what does light travel through in space

How Does Light Travel Through Space? Facts & FAQ

Last Updated on Mar 15 2024

Light is such a fundamental part of our lives. From the moment we’re born, we are showered with all kinds of electromagnetic radiation, both colorful, and invisible. Light travels through the vacuum of space at 186,828 miles per second as transverse waves , outside of any material or medium, because photons—the particles that make up light—also behave as waves. This is referred to as the wave-particle duality of light.  

• What Is Light?

The wave-particle duality of light simply means that light behaves as both waves and particles . Although this has been long accepted as fact, scientists only managed to observe both these properties of light ¹ simultaneously for the first time in 2015.

As a wave, light is electromagnetic radiation—vibrations, or oscillations, of the electric and magnetic fields. As particles, light is made up of little massless packets of energy called photons ¹ .

• What Are Light Waves?

Waves are the transference of energy from one point to another. If we dropped a pebble into a small pond, the energy that the impact creates would transfer as a ripple, or a wave, that travels through the surface of the water, from one water particle to another, until eventually reaching the edge of the pond.

This is also how sound waves work—except that, with sound, it’s the pressure or vibrations of particles in the air that eventually reach our ears.

Unlike water and sound, light itself is electromagnetic radiation—or light waves—so it doesn’t need a medium to travel through.

• What Are Transverse Waves?

Light propagates through transverse waves. Transverse waves refer to a way in which energy is transferred.

Transverse waves oscillate at a 90-degree angle (or right angle) to the direction the energy is traveling in. An easy way to picture this is to imagine an S shape flipped onto its side. The waves would be going up and down, while the energy would be moving either left or right.

With light waves ¹ , there are 2 oscillations to consider. If the light wave is traveling on the X axis, then the oscillations of the electric field would be at a right angle, either along the Y or Z axes, and the oscillations of the magnetic field would be on the other.

• Can Anything Travel Faster Than Light?

The simple answer to this question is no, as far as we know at this time, nothing can go faster than the speed of light ¹ . Albert Einstein’s special theory of relativity states that “no known object can travel faster than the speed of light in a vacuum.”

Space and time don’t yet exist beyond the speed of light—if we were to travel that fast, the closer we get to the speed of light, the more our spatial dimension would shrink, until eventually collapsing.

Beyond this, the laws of physics state that as an object approaches the speed of light , its mass would become infinite, and so would the energy it would need to propel it. Since it’s probably impossible to create an infinite amount of energy, it would be difficult for anything to travel faster than light.

Tachyon, a hypothetical particle, is said to travel faster than the speed of light. However, because its speed would not be consistent with the known laws of physics, physicists believe that tachyon particles do not exist.

• Final Thoughts

Light travels through space as transverse, electromagnetic waves. Its wave-particle duality means that it behaves as both particles and waves. As far as we know, nothing in the world travels as fast as light.

• https://phys.org/news/2015-03-particle.html
• https://www.nature.com/articles/ncomms7407
• https://www.wtamu.edu/~cbaird/sq/2017/07/20/is-the-reason-that-nothing-can-go-faster-than-light-because-we-have-not-tried-hard-enough/
• https://www.physics.brocku.ca/PPLATO/h-flap/phys6_1f_1.png
• https://science.nasa.gov/ems/02_anatomy

Featured Image Credit: NASA, Unsplash

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• Sound & Light (Physics): How are They Different?

How Does Light Travel?

Sound & Light (Physics): How are They Different?

The question of how light travels through space is one of the perennial mysteries of physics. In modern explanations, it is a wave phenomenon that doesn't need a medium through which to propagate. According to quantum theory, it also behaves as a collection of particles under certain circumstances. For most macroscopic purposes, though, its behavior can be described by treating it as a wave and applying the principles of wave mechanics to describe its motion.

Electromagnetic Vibrations

In the mid 1800s, Scottish physicist James Clerk Maxwell established that light is a form of electromagnetic energy that travels in waves. The question of how it manages to do so in the absence of a medium is explained by the nature of electromagnetic vibrations. When a charged particle vibrates, it produces an electrical vibration that automatically induces a magnetic one -- physicists often visualize these vibrations occurring in perpendicular planes. The paired oscillations propagate outward from the source; no medium, except for the electromagnetic field that permeates the universe, is required to conduct them.

A Ray of Light

When an electromagnetic source generates light, the light travels outward as a series of concentric spheres spaced in accordance with the vibration of the source. Light always takes the shortest path between a source and destination. A line drawn from the source to the destination, perpendicular to the wave-fronts, is called a ray. Far from the source, spherical wave fronts degenerate into a series of parallel lines moving in the direction of the ray. Their spacing defines the wavelength of the light, and the number of such lines that pass a given point in a given unit of time defines the frequency.

The Speed of Light

The frequency with which a light source vibrates determines the frequency -- and wavelength -- of the resultant radiation. This directly affects the energy of the wave packet -- or burst of waves moving as a unit -- according to a relationship established by physicist Max Planck in the early 1900s. If the light is visible, the frequency of vibration determines color. The speed of light is unaffected by vibrational frequency, however. In a vacuum, it is always 299,792 kilometers per second (186, 282 miles per second), a value denoted by the letter "c." According to Einstein's Theory of Relativity, nothing in the universe travels faster than this.

Refraction and Rainbows

Light travels slower in a medium than it does in a vacuum, and the speed is proportional to the density of the medium. This speed variation causes light to bend at the interface of two media -- a phenomenon called refraction. The angle at which it bends depends on the densities of the two media and the wavelength of the incident light. When light incident on a transparent medium is composed of wave fronts of different wavelengths, each wave front bends at a different angle, and the result is a rainbow.

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What is the speed of light? Here’s the history, discovery of the cosmic speed limit

On one hand, the speed of light is just a number: 299,792,458 meters per second. And on the other, it’s one of the most important constants that appears in nature and defines the relationship of causality itself.

As far as we can measure, it is a constant. It is the same speed for every observer in the entire universe. This constancy was first established in the late 1800’s with the experiments of Albert Michelson and Edward Morley at Case Western Reserve University . They attempted to measure changes in the speed of light as the Earth orbited around the Sun. They found no such variation, and no experiment ever since then has either.

Observations of the cosmic microwave background, the light released when the universe was 380,000 years old, show that the speed of light hasn’t measurably changed in over 13.8 billion years.

In fact, we now define the speed of light to be a constant, with a precise speed of 299,792,458 meters per second. While it remains a remote possibility in deeply theoretical physics that light may not be a constant, for all known purposes it is a constant, so it’s better to just define it and move on with life.

How was the speed of light first measured?

In 1676 the Danish astronomer Ole Christensen Romer made the first quantitative measurement of how fast light travels. He carefully observed the orbit of Io, the innermost moon of Jupiter. As the Earth circles the Sun in its own orbit, sometimes it approaches Jupiter and sometimes it recedes away from it. When the Earth is approaching Jupiter, the path that light has to travel from Io is shorter than when the Earth is receding away from Jupiter. By carefully measuring the changes to Io’s orbital period, Romer calculated a speed of light of around 220,000 kilometers per second.

Observations continued to improve until by the 19 th century astronomers and physicists had developed the sophistication to get very close to the modern value. In 1865, James Clerk Maxwell made a remarkable discovery. He was investigating the properties of electricity and magnetism, which for decades had remained mysterious in unconnected laboratory experiments around the world. Maxwell found that electricity and magnetism were really two sides of the same coin, both manifestations of a single electromagnetic force.

As Maxwell explored the consequences of his new theory, he found that changing magnetic fields can lead to changing electric fields, which then lead to a new round of changing magnetic fields. The fields leapfrog over each other and can even travel through empty space. When Maxwell went to calculate the speed of these electromagnetic waves, he was surprised to see the speed of light pop out – the first theoretical calculation of this important number.

What is the most precise measurement of the speed of light?

Because it is defined to be a constant, there’s no need to measure it further. The number we’ve defined is it, with no uncertainty, no error bars. It’s done. But the speed of light is just that – a speed. The number we choose to represent it depends on the units we use: kilometers versus miles, seconds versus hours, and so on. In fact, physicists commonly just set the speed of light to be 1 to make their calculations easier. So instead of trying to measure the speed light travels, physicists turn to more precisely measuring other units, like the length of the meter or the duration of the second. In other words, the defined value of the speed of light is used to establish the length of other units like the meter.

How does light slow down?

Yes, the speed of light is always a constant. But it slows down whenever it travels through a medium like air or water. How does this work? There are a few different ways to present an answer to this question, depending on whether you prefer a particle-like picture or a wave-like picture.

In a particle-like picture, light is made of tiny little bullets called photons. All those photons always travel at the speed of light, but as light passes through a medium those photons get all tangled up, bouncing around among all the molecules of the medium. This slows down the overall propagation of light, because it takes more time for the group of photons to make it through.

In a wave-like picture, light is made of electromagnetic waves. When these waves pass through a medium, they get all the charged particles in motion, which in turn generate new electromagnetic waves of their own. These interfere with the original light, forcing it to slow down as it passes through.

Either way, light always travels at the same speed, but matter can interfere with its travel, making it slow down.

Why is the speed of light important?

The speed of light is important because it’s about way more than, well, the speed of light. In the early 1900’s Einstein realized just how special this speed is. The old physics, dominated by the work of Isaac Newton, said that the universe had a fixed reference frame from which we could measure all motion. This is why Michelson and Morley went looking for changes in the speed, because it should change depending on our point of view. But their experiments showed that the speed was always constant, so what gives?

Einstein decided to take this experiment at face value. He assumed that the speed of light is a true, fundamental constant. No matter where you are, no matter how fast you’re moving, you’ll always see the same speed.

This is wild to think about. If you’re traveling at 99% the speed of light and turn on a flashlight, the beam will race ahead of you at…exactly the speed of light, no more, no less. If you’re coming from the opposite direction, you’ll still also measure the exact same speed.

This constancy forms the basis of Einstein’s special theory of relativity, which tells us that while all motion is relative – different observers won’t always agree on the length of measurements or the duration of events – some things are truly universal, like the speed of light.

Can you go faster than light speed?

Nope. Nothing can. Any particle with zero mass must travel at light speed. But anything with mass (which is most of the universe) cannot. The problem is relativity. The faster you go, the more energy you have. But we know from Einstein’s relativity that energy and mass are the same thing. So the more energy you have, the more mass you have, which makes it harder for you to go even faster. You can get as close as you want to the speed of light, but to actually crack that barrier takes an infinite amount of energy. So don’t even try.

How is the speed at which light travels related to causality?

If you think you can find a cheat to get around the limitations of light speed, then I need to tell you about its role in special relativity. You see, it’s not just about light. It just so happens that light travels at this special speed, and it was the first thing we discovered to travel at this speed. So it could have had another name. Indeed, a better name for this speed might be “the speed of time.”

Related: Is time travel possible? An astrophysicist explains

We live in a universe of causes and effects. All effects are preceded by a cause, and all causes lead to effects. The speed of light limits how quickly causes can lead to effects. Because it’s a maximum speed limit for any motion or interaction, in a given amount of time there’s a limit to what I can influence. If I want to tap you on the shoulder and you’re right next to me, I can do it right away. But if you’re on the other side of the planet, I have to travel there first. The motion of me traveling to you is limited by the speed of light, so that sets how quickly I can tap you on the shoulder – the speed light travels dictates how quickly a single cause can create an effect.

The ability to go faster than light would allow effects to happen before their causes. In essence, time travel into the past would be possible with faster-than-light travel. Since we view time as the unbroken chain of causes and effects going from the past to the future, breaking the speed of light would break causality, which would seriously undermine our sense of the forward motion of time.

Why does light travel at this speed?

No clue. It appears to us as a fundamental constant of nature. We have no theory of physics that explains its existence or why it has the value that it does. We hope that a future understanding of nature will provide this explanation, but right now all investigations are purely theoretical. For now, we just have to take it as a given.

