifer to 2015 to save their kids from going to jail, but leads to having to correct old Biff Tannen’s betting streak starting in 1955, and preventing Doc from being murdered by Mad Dog Tannen in 1885. Last, but not least, Marty has to go home to 1985 when all is said and done; because the time continuum.

How Time Travel Happens In Back To the Future

The two main methods of travel in Back to the Future’s trilogy are a converted DeLorean and a converted locomotive. Both vehicles, whether through nuclear radiation, burning garbage, or steam power, need to get to 88 miles per hour, and generate a charge of 1.21 Gigawatts in order to do the thing. When your vehicle of choice hits those milestones, you’re going to see some serious shit… time travel shit!

One very important thing to keep in mind is you need to be mindful of where you’re travelling. The exact spot you’re traveling from is where you’ll arrive when you reach the date of your destination, and what was once a mall parking lot in 1985 could be a pine tree farm in 1955. Hover conversion is recommended, so that whenever and wherever you’re going, you won’t need roads. And thanks to some script changes early on in the franchise’s history, you won’t need Coca Cola either!

Can History Be Changed As A Result Of Time Travel In Back to the Future?

Oh boy, can it. Throughout Back to the Future history, we’ve seen the McFly kids almost wiped out of existence, Doc Brown almost murdered over a simple amount of money, and an entirely different 1985 where Biff Tannen runs Hill Valley, and is rich beyond his wildest dreams. There is a lot of history that’s almost changed in the Back to the Future saga. However, some pieces of history do change permanently, and for the better. One of the most classic examples of the perils of time travel, the Back to the Future trilogy is a single timeline, rewritten as events progress.

Artifacts like photographs, faxes, and matchbooks change as quickly as events are being changed in the timeline. So the better your chances of seeing an event come to pass, the longer that evidence is going to stick around. See also: Jennifer’s fax from Back to the Future Part II surviving until the end of Back to the Future Part III , when a newly wisened Marty rewrites his future by not engaging in 1985’s fateful drag race.

What Are The Consequences Of Time Travel In Back To The Future?

While Back to the Future’s time travel was a messy affair, the end result could be seen as a net positive. And the consequences present themselves in very similar scenarios that hit three main characters in pretty unique ways.

Doc's Consequences

As Doc Brown, his wife Clara, and their sons Jules and Verne are still traveling through the whole of space and time in their souped up locomotive, this could lead to even more chaos throughout the timeline. That’s great for a film and media franchise, but that’s horrible if you want to sleep at night knowing you won’t have to adjust for a consequences of an accidentally generated tangent timeline. Still, Doc got a happy ending, finally finding himself bound to a family he never even knew he wanted until he met Clara, whisking her away to be his companion for all of time and space. Now, why does that sound so familiar ?

Marty's Consequences

Seeing the consequences of the actions his children, his enemies, and even his own self take in their lifetimes, he learns to have more confidence in himself. Marty, much like Doc, found himself a changed man, in relationships that will keep him grounded. But learning not to give in to his more impulsive nature, and to turn the cheek when called a chicken, puts Marty on the presumed path to success as a musician; instead of the working stiff he’d have become if he got into the accident with the Rolls Royce. Like famed science fiction author/father George McFly once said, when you put your mind to it… you can accomplish anything. Which brings us to the evolution of Marty’s father being one of the lynchpins of the Back to the Future series’ altered history.

George McFly's Consequences

George McFly never traveled through time, but he certainly benefited from time travel.

When George McFly and Lorraine Baines first meet, their relationship begins out of pity after he falls out of a tree… while trying to creep on an undressing Lorraine. The course of their love runs in a safe and predictable manner, with a first kiss acting as the highlight to their steady but waning romance. However, once Marty helps his young father discover confidence, and thanks to the timeline presenting George with the opportunity to dethrone Biff Tannen as the big dog, the new George and Lorraine McFly are a pair of lovers that embrace romance and confidence. Proving that so long as you follow the rules of time travel, and know how to play a ripping guitar solo 30 years before it’s ever invented, you too could change the future for the better.

Let's Do Another One!

So there you have it: the world of Back to the Future’s time travel explained, in a simple guide! It’s a process that’s so much fun, we here at CinemaBlend are dedicating ourselves to keeping this subject going. Time travel is a well-beloved staple in sci-fi, and with so many variants on the subject, it’s a handy topic to be an expert on… just in case you find yourself somewhere, or some time, you don’t belong.

If there’s any particular time travel stories you’d like to send to our labs for deconstruction, feel free to suggest them in the comments below! As for the next time you’ll see us in the mood for time travel, it feels like a good time for a Star Trek! And dear readers, if you thought we went on a tangent about tangent timelines this time out, just wait until we break down one of the most iconic installments of that series, Star Trek IV: The Voyage Home .

Though that could always change, as the timeline could always skew in the course of events between here and now. Wibbley wobbley, timey wimey… stuff always comes up, and you never know where or when you’ll be until you get there. So until our next meeting, don’t swipe any sports almanacs, and if a crazy wild-eyed scientist or a kid show up asking about this write up, send them our way. We’ve got some further questions we need to ask them. See you in the future!

Mike Reyes is the Senior Movie Contributor at CinemaBlend, though that title’s more of a guideline really. Passionate about entertainment since grade school, the movies have always held a special place in his life, which explains his current occupation. Mike graduated from Drew University with a Bachelor’s Degree in Political Science, but swore off of running for public office a long time ago. Mike's expertise ranges from James Bond to everything Alita, making for a brilliantly eclectic resume. He fights for the user.

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NASA-funded pulsed plasma rocket concept aims to send astronauts to Mars in 2 months

"The PPR enables a whole new era in space exploration."

An innovative rocket system could revolutionize future deep space missions to Mars, reducing travel time to the Red Planet to just a few months. 

The goal of landing humans on Mars has presented a myriad of challenges, including the need to quickly transport large payloads to and from the distant planet, which, depending on the positions of Earth and Mars, would take almost two years for a round trip using current propulsion technology.

The Pulsed Plasma Rocket (PPR), under development by Howe Industries, is a propulsion system designed to be far more efficient than current methods of deep space propulsion, enabling the trip between Earth and the Red Planet to be made in just two months. Specifically, the rocket will have a high specific impulse or Isp, a measure of how efficiently an engine generates thrust. This technology could therefore enable astronauts and cargo to travel to and from Mars more efficiently and rapidly than existing spacecraft, according to a statement from NASA. 

Related: How long does it take to get to Mars?

Stemming from the Pulsed Fission Fusion concept, the PPR uses a fission-based nuclear power system, which obtains energy from the controlled splitting of atoms, to generate thrust for spacecraft propulsion. However, the PPR is smaller, simpler and more affordable than previous concepts. 

