time in light travel

A beginner's guide to time travel

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

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

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

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

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

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

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

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

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

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

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

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

A party for time travelers 

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

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

The arrow of time 

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

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

Time travel paradox 

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

Killing Hitler

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

Killing your grandfather

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

A closed loop

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

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Universe Today

Space and astronomy news

How Does Light Travel?

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 era, the 20th century led to breakthroughs that showed us 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 unanswered questions about 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 to 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 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 divert it, or arrest it, 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!

We have written many articles about light here at Universe Today. For example, here’s How Fast is the Speed of Light? , How Far is a Light Year? , What is Einstein’s Theory of Relativity?

If you’d like more info on light, check out these articles from The Physics Hypertextbook and NASA’s Mission Science page.

We’ve also recorded an entire episode of Astronomy Cast all about Interstellar Travel. Listen here, Episode 145: Interstellar Travel .

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56 Replies to “How Does Light Travel?”

“HOW DOES LIGHT TRAVEL?”

it travels lightly. 😀

Light doesn’t exist. This is an observation from light’s point of view and not ours. Traveling at the speed of (wait for it) light, absolutely no time passes between leaving it’s source and reaching it’s destination for the photon. This means, to the photon hitting your retina, it is also still on that star you are observing 10 light years away. How is this possible? Maybe John Wheeler was right when he told Richard Feynman that there is only one electron in the universe and it travels forward in time as an electron, then back in time as a positron and every electron we see is the same electron.

MY QUESTION IS: Whether light is a wave , particle or both.. where does it get the energy to move through space/time. In other words is the energy of light infinite? Does it continue on without lose of energy…..forever…….

I believe that Special Relativity says that the energy of light is infinite due to the very fact it has no mass. E=MC^2

In reverse, this is also why something with mass to begin with. If accelerated toward the speed of light, will see their mass and gravity increase to infinite points as they near relativistic speed (it actually starts around 95% with a steep upward curve from there), with a relative slowing to a stop of time.

Join the discussion

Light and the universe are only illusions that are formed in our minds via technology that sends information from the simulation program we’re living in. That information comes in the form of invisible wavelengths that includes wavelengths that we perceive as light. The visible retinas in our eyes are like tiny video screens where these particles are arranged into patterns that form into all the various objects we think are real objects. This information is also converted into thoughts within our minds which are like computer processors that process that information.

We are living in a computer simulation that is much more advanced than anything the characters in the program have built according to the information called the Beast.

Brad,…So You’re suggesting that “life” as we know and call it “is some kind of retro-virus” or “bio-intelligent format” heaped upon a perceived “set of accepted data sets” that are not in sync with each other in most cases with exception to Math 94% of the time….Even then it can vary which suggests Your idea would mean we all live in a fairy tale. That is what you suggest,…right?……

Brad has watched the Matrix too many times.

Correction: Even gravity doesn’t slow light down. Light (EM radiation of any wavelength) always travels at speed c, relative to any local inertial (Lorentz) frame. It could also be noted that the wavelength of an EM wave is not a characteristic of that wave alone; it also depends on the state of motion of the observer. You might even say, “One man’s radio wave is another man’s gamma ray.”

Light actually “slows down” every time it has to travel through anything but a vacuum. Look up Cherenkov radiation to see what happens when light initially travels faster than it can through a particular substance, like water. Light speed is not constant when traveling through any medium except pure vacuum. In fact that is why your pencil looks bent when you drop it in a glass of water. Light bends to find it’s fastest path through any medium, and it slows down in that medium.

if all you scientist could ever get it in your pie brain that there is no time, no light speed, no warping space, no black holes for the purpose of moving through space quickly, no smallest no biggest when it comes to space and that all of everything has always been in existence but not necessarily as it is now. you will never find the smallest because if it exist it has an inside, and you will never find the end of space because it is infinite.

What are you smoking?

The article started out nicely, but I lost interest as mistakes began to appear. First Einstein did not “propose” the photoelectric effect. The photoelectric effect was first observed by Heinrich Hertz in 1887. Einstein used the idea of photons to explain the photoelectric effect and derive the photoelectric equation. Also, Max Plank had already derived the blackbody distribution, by assuming that electromagnetic energy of frequency f could only be emitted in multiples of energy E=hf, by 1900. Einstein’s paper on the photoelectric effect was published in his “miracle” year of 1905. The photoelectric effect has nothing to do with black body radiation.