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Why is the speed of light the way it is?

It's just plain weird.

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of Ask a Spaceman and Space Radio , and author of " How to Die in Space ." He contributed this article to Space.com's Expert Voices: Op-Ed & Insights . 

We all know and love the speed of light — 299,792,458 meters per second — but why does it have the value that it does? Why isn't it some other number? And why do we care so much about some random speed of electromagnetic waves? Why did it become such a cornerstone of physics? 

Well, it's because the speed of light is just plain weird.

Related: Constant speed of light: Einstein's special relativity survives a high-energy test

Putting light to the test

The first person to realize that light does indeed have a speed at all was an astronomer by the name of Ole Romer. In the late 1600s, he was obsessed with some strange motions of the moon Io around Jupiter. Every once in a while, the great planet would block our view of its little moon, causing an eclipse, but the timing between eclipses seemed to change over the course of the year. Either something funky was happening with the orbit of Io — which seemed suspicious — or something else was afoot.

After a couple years of observations, Romer made the connection. When we see Io get eclipsed, we're in a certain position in our own orbit around the sun. But by the next time we see another eclipse, a few days later, we're in a slightly different position, maybe closer or farther away from Jupiter than the last time. If we are farther away than the last time we saw an eclipse, then that means we have to wait a little bit of extra time to see the next one because it takes that much longer for the light to reach us, and the reverse is true if we happen to be a little bit closer to Jupiter.

The only way to explain the variations in the timing of eclipses of Io is if light has a finite speed.

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Making it mean something

Continued measurements over the course of the next few centuries solidified the measurement of the speed of light, but it wasn't until the mid-1800s when things really started to come together. That's when the physicist James Clerk Maxwell accidentally invented light.

Maxwell had been playing around with the then-poorly-understood phenomena of electricity and magnetism when he discovered a single unified picture that could explain all the disparate observations. Laying the groundwork for what we now understand to be the electromagnetic force , in those equations he discovered that changing electric fields can create magnetic fields, and vice versa. This allows waves of electricity to create waves of magnetism, which go on to make waves of electricity and back and forth and back and forth, leapfrogging over each other, capable of traveling through space.

And when he went to calculate the speed of these so-called electromagnetic waves, Maxwell got the same number that scientists had been measuring as the speed of light for centuries. Ergo, light is made of electromagnetic waves and it travels at that speed, because that is exactly how quickly waves of electricity and magnetism travel through space.

And this was all well and good until Einstein came along a few decades later and realized that the speed of light had nothing to do with light at all. With his special theory of relativity , Einstein realized the true connection between time and space, a unified fabric known as space-time. But as we all know, space is very different than time. A meter or a foot is very different than a second or a year. They appear to be two completely different things.

So how could they possibly be on the same footing?

There needed to be some sort of glue, some connection that allowed us to translate between movement in space and movement in time. In other words, we need to know how much one meter of space, for example, is worth in time. What's the exchange rate? Einstein found that there was a single constant, a certain speed, that could tell us how much space was equivalent to how much time, and vice versa.

Einstein's theories didn't say what that number was, but then he applied special relativity to the old equations of Maxwell and found that this conversion rate is exactly the speed of light.

Of course, this conversion rate, this fundamental constant that unifies space and time, doesn't know what an electromagnetic wave is, and it doesn't even really care. It's just some number, but it turns out that Maxwell had already calculated this number and discovered it without even knowing it. That's because all massless particles are able to travel at this speed, and since light is massless, it can travel at that speed. And so, the speed of light became an important cornerstone of modern physics.

But still, why that number, with that value, and not some other random number? Why did nature pick that one and no other? What's going on?

Related: The genius of Albert Einstein: his life, theories and impact on science

Making it meaningless

Well, the number doesn't really matter. It has units after all: meters per second. And in physics any number that has units attached to it can have any old value it wants, because it means you have to define what the units are. For example, in order to express the speed of light in meters per second, first you need to decide what the heck a meter is and what the heck a second is. And so the definition of the speed of light is tied up with the definitions of length and time.

In physics, we're more concerned with constants that have no units or dimensions — in other words, constants that appear in our physical theories that are just plain numbers. These appear much more fundamental, because they don't depend on any other definition. Another way of saying it is that, if we were to meet some alien civilization , we would have no way of understanding their measurement of the speed of light, but when it comes to dimensionless constants, we can all agree. They're just numbers.

One such number is known as the fine structure constant, which is a combination of the speed of light, Planck's constant , and something known as the permittivity of free space. Its value is approximately 0.007. 0.007 what? Just 0.007. Like I said, it's just a number.

So on one hand, the speed of light can be whatever it wants to be, because it has units and we need to define the units. But on the other hand, the speed of light can't be anything other than exactly what it is, because if you were to change the speed of light, you would change the fine structure constant. But our universe has chosen the fine structure constant to be approximately 0.007, and nothing else. That is simply the universe we live in, and we get no choice about it at all. And since this is fixed and universal, the speed of light has to be exactly what it is.

So why is the fine structure constant exactly the number that it is, and not something else? Good question. We don't know.

Learn more by listening to the episode "Why is the speed of light the way it is?" on the Ask A Spaceman podcast, available on iTunes and on the Web at http://www.askaspaceman.com. Thanks to Robert H, Michael E., @DesRon94, Evan W., Harry A., @twdixon, Hein P., Colin E., and Lothian53 for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter.

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].

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars," Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.

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• voidpotentialenergy This is just my opinion but i think L speed is it's speed because the particle part of it is the fastest it can interact with the quanta distance in quantum fluctuation. Light is particle and wave so the wave happens in the void between quanta. Gravity probably travels in that void and why gravity seems instant. Reply
• rod The space.com article wraps up the discussion with, "So on one hand, the speed of light can be whatever it wants to be, because it has units and we need to define the units. But on the other hand, the speed of light can't be anything other than exactly what it is, because if you were to change the speed of light, you would change the fine structure constant. But our universe has chosen the fine structure constant to be approximately 0.007, and nothing else. That is simply the universe we live in, and we get no choice about it at all. And since this is fixed and universal, the speed of light has to be exactly what it is. So why is the fine structure constant exactly the number that it is, and not something else? Good question. We don't know." It seems that the *universe* made this decision, *But our universe has chosen the fine structure constant to be...* I did not know that the universe was capable of making decisions concerning constants used in physics. E=mc^2 is a serious constant. Look at nuclear weapons development, explosive yields, and stellar evolution burn rates for p-p chain and CNO fusion rates. The report indicates why alpha (fine structure constant) is what it is and c is what it is, *We don't know*. Reply

Admin said: We all know and love the speed of light, but why does it have the value that it does? Why isn't it some other number? And why did it become such a cornerstone of physics? Why is the speed of light the way it is? : Read more

rod said: The space.com article wraps up the discussion with, "So on one hand, the speed of light can be whatever it wants to be, because it has units and we need to define the units. But on the other hand, the speed of light can't be anything other than exactly what it is, because if you were to change the speed of light, you would change the fine structure constant. But our universe has chosen the fine structure constant to be approximately 0.007, and nothing else. That is simply the universe we live in, and we get no choice about it at all. And since this is fixed and universal, the speed of light has to be exactly what it is. So why is the fine structure constant exactly the number that it is, and not something else? Good question. We don't know." It seems that the *universe* made this decision, *But our universe has chosen the fine structure constant to be...* I did not know that the universe was capable of making decisions concerning constants used in physics. E=mc^2 is a serious constant. Look at nuclear weapons development, explosive yields, and stellar evolution burn rates for p-p chain and CNO fusion rates. The report indicates why alpha (fine structure constant) is what it is and c is what it is, *We don't know*.

• rod FYI. When someone says *the universe has chosen*, I am reminded of these five lessons from a 1982 Fed. court trial. The essential characteristics of science are: It is guided by natural law; It has to be explanatory by reference to natural law; It is testable against the empirical world; Its conclusions are tentative, i.e., are not necessarily the final word; and It is falsifiable. Five important points about science. Reply
• Gary If the universe is expanding , how can the speed of light be constant ( miles per second , if each mile is getting longer ) ? Can light's velocity be constant while the universe expands ? So, with the expansion of the universe , doesn't the speed of light need to increase in order to stay at a constant velocity in miles per second ? Or, do the miles in the universe remain the same length as the universe 'adds' miles to its diameter ? Are the miles lengthening or are they simply being added / compounded ? Reply
• Gary Lets say we're in outer space and we shoot a laser through a block of glass. What causes the speed of the laser light to return to the speed it held prior to entering the block of glass ? Is there some medium in the vacuum of space that governs the speed of light ? Do the atoms in the glass push it back up to its original speed. If so, why don't those same atoms constantly push the light while it travels through the block of glass ? Reply

Gary said: Lets say we're in outer space and we shoot a laser through a block of glass. What causes the speed of the laser light to return to the speed it held prior to entering the block of glass ? Is there some medium in the vacuum of space that governs the speed of light ? Do the atoms in the glass push it back up to its original speed. If so, why don't those same atoms constantly push the light while it travels through the block of glass ?

Gary said: If the universe is expanding , how can the speed of light be constant ( miles per second , if each mile is getting longer ) ? Can light's velocity be constant while the universe expands ? So, with the expansion of the universe , doesn't the speed of light need to increase in order to stay at a constant velocity in miles per second ? Or, do the miles in the universe remain the same length as the universe 'adds' miles to its diameter ? Are the miles lengthening or are they simply being added / compounded ?

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A Journey of Light through Space and Time

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Physics Fox

How Light moves through Space

A light introduction the law of reflection.

• Light always moves through space in a straight line . This is easiest to see with a ray box or a laser.

• Light is the fastest thing in the universe when moving through empty space (aka. a vacuum ).

Straight lines

I'm travelling at the speed of light I wanna make a supersonic woman of you

How does light move through space? Can it travel whatever path it feels like?

Not quite — in fact there's a law that describes this:

If light didn't move in a straight line, you'd be able to see round corners!

Most luminous objects emit light in all directions , but this is still only in straight lines. We can check this by blocking almost all the light from bulb, apart from a small slit. This contraption is called a ray box.

Shadows are also an example of light moving in a straight line. A shadow is simply a region where light doesn't reach (because something's in the way). If you trace the line between a light source, the edge of an object, and the edge of its shadow, you will always get a straight line.

The speed of light

Anything that travels must have a speed . A car might travel at 60 miles per hour, or a plane might fly at 600 miles per hour.

A rocket can travel at 6000 miles per hour.

The Earth moves round the sun at 67,000 miles per hour.

This seems very fast, but it pales in comparison to the speed of light. Light travels at 670,000,000 miles per hour (= 300,000,000 m/s ).

This is outrageously fast. In fact, it's so fast that nothing else can keep up — light is the fastest thing in the universe .

Here's something to put that speed into perspective: It takes light just 1 second to reach the moon from Earth, whereas it would take a jumbo jet over 15 days (if planes could fly through space). That's over a million times longer!

Technically, light only moves at this speed when travelling through empty space (also known as a vacuum ). Light travels slower (although still incredibly quickly) when moving though materials, such as glass and water.

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May 20, 2016

How does light travel?

by Matt Williams, Universe Today

Ever since Democritus – a Greek philosopher who lived between the 5th and 4th century's BCE – argued that all of existence was made up of tiny indivisible atoms, scientists have been speculating as to the true nature of light. Whereas scientists ventured back and forth between the notion that light was a particle or a wave until the modern, the 20th century led to breakthroughs that showed that it behaves as both.

These included the discovery of the electron, the development of quantum theory, and Einstein's Theory of Relativity. However, there remains many fascinating and unanswered questions when it comes to light, many of which arise from its dual nature. For instance, how is it that light can be apparently without mass, but still behave as a particle? And how can it behave like a wave and pass through a vacuum, when all other waves require a medium to propagate?