In addition to enabling further range missions, the PPR could support much heavier spacecraft, meaning additional shielding could be installed to reduce a crew's exposure to harmful high-energy particles , called Galactic Cosmic Rays, endured during long-duration spaceflight.

"The PPR enables a whole new era in space exploration," NASA officials said. 

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"The exceptional performance of the PPR, combining high Isp and high thrust, holds the potential to revolutionize space exploration," the statement reads. "The system's high efficiency allows for manned missions to Mars to be completed within a mere two months."

—  NASA funds Venus sample-return, interstellar probes and other far-out space tech

 — NASA, DARPA to launch nuclear rocket to orbit by early 2026

— NASA and DARPA will build a nuclear rocket by 2027

The PPR concept is now moving into Phase II of the NASA Innovative Advanced Concept (NIAC) study, having completed Phase I, which focused on the neutronics of the propulsion system, designing the spacecraft, power system and necessary subsystems, analyzing the magnetic nozzle capabilities, and determining trajectories and benefits, according to the statement. 

During Phase II, developers will build upon the assessments from Phase I to optimize the engine design, perform proof-of-concept experiments and design a spacecraft concept to better protect crewed flights to Mars. Currently visited only by robotic explorers, the PPR could one day bring NASA closer to establishing a permanent base on Mars .  

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Samantha Mathewson joined Space.com as an intern in the summer of 2016. She received a B.A. in Journalism and Environmental Science at the University of New Haven, in Connecticut. Previously, her work has been published in Nature World News. When not writing or reading about science, Samantha enjoys traveling to new places and taking photos! You can follow her on Twitter @Sam_Ashley13. 

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• Unclear Engineer This article is long on assertions and very lacking in explanations. I found this to help explain what a pulsed plasma rocket is https://en.wikipedia.org/wiki/Pulsed_plasma_thruster . And, it sounds like it is not very new or very powerful in its previous versions. So, the development process here is to make a big and powerful version. It is not the plasma fusion created thrust concept that others have been developing. For something about that, see https://pulsarfusion.com/products-development/fusion-propulsion/ . Reply
• danR That (sub-par) video is 3 years old and explains nothing. The text is hardly more helpful. Reply

Unclear Engineer said: This article is long on assertions and very lacking in explanations.

• Unclear Engineer I did not drill down into the article references. But, I would expect NASA to "smell a rat" if the proposal was simply a hoax. The idea seems to be to scale up an existing technology by adding a more powerful energy source to make the electricity needed to create the plasma and direct it aft. The proposal is to use a fission type nuclear reactor instead of solar cells. That seems logical and conceptually doable. We have already build nuclear fission reactors and operated them in space (the SNAP reactors) decades ago. So, it is just a scale-up issue for development, at least conceptually. And the bit about shielding goes along with that. The shielding needed to keep the crew from getting seriously irradiated by the fission reactor in the spacecraft can also be part of the shielding needed to protect the crew from other radiation from the Sun and "cosmic rays". Reply
• Funnyman53(Voytek) Hi, This kind of Theoretical Exercise about Non-existing Space PROPULSION system is A harassment for Logical human mind by NASA... First of all, the Starship from SpaceX will take 90 days to travel to Mars.... So, you telling me that NASA will spend Billions of dollars on Third-party development to "Save" 30days of travel time?! Not to mention this Craft will have Nuclear Reactor on board And we Launch "it" in to Space! WHAT COULD GO WRONG.....?! Reply
• billslugg The pulse rocket is old technology that never panned out due to excessive energy usage, only 10% efficient as compared to other electric propulsion methods such as ion drive. The advantages are simplicity of construction, very small fuel requirements, extremely high exhaust velocity. Reply
• Unclear Engineer There is a good discussion of the differences between "pulsed plasma" and "ion drive" thrusters here: https://en.wikipedia.org/wiki/Plasma_propulsion_engine . Reply

danR said: If you drill down to Dr. Howe's site for details on Howe Industries' PPR concept, and NASA's May 1 rendition ("Pulsed Plasma Rocket (PPR): Shielded, Fast Transits for Humans to Mars" Loura Hall), there's a ramshackle impression redolent of hoaxiness. I don't know why NASA is mixed up with this, and perhaps a Congressional inquiry is what's called for.

• Atlan0001 To heck with velocity, which should only be averaged! Does its pulsed plasma system develop continuous accelerations / decelerations over necessary travel times?! And another question! Mars can get quite a long way from the Earth in its longer orbit of the Sun! Are they talking only periods of time for traveling when Mars closes up in orbit of the Sun nearer to Earth in the two orbits? Which is about every two years in my understanding. They just about have to be talking best orbital closure time (every two years?!) for a heads-on meeting shorter two-month trip! They certainly aren't going to stern chase Mars in any case if they can help it. But there is a longer heads-on to meeting and a shorter heads-on to meeting, per relative positions in orbits. It is one of those matters of intercepting a moving target! Reply
• Unclear Engineer Atlan001, you need to do some study of orbital dynamics, particularly "transfer orbits" to understand what you are asking about. Basically, a spacecraft needs to go from one planet's stable orbit to another planet's stable orbit along a path that is either (1) an elliptical orbit that intersects both planetary orbits, with acceleration at one end and deceleration at the other end, or (2) a path with constant acceleration to (approximately) half way there and deceleration the second half of the trip. (Yes, there are combinations of the 2 concepts that are also possible). The technical approach to defining a specific transfer orbit involves writing a Lagrange equation for the intended process and solving it. It is not trivial to learn. You could start here: https://www.researchgate.net/publication/253281043_ANALYSIS_OF_LOW_THRUST_ORBIT_TRANSFERS_USING_THE_LAGRANGE_PLANETARY_EQUATIONS Reply
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Self-Esteem

Mental time travel boosts sense of control and self-esteem, imagining oneself in the future or recalling a nostalgic past can be beneficial..

Posted May 12, 2024 | Reviewed by Jessica Schrader

• What Is Self-Esteem?
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• “Mental time travel” may increase self-esteem and a sense of coherence and control.
• One aspect of mental time travel is reliving nostalgic events from the past (called retrospection).
• Another aspect involves imagining oneself in the future (called prospection).

Published in Personality and Social Psychology Review , a recent study by Stephan and Sedikides suggests mental time travel can increase self-esteem , coherence, and sense of control.

But what is mental time travel? Let me use an example.

A friend of mine who is in a committed romantic relationship and very much in love tells me that he often relives the day he and his partner first met. He also imagines what their future would be like (e.g., their wedding day, their life as parents).

In both cases, my friend is engaging in mental time travel .

Simply put, mental time travel involves projecting oneself either forward or backward in time. As illustrated, reliving a past event requires reconstructing it from memory , whereas pre-living a potential future event requires imagination .

Benefits of Imagining the Future

Imagining yourself in the distant future (called prospection) allows you to step back and see the bigger picture—to focus on living according to your core values, achieving long-term goals , and living a satisfying and meaningful life.