Einstein did not coin the name “photons” for light quanta, as stated in this article. This term was first used by Arthur Compton in 1928.

I have to say that I do not know what the author of the article means when he says ” calculating the wavelength at which light functioned” in reference to Louis-Victor de Broglie. Louis de Broglie used the dual nature of light to suggest that electrons, previously thought of as particles, also had wave characteristics and used this notion to explain the Bohr orbits in the hydrogen atom.

I gave up on the article after seeing these errors. I’m afraid I have a low tolerance for sloppy writing.

Oh, it’s BCE now, “Before the Common Era” BC has worked for 2000 years but now the PC police have stepped in so as not to offend who? Some Muslims?

mecheng1, you must be very young. BCE has been in used in academia for decades. It’s nothing “new”, just out of your circle of knowledge.

Decades??? Really?? How does that compare to 2000 years?

Only in Euro-centric texts have your assertions been true, McCowen. The rest of the world not influenced by Christianity have used their own calendars and a “0” year or a “year 1” from which to reckon the passage of time, largely based on their own religions or celestial observations.

Over the last century or so, through commerce, most of the world has generally accepted the use of a Western calendar (or use it along with their own for domestic purposes, like we here in the US still use Imperial units of measure that have to be converted to metric for international commerce). So, we are in a “common era” insofar as non-Christian societies are incorporating the Gregorian Calendar and the generally-accepted “year 1” established by that calendar (which is supposed to be the year of Jesus’s birth, but it probably isn’t according to current scholarship). Besides, the Gregorian calendar is an improved derivative of the Roman calendar – even the names of the months come from the Romans.

In short, it is more accurate, as well as respectful, to go with BCE in these global times.

Where is the information carried on a photon hitting my eye(s), or cluster/group/pack of photons hitting my eyes(s), that I see as other distant galaxies and planets going around stars?

That’s the mystery, isn’t it? Even in scattering, light remains coherent enough to convey an enormous amount of information.

Since the miniscule equal masses with opposite charges, that make up the photon structure, interact at 90 degrees, this induces a spin (a finding from the 80’s by the LANL plasma physics program) which creates a centrifugal force that counterbalances the charge attraction of the opposite charges. This establishes a stable structure for energies less than 1.0216 MeV, the pair-formation threshold, separating these “neutrino” sub-components by a specific distance providing wavelengths varying with photon energy. This composite photon propagates transversely at c/n, the speed of light divided by the index of refraction of the material traversed. In spite of the mass being defined as zero, for convenience in calculating atomic masses, there is actually an infinitesimal but non-zero mass for the photon that is required for calculations that describe its properties.

Tim, you poor guy! You have a discombobulated brain! Everything you wrote is just gibberish.

i would like to know the temperature in a black hole…maybe absolute zero? is absolute zero the moment that time stop?

I think the temp inside a black hole would be extremely high since temperature seems to increase with mass. Comparing absolute zero to time stopping is very interesting though. To the observer they would appear the same.

Theoretically there is no temperature in a black hole from any observer POV because time is stopped. Although JALNIN does bring up that point, and he also brings up the point of increasing mass corresponding to increasing energy. Everything in Hawking and Einstein’s equations though, suggest that any energy would be absorbed back by the singularity, so there wouldn’t be any heat. In fact it should be infinitely cold. But time is no more, so technically no heat or energy is emitted anyway from any observers POV. Yet recent images of black holes from Chandra show that they emit powerful Gamma Jets along their spin axis just like Neutron stars, and Pulsars. BTW edison. The accretion disk can reach temperatures of 20MN Kelvin on a feeding SM black hole (quasar). NASA just published an article on it through the Chandra feed a while back.

Light doesn’t travel, it just IS. It is we, the condensed matter, that travels, through time.

Oh really? Is this just your imagination/illusion or you have published a paper on it?

So you don’t believe you travel through time?

I wish I understood just a portion of I just read, love sicence so bad BUT, sighs

It would be easier to understand if it wasn’t pure gibberish written by someone with no science background.

I have two “mind-bending relativity side effects” to share. At least they are mind-bending to me.

1) Light travels the same speed relative to all particles of mass, regardless of how those particles move relative to each other:

I can conceptualize this if we are only talking about two mass-particles/observers and the examples I’ve seen always involve only two observers. But if you have many mass-particles/observers, how does the space-time seem to know to adjust differently for all of them. I am sure i am understanding this correctly as it is a basic concept of special relativity and nobody seems to bring this issue up. But it “bends my mind” when i try to include more than two observers. Maybe you can help.