Theory of Light in the 19th Century:

During the Scientific Revolution, scientists began moving away from Aristotelian scientific theories that had been seen as accepted canon for centuries. This included rejecting Aristotle's theory of light, which viewed it as being a disturbance in the air (one of his four "elements" that composed matter), and embracing the more mechanistic view that light was composed of indivisible atoms.

In many ways, this theory had been previewed by atomists of Classical Antiquity – such as Democritus and Lucretius – both of whom viewed light as a unit of matter given off by the sun. By the 17th century, several scientists emerged who accepted this view, stating that light was made up of discrete particles (or "corpuscles"). This included Pierre Gassendi, a contemporary of René Descartes, Thomas Hobbes, Robert Boyle, and most famously, Sir Isaac Newton.

Newton's corpuscular theory was an elaboration of his view of reality as an interaction of material points through forces. This theory would remain the accepted scientific view for more than 100 years, the principles of which were explained in his 1704 treatise "Opticks, or, a Treatise of the Reflections, Refractions, Inflections, and Colours of Light". According to Newton, the principles of light could be summed as follows:

• Every source of light emits large numbers of tiny particles known as corpuscles in a medium surrounding the source.
• These corpuscles are perfectly elastic, rigid, and weightless.

This represented a challenge to "wave theory", which had been advocated by 17th century Dutch astronomer Christiaan Huygens. . These theories were first communicated in 1678 to the Paris Academy of Sciences and were published in 1690 in his "Traité de la lumière" ("Treatise on Light"). In it, he argued a revised version of Descartes views, in which the speed of light is infinite and propagated by means of spherical waves emitted along the wave front.

Double-Slit Experiment:

By the early 19th century, scientists began to break with corpuscular theory. This was due in part to the fact that corpuscular theory failed to adequately explain the diffraction, interference and polarization of light, but was also because of various experiments that seemed to confirm the still-competing view that light behaved as a wave.

The most famous of these was arguably the Double-Slit Experiment, which was originally conducted by English polymath Thomas Young in 1801 (though Sir Isaac Newton is believed to have conducted something similar in his own time). In Young's version of the experiment, he used a slip of paper with slits cut into it, and then pointed a light source at them to measure how light passed through it.

According to classical (i.e. Newtonian) particle theory, the results of the experiment should have corresponded to the slits, the impacts on the screen appearing in two vertical lines. Instead, the results showed that the coherent beams of light were interfering, creating a pattern of bright and dark bands on the screen. This contradicted classical particle theory, in which particles do not interfere with each other, but merely collide.

The only possible explanation for this pattern of interference was that the light beams were in fact behaving as waves. Thus, this experiment dispelled the notion that light consisted of corpuscles and played a vital part in the acceptance of the wave theory of light. However subsequent research, involving the discovery of the electron and electromagnetic radiation , would lead to scientists considering yet again that light behaved as a particle too, thus giving rise to wave-particle duality theory.

Electromagnetism and Special Relativity:

Prior to the 19th and 20th centuries, the speed of light had already been determined. The first recorded measurements were performed by Danish astronomer Ole Rømer, who demonstrated in 1676 using light measurements from Jupiter's moon Io to show that light travels at a finite speed (rather than instantaneously).

By the late 19th century , James Clerk Maxwell proposed that light was an electromagnetic wave, and devised several equations (known as Maxwell's equations) to describe how electric and magnetic fields are generated and altered by each other and by charges and currents. By conducting measurements of different types of radiation (magnetic fields, ultraviolet and infrared radiation), he was able to calculate the speed of light in a vacuum (represented as c).

In 1905, Albert Einstein published "On the Electrodynamics of Moving Bodies", in which he advanced one of his most famous theories and overturned centuries of accepted notions and orthodoxies. In his paper, he postulated that the speed of light was the same in all inertial reference frames, regardless of the motion of the light source or the position of the observer.

Exploring the consequences of this theory is what led him to propose his theory of Special Relativity, which reconciled Maxwell's equations for electricity and magnetism with the laws of mechanics, simplified the mathematical calculations, and accorded with the directly observed speed of light and accounted for the observed aberrations. It also demonstrated that the speed of light had relevance outside the context of light and electromagnetism.

For one, it introduced the idea that major changes occur when things move close the speed of light, including the time-space frame of a moving body appearing to slow down and contract in the direction of motion when measured in the frame of the observer. After centuries of increasingly precise measurements, the speed of light was determined to be 299,792,458 m/s in 1975.

Einstein and the Photon:

In 1905, Einstein also helped to resolve a great deal of confusion surrounding the behavior of electromagnetic radiation when he proposed that electrons are emitted from atoms when they absorb energy from light. Known as the photoelectric effect, Einstein based his idea on Planck's earlier work with "black bodies" – materials that absorb electromagnetic energy instead of reflecting it (i.e. white bodies).

At the time, Einstein's photoelectric effect was attempt to explain the "black body problem", in which a black body emits electromagnetic radiation due to the object's heat. This was a persistent problem in the world of physics, arising from the discovery of the electron, which had only happened eight years previous (thanks to British physicists led by J.J. Thompson and experiments using cathode ray tubes).

At the time, scientists still believed that electromagnetic energy behaved as a wave, and were therefore hoping to be able to explain it in terms of classical physics. Einstein's explanation represented a break with this, asserting that electromagnetic radiation behaved in ways that were consistent with a particle – a quantized form of light which he named "photons". For this discovery, Einstein was awarded the Nobel Prize in 1921.

Wave-Particle Duality:

Subsequent theories on the behavior of light would further refine this idea, which included French physicist Louis-Victor de Broglie calculating the wavelength at which light functioned. This was followed by Heisenberg's "uncertainty principle" (which stated that measuring the position of a photon accurately would disturb measurements of it momentum and vice versa), and Schrödinger's paradox that claimed that all particles have a " wave function ".

In accordance with quantum mechanical explanation, Schrodinger proposed that all the information about a particle (in this case, a photon) is encoded in its wave function, a complex-valued function roughly analogous to the amplitude of a wave at each point in space. At some location, the measurement of the wave function will randomly "collapse", or rather "decohere", to a sharply peaked function. This was illustrated in Schrödinger famous paradox involving a closed box, a cat, and a vial of poison (known as the "Schrödinger's Cat" paradox).

According to his theory, wave function also evolves according to a differential equation (aka. the Schrödinger equation). For particles with mass, this equation has solutions; but for particles with no mass, no solution existed. Further experiments involving the Double-Slit Experiment confirmed the dual nature of photons. where measuring devices were incorporated to observe the photons as they passed through the slits.

When this was done, the photons appeared in the form of particles and their impacts on the screen corresponded to the slits – tiny particle-sized spots distributed in straight vertical lines. By placing an observation device in place, the wave function of the photons collapsed and the light behaved as classical particles once more. As predicted by Schrödinger, this could only be resolved by claiming that light has a wave function, and that observing it causes the range of behavioral possibilities to collapse to the point where its behavior becomes predictable.

The development of Quantum Field Theory (QFT) was devised in the following decades to resolve much of the ambiguity around wave-particle duality. And in time, this theory was shown to apply to other particles and fundamental forces of interaction (such as weak and strong nuclear forces). Today, photons are part of the Standard Model of particle physics, where they are classified as boson – a class of subatomic particles that are force carriers and have no mass.

So how does light travel? Basically, traveling at incredible speeds (299 792 458 m/s) and at different wavelengths, depending on its energy. It also behaves as both a wave and a particle, able to propagate through mediums (like air and water) as well as space. It has no mass, but can still be absorbed, reflected, or refracted if it comes in contact with a medium. And in the end, the only thing that can truly slow down or arrest the speed of light is gravity (i.e. a black hole).

What we have learned about light and electromagnetism has been intrinsic to the revolution which took place in physics in the early 20th century, a revolution that we have been grappling with ever since. Thanks to the efforts of scientists like Maxwell, Planck, Einstein, Heisenberg and Schrodinger, we have learned much, but still have much to learn.

For instance, its interaction with gravity (along with weak and strong nuclear forces) remains a mystery. Unlocking this, and thus discovering a Theory of Everything (ToE) is something astronomers and physicists look forward to. Someday, we just might have it all figured out!

Source: Universe Today

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Science Struck

How Does Light Travel Through Space and Other Media?

Light is one of the most enigmatic of entities in the universe. You are not the first person to carefully reflect upon this question about light travel. From Galileo, Newton, to Einstein, every one of the great minds has thought about this question and thanks to them, we have an answer today, in terms of the classical theory of electromagnetism.

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The Cosmic Speed Limit

According to Einstein’s special theory of relativity, the speed of light is constant in vacuum and no object can exceed it. In short, nothing can travel faster than the speed of light. It is the cosmic speed limit for information exchange.

Scientists have measured the speed of light to be 299,792,458 meters per second. It is the highest speed that can be achieved by any entity. So far, no object has been found to travel at a velocity that exceeds the speed of light.

One of the central pillars of modern physics, the special theory of relativity, will turn out to be wrong, if light speed is exceeded by any other entity. In short, light is the fastest thing in our universe and no information can travel faster than it. How does light achieve this phenomenal speed? How does it travel at all? Let us find out.

The Nature of Light: Wave/Photons

One can understand the phenomenon of light travel, once its nature is understood. The first glimpses of the nature of light were provided by the ingenuity of James Clark Maxwell. It came as a brilliant revelation to him as he was constructing a theory that describes the electric and magnetic forces between stationary and moving charged objects.

He discovered that electricity and magnetism were two sides of the same coin. His theory combined electricity and magnetism into the unified force of electromagnetism and light was found to be an electromagnetic wave. This theory pictures light as a transverse electromagnetic wave, traveling through space. This is the classical perspective.

However, light can also be alternately perceived as a particle, known as a photon, if you look at it, from the perspective of quantum mechanics, which quantizes all matter and energy. In fact, according to quantum field theory, everything behaves like a particle and a wave. Not just photons, but electrons, which were earlier thought to be particles, are now known to behave as waves. Both, particle and wave viewpoints are equivalent, and for this discussion, we will focus on the wave perspective, which provides a simpler explanation of light travel.

How Light Travels Through Space

So light is a kind of wave. However every wave, waves something. That is, every wave like a sea wave, travels through a medium, in which it causes disturbances and creates undulations.

If a sea wave is a ripple or a disturbance that travels through water, then what is the medium in which light travels as a wave? The answer is none. This is where light is different from any other kind of a wave. It can travel through vacuum and it does not require a medium to propagate.

How does light manage to do this? The answer lies in the fact that it is an electromagnetic wave, carrying energy. Maxwell discovered how light travels through vacuum. Here is an illustration of an electromagnetic wave, that illuminates its nature and clearly presents its component parts.

Here’s an explanation of what makes light travel possible, in a nutshell. Any charged object has an electric field associated with it. When that electric field changes, a changing magnetic field is created. Consequently, the changing magnetic field again creates an electric field. This continues ad infinitum, creating an electromagnetic wave, traveling in space. This is how light travels, as a disturbance or ripple in the electromagnetic field.

n short, an accelerated charge radiates electromagnetic waves. Mathematically, this relation can be understood through the solution of Maxwell’s equations for free space.

Visible light, radio waves, and even X-rays are all electromagnetic waves of different wavelengths and frequencies. The wavelength of visible light is such that our eyes are tuned to it, just like a radio receiver is tuned to radio waves. Ergo, our eyes can perceive that part of the electromagnetic spectrum.

Light travels in straight lines in vacuum. However, in a material medium, light shows two properties of reflection and refraction. When a light wave cannot penetrate an object, it gets reflected back and when a light wave travels inside a medium, it bends or gets refracted.

When light travels through a medium, it interacts with its electric field. Depending on the nature of that field, one can predict the degree of bending or refraction that light undergoes, when passing through it.