It also enhances the feeling that future outcomes are under your control. It promotes the belief that your intentions, determination, and commitment will make goal pursuit possible no matter what challenges come your way. Finally, prospection may even increase self-esteem.

Benefits of Nostalgia and Recalling the Past

The same is true of moving backward in time and nostalgizing.

Nostalgia refers to longing and affection for valued past events and a desire to re-experience them. Previous research shows nostalgia can be an important psychological and relationship resource.

For instance, it can help people cope with boredom and meaninglessness . Romantic nostalgia may enhance passion, intimacy, commitment, and relationship satisfaction. Even nostalgic memories of an ex-romantic partner may have benefits and influence perceptions of self-growth .

Self-Affirmation

Mental time travel emphasizes aspects of the self that are positive, abstract, and central to one’s identity , as opposed to aspects that are negative or situation-specific. In other words, it stresses long-term goals, personal values, and positive personality traits, instead of current behaviors and more immediate plans and goals.

Therefore, mental time travel serves as self-affirmation . The core facets of self-affirmation include:

• Control: Feeling empowered to pursue desired goals; believing one can influence valued outcomes.
• Self-esteem: Having a positive subjective evaluation of one’s worth (i.e., liking yourself).
• Coherence: Being able to make sense of one’s experiences and to see life as meaningful.

How Does Mental Time Travel Foster Self-Validation?

To explain how mental time travel can promote self-validation and self-affirmation, let's look at another example, this one courtesy of an old classmate (let’s call her Emma).

Emma told me that before applying to nursing school, she failed a genetics course, which really affected her self-confidence . She felt stupid, incompetent, and worthless.

Eventually, Emma decided to engage in mental time travel—both recalling nostalgic events and imagining herself in the future. Doing so facilitated perspective-taking and seeing the bigger picture: She became more deeply aware of her core values (e.g., authenticity , social justice, making a difference) and positive personality traits (e.g., creativity , compassion , sensitivity, and gratitude ).

And failing genetics no longer defined her.

Additionally, Emma found that by engaging in prospection and retrospection regularly, subsequent challenges became increasingly manageable, including those she faces now in her teaching career as a nursing professor. Consistent with this, Stephan and Sedikides propose that “self-affirmation might serve to strengthen the psychological immune system in non-threatening situations, thus protecting against potential future threats.”

Threats to the adequacy and integrity of one’s sense of self come in many shapes and forms: getting fired, being rejected romantically by a desired mate, receiving negative health news, failing a course or getting a bad grade, etc.

The research discussed suggests that by imagining one’s future self or recalling nostalgic memories, one could get in touch with who they truly are—as defined by their positive personality traits, core values, and long-term goals.

Several positive psychology interventions could be helpful for this purpose, such as nostalgia interventions .

Or, consider the Best Possible Self exercise. Take some time to picture a future where everything in your life has gone as well as possible. Imagine living life in full accordance with your values, having accomplished all your most important goals and realized all your dreams .

What does such a happy, successful life look like? Write about it. This exercise has been shown to improve mood, optimism , and well-being.

Arash Emamzadeh attended the University of British Columbia in Canada, where he studied genetics and psychology. He has also done graduate work in clinical psychology and neuropsychology in U.S.

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Play School: Big Ted's Time Machine

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Get ready to time travel as Play School steps back in time and looks to the future. Play School rediscovers how music was played, retro fashion, games and more. And what the future may be like with gadgets and gizmos galore!

10 Movies Where the Main Character Meets Their Past or Future Self

Facing yourself has never been so literal.

Read update

There's no shortage of time travel movies that feature moments where characters confront their past or future selves, which often become unforgettable scenes and central aspects of the films themselves.

Time travel can be tricky business as there’s always the looming threat of changing events too much and unintentionally changing the world for the worse. However, while most time travel movies keep this danger in mind throughout, others throw caution to the wind and have their protagonist interact directly with a past/future version of themselves. Whether the interaction is just for a second or for the whole movie, there’s always some interesting growth and possible conflict that comes from the main character coming across a younger/older version of themselves.

Recently, Ryan Reynolds came across a younger version of his character Adam, played by Walker Scobell , in Netflix's The Adam Project and plenty of MCU fans are wondering which versions of Doctor Strange will appear in the upcoming Doctor Strange in the Multiverse of Madness . So, before another time travel encounter happens on the big screen, it’s a good time to look at movies where the main character has an unexpected look in the mirror.

Updated on May 19, 2023, by Hannah Saab:

10 'the kid' (2000).

An unfairly overlooked film from the 2000s , Disney’s live-action film The Kid embodies the sweet, heartwarming impact that stories about meeting your younger self can have.

The film follows abrasive image consultant Russ ( Bruce Willis ) as he meets his eight-year-old self ( Spencer Breslin ) and develops a strong bond that makes him rethink his life and try to work towards a better future. Willis and Breslin have fun chemistry and make their growing bond easily touch your heart.

Watch on Disney+

9 'Zathura' (2005)

Although the arrival of Dax Shepard ’s Astronaut in Zathura seems like the sci-fi board game simply giving feuding brothers Danny ( Jonah Bobo ) and Walter ( Josh Hutcherson ) a mediator as they try to reach the end of the game, he ends up having a deeper connection to Walter.

As the Astronaut talks about his own experience in the game, he acts more as a personal mentor for Walter and the big heartfelt reveal of the Astronaut being an older version of Walter adds another surprisingly emotional layer to Zathura ’s story.

8 'Austin Powers: The Spy Who Shagged Me' (1999)

The second Austin Powers movie, The Spy Who Shagged Me , had plenty of fun antics with time-traveling, but none were as great as Austin ( Mike Myers ) working with himself to stop Dr. Evil (also Myers).

To save his partner Felicity Shagwell ( Heather Graham ), from a terrible death, Austin jumps back in time to get some help from himself in saving his girl and the world. Although it’s short, two Austin Powers coming together ( played by the same actor ) is hilarious with how can’t resist each other’s “sex appeal.”

7 'The Adam Project' (2022)

Netflix’s blockbuster, The Adam Project , sees Ryan Reynolds meet his comedic match in Walker Scobell as the two play older and younger versions of Adam, respectively, as they attempt to save the world.

Reynolds and Scobell show strong comedic chemistry with one another that makes them feel like the same person. The growth they each have in meeting one another, as well as their deceased father ( Mark Ruffalo ), lead to some surprisingly emotional conclusions.

Watch on Netflix

6 'Meet the Robinsons' (2007)

Throughout Disney’s heavily underrated animated film Meet the Robinsons , you can’t help but hope that boy genius Lewis (voiced by Jordan Fry ) eventually finds his older self as he meets his future family, and the moment he finally does, it’s genuinely special.

Lewis meeting his older self, who goes by the name Cornelius (voiced by Tom Selleck ), causes him to rethink his life and ultimately not change the instance of him becoming an orphan that guided his life going forward. It’s truly the mentorship he needs and excellently reemphasizes the film’s central message to “keep moving forward.”

5 'Looper' (2012)

Rian Johnson ’s 2012 hit sci-fi action thriller Looper was likely one of the first films to come to mind when thinking about characters coming face to face with themselves as it’s a central aspect of its iconic premise.

Looper sees its main hitman Joe ( Joseph Gordon-Levitt ) pitted in a terrible twist of fate when he’s forced to eliminate his future self, played by Bruce Willis, to “close his loop.” The meeting between Joe and his older self certainly isn’t as happy as others on this list, but it’s a thrilling encounter that leads to one of the more original and tragic sci-fi thrill rides of the last decade.

Watch on Prime Video

4 'Deadpool 2' (2018)

While Cable ( Josh Brolin ) does most of the time traveling in Deadpool 2 , Marvel’s merc with a mouth gets his chance to rewrite history in the film’s post-credits scene.

Along his journey in taking out Ryan Reynolds before he becomes Green Lantern and stopping Vanessa ( Morena Baccarin ) from being killed, Deadpool (Reynolds) heads back to X-Men Origins: Wolverine to put a bullet in that film’s incarnation of the character and officially become the one and only Deadpool.

3 'Star Trek' (2009)

One of the best surprises of J.J. Abrams ’ 2009 Star Trek reboot was Leonard Nimoy 's return as Spock as it leads to an amazing generational connection.

Nimoy and Zachary Quinto 's Spock interacting with each other is a perfect passing of the torch moment that connects fans, past and present, in a heartfelt way. It pays great respect to Spock’s legacy and ends up playing a strong role in Spock’s character arc throughout the reboot series.

Watch on Paramount+

2 'X Men: Days of Future Past' (2014)

X Men: Days of Future Past has plenty of moments X-Men fans still rave about, including the introduction to Evan Peters ’ Quicksilver and watching Hugh Jackman ’s Wolverine fight in the past, but nothing compared to watching both Patrick Stewart 's and James McAvoy 's Professor X share the screen.

It’s the quintessential moment of the past and present colliding in the film and it’s incredibly touching to see Stewart’s Xavier convince McAvoy’s Xavier to hope again and save mutant kind.

1 '2001: A Space Odyssey' (1968)

Stanley Kubrick’s iconic 2001: Space Odyssey features a more horrifying and chilling look at scientist David Bowman ( Keir Dullea ) seeing his future self.

As Bowman makes his way to Jupiter to investigate the alien monolith, he’s eventually brought into a room that has him see a rapidly aging version of himself that he eventually becomes. There’s a kind of cosmic horror vibe to the scene: it's haunting yet it feels like a fitting end to David’s harrowing journey.

Watch on HBO Max

NEXT: The Best Time Travel Movies, Ranked

The most memorable time travel movies

Posted: March 7, 2024 | Last updated: March 7, 2024

There are fun travel movies, often involving road trips. Bob Hope and Bing Crosby did it over and over. Sometimes, though, the travel isn’t across the globe, or even across space. They are across time. Time travel has been an oft-used trope of science fiction and other fantastical genres for years. Some of the biggest movies of all time involve time travel, but they aren’t the only memorable ones. These are the most memorable time travel films. If you don’t have time to read them now, well, maybe you need a time machine of your own.

'Back to the Future' (1985)

The quintessential time travel movie. One of the biggest hits of all time. The progenitor of two very good sequels. (Yes, we like the third movie.) Marty McFly goes back in time in a DeLorean thanks to his friend Doc Brown and ends up intertwined in the life of his eventual parents back in 1955. Plus, all that Huey Lewis!

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'Bill & Ted’s Excellent Adventure' (1989)

Another film that spawned a trilogy. This comedy is on the sillier side. Bill and Ted are dimwitted high school students who use their time machine to collect important historical figures so they can avoid failing. One of the breakthrough roles for Keanu Reeves, it’s indeed most excellent.

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'Terminator 2: Judgment Day' (1991)

This time around, we had to go with a sequel in a series. The Terminator is a good movie, but a bleak horror film. Terminator 2 got a bigger budget and a much larger scope. It’s an epic ‘90s action film, the one that really made this a franchise with legs. It also helped take Arnold Schwarzenegger’s career to the next level.

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'12 Monkeys' (1995)

Based on a French short film, Terry Gilliam made time travel trippy and grim. In the future, humanity has almost entirely been wiped out by a disease. Bruce Willis is sent back in time in order to figure out the cause of the disease, but he’s sent to the wrong time and ends up in a mental hospital. That just makes his quest that much harder.

'Army of Darkness' (1992)

After spending two movies dealing with evil spirits in a cabin in the woods, Ash finds himself traveled back to medieval times, but that doesn’t give him a break from all the ghouls that torment him. Army of Darkness is a slapstick horror comedy from Sam Raimi and star Bruce Campbell, but that works better than you might think. Hail to the king, baby.

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'Interstellar' (2014)

Christopher Nolan loves to mess with time and create notable imagery. Interstellar was daunting even to people who watched Inception , as much for its lengthy run time as its heady plot. That being said, it delved headlong into a scientific notion of time travel, and the cast is also quite impressive. Time has been kind to the reputation of  Interstellar .

'Austin Powers: The Spy Who Shagged Me' (1999)

In a way, Austin Powers travels through time in the first film, but that’s more due to cryogenic freezing. In the sequel, he actually travels through time. The Spy Who Shagged Me was a massive hit, and while a lot of it feels like rehashes of the first film, there was enough fresh stuff to keep the movie fun.

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'A Connecticut Yankee in King Arthur’s Court' (1949)

Mark Twain’s novel has been adapted several times, something loosely. This 1949 version is fairly faithful, and it also has quite the cast, led by Bing Crosby. With Crosby involved, they turned the film into a musical naturally.

'The Final Girls' (2015)

If you like horror comedies, this under-the-radar film is one worth seeking out. A group of friends find themselves transported into a 1986 slasher film called Camp Bloodbath . The star of that film happened to be one of the character’s mother, who happened to die a few years earlier. As such, they are technically traveling through time and into a film.

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'Last Night in Soho' (2021)

Edgar Wright has done horror-movie pastiches in the past, but they were often loving comedic takes on the genre. This time, he made a straight-up horror film. A young woman in modern London travels back in time when she sleeps, but then she quickly realizes the past that she romanticized was far from ideal.

'Kate & Leopold' (2001)

A fish-out-of-water romantic comedy, this time that fish isn’t just some fancy city folk in the country. No, he’s a duke from the 1800s, and he’s played by Hugh Jackman. You’d think that would be detrimental to Meg Ryan falling in love with him, but you’d be wrong.