Here’s how you perceive light, through your eyes. Light entering inside the white of your eyes (cornea), through the lens, bends or refracts, to get focused on your retina. The retina converts the incident light into electric signals, from which your brain creates an image, that you perceive.

Light Travel Through Different Media

Though the speed of light is constant in vacuum, when traveling through denser media, it slows down considerably. The degree of bending or slowing down of light velocity in different media, is measured by the refractive index of a particular medium. Light undergoes bending or slowing down, when entering a denser medium, from a rarer one and speeds up when entering a rarer medium, from a denser one. Let us see what happens in both cases.

As illustrated in the diagram presented below, when light enters a denser medium, it slows down and bends towards the normal. Here, the angle of refraction (r) is lesser than the angle of incidence (r < i).

As demonstrated by the diagram presented below, when entering a rarer medium, from a denser medium, light speeds up, and bends away from the normal. Here, the angle of refraction is greater than the angle of incidence (r > i).

If the refractive index of one medium is known, the other one can be deduced from Snell’s law, if the angles of incidence (i) and refraction (r) are known. It’s stated as: sin i/sin r = n2/n1 where, ‘i’ is the angle of incidence, ‘r’ is the angle of refraction, and n1 is the refractive index of the medium of incidence, while n2 is the refractive index of the medium of refraction.

To fully understand how the dynamic nature of the electromagnetic field leads to the creation of waves, you will have to dig deep into Maxwell’s equations, presented in the graphic below. A good starting point is The Feynman Lectures on Physics, Vol.II. If God is perceived to be the laws of nature, one could say the following.

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Why Can Light Travel Through Space: Unraveling the Mysteries of Cosmic Illumination

The Physics Behind Light’s Journey through the Cosmos

Light is a fascinating phenomenon that has puzzled scientists and thinkers for centuries. One of the most intriguing questions surrounding light is why it can travel through space. To unravel this mystery, we must delve into the realm of physics and explore the fundamental principles that govern the behavior of light.

At its core, light is an electromagnetic wave. It consists of oscillating electric and magnetic fields that propagate through space. These fields are perpendicular to each other and the direction of the wave’s motion. This unique property allows light to travel in a vacuum, such as the vast expanse of space.

The Role of Electromagnetic Waves in Space Travel

Electromagnetic waves play a crucial role in the transmission of energy through space. They are characterized by their wavelength and frequency, which determine the properties of different types of electromagnetic radiation. Light, as a form of electromagnetic radiation, falls within a specific range of wavelengths and frequencies that enable it to travel through space.

Exploring the Vacuum of Space: A Perfect Medium for Light

Space is often referred to as a vacuum, devoid of matter and air. This unique environment provides an ideal medium for light to propagate. Unlike other forms of energy, such as sound or mechanical waves, light does not require a material medium to travel. The absence of particles in space allows light to travel unimpeded, covering vast distances without encountering any resistance.

The Speed of Light: A Universal Constant that Defies Boundaries

One of the most remarkable aspects of light is its speed. The speed of light in a vacuum is approximately 299,792 kilometers per second or about 186,282 miles per second. This incredible velocity makes light one of the fastest phenomena in the universe. It allows light to traverse immense cosmic distances and reach us from distant stars and galaxies.

Why Other Forms of Energy Struggle to Travel through Space

While light can effortlessly travel through space, other forms of energy face significant challenges. Sound, for example, relies on the vibration of particles to propagate. In the absence of a material medium like air or water, sound waves cannot travel. Similarly, mechanical waves require a medium to transfer energy, making them unsuitable for space travel.

The Interplay Between Light and Dark Matter in the Universe

Dark matter is another intriguing cosmic element that interacts with light. Although invisible and mysterious, dark matter exerts a gravitational pull on surrounding matter, including light. This interaction can cause light to bend or be lensed as it travels through space. Understanding the interplay between light and dark matter is an ongoing area of research in astrophysics.

Frequently Asked Questions about why can light travel through space

Q: Why can light travel through space while other forms of energy cannot?

A: Light is an electromagnetic wave that does not require a material medium to propagate. This allows it to travel through the vacuum of space without encountering any resistance.

Q: How fast does light travel through space?

A: The speed of light in a vacuum is approximately 299,792 kilometers per second or about 186,282 miles per second.

Q: Can sound waves travel through space?

A: No, sound waves require a material medium, such as air or water, to propagate. In the vacuum of space, where there is no air or matter, sound waves cannot travel.

Q: What is the role of dark matter in the interaction of light in space?

A: Dark matter exerts a gravitational pull on surrounding matter, including light. This interaction can cause light to bend or be lensed as it travels through space.

Expert Advice

Understanding the phenomenon of why light can travel through space is a complex topic that requires a deep understanding of physics and electromagnetic waves. Scientists continue to investigate this intriguing aspect of our universe, unraveling the mysteries of cosmic illumination. The ability of light to traverse the vastness of space has allowed us to explore distant celestial objects and gain valuable insights into the workings of the cosmos.

• astrophysics
• cosmic distances
• cosmic illumination
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• dark matter and light
• electromagnetic radiation
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How Light Travels: The Reason Why Telescopes Can See the Invisible Parts of Our Universe

Due to how light travels, we can only see the most eye-popping details of space—like nebulas, supernovas, and black holes—with specialized telescopes.

• Our eyes can see only a tiny fraction of these wavelengths , but our instruments enable us to learn far more.
• Here, we outline how various telescopes detect different wavelengths of light from space.

Light travels only one way: in a straight line. But the path it takes from Point A to Point B is always a waveform, with higher-energy light traveling in shorter wavelengths. Photons , which are tiny parcels of energy, have been traveling across the universe since they first exploded from the Big Bang . They always travel through the vacuum of space at 186,400 miles per second—the speed of light—which is faster than anything else.

Too bad we can glimpse only about 0.0035 percent of the light in the universe with our naked eyes. Humans can perceive just a tiny sliver of the electromagnetic spectrum: wavelengths from about 380–750 nanometers. This is what we call the visible part of the electromagnetic spectrum. The universe may be lovely to look at in this band, but our vision skips right over vast ranges of wavelengths that are either shorter or longer than this limited range. On either side of the visible band lies evidence of interstellar gas clouds, the hottest stars in the universe, gas clouds between galaxies , the gas that rushes into black holes, and much more.

Fortunately, telescopes allow us to see what would otherwise remain hidden. To perceive gas clouds between stars and galaxies, we use detectors that can capture infrared wavelengths. Super-hot stars require instruments that see short, ultraviolet wavelengths. To see the gas clouds between galaxies, we need X-ray detectors.

We’ve been using telescopes designed to reveal the invisible parts of the cosmos for more than 60 years. Because Earth’s atmosphere absorbs most wavelengths of light, many of our telescopes must observe the cosmos from orbit or outer space.

Here’s a snapshot of how we use specialized detectors to explore how light travels across the universe.

Infrared Waves

We can’t see infrared waves, but we can feel them as heat . A sensitive detector like the James Webb Space Telescope can discern this thermal energy from far across the universe. But we use infrared in more down-to-Earth ways as well. For example, remote-control devices work by sending infrared signals at about 940 nanometers to your television or stereo. These heat waves also emanate from incubators to help hatch a chick or keep a pet reptile warm. As a warm being, you radiate infrared waves too; a person using night vision goggles can see you, because the goggles turn infrared energy into false-color optical energy that your eyes can perceive. Infrared telescopes let us see outer space in a similar way.

Astronomers began the first sky surveys with infrared telescopes in the 1960s and 1970s. Webb , launched in 2021, takes advantage of the infrared spectrum to probe the deepest regions of the universe. Orbiting the sun at a truly cold expanse—about one million miles from Earth—Webb has three infrared detectors with the ability to peer farther back in time than any other telescope has so far.

Its primary imaging device, the Near Infrared Camera (NIRCam), observes the universe through detectors tuned to incoming wavelengths ranging from 0.6 to 5 microns, ideal for seeing light from the universe’s earliest stars and galaxies. Webb’s Mid-Infrared Instrument (MIRI) covers the wavelength range from 5 to 28 microns, its sensitive detectors collecting the redshifted light of distant galaxies. Conveniently for us, infrared passes more cleanly through deep space gas and dust clouds, revealing the objects behind them; for this and many other reasons, the infrared spectrum has gained a crucial foothold in our cosmic investigations. Earth-orbiting satellites like NASA’s Wide Field Infrared Survey Telescope ( WFIRST ) observe deep space via longer infrared wavelengths, too.

Yet, when stars first form, they mostly issue ultraviolet light . So why don’t we use ultraviolet detectors to find distant galaxies? It’s because the universe has been stretching since its beginning, and the light that travels through it has been stretching, too; every planet, star, and galaxy continually moves away from everything else. By the time light from GLASS-z13—formed 300 million years after the Big Bang—reaches our telescopes, it has been traveling for more than 13 billion years , a vast distance all the way from a younger universe. The light may have started as ultraviolet waves, but over vast scales of time and space, it ended up as infrared. So, this fledgling galaxy appears as a red dot to NIRCam. We are gazing back in time at a galaxy that is rushing away from us.

Radio Waves

If we could see the night sky only through radio waves, we would notice swaths of supernovae , pulsars, quasars, and gassy star-forming regions instead of the usual pinprick fairy lights of stars and planets.

Tools like the Arecibo Observatory in Puerto Rico can do the job our eyes can’t: detect some of the longest electromagnetic waves in the universe. Radio waves are typically the length of a football field, but they can be even longer than our planet’s diameter. Though the 1,000-foot-wide dish at Arecibo collapsed in 2020 due to structural problems, other large telescopes carry on the work of looking at radio waves from space. Large radio telescopes are special because they actually employ many smaller dishes, integrating their data to produce a really sharp image.

Unlike optical astronomy, ground-based radio telescopes don’t need to contend with clouds and rain. They can make out the composition, structure, and motion of planets and stars no matter the weather. However, the dishes of radio telescopes need to be much larger than optical ones to generate a comparable image, since radio waves are so long. The Parkes Observatory’s dish is 64 meters wide, but its imaging is comparable to a small backyard optical telescope, according to NASA .

Eight different radio telescopes all over the world coordinated their observations for the Event Horizon Telescope in 2019 to put together the eye-opening image of a black hole in the heart of the M87 galaxy (above).

Ultraviolet Waves

You may be most familiar with ultraviolet, or UV rays, in warnings to use sunscreen . The sun is our greatest local emitter of these higher-frequency, shorter wavelengths just beyond the human visible spectrum, ranging from 100 to 400 nanometers. The Hubble Space Telescope has been our main instrument for observing UV light from space, including young stars forming in Spiral Galaxy NGC 3627, the auroras of Jupiter, and a giant cloud of hydrogen evaporating from an exoplanet that is reacting to its star’s extreme radiation.

Our sun and other stars emit a full range of UV light, telling astronomers how relatively hot or cool they are according to the subdivisions of ultraviolet radiation: near ultraviolet, middle ultraviolet, far ultraviolet, and extreme ultraviolet. Applying a false-color visible light composite lets us see with our own eyes the differences in a star’s gas temperatures.

Hubble’s Wide Field Camera 3 (WFC3) breaks down ultraviolet light into specific present colors with filters. “Science visuals developers assign primary colors and reconstruct the data into a picture our eyes can clearly identify,” according to the Hubble website . Using image-processing software, astronomers and even amateur enthusiasts can turn the UV data into images that are not only beautiful, but also informative.

X-Ray Light

Since 1999, the orbiting Chandra X-Ray Observatory is the most sensitive radio telescope ever built. During one observation that lasted a few hours, its X-ray vision saw only four photons from a galaxy 240 million light-years away, but it was enough to ascertain a novel type of exploding star . The observatory, located 86,500 miles above Earth, can produce detailed, full-color images of hot X-ray-emitting objects, like supernovas, clusters of galaxies and gases, and jets of energy surrounding black holes that are millions of degrees Celsius. It can also measure the intensity of an individual X-ray wavelength, which ranges from just 0.01 to 10 nanometers. Its four sensitive mirrors pick up energetic photons and then electronic detectors at the end of a 30-foot optical apparatus focus the beams of X-rays.