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'Hot Tub Time Machine' (2010)

Hey, the ‘80s, right? Hot Tub Time Machine is a raunchy comedy that is mostly a series of jokes about how the ‘80s were different. It’s not going to win any Oscars. However, it is called Hot Tub Time Machine , and it did spawn a sequel. It’s not a great movie, but it has a good cast and some memorable jokes.

'Avengers: Endgame' (2019)

Well, Avengers: Endgame is one of the highest-grossing movies ever, and the culmination of over a decade of films in the biggest movie series in the world. We’d call that fairly memorable. It’s hard to spoil a film that a ton of people have seen, so we’re OK with mentioning the fact that the surviving Avengers decide to use time travel to try and defeat Thanos after failing to do so initially.

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'Looper' (2012)

What if time travel was verboten and also kind of banal? That’s the world of Looper . Joseph Gordon-Levitt plays a hitman who kills people sent back from the future by the future mob. However, someday he will have to “close his loop,” which is to say kill the future version of himself. Then, when his future self shows up — played by Bruce Willis — he manages to escape, and that really complicates things.

'Source Code' (2011)

Source Code kind of ratchets up 12 Monkeys to a whole new level. A train has been exploded by a bomb, and Jake Gyllenhaal is sent into a digital recreation of the event to try and identify the perpetrator. He has to go into the same eight-minute stretch over and over, with things bending and shaping over time.

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'Star Trek' (2009)

When they decided to reboot  Star Trek , they also decided to add some time travel into the mix. This made for a time-and-space hopping story, for starters. However, it also allowed them to have Leonard Nimoy show up to play older Spock, giving this movie two different Spocks!

'Men in Black 3' (2012)

Men in Black was really good, but Men in Black II was lackluster. In order to add some spice back into the proceedings, time travel was added into the mix. Will Smith’s Agent J has to go back in time to try and save K from death. Then, he runs into young K, played by Josh Brolin doing a great Tommy Lee Jones impression.

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'Time Bandits' (1981)

Another Terry Gilliam film for the list. This is a lighter film than 12 Monkeys , though more a fantasy adventure than a comedy. It’s a story about a boy who joins up with, well, time pirates essentially. The crew of a ship travel through spacetime to steal treasures throughout the ages.

'Timecop' (1994)

Hey, it may not be all that good, but Timecop delivers what it promises. It’s a silly Jean-Claude Van Damme action movie involving time travel. Basically, it’s what you expect from a movie called Timecop . It was a big hit, though, and it also featured a memorable end to Ron Silver’s character.

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'Tenet' (2020)

Nolan saw people’s reaction to Interstellar and thought, “Ah, clearly I made that film too straightforward.”  Tenet is trippy and basically everybody is going to have trouble following it at least in fits and starts. It involves people experiencing time forwards and backwards simultaneously. John David Washington fights a backwards version of himself. Tenet is bonkers, but it’s also a ton of fun. Sometimes you just want to go along for the ride.

'Indiana Jones and the Dial of Destiny' (2023)

After all these years, we got one last Indiana Jones movie. Harrison Ford has often come across like playing even, say, Han Solo, is akin to pulling teeth for him. However, he always seemed to genuinely love playing Indy. In the past he was present as the Ark of the Covenant melted Nazis, and he met a centuries-old knight and found the Holy Grail. In "Dial of Destiny," he also finally time travels. The film is merely fine, but it is nice that Ford got to bid adieu to the character.

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Money blog: Can my lender end my fixed-rate mortgage early?

A reader wants to know why her two-year fixed mortgage is ending after 18 months - we get an expert to take a look. Read this in our weekend edition of the Money blog below and leave your thoughts in the comments box. We'll be back with regular updates after the bank holiday on Tuesday.

Monday 27 May 2024 08:19, UK

Weekend Money

• 'My mortgage lender is ending my two-year fix and I haven't been in the house for two years - can they do this?'
• How much is pocket money in 2024 and where are kids spending it? New data reveals all
• Inflation, election and energy bills: What a big week of announcements means for your pocket
• Ford engine problems, inflation data scepticism and BT landline switch: What readers have said this week

Best of the week

• What now for mortgages after inflation and election announcements?
• Ian King : Here's why price cap is still £300 more than before Ukraine war
• Which biscuits have the least sugar? Your guide to elevenses
• Savings Guide: Britons urged to act quickly to grab above-inflation savings rates while they last
• Best of the Money blog - an archive

Ask a question or make a comment

Every Monday we get an expert to answer your money problems or consumer disputes. Find out how to submit yours at the bottom of this post. Today's question is...

I bought my first flat in April 2023 with a two-year fixed-rate mortgage. I got the deal with the help of a broker, who has now contacted me saying my deal is due to end in November - significantly earlier than I had expected. I've spoken to my lender - they said the deal I was on no longer exists. Is there anything I can do to keep my current rate?  Michelle, Kent

We asked David Hollingworth, associate director at L&C Mortgages , to answer this one...

Fixed mortgage rates do what they say on the tin and lock in the interest rate payable for a specified period of time.  Those periods will generally be blocked into market sectors and so are usually tagged as two, three or five-year fixed rates.  

Once that deal is taken, the terms cannot be changed by the lender and the rate can't be brought to an end early.

Some lenders will fix their deals for a specific number of years from completion, but a lot of lenders' rates will be fixed until a specific end date. That could mean that the fix will last even longer than two years at the point that the application is made.

However, it can take time to complete a deal, especially when purchasing a property which may be subject to a lengthy chain. 

Mortgage offers will typically be valid for up to six months. If you originally agreed to buy your flat before the end of 2022 then the deal on offer at the time could feasibly have been fixed until November 2024. 

That could have equated to two years or more when you applied but if it took some time to complete the purchase, it would explain why you feel that you haven't benefited from a full two years of the fixed rate.

It would be a good idea to look back at the original mortgage offer, which will specify all the product details. That will detail when the fixed rate ends and what rate the mortgage will move onto after that. 

That's likely to be a higher variable rate, so it makes sense to shop around for a better deal well before the current rate comes to an end. 

A broker will be able to help you work out the best available rates for you, whether from your current lender or from across the whole market. 

This feature is not intended as financial advice - the aim is to give an overview of the things you should think about.  Submit your dilemma or consumer dispute via:

• The form above - you need to leave a phone number or email address so we can contact you for further details
• Email [email protected] with the subject line "Money blog"
• WhatsApp us  here

By Bhvishya Patel , Money team

Pocket money is in decline, data shows - but kids are finding new ways to pay for their everyday "essentials".

Data from the Natwest pocket money index  (looking at transactions from 308,000 children in the Rooster app) shows only 30% of families now pay pocket money as part of a regular routine (down 2%), with children getting £3.78 on average a week (down 10p from last year).

In fact, pocket money now makes up just 14% of children's income. Instead they're finding new income streams - with a typical child netting £479.96 a year (£9.23 a week) for one-off chores or entrepreneurship.

These "salaries" obviously differ for age groups... 

• £5.68 for a six-year-old 
• £24.71 for a 17-year-old

British children are now charging extra for chores and squeezing more money out of their side hustles.

• Car cleaning earned £3.25 on average - 32% (79p) more than a year ago
• Paper round earnings increased 2% (45p) to £23.10 a week
• However, it's been a less good year for reselling - with earnings down 15% to £22.62 a week.

Arguably the most interesting part of the data is where kids are spending their money.

Amazon was top, with Tesco and McDonald's next. Primark, Co-op, PlayStation, Xbox, Sainsbury's and Asda are next in that order - but there's no place this year for Apple, which has been replaced by fashion brand Shein, rounding off the top 10.

NatWest Rooster Money said "kids' money is completely changing shape"... 

"Kids are increasingly complementing [pocket money] in other, more sophisticated ways. This move to greater independence and maturity in their earning has been fantastic to see and bodes well for some bright, financially confident futures ahead." Will Carmichael, chief executive and founder of NatWest Rooster Money

An illustration of this maturity is kids' saving rate of 9.5% - not far off the adult average of 10.2%. Gaming, holidays and the future were the top three saving incentives, in that order.

Is there a right answer?

Kirsty Ketley, a parenting specialist from Surrey, said she gave her 11-year-old daughter Ella £5 and her seven-year-old son Leo £2 a week in cash.

They both started receiving pocket money when they were six.

"I often say to parents, even with children as young as four, it's fine to start giving a bit of pocket money because it's such an important life skill to have – to learn how to manage money because you don't get taught it," she said.

Presenter and children's author Konnie Huq, who has two sons, Covey, 12, and Huxley, 10, told the Money team that a regular pocket money allowance was a "really good way" of getting children into the habit of earning and spending.

She said receiving a regular allowance helped teach children "responsibility" and "financial literacy".

"That's what they will be doing as the grown-ups they become," she said. "I've always said kids are shaping and forming between 0 to seven. You want to put the values in them now in these younger years that they will take through with them in their life."

Sharon Olivero-Chapman, chief executive and founder of Harrienna Health, disagrees. She has always thought a regular pocket money figure is the "wrong message to give to children" - and her daughter Harriet, 13, is one of those raking it in from side hustles.

"Pocket money gives them the wrong association with money," she said. "They're just given money on a plate, whereas that's not real life, is it?"

Ms Olivero-Chapman said if her daughter did want to buy something she had to work out how she could get that money and would then be given chores to earn it. She said it was £1 to unload and fill the dishwasher, £1 to fill and empty the washing machine and 50p to make her bed.

"It's not a regular thing every week," she explained.

Ms Olivero-Chapman said the family's entrepreneurial bug had rubbed off on Harriet and she began running her own Etsy store business last year which sees her personalise phone cases. Her business has earned nearly £1,000 so far.

Your pocket money stories - how much, how and in return for what

The Dursuns, Scotland

Aga Dursun, 41, a PMO analyst from Erskine, gives her 13-year-old son Galip £3 a day and her nine-year-old son Troy £1 a day via transfers into a Starling account. They also get £20 each on her pay day. No chores are required.

"It gives them a lot of freedom and they learn the value of money as well because for example now if they want more expensive trainers they have to save up," she says.

"It's mostly spent on games which breaks my heart."

The Shaws, London

Sammy Shaw, from Enfield, said she gave her eight-year-old twins Teddy and Hope £3.50 a week via the Natwest Rooster Money card.

To earn the money, her son and daughter are set a number of activities which they must complete  - if they don't, money is deducted.

"My two have got an exceptional amount they have got to do. The first thing they've got to do is make their bed, get dressed independently. When they go downstairs they've got to do 10 minutes of practice on the keyboard, they do Times Tables Rock Stars (a digital maths app) and then 10 minutes of reading. 

"The parent has to go into the app and approve these activities and if they don't do them it takes percentages off."

Last year, the twins saved up to buy theatre tickets for the family at £35 a pop.

The Regulskis, Wales

Over in Caerphilly, Dean Regulski, 44, has a fairly similar routine: money in return for washing, ironing, dog walking, laundry and vacuuming. He and his wife give kids Emmeline, Nancy and Abraham (aged 12 to 15) £10 a week also using Rooster.

"Every time they want to make a transaction, it pings my phone so straight away I can have a conversation with them about what they are buying and if it's just sweets I can limit it on the app so it's a £1 transaction," Dean says.

"My son the other day was asking if he could buy something that was beyond the £40 and I said he can take it out next month but that will cost extra chores. I explained the concept of interest to him."

The Moores, West Midlands

Ben Moore, 40, from Solihull, said his 13-year-old twin daughters had got £5 a week in pocket money for the past two years.

They used GoHenry before switching to a debit card.

"We spent a year on GoHenry and it was good because we could say 'you can't spend it on McDonald's' and restrict the type of spending but there was a monthly fee for it," he said.

Chores are not a requirement as he is "really keen" his daughters use the money to "go out with their friends rather than just sit on their phones".

The Scotts, Wiltshire

Fiona Scott, 58, from Swindon in Wiltshire, said her three children Samantha, 24, Georgia, 22, and David, 17, all got pocket money until they were able to make their own money.

"We've always had a little book at home showing this is what is coming in and going out and this is what we've got to spend, so I've encouraged them all to do that in different ways. They've got used to seeing and understanding what a household budget is," she said.

The Joneses, West Midlands

Mother-of-three Jenny Jones, 43, said her 11-year-old daughter Rebecca receives £10 a month - no chores, but everyone is expected to muck in.

It started off with 50p a week when she was seven but when she turned 11, Ms Jones opened up a junior account at Barclays and money goes in monthly.

"It's taught her general management around money. At the moment she loves bubble tea and she loves getting bits of jewellery so it's a case of her thinking what does she want, can she afford both? It enables her to make those decisions.

"It's just those life lessons, isn't it? We can't have everything we want and you've got to make those decisions - and it's okay to make the wrong decision, which is normal."

The main topics from the Money blog that got you commenting this week were...

• Known issues with Ford EcoBoost engines
• Inflation drops to 2.3% 

BT delays switch from analogue landlines

'My second-hand Ford is being written off with a known issue - but no one is taking responsibility'

Every Monday, we get an expert to answer your money problems or consumer disputes. 

This week, Rory Raftery told us about a known issue with his Ford C-Max which had caused it to be written off. He asked if there was anything he could do. 

Dozens of readers wrote in to say they had similar issues. 