Closer to home, the Aurora Borealis at the poles emits X-rays too. And down on Earth, this high-frequency, low-wavelength light passes easily through the soft tissue of our bodies, but not our bones, yielding stellar X-ray images of our skeletons and teeth.

Visible Light

Visible color gives astronomers essential clues to a whole world of information about a star, including temperature, distance, mass, and chemical composition. The Hubble Telescope, perched 340 miles above our planet, has been a major source of visible light images of the cosmos since 1990.

Hotter objects, like young stars, radiate energy at shorter wavelengths of light; that’s why younger stars at temperatures up to 12,000 degrees Celsius, like the star Rigel, look blue to us. Astronomers can also tell the mass of a star from its color. Because mass corresponds to temperature, observers know that hot blue stars are at least three times the mass of the sun. For instance, the extremely hot, luminous blue variable star Eta Carina’s bulk is 150 times the mass of our sun, and it radiates 1,000,000 times our sun’s energy.

Our comparatively older, dimmer sun is about 5,500 degrees Celsius, so it appears yellow. At the other end of the scale, the old star Betelgeuse has been blowing off its outer layer for the past few years, and it looks red because it’s only about 3,000 degrees Celsius.

A View of Earth

Scientists use different wavelengths of light to study phenomena closer to home, too.

Detectors in orbit can distinguish between geophysical and environmental features on Earth’s changing surface, such as volcanic action. For example, infrared light used alongside visible light detection reveals areas covered in snow, volcanic ash, and vegetation. The Moderate Resolution Imaging Spectroradiometer ( MODIS ) infrared instrument onboard the Aqua and Terra satellites monitors forest fire smoke and locates the source of a fire so humans don’t have to fly through smoke to evaluate the situation.

Next year, a satellite will be launched to gauge forest biomass using a special radar wavelength of about 70 centimeters that can penetrate the leafy canopy.

💡 Why is the sky blue? During the day, oxygen and nitrogen in Earth’s atmosphere scatters electromagnetic energy at the wavelengths of blue light (450–485 nanometers). At sunset, the sun’s light makes a longer journey through the atmosphere before greeting your eyes. Along the way, more of the sun’s light is scattered out of the blue spectrum and deeper into yellow and red.

Before joining Popular Mechanics , Manasee Wagh worked as a newspaper reporter, a science journalist, a tech writer, and a computer engineer. She’s always looking for ways to combine the three greatest joys in her life: science, travel, and food.

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What is the speed of light?

Light is faster than anything else in the known universe, though its speed can change depending on what it's passing through.

The universe has a speed limit, and it's the speed of light. Nothing can travel faster than light — not even our best spacecraft — according to the laws of physics.

So, what is the speed of light? 

Light moves at an incredible 186,000 miles per second (300,000 kilometers per second), equivalent to almost 700 million mph (more than 1 billion km/h). That's fast enough to circumnavigate the globe 7.5 times in one second, while a typical passenger jet would take more than two days to go around once (and that doesn't include stops for fuel or layovers!). 

Light moves so fast that, for much of human history, we thought it traveled instantaneously. As early as the late 1600s, though, scientist Ole Roemer was able to measure the speed of light (usually referred to as c ) by using observations of Jupiter's moons, according to Britannica . 

Around the turn of the 19th century, physicist James Clerk Maxwell created his theories of electromagnetism . Light is itself made up of electric and magnetic fields, so electromagnetism could describe the behavior and motion of light — including its theoretical speed. That value was 299,788 kilometers per second, with a margin of error of plus or minus 30. In the 1970s, physicists used lasers to measure the speed of light with much greater precision, leaving an error of only 0.001. Nowadays, the speed of light is used to define units of length, so its value is fixed; humans have essentially agreed the speed of light is 299,792.458 kilometers per second, exactly.

Light doesn't always have to go so fast, though. Depending on what it's traveling through — air, water, diamonds, etc. — it can slow down. The official speed of light is measured as if it's traveling in a vacuum, a space with no air or anything to get in the way. You can most clearly see differences in the speed of light in something like a prism, where certain energies of light bend more than others, creating a rainbow.

— How many moons does Earth have ?

— What would happen if the moon were twice as close to Earth?

— If you're on the moon, does the Earth appear to go through phases?

Interestingly, the speed of light is no match for the vast distances of space, which is itself a vacuum. It takes 8 minutes for light from the sun to reach Earth, and a couple years for light from the other closest stars (like Proxima Centauri) to get to our planet. This is why astronomers use the unit light-years — the distance light can travel in one year — to measure vast distances in space.

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Because of this universal speed limit, telescopes are essentially time machines . When astronomers look at a star 500 light-years away, they're looking at light from 500 years ago. Light from around 13 billion light-years away (equivalently, 13 billion years ago) shows up as the cosmic microwave background, remnant radiation from the Big Bang in the universe's infancy. The speed of light isn't just a quirk of physics; it has enabled modern astronomy as we know it, and it shapes the way we see the world — literally.

Briley Lewis (she/her) is a freelance science writer and Ph.D. Candidate/NSF Fellow at the University of California, Los Angeles studying Astronomy & Astrophysics. Follow her on Twitter  @briles_34 or visit her website  www.briley-lewis.com .

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Science News Explores

Understanding light and other forms of energy on the move.

This radiation includes visible light, radio signals — even medical X-rays

Light is a form of energy created by the movement of electrons. Different wavelengths appear as different colors, although most wavelengths are not visible to the human eye.

Natasha Hartano/Flickr ( CC BY-NC 2.0 ); adapted by L. Steenblik Hwang

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By Jennifer Look

July 16, 2020 at 6:30 am

Light is a form of energy that travels as waves. Their length — or wavelength — determines many of light’s properties. For instance, wavelength accounts for light’s color and how it will interact with matter. The range of wavelengths, from super short to very, very long, is known as the light spectrum. Whatever its wavelength, light will radiate out infinitely unless or until it is stopped. As such, light is known as radiation.

Light’s formal name is electromagnetic radiation. All light shares three properties. It can travel through a vacuum. It always moves at a constant speed, known as the speed of light, which is 300,000,000 meters (186,000 miles) per second in a vacuum. And the wavelength defines the type or color of light.

Just to make things interesting, light also can behave as photons , or particles. When looked at this way, quantities of light can be counted, like beads on a string.

Humans have evolved to sense a small part of the light spectrum. We know these wavelengths as “visible” light. Our eyes contain cells known as rods and cones. Pigments in those cells can interact with certain wavelengths (or photons) of light. When this happens, they create signals that travel to the brain. The brain interprets the signals from different wavelengths (or photons) as different colors.

The longest visible wavelengths are around 700 nanometers and appear red. The range of visible light ends around 400 nanometers. Those wavelengths appear violet. The whole rainbow of colors falls in between.

Most of the light spectrum, however, falls outside that range. Bees, dogs and even a few people can see ultraviolet (UV) light . These are wavelengths a bit shorter than violet ones. Even those of us without UV vision can still respond to UV light, however. Our skin will redden or even burn when it encounters too much.

Many things emit heat in the form of infrared light. As that name suggests, infrared wavelengths are somewhat longer than red’s. Mosquitoes and pythons can see in this range. Night-vision goggles work by detecting infrared light.

Light also comes in many other types. Light with really short, high-energy waves can be gamma rays and X-rays (used in medicine). Long, low-energy waves of light fall in the radio and microwave part of the spectrum.

Desiré Whitmore is a physics educator at the Exploratorium in San Francisco, Calif. Teaching people about light as radiation can be difficult, she says. “People are afraid of the word ‘radiation.’ But all it means is that something is moving outward.”

The sun emits lots of radiation in wavelengths that span from X-rays to infrared. Sunlight provides almost all of the energy required for life on Earth. Small, cool objects release much less radiation. But every object emits some. That includes people. We give off small amounts of infrared light generally referred to as heat.

Whitmore points to her cell phone as a common source of many types of light. Smartphones use visible wavelengths to light up the screen display. Your phone talks to other phones via radio waves. And the camera has the ability to detect infrared light that human eyes cannot see. With the right app, the phone transforms this infrared light into visible light that we can see on the phone’s screen.

“This is fun to try out with your cell phone’s front-facing camera,” Whitmore says. Use a remote control for a television or other device. Its light is infrared, she notes, “so we cannot see it. But when you point the controller at your phone’s camera and press a button, “you can see a bright pink light appear on the screen!”   

“All these different types of radiation help improve our lives,” Whitmore says. They “have been shown to be safe when used in reasonable amounts,” she notes — but can be “dangerous when you use too much of it.”

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Warp drives: Physicists give chances of faster-than -light space travel a boost

Associate Professor of Physics, Oklahoma State University

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Mario Borunda 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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The closest star to Earth is Proxima Centauri. It is about 4.25 light-years away, or about 25 trillion miles (40 trillion km). The fastest ever spacecraft, the now- in-space Parker Solar Probe will reach a top speed of 450,000 mph. It would take just 20 seconds to go from Los Angeles to New York City at that speed, but it would take the solar probe about 6,633 years to reach Earth’s nearest neighboring solar system.

If humanity ever wants to travel easily between stars, people will need to go faster than light. But so far, faster-than-light travel is possible only in science fiction.

In Issac Asimov’s Foundation series , humanity can travel from planet to planet, star to star or across the universe using jump drives. As a kid, I read as many of those stories as I could get my hands on. I am now a theoretical physicist and study nanotechnology, but I am still fascinated by the ways humanity could one day travel in space.

Some characters – like the astronauts in the movies “Interstellar” and “Thor” – use wormholes to travel between solar systems in seconds. Another approach – familiar to “Star Trek” fans – is warp drive technology. Warp drives are theoretically possible if still far-fetched technology. Two recent papers made headlines in March when researchers claimed to have overcome one of the many challenges that stand between the theory of warp drives and reality.

But how do these theoretical warp drives really work? And will humans be making the jump to warp speed anytime soon?

Compression and expansion

Physicists’ current understanding of spacetime comes from Albert Einstein’s theory of General Relativity . General Relativity states that space and time are fused and that nothing can travel faster than the speed of light. General relativity also describes how mass and energy warp spacetime – hefty objects like stars and black holes curve spacetime around them. This curvature is what you feel as gravity and why many spacefaring heroes worry about “getting stuck in” or “falling into” a gravity well. Early science fiction writers John Campbell and Asimov saw this warping as a way to skirt the speed limit.

What if a starship could compress space in front of it while expanding spacetime behind it? “Star Trek” took this idea and named it the warp drive.

In 1994, Miguel Alcubierre, a Mexican theoretical physicist, showed that compressing spacetime in front of the spaceship while expanding it behind was mathematically possible within the laws of General Relativity . So, what does that mean? Imagine the distance between two points is 10 meters (33 feet). If you are standing at point A and can travel one meter per second, it would take 10 seconds to get to point B. However, let’s say you could somehow compress the space between you and point B so that the interval is now just one meter. Then, moving through spacetime at your maximum speed of one meter per second, you would be able to reach point B in about one second. In theory, this approach does not contradict the laws of relativity since you are not moving faster than light in the space around you. Alcubierre showed that the warp drive from “Star Trek” was in fact theoretically possible.

Proxima Centauri here we come, right? Unfortunately, Alcubierre’s method of compressing spacetime had one problem: it requires negative energy or negative mass.

A negative energy problem

Alcubierre’s warp drive would work by creating a bubble of flat spacetime around the spaceship and curving spacetime around that bubble to reduce distances. The warp drive would require either negative mass – a theorized type of matter – or a ring of negative energy density to work. Physicists have never observed negative mass, so that leaves negative energy as the only option.

To create negative energy, a warp drive would use a huge amount of mass to create an imbalance between particles and antiparticles. For example, if an electron and an antielectron appear near the warp drive, one of the particles would get trapped by the mass and this results in an imbalance. This imbalance results in negative energy density. Alcubierre’s warp drive would use this negative energy to create the spacetime bubble.

But for a warp drive to generate enough negative energy, you would need a lot of matter. Alcubierre estimated that a warp drive with a 100-meter bubble would require the mass of the entire visible universe .

In 1999, physicist Chris Van Den Broeck showed that expanding the volume inside the bubble but keeping the surface area constant would reduce the energy requirements significantly , to just about the mass of the sun. A significant improvement, but still far beyond all practical possibilities.

A sci-fi future?

Two recent papers – one by Alexey Bobrick and Gianni Martire and another by Erik Lentz – provide solutions that seem to bring warp drives closer to reality.

Bobrick and Martire realized that by modifying spacetime within the bubble in a certain way, they could remove the need to use negative energy. This solution, though, does not produce a warp drive that can go faster than light.

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Independently, Lentz also proposed a solution that does not require negative energy. He used a different geometric approach to solve the equations of General Relativity, and by doing so, he found that a warp drive wouldn’t need to use negative energy. Lentz’s solution would allow the bubble to travel faster than the speed of light.

It is essential to point out that these exciting developments are mathematical models. As a physicist, I won’t fully trust models until we have experimental proof. Yet, the science of warp drives is coming into view. As a science fiction fan, I welcome all this innovative thinking. In the words of Captain Picard , things are only impossible until they are not.

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Does Light Travel Forever?

Most recent answer: 01/23/2013

Hi Raja, Good question. First, let's think about why sound does not travel forever. Sound cannot travel through empty space; it is carried by vibrations in a material, or medium (like air, steel, water, wood, etc). As the particles in the medium vibrate, energy is lost to heat, viscous processes, and molecular motion. So, the sound wave gets smaller and smaller until it disappears. In contrast, light waves can travel through a vacuum, and do not require a medium. In empty space, the wave does not dissipate (grow smaller) no matter how far it travels, because the wave is not interacting with anything else. This is why light from distant stars can travel through space for billions of light-years and still reach us on earth. However, light can also travel within some materials, like glass and water. In this case, some light is absorbed and lost as heat, just like sound. So, underwater, or in our atmosphere, light will only travel some finite range (which is different depending on the properties of the material it travels through). There is one more aspect of wave travel to consider, which applies to both sound and light waves. As a wave travels from a source, it propagates outward in all directions. Therefore, it fills a space given approximately by the surface area of a sphere. This area increases by the square of the distance R from the source; since the wave fills up all this space, its intensity decreases by R squared. This effect just means that the light/sound source will appear dimmer if we are farther away from it, since we don't collect all the light it emits. For example, light from a distant star travels outward in a giant sphere. Only one tiny patch of this sphere of light actually hits our eyes, which is why stars don't blind us! David Schmid

(published on 01/23/2013)

Follow-Up #1: How far does light go?

Light just keeps going and going until it bumps into something.  Then it can either be reflected or absorbed.  Astronomers have detected some light that has been traveling for more that 12 billion years, close to the age of the universe.   

Light has some interesting properties.   It comes in lumps called photons.  These photons carry energy and momentum in specific amounts related to the color of the light.  There is much to learned about light.   I suggest you log in to our website and type  LIGHT into the search box.   Lots of interesting stuff there.

To answer your previous question "Can light go into a black hole?" ,  the answer is yes.

(published on 12/03/2015)

Follow-Up #2: less than one photon?

Certainly you can run the ouput of a single-photon source through a half-silvered mirror, and get a sort of half-ghost of the photon in two places. If you put ordinary photon detectors in those places, however, each will either detect zero or one. For each source photon, you'll get at most one of the detectors to find it. How does the half-ghost at the other one know whether it's detectably there or not? The name of that mystery is "quantum entanglement". At some level we don't really know the answer.

(published on 02/04/2016)

Follow-Up #3: stars too far away to see?

Most stars are too far for us to see them as individual stars even with our best telescopes. Still, we can get light from them, mixed with light from other stars. If our understanding of the universe is at all right, there are also stars that once were visible from here but now are outside our horizon so no light from them reaches us. It's probable that there are many more stars outside our horizon than inside, maybe infinitely more. It's hard to check, however, what's happening outside our horizon! It's even hard to define what we mean by "now" for things outside the horizon.

(published on 07/22/2016)

Follow-Up #4: light going out to space

Certainly ordinary light travels out to space. That's how spy cameras and such can take pictures of things here on the Earth's surface.

(published on 09/01/2016)

Follow-Up #5: end of the universe?

We don't think there's any "end" in the sense of some spatial boundary. Unless something changes drastically, there also won't be an end in time. The expansion looks like it will go on forever. So that wouldn't give a maximum range.

(published on 03/26/2017)

Follow-Up #6: seeing black holes

In principle a well-aimed beam would loop around the outside of the black hole and return to Earth. There aren't any black holes close enough to make this practical. Instead the bending of light by black holes is observed by their lensing effect on light coming from more distant objects.

The amazing gravitational wave signals observed from merging black holes provide even more direct and convincing proof that black holes exist and follow the laws of General Relativity.

(published on 01/29/2018)

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Unlocking the secrets of energy: how does light travel?

Our world is full of wonders, and one of the most amazing ones is … light. How does light travel? What is the speed of light in water, in space, in a vacuum, how it passes through obstacles, which is faster, light or sound?

This article will answer these and other questions about this unique natural phenomenon and the main energy source for all living things.

What is light?

In physical optics, light is electromagnetic wave radiation visible to the human eye. As a rule, these are waves with a length of 380 – 760 nm and a frequency of 790 – 400 THz. Also, light is often referred to as radiation outside these ranges. There are radio waves, microwaves, infrared, ultraviolet, x-ray and gamma waves but in this case, the term “light” is synonymous with the term “electromagnetic radiation”, regardless of its parameters, especially when the specification is not important, but one wants to use a shorter word. Further on, we will be discussing visible light.

How does light travel to your eyes?

You may be surprised, but our eyes capture light in the same way as a digital camera. The light flux is refracted in the crystalline eye lens (similar to the camera lens), hits the retina (matrix) and creates an impulse that the brain (processor) decodes into an image.

Where does light come from?

The entire world around us consists of atoms, which, in turn, consist of a nucleus and electrons. The nucleus is positively charged, and the electron is negatively charged, so they are attracted to each other. When heated or irradiated, the atom receives energy, which causes the electrons to go into an excited state and move away from the nucleus. However, the electron and the nucleus will still strive to get closer. When an electron returns to its ground state, it releases energy in a stream of light particles, also called photons or quanta.

What light sources are there?

Light sources are usually divided into natural and artificial ones. The brightest (both literally and figuratively) example of a natural light source is the Sun. Also, these are other stars, auroras, lightning, the bioluminescence of living organisms, the glow of oxidizing organic products and minerals, etc. Artificial sources include various types of lamps, lamps, LEDs, gas burners, and lasers.

And now, let’s find out how light travels in different environments.

How does light travel in the air?

As mentioned above, light is a wave, or a stream of photons called a beam. It does not require any mechanical medium, matter, or materials to propagate. This means that light can travel through a vacuum — absolutely airless space. In a homogeneous medium, the rays are straight lines. Still, when the light flux encounters an obstacle, such as an opaque object or an object with a high density, the atoms of which have many free electrons capable of absorbing photon energy in a wide range, the light is reflected from this object, absorbed by it or refracted. Whereas glass and water are transparent at these frequencies, so their atoms cannot absorb photons and, thus, transmit light.

How fast does light travel in space?

Space is a very rarefied medium, close to vacuum, so the light of the Sun and other stars reaches us at a tremendous speed called the speed of light. It is equal to 299,792,458 m/s. To understand how fast it is, it is enough to answer the question of how long does it take light to travel from Mars to Earth? A little over three minutes. In other words, if our spaceships could travel at the speed of light, we would be to reach Mars faster than a cafe on the next block.

But even in space, there are obstacles to light. A good example of this is a solar or lunar eclipse. In the first case, the Moon is in the path of the Sun’s rays flying to the Earth, so for a moment, it obscures the star from us; in the second case, the Earth becomes an obstacle between the Moon and the Sun, preventing the Moon from reflecting the star’s light.

How fast does light travel in water?

Water is an “optically” denser medium than air, so light propagates in it not only more slowly but also with a higher refractive index. In other words, when light passes from one transparent medium to another, it is refracted at the boundary of these two media. So, how fast does light travel through water? In water, the refractive index is about 1.3, so the speed of light is reduced to 230,769 kilometres per second. Refraction can make things appear closer than they actually are. This is why, for example, a 13-foot pool appears to be only 10 feet deep.

Why does light travel faster than sound?

To answer this question, let’s recall what type of wave light is. Light is an electromagnetic wave that does not need a medium to in which to propagate. But sound is a pressure wave that definitely needs a physical medium. It is because of the interaction with the physical medium that the sound waves arise, and the denser this medium is, the faster the sound propagates. In the air, it moves at a speed of 330 meters per second; in water — 1450 meters per second; and in solid materials — up to 6000 m/s. But the sound is slower than light by about a million times, which is why we first see the lightning, and later hear the thunder. In a vacuum, sound cannot exist because there is no matter there. By the way, read this article of ours if you want to know more — Can We Hear The Sounds Of Space .

Final thoughts

So, how does light travel? Faster than sound, rockets, and anything else known to us. In space, it feels like a fish in water, but still, it is not omnipotent, so it cannot overcome every obstacle. Seems unbelievable? Think about this when seeing a bizarre shadow or watching a solar eclipse.

An amateur rocket enthusiast with a keen interest in all space-related activity. Looking forward to the day when the UK starts launching rockets into space and I'm able to watch launches (from a safe distance of course).

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How Does Light Travel Through Space?

"Don't criticize what you can't understand..."

• Jun 7, 2020

I like your posts very much.  

• Jun 8, 2020

Nice. Many like to refer to light packets, where photons travel in great numbers, even when diminished by distance by the inverse square law. But some of those photons do become absorbed or scattered. The dark regions in your nice galaxy image are very likely due to photons that were absorbed or scattered by a cloud of gas and dust. This dimming effect, along with specific bands of scattering, provide astronomers with very useful information of these nebulae.  

• Jun 13, 2020

SaraRayne said: Every point of light you see in the sky is an entire world sending out energy in the form of light. Your ability to perceive this light even across such vast distances says a lot about not just the nature of light, but how powerful the sources of that light really are. Here’s what it takes for light to travel through space. 1. Photons may be particles, but light travels as a wave. The double-slit experiment is a famous one for good reason: it demonstrated that light can behave both as individual particles and as a wave. When light travels through space, it propagates as a wave, but in a different way than other types of waves. Sound waves, for example, need a medium to interact with, and since there’s not enough densely packed matter in space for sound to travel on, soundwaves don’t carry through a vacuum. Light waves, on the other hand, don’t need anything to travel through, so they can move quite easily through space. 2. There’s nothing for the light to interact with, so it travels on and on. Since the light doesn’t need a medium to travel with, it isn’t hindered in any way and will keep on going. It won’t dissipate, and it will continue to expand out forever. 3. Stars send out light in every direction. If light doesn’t dissipate, why do some stars appear dimmer? This has to do with the amount of light we receive from the source. The light from a distant star is being sent out in all directions in a spherical configuration, and it will fill the entire space afforded to it. This means that for a star that’s very distant, only a tiny sliver of the light being sent out actually reaches our eyes. The light itself hasn’t dimmed on the way; the amount we receive has reduced. Click to expand...

• Feb 2, 2022

The Electromagnetic Universe.docx

Jzz: Conflict (if there is any) or not, I find your views quite interesting and thought provoking.  