Money Blog, I had a Ford Focus with an EcoBoost Engine that failed after 62k miles on it, and Ford won't entertain any responsibility because not full Ford service history, offered no help whatsoever, have and are being treated appallingly at every level. Damian Moynihan

Bought a second hand EcoBoost 1.0 13 plate Focus from a broker… had it less than three months and the car has had sudden coolant loss and engine failure due to a cylinder head crack, almost a £5,000 repair. Ford need to be held accountable for this, it's ridiculous... no warning light, no temperature rises and then bang the car's engine is finished. The car has covered 73,000 miles. Gareth from Wigan

The Ford EcoBoost problem has prompted a recall for US cars with the exact same issue. Yet in the UK Ford are doing nothing about the issue. There is a Facebook page with over 20k members all experiencing the same issue and Ford refuse to acknowledge the issue, in the UK at least. anonymous

Here's what Ford had to say when we published Rory's problem: "Ford is confident in the robustness and reliability of its EcoBoost engine technology when the stated guidelines for maintenance and service are followed. 

"Ford UK is happy to investigate service support and/or compensation measures for any customer who believes they have had an EcoBoost engine issue and is happy to review cases with a full-service history for vehicles up to 10 years old with less than 150,000 miles.

"For any customers in the UK whose vehicle meets these parameters, you can speak to our customer relationship team and contact details can be found on our website  here ." 

The company said timely and correct servicing as outlined in the owner's manual was key for wet belt maintenance and any illuminated dashboard warning lights should always receive attention. 

On Wednesday, we got the latest inflation figures, showing it had dropped to 2.3% in April - down from 3.2% in March.

A drop to 2.1% had been expected by the Bank of England, but it showed the fight against price rises was being won.

Here's what some readers had to say about it... 

All my experiences when I go grocery shopping don't fill me with optimism that prices are almost stabilising. Particularly household items, such as cleaning costs, are still rising steadily and frequently. An item I buy was £3 something a matter of weeks ago. This morning... £5. Su H

Am I the only person who thinks that increasing the minimum wage by 10% in April and the knock-on effect of increasing wages by more than 8% in labour intensive industries is going to cause an increase in inflation that will make a reduction in interest rates very unlikely? Rayayre

The national living wage for workers increased by 9.8% on 1 April from £10.42 to £11.44.  

Since the recent decline in inflation is largely due to energy prices, can anyone name a specific government action that influenced energy prices traded on the international market? This government can't resist taking credit for everything! Marek

You have written this story as a failure of government to bring inflation down to a level some analysts forecast, despite it being a huge drop and within a whisker of the 2% target. It reads like a piece one would expect to hear coming from a Labour politician. Tom Jeffries

I don't believe this for one moment, did my shopping yesterday the price of food is disgracefully high still and takes up most of my income as a family. Andrea

I have seen no change in the cost of living, my car insurance is up 10%, council tax did the same. Shrinkflation is still going on. Food prices may have stopped increasing, but they have not gone down. My job as an assessor had its hours and pay cut of 1/3, bills remain! StevieB

Inflation down but prices remain high, my mortgage and day-to-day bills are still cripplingly high while my wages stagnate. In real terms I've never had so little disposable income. The cost of living crisis is far from over. Kingsholm_Neil

How does UK inflation compare around the world ? KevinPB

We found the answer to this one on Wednesday...

Why are prices on certain things still expensive and will they ever go down? Nick12

On Nick's question, inflation coming down doesn't mean prices are. It just means prices are rising at a slower rate. 

For prices to drop, we would need negative inflation, which isn't common. 

But, in the April data, we did see it in the energy sector thanks to the price cap change. 

On Monday, BT Group pushed back its timetable for moving all customers off the Public Switched Telephone Network (PSTN) and on to digital landlines.

From this summer, customers who have not used their landline in the past 12 months, who do not identify as vulnerable or have additional needs, have not contacted an Alarm Receiving Centre (ARC) in the past 24 months and live in an area where a data sharing agreement is in place, will be switched - unless they have opted out.

Vulnerable customers or those with additional needs will start to be switched from summer 2025, with the aim to have all customers moved off the old analogue PSTN by the end of January 2027.

We have a thatched house and no mobile signal. We signed up to Fibre-to-the-Premises (FttP) and despite protests, we were "upgraded" to digital voice at "no extra cost". Time to give us back our copper which always works - even when we have no electricity. Ian P

Living in a rural area where we have power cuts for different reasons and internet signal is non-existent without Wi-Fi, how will we stay connected? Melanie

I live in Lancaster but my signal is so poor that I have to ask family to call me on my landline. How on earth are we supposed to manage without one? Pat

Three big announcements this week could have significant implications for the money in your pocket.

First, April's inflation data , which on the face of it was good news. 

Price rises slowed to 2.3%, within touching distance of the Bank of England's 2% target and into what economists regard as normal levels.

The Bank has repeatedly stressed that interest rates (which have been elevated to squeeze spending and encourage saving, which usually stops prices going up so quickly) would start to fall when the 2% figure was sustainably hit.

Herein lies the issue - sustainability. Because while headline CPI has fallen dramatically from highs of more than 11% in 2022, a closer look at the numbers suggests the fight against price rises isn't over just yet.

Core inflation, which strips out the volatile elements like energy and food, remains at 3.9% - while service inflation is at 5.9%. All of these numbers, including the headline figure, are above forecasts.

All of which has prompted markets to price in an August rate cut from 5.25% to 5% - previously they'd expected June.

Economics editor Ed Conway wrote this analysis...

Some suggested the fall in inflation, combined with the IMF upgrading UK growth forecasts , provided Rishi Sunak with a positive platform on which to call a summer election.

Conway isn't so sure.

He says: "We're out of recession. That's one of the key things they were waiting for. Inflation is now down to a normal level. Those things have been ticked off [but] there are a couple of issues. 

"First of all, it doesn't look like, with inflation not falling quite as far as everyone would have expected, that the final thing they were hoping for, the Bank of England cutting interest rates, is going to happen in June. There probably is not going to be an interest rate cut before the election. That's quite significant.

"Secondly, when people look at this election, it's that old question: do you feel better off than you did four or five years ago? 

"And in this case, there is no parliamentary period in history where people have seen their real disposable incomes squeezed as much as this one. 

"That's what the prime minister's fighting against."

We took a closer look at what the election and new interest rate forecasts mean for mortgages and the housing market here...

We also examined what the election result on 4 July could mean for people's finances, honing in on what we know about the major parties' plans from childcare to train fares to tax...

Finally, energy bills will fall again in July after Friday's price cap announcement.

They'll be £122 (annually) below the April-June figure.

However, daily standing charges are going up - which means those who use more energy will feel the most benefit from the price cap fall...

Sir Keir Starmer told us that Labour's plan for a new company called Great British Energy would help bring prices down...

And business presenter Ian King explained why energy bills are still £300 more than before the Ukraine war...