Numbered mile marker-like light fronts, developing flexible accordion-like corridors, are space-time travelers traveling as two way streets (+/-) of time throughout space. Externally, they travel into the future (+) (into futures (+)). Internally, they travel into the past (-) (into pasts (-)). The net is the constants of 'c' ((+/-) 186,000mps) and 't = 0'. Any other space-time traveler (t = 0) exists in the observable past (-) of his destinations upon departures, bound to travel an observable future (+) to arrivals everywhere situate 'Now' (t = 0). He travels futures (+) to arrivals (always equal distant ('1/2') in horizon between ultimate horizons). He always observes his departure point to travel pasts (-) (recoiling, rebounding, in time past (-)) in order to arrive in all light-time pasts (-) relative to him -- always pointing toward the collapsed horizon of ultimate origin -- behind him in space-time. The traveler traveled ahead ascending into a future (+) and toward radius physic '1/2'. At once, the traveler traveled behind him descending toward and into a past (-): a past pointing ultimately in descent toward the collapsed horizon of infinity and a superposition dimension of origin. Upon all arrivals he looks out to the surrounding universe and finds himself (t = 0) observably centered (t = 0) (radius, physic, '1/2') between negative time (-) horizons, exactly the same horizon, and observably surrounded by pasts (-) to unobserved and unobservable futures (+), to Now (t = 0) (radius, physic, '1/2'). To the Universe (U) and universe (u), he never leaves center. To them he will always exist at departure point, a. k. a. beginning (Hawking's "Grand Central Station" with its centrally located special "clock" (t = 0)). The Traveler traveled the numbered mile marker-like light fronts, the flexible accordion-like time corridors, as a space-time traveler traveling two-way streets (+/-) of time through space.  

• Feb 3, 2022

Numbered mile marker-like light fronts . "Flexible accordion-like light-time corridors," "two-way streets (+/-) of time through space." Time tunnels through space. Wormholes. 4-dimensional tractable warp (tractable bubbles of....) space-time. We can actually move, go in motion, travel, whether just a little, or titanically big time. All the same if and when internally self-powered (self-accelerative) in and through universe (which itself appears the prime example, prime show, of hyper space-time plane . . . down plane to a physic, or physics, of "self-acceleration" (and/or "inertialessness")). Driving the environment versus being driven by environment (such as particles being closed systematically controlled by and externally driven by the forces of the LHC) makes all the difference. -------------------------- It's a multifaceted, multi-dimensional, Multiverse Universe.  

murphybridget

• Jan 19, 2024

That's a mind-bending journey, I can definitely appreciate the harmonies of your exploration.  

• Classical Motion

I believe the slit experiments shows that light travels like particles.....discreet and intermittent. But much faster. The light pattern is painted too, just like the electrons. Check out the interference pattern for neutrons.  

• Feb 5, 2024

Let's keep exploring these accordion-like folds in the fabric of space-time!  

• Feb 11, 2024

How does mass travel in space? If we can see the light of the first young galaxies, and if all matter came from the big bang, and if it took that light 14 billion LY to get here, How did the matter that we stand on, get here before that light? How did the evolved with life MW get 14 BLY away from that first lit galaxy? In only 14 BY?  

Classical Motion said: How does mass travel in space? If we can see the light of the first young galaxies, and if all matter came from the big bang, and if it took that light 14 billion LY to get here, How did the matter that we stand on, get here before that light? How did the evolved with life MW get 14 BLY away from that first lit galaxy? In only 14 BY? Click to expand...

Right, that's what I thought.  

Classical Motion said: Right, that's what I thought. Click to expand...

Glad to help you out. But my last comment was in jest. I am in the dark of your concepts. For me the concepts of light and matter do not puzzle, but the mansense of it is most confounding. Man's reasoning is the ultimate mystery dynamic.  

• Feb 12, 2024

Classical Motion said: Glad to help you out. But my last comment was in jest. I am in the dark of your concepts. For me the concepts of light and matter do not puzzle, but the mansense of it is most confounding. Man's reasoning is the ultimate mystery dynamic. Click to expand...

Light travels as a dissolving flux.  

Does light 'travel' at all? Is the wavefront a superposition probability state until it is 'observed' into a photon?  

• Feb 13, 2024

You walk into a dark room and turn on the light switch. How come you see anything at all? You walk inside, outside, and see a lot of things in your view. How come it is all always coming to you rather than always going away and leaving you always in absolute darkness? If even darkness. Even when you think you've seen beams of light traveling, light came to you to inform you other light was doing something elsewhere. You are always the end game of the light. An object real is always the end game of a front of light energy. An advancing front oncoming is the only light you, or any object real, deal in! You will always be facing into it, heading into it, or it heading into you. Always personally experiencing it in your face, or in the face of some instrumentation, can you understand what that means regarding light, time, and the speed of light?! It always being in your face, or some other face, it has no back, no rear, at all! You will always only see and travel into some oncoming face of light energy. It still comes to you even in your rearview mirror. Only the image in your rearview mirror goes away from you in time, not the light in your face!  

• Feb 16, 2024

Atlan0001 said: You walk into a dark room and turn on the light switch. How come you see anything at all? You walk inside, outside, and see a lot of things in your view. How come it is all always coming to you rather than always going away and leaving you always in absolute darkness? If even darkness. Even when you think you've seen beams of light traveling, light came to you to inform you other light was doing something elsewhere. You are always the end game of the light. An object real is always the end game of a front of light energy. An advancing front oncoming is the only light you, or any object real, deal in! You will always be facing into it, heading into it, or it heading into you. Always personally experiencing it in your face, or in the face of some instrumentation, can you understand what that means regarding light, time, and the speed of light?! It always being in your face, or some other face, it has no back, no rear, at all! You will always only see and travel into some oncoming face of light energy. It still comes to you even in your rearview mirror. Only the image in your rearview mirror goes away from you in time, not the light in your face! Click to expand...

Space time, expanding space, light cones and red shift come from the fallacy of light. Once understood, space time, expanding space, light cones disappear. And red shift is easily explained. Light being measured at c velocity from all observers is a joke. We have never measured the velocity of light. Just like professing perpetual motion is impossible. ALL physical entities have perpetual motion. ALL mass is a perpetual motion. As is all propagation. Light is our most ignorant foundation. And it perverts all science. Light is a duty cycle dynamic, not a wave dynamic. Try it........and the cosmos becomes clear. A simple blink has hidden the cosmos from us. There is NO back and forth in space. There is only an on and an off. Present and not present. Light is chunky. A flux of dissolving chunks.  

"There is no such thing as absolute motion . . . there is only relative motion." If one goes in motion traveling toward or at the speed of light, one cannot tell it (Heisenberg uncertainty principle) due to all that relative motion, all of those relative motions, everywhere enclosing one. Again, "There is no such thing as absolute motion . . . there is only relative motion." Look up Newton's three laws of motion, too! There are two different physics for the speed of light, one closed systemic (inside it) and one open systemic (outside it).  

Every particle has absolute motion. Inertia IS absolute motion.  

Classical Motion said: Every particle has absolute motion. Inertia IS absolute motion. Click to expand...

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NASA’s Webb Maps Weather on Planet 280 Light-Years Away

An international team of researchers has successfully used NASA’s James Webb Space Telescope to map the weather on the hot gas-giant exoplanet WASP-43 b.

Precise brightness measurements over a broad spectrum of mid-infrared light, combined with 3D climate models and previous observations from other telescopes, suggest the presence of thick, high clouds covering the nightside, clear skies on the dayside, and equatorial winds upwards of 5,000 miles per hour mixing atmospheric gases around the planet.

The investigation is just the latest demonstration of the exoplanet science now possible with Webb’s extraordinary ability to measure temperature variations and detect atmospheric gases trillions of miles away.

Image: Hot Gas-Giant Exoplanet WASP-43 b (Artist’s Concept)

Tidally locked “hot jupiter”.

WASP-43 b is a “hot Jupiter” type of exoplanet: similar in size to Jupiter, made primarily of hydrogen and helium, and much hotter than any of the giant planets in our own solar system. Although its star is smaller and cooler than the Sun, WASP-43 b orbits at a distance of just 1.3 million miles – less than 1/25 th the distance between Mercury and the Sun.

With such a tight orbit, the planet is tidally locked , with one side continuously illuminated and the other in permanent darkness. Although the nightside never receives any direct radiation from the star, strong eastward winds transport heat around from the dayside.

Since its discovery in 2011, WASP-43 b has been observed with numerous telescopes, including NASA’s Hubble and now-retired Spitzer space telescopes.

“With Hubble , we could clearly see that there is water vapor on the dayside. Both Hubble and Spitzer suggested there might be clouds on the nightside,” explained Taylor Bell, researcher from the Bay Area Environmental Research Institute and lead author of a study published today in Nature Astronomy . “But we needed more precise measurements from Webb to really begin mapping the temperature, cloud cover, winds, and more detailed atmospheric composition all the way around the planet.”

Mapping Temperature and Inferring Weather

Although WASP-43 b is too small, dim, and close to its star for a telescope to see directly, its short orbital period of just 19.5 hours makes it ideal for phase curve spectroscopy , a technique that involves measuring tiny changes in brightness of the star-planet system as the planet orbits the star.

Since the amount of mid-infrared light given off by an object depends largely on how hot it is, the brightness data captured by Webb can then be used to calculate the planet’s temperature.

Image: Hot Gas-Giant Exoplanet WASP-43 b (MIRI Phase Curve)

The team used Webb’s MIRI (Mid-Infrared Instrument) to measure light from the WASP-43 system every 10 seconds for more than 24 hours. “By observing over an entire orbit, we were able to calculate the temperature of different sides of the planet as they rotate into view,” explained Bell. “From that, we could construct a rough map of temperature across the planet.”

The measurements show that the dayside has an average temperature of nearly 2,300 degrees Fahrenheit (1,250 degrees Celsius) – hot enough to forge iron. Meanwhile, the nightside is significantly cooler at 1,100 degrees Fahrenheit (600 degrees Celsius). The data also helps locate the hottest spot on the planet (the “hotspot”), which is shifted slightly eastward from the point that receives the most stellar radiation, where the star is highest in the planet’s sky. This shift occurs because of supersonic winds, which move heated air eastward.

“The fact that we can map temperature in this way is a real testament to Webb’s sensitivity and stability,” said Michael Roman, a co-author from the University of Leicester in the U.K.  

To interpret the map, the team used complex 3D atmospheric models like those used to understand weather and climate on Earth. The analysis shows that the nightside is probably covered in a thick, high layer of clouds that prevent some of the infrared light from escaping to space. As a result, the nightside – while very hot – looks dimmer and cooler than it would if there were no clouds.

Image: Hot Gas-Giant Exoplanet WASP-43 b (Temperature Maps)

Animation: Hot Gas-Giant Exoplanet WASP-43 b (Temperature Maps)

Missing methane and high winds.

The broad spectrum of mid-infrared light captured by Webb also made it possible to measure the amount of water vapor (H 2 O) and methane (CH 4 ) around the planet. “Webb has given us an opportunity to figure out exactly which molecules we’re seeing and put some limits on the abundances,” said Joanna Barstow, a co-author from the Open University in the U.K.

The spectra show clear signs of water vapor on the nightside as well as the dayside of the planet, providing additional information about how thick the clouds are and how high they extend in the atmosphere.  

Surprisingly, the data also shows a distinct lack of methane anywhere in the atmosphere. Although the dayside is too hot for methane to exist (most of the carbon should be in the form of carbon monoxide), methane should be stable and detectable on the cooler nightside.

“The fact that we don't see methane tells us that WASP-43b must have wind speeds reaching something like 5,000 miles per hour,” explained Barstow. “If winds move gas around from the dayside to the nightside and back again fast enough, there isn’t enough time for the expected chemical reactions to produce detectable amounts of methane on the nightside.”

The team thinks that because of this wind-driven mixing, the atmospheric chemistry is the same all the way around the planet, which wasn’t apparent from past work with Hubble and Spitzer.

The MIRI observation of WASP-43 b was conducted as part of the Webb Early Release Science programs, which are providing researchers with a vast set of robust, open-access data for studying a wide array of cosmic phenomena. The James Webb Space Telescope is the world's premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Right click the images in this article to open a larger version in a new tab/window. Download full resolution images for this article from the Space Telescope Science Institute. The research results can be viewed in the Nature Astronomy.

Media Contacts

Laura Betz - [email protected] , Rob Gutro - [email protected] NASA’s Goddard Space Flight Center , Greenbelt, Md.

Margaret Carruthers   [email protected] , Christine Pulliam - [email protected] Space Telescope Science Institute , Baltimore, Md.

Related Information

What is an Exoplanet?

What is a Gas Giant?

Hubble's View of WASP- 43b

More Webb News - https://science.nasa.gov/mission/webb/latestnews/

More Webb Images - https://science.nasa.gov/mission/webb/multimedia/images/

Webb Mission Page - https://science.nasa.gov/mission/webb/

Related For Kids

What is a exoplanet?

What is the Webb Telescope?

SpacePlace for Kids

Para Niños : Qué es una exoplaneta?

Ciencia de la NASA

NASA en español 

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Related Topics

James Webb Space Telescope

Related Terms

• Astrophysics
• Exoplanet Atmosphere
• Exoplanet Science
• Gas Giant Exoplanets
• Hubble Space Telescope
• James Webb Space Telescope (JWST)
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• The Universe

What If Humans Traveled at the Speed of Light? Here's What Happens

S pace is always ripe for theoretical thought exercises, such as the intriguing question, “What would happen if humans traveled at the speed of light?”

Knewz.com has learned that humans would probably not realize we were moving at the speed of light because we cannot feel constant velocity.

However, the main problem would be accelerating to the 671 million miles per hour that light travels, according to an interview published by Space.com .

Rapid acceleration can be extremely painful and even deadly to humans, and we can only handle forces of four to six times the pull of gravity (4 to 6 gs). That makes the 6,000 gs of accelerating to the speed of light completely untenable.

Even more reasonable gs from endeavors like taking off on a space rocket or flying a fighter jet can kill a person because the force makes it difficult for the body to pump blood from the feet to the brain, which is why passing out is such a threat for pilots.

“Your blood will have a hard time pumping to your extremities,” said Michael Pravica, a professor of physics at the University of Nevada, Las Vegas, in the article.

If the g-force does not subside, the person will die because the blood is no longer transporting oxygen throughout the body.

That being said, 6,000 gs would flatten the person like a pancake before that ever became an issue.

The article posited that humans could potentially travel at the speed of light if they accelerated slowly. At the rate of a free fall (1 g), it would take 11 months to reach the speed of light.

Unfortunately, physics still presents a problem, specifically Einstein’s theory of relativity. As objects travel closer to the speed of light, their mass starts to grow, and the theory has proven that it would require infinite mass to travel at the speed of light.

This problem of physics is why humans have never managed to get anything to travel at the speed of light. Scientists have pushed sub-atomic particles to move at 99.9% the speed of light, but never 100%.

As humans are much larger than sub-atomic particles, the amount of energy required to push a human even to 99.9% the speed of light would be “extremely improbable” said Pravica.

However, suppose we allow ourselves to break physics and enable a person to travel at the speed of light, Einstein's theory of relativity argues that the person would age incredibly slowly thanks to time dilation.

Additionally, despite aging slower, people moving at normal speed would appear to be moving in slow motion. So, the speed-of-light travellers would simultaneously be moving much faster than their slow-motion peers while also aging slower.

One fascinating idea is that the speed of light is a foundation of modern physics, but there is no true rule that light must be the fastest object in the universe, according to Discover Magazine .

Our current understanding of physics puts light as the limit of speed, but humans in the distant future could theoretically experience a breakthrough and discover a means to travel faster than the speed of light.

While the idea is fun to ponder, there are significant hurdles that essentially guarantee humans will not be able to travel at the speed of light anytime in the foreseeable future.

Politics latest: Keir Starmer accused of 'rank hypocrisy' by Rishi Sunak after setting out what he'll do to tackle small boat crossings

Labour leader Sir Keir Starmer lays out his party's plans to try and tackle small boat crossings if it wins power. Listen to the latest episode of the Electoral Dysfunction podcast as you scroll.

Friday 10 May 2024 18:30, UK

• Starmer says small boat crossings 'one of the greatest challenges we face'
• Explained: What's in Labour's plan to try and tackle problem
• Darren McCaffrey: Will Labour's plan cut it with voters?
• Starmer says no flights to Rwanda will take off under Labour
• Sunak accuses Starmer of 'rank hypocrisy'
• Electoral Dysfunction:  Jess Phillips says Elphicke defection like 'being punched in gut'
• UK exits recession | Economy 'returning to full health'
• Faultlines:   Can British farming survive?
• Live reporting by Tim Baker

Across the UK, anger is brewing amongst some farmers.  

Protests have already been held in London, Dover and Cardiff, with more planned - mirroring similar tensions seen across Europe in the last six months.     

They say they’re annoyed about cheap foreign imports and changes to subsidies forcing them to give up land in favour of environmental schemes.    

But what does this mean for the food on our table - and does British produce risk becoming a luxury product for the wealthy only?    

On the Sky News Daily , Niall Paterson is joined by West of England and Wales correspondent Dan Whitehead to find out why farmers are so concerned, and speaks to Liz Webster, the founder of Save British Farming, about why she believes eating British isn't just good for our farmers - it's good for the nation's health, too.   

In response to our report, Farming Minister Mark Spencer, said: "We firmly back our farmers. British farming is at the heart of British trade, and we put agriculture at the forefront of any deals we negotiate, prioritising new export opportunities, protecting UK food standards and removing market access barriers. 

"We've maintained the £2.4bn annual farming budget and recently set out the biggest ever package of grants which supports farmers to produce food profitably and sustainably."

The Welsh government said: "A successful future for Welsh farming should combine the best of our traditional farming alongside cutting-edge innovation and diversification. 

"It will produce the very best of Welsh food to the highest standards, while safeguarding our precious environment and addressing the urgent call of the climate and nature emergencies."

👉  Listen above then tap here to follow the Sky News Daily wherever you get your podcasts   👈

Following the defection of the Dover and Deal MP Natalie Elphicke to Labour, Beth, Ruth and Jess discuss the surprise move and whether it could have been handled differently by Sir Keir Starmer.

They also talk about Beth's interview with the former immigration minister Robert Jenrick and his warnings about Reform UK.

Plus, how significant was the defeat of former Conservative mayor of the West Midlands Andy Street? Beth and Jess were both there to tell the story.

And they answer a question on Labour and the Muslim vote, and what the party can do to restore confidence and trust.

Email Beth, Jess, and Ruth at [email protected] , post on X to @BethRigby, or send a WhatsApp voice note on 07934 200 444.     

👉 Listen above then tap here to follow Electoral Dysfunction wherever you get your podcasts 👈

In January 2023, Rishi Sunak made five promises.

Since then, he and his ministers have rarely missed an opportunity to list them. In case you haven't heard, he promised to:

• Halve inflation • Grow the economy • Reduce debt • Cut NHS waiting lists and times • Stop the boats

See below how he is doing on these goals:

The Sky News live poll tracker - collated and updated by our Data and Forensics team - aggregates various surveys to indicate how voters feel about the different political parties.

With the local elections complete, Labour is still sitting comfortably ahead, with the Tories trailing behind.

See the latest update below - and you can read more about the methodology behind the tracker  here .

Speaking to Sky political editor  Beth Rigby , Sir Keir Starmer has defended his decision to allow Tory MP Natalie Elphicke into Labour.

Ms Elphicke was on the right of the Conservative spectrum, and previously defended her sex-offender ex-husband, comments which she apologised for this week following her defection.

Addressing Tory voters, Sir Keir says he wants Labour to be a "place where they who have ambitions about their families, their communities, their country, can join and be part of what we are trying to build for their country".

Asked by Beth if he was ruthless, Sir Keir said: "Yes, I'm ruthless in trying to ensure we have a Labour government that can change this country for the better.

"Not ruthless for my own ambition, not ruthlessness particularly for the Labour Party - I'm ruthless for the country. 

"The only way we'll bring about a change in this country is if we're ruthless about winning that general election and putting in place a government of public service, that’ll be a major change.

"Politics, I believe, should be about public service, that's what I've been about all my life."

More now from political editor Beth Rigby's interview with Labour leader Sir Keir Starmer.

She reminded him that he previously ruled out doing a deal with the SNP - but has not done so for the Liberal Democrats.

Sir Keir again ruled out a coalition with the SNP - adding that he is aiming for a "majority Labour government".

He says Labour needs "to keep working hard, keep disciplined and getting our message across, which is something fundamental to me".

Pushed on his lack of ruling out a possible agreement with the Lib Dems, Sir Keir says: "I'm going for a majority.

"That's the answer I gave you a year ago. It's the same answer I'm giving you now."

Sir Keir Starmer was earlier today pushed on whether Rwanda deportation flights will take off if he was prime minister - although it was not clear if he would cancel flights which had already been organised.

Sky News understood that previously booked deportation flights to Rwanda would still go ahead if Sir Keir entered Number 10. 

But the Labour leader has now gone further.

Speaking to political editor Beth Rigby , Sir Keir has ruled out any flights taking off.

"There will be no flights scheduled or taking off after general election if Labour wins that general election," he says.

He says: "Every flight that takes off carries with it a cheque to the Rwanda government. 

"So I want to scrap the scheme - so that means the flights won't be going."

Sir Keir says he would rather spend the money on his own measures to counter small boats.

"No flights, no Rwanda scheme. It's a gimmick," he says.

By Alix Culbertson , political reporter

Scotland's new first minister has told Sky News that the controversial gender recognition reforms "cannot be implemented."

John Swinney,  who became first minister this week , has faced questions over his stance on gender recognition after MSPs voted in 2022 to pass a bill to make it simpler for people to change their gender without having to obtain a medical diagnosis.

The UK government blocked the bill from being made into law and the Supreme Court rejected a request by the Scottish government for a judicial review.

Asked if he would be fighting to push the bill through, Mr Swinney told Sky News: "The reality of the situation we face is that the Supreme Court has said that we can't legislate in that area. We can't take forward that legislation."

The UK economy is no longer in recession, according to official figures.

Gross domestic product (GDP) grew by a better-than-expected 0.6% between January and March, the Office for National Statistics (ONS) said.

Economists had predicted the figure would be 0.4%.

Prime Minister Rishi Sunak said it showed the economy had "turned a corner".

He told Sky News's Ed Conway: "I am pleased that while there's more work to do, today's figures show that the economy now has real momentum, and I'm confident that with time, people will start to feel the benefits of that.

"We've had multiple months now where wages are rising, energy bills have fallen, mortgage rates are down and taxes are being cut... I'm pleased with the progress that we're making."

Mr Sunak added: "I am confident the economy is getting healthier every week."

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Rishi Sunak has criticised Sir Keir Starmer's position on Rwanda as "rank hypocrisy".

Speaking to broadcasters, the prime minister says the Labour leader has announced things the government is "already doing".

He gives the example of "punching through the backlog, having more law enforcement officers do more, that's all happening already".

"We've announced all of that more than a year ago," the prime minister adds.

"The question for Keir Starmer if he cares so much about that, why did he vote against the new laws that we passed to give our law enforcement officers new powers? 

"They've now used those to arrest almost 8,000 people connected with illegal migration, sentenced them to hundreds of years in prison.

"And if it was up to him, all those people would be out on our streets, so I think it's rank hypocrisy property of his position."

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