The Money blog is your place for consumer news, economic analysis and everything you need to know about the cost of living - bookmark news.sky.com/money.

It runs with live updates every weekday - while on Saturdays we scale back and offer you a selection of weekend reads.

Check them out this morning and we'll be back on Monday with our regular Money Problem feature - and full rolling news and features after the bank holiday on Tuesday. 

The Money team is Emily Mee, Bhvishya Patel, Jess Sharp, Katie Williams, Brad Young and Ollie Cooper, with sub-editing by Isobel Souster. The blog is edited by Jimmy Rice.

Cara Delevingne's childhood home is up for sale - but it's come to market with a huge £23.5m price tag. 

The 5,456 sq ft property in London's Belgravia was also home to controversial casino and zoo owner John Aspinall in the 1960s. 

Mr Aspinall and the mansion were also linked to the disappearance of Lord Lucan in 1974 - a mystery that still hasn't been solved. 

After he died in 2000, the five-bedroom house was bought by Charles and Pandora Delevingne - the parents of supermodel Cara and her older sisters Chloe and Poppy.

The Grade II-listed building on Lyall Street comes with two reception rooms, a study, a home cinema and a professional chef's kitchen. 

A gym, sauna, steam room and rooftop cocktail bar are also included. 

In around 2014, with their daughters grown up, the Delevingnes moved from the Lyall Street mansion and downsized.

The current owners bought the house a couple of years later and have given the mansion an extensive renovation and modernisation. 

"It is one of the best houses currently available for sale in Belgravia and is immaculately presented and beautifully interior designed," said Charles Lloyd, head of Beauchamp Estates. 

The reason for the fall in the household energy price cap is pretty straightforward - wholesale electricity and gas prices have fallen since the price cap was last set in February this year.

Wholesale gas and electricity prices make up by far the biggest proportion of the energy bills - £720 of the current £1,690 - and Ofgem is assuming, for July, August and September, a wholesale electricity price of 22.36 pence per kilowatt hour (kWh), down from 24.50 pence per kWh during the current quarter.

It is also assuming a wholesale gas price of 5.48 pence per kWh from July to September, down from 6.04 pence per kWh during the current quarter.

That brings down the wholesale energy component of the typical bill (which is based on an assumption that a household will use 12,000 kWh per year of gas and 2,900 kWh of electricity) from £720 to £619.

The question some people may have, though, is why the energy price cap that Ofgem has set for the three months from July remains higher, at £1,568, than the level at which it was set - £1,277 - at the time the energy crisis was sparked by Russia's invasion of Ukraine.

At first blush, this seems a reasonable enough question, given that a barrel of Brent Crude - a reasonable enough proxy for wholesale energy prices - stands today at $80.78 (£63.50) per barrel, down from the heights it hit after the invasion.

But bear in mind that, in those days, the price cap was only set by Ofgem every six months, rather than quarterly as at present.

The price cap in place immediately before the crisis came into effect on 1 October 2021 having been set on 6 August that year.

Prior to that, wholesale energy prices had been lower than they are now. The wholesale energy component for the price cap for the winter of 2021/22 was, accordingly, £528 - lower than the £619 it will be from July.

Other costs taken into account by Ofgem are also higher now than they were before Russia invaded Ukraine.

The UK needs "longer term solutions" on energy prices because they are still "record high almost", Sir Keir Starmer has said.

The Labour leader was commenting on a fall in the energy price cap.

From 1 July it will be £1,568 a year - a drop of £122 from the previous quarter. 

But Sir Keir said many people were still struggling to make ends meet.

"Everywhere I go, so many people tell me the cost of living is still bearing down on them," he told Sky News.

"People on a mortgage, [those] coming off a fixed mortgage, know their mortgages are going up by hundreds of pounds.

"Everybody knows prices are still going up - energy prices are still record high almost."

He added: "We need longer term solutions."

Labour's proposed Great British Energy (GBE) would help energy prices "come down for good", Sir Keir claimed.

GBE would be a publicly owned company with a mandate to invest in clean energy – wind, solar, tidal, nuclear and other emerging technologies. It would be designed to invest in riskier areas where the private sector might be reluctant.

Asked when energy prices would drop under GBE, and how quickly it could be established, he said: "Certainly by the end of the parliament, and a lot sooner than that.

"We can set up Great British Energy pretty quickly."

Discussions are already under way with potential partners, he added.

Claire Coutinho, the energy secretary, told Sky News that Great British Energy is a "complete gimmick" and a "drop in the ocean".

She also accused Labour of having "no plan" on energy security.

Putting off "life admin" could be costing you thousands of pounds a year, research has suggested.

It is estimated that adults in the UK could save £300 a year by cancelling unused subscriptions, £420 by reviewing their day-to-day finances, and £372 by re-evaluating a gym membership. 

"On average, Brits admit to putting off simple tasks by four to six months," Lloyds Bank said.

When asked why they had been delaying, almost a fifth (18%) said there was no deadline, one in seven (16%) said it was easier to take no action, while for 13% the memory of previous difficulties was off-putting.

Turning to the future, a fifth (20%) admitted not having a pension, while only two fifths (42%) knew how to add more money to their pension if they had one. 

If you are looking for a detailed analysis of today's cut in the energy price cap (see our breaking news post from 7am) then the following from Martin Lewis is worth digesting.

The founder of Money Saving Expert has split his reaction into three sections.

Lewis says the cap will drop on 1 July by an average of 7.2% for Direct Debit customers, 6.9% for prepay customers, and 7.1% for those who pay when they get a bill.

The cap will fall to £1,568 a year - a drop of £122 from the previous quarter. 

Standing charges (what you pay regardless of how much energy you use) "remain high" and are "virtually unchanged", Lewis says.

"All the cut" is via unit rates, he adds.

That means those who use more energy will be seeing bigger savings.

The electricity unit rate for Direct Debit customers from July will be 22.36p/kwH - down 9% from 24.5p, Lewis says.

The electricity standing charge will be 60.12p a day - up from 60.1p.

The gas unit rate will be 5.48p/kwH - down 9% from 6.04p.

And the gas standing charge will be 31.41p - slightly down from 31.43p.

Lewis says the results of a consultation on standing charges are likely to be published sometime in the "summer", adding: "Whenever that is."

As we reported in our post at 7.34am, respected market researcher Cornwall Insight is predicting that bills are likely to rise once more in the run-up to winter. 

Lewis comments: "If they're right this is the last fall, and the coming rises are big.

"On 1 July it's confirmed [the cap] drops 7%, so for every £100 paid today you pay £93. 

"Then on 1 Oct it's predicted to rise 12%, so you'll go back up and be paying £104. 

"Then on 1 Jan the crystal ball is saying it'll stay flat (at £104). 

"All this makes the cheapest fixes, which are currently 9% cheaper than now (so £91 per £100 on the price cap), look a decent bet."

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