2) General Relativity’s (“GR”) prediction that the big bang started with “Infinite” energy and now the universe appears to have finite mass energy and Regarding the first effect: How can something infinite turn into something finite? Is the answer that at that early in the universe, quantum takes over and GR’s prediction of infinite mass-energy at the start of the universe is just wrong?

I need to correct a typo in my previous comment. Where i say “i am sure am understanding this correctly” I meant to include the word NOT. so it should read “i am sure am NOT understanding this correctly” Mark L.

Mark,….I think you’re understanding it just fine from the standpoint of multiple observers, The point might be that in space, the density of “emptiness” or “lack of emptiness” might be impacted from one area of observation to another by an observer who’s perceptions are not equal but not being taken into consideration by each observer. ( an example if I may?) If you were to use a Clear medium which is oil based beginning with 5 gallons of mineral spirits in a large barrel and keep adding 5 gallons of thicker clear oil and then heavy grease and stop with using a clear heavy wax,…what happens is you end up with a barrel of clear fluid that begins with a floating substrate but the liquid begins to keep floating and the heaviest stuff goes to the bottom,…You end up with a sort of solid tube of clear fluids which if you could keep them in shape here on the earth, “you could observe them” from several positions, #1. the fluid end #2, the less fluid part, #3, the semi solid part #4. the seemingly solid part #5. the almost solid part & #6. the solid part……all of which would be transparent….You could then shine a laser through all of it and perhaps do that again from different places and see what happens at different angles…..I think what happens as a result would be, an observer would end up be influenced as per his or her ideas thusly because of the quasi-nature of what the density of space is at the point of space is where the observation is made. just a guess.

All Special Relativity really says about light is that it appears to move at the same rate from any observer POV. There are other more advanced rules relating to light speeds. One of them is the implication of infinite energy in a photon because of the fact it’s mass-less, therefore it can move at the maximum rate a mass-less particle or wave can (not necessarily that it does) Later when the electron was discovered (also mass-less particle or wave), it was also found to conform to the rules of special relativity.

As far as the big bang, there are a lot of cracks in that theory, and many different ones are beginning to dispute some of the common ideas behind the “Big Bang” as well as “Inflationary Cosmology”. Honestly though, both standard and quantum physics applied, and yet both went out the window at the same time at some point. That’s what all the theories really say. At some point, everything we know or think we know was bunk, because the math just breaks down, and doesn’t work right anymore.

i think until there is an understanding of the actual “fabric” of space itself, the wave vs particle confusion will continue. another interesting article recently was the half integer values of rotating light. planck’s constant was broken? gravity? a bump in the data? lol these are interesting times.

There’s no fabric.

Tesla insists there is an aether, Einstein says not. Tesla enjoyed far less trial and error than Einstein. The vast majority of Tesla’s projects worked the first time around and required no development or experimentation. I’ll go with Tesla; there is an aether as a fabric of space.

http://weinsteinsletter.weebly.com/aether.html

Maybe Special Relativity is not correct? 🙂

Feynman said unequivocally that QED is NOT a wave theory. In fact, the math only looks like Maxwell’s wave function when you are looking at a single particle at a time, but the analogy breaks down as soon as you start looking at the interactions of more than one, which is the real case. There’s no light acting alone, but always an interaction between a photon and some other particle, an electron, another photon, or whatever. He said “light is particles.” So the question re: how can light travel through a vacuum if it’s waves is a nonsensical question. There are no collapsing wave functions in light. There’s only probabilities of position that look like waves on a freaking piece of paper. Even calling light properties as “wavelengths” is nonsensical. Light comes in frequencies, i.e., the number of particles traveling tightly together. Higher frequency is more energy because it’s more particles (E=MC[squared]). “Wavicles” is pure bullshit.

I don’t agree with the John Wheeler theory that there is only one electron since the computer I am using was built by ion implantation and uses a very large number of them simultaneously to function.

Black holes don’t stop or slow light, if they even exist. A black hole could phase shift light, which is why we see things emitting xrays and call them black holes….but they could be something else too.

Photons have no mass but they do have energy. Energy and mass are transformable into each other. Gravity works on energy as well as mass. As massive particles approach the speed of light their measurable mass increases to infinity. But since energy is equivalent to mass, why doesn’t the photon, which has energy, not seem to have infinite mass?

NO other wave travels thru a vacuum? what about radio?

Radio waves are a specific frequency range of light.

Technically speaking, radio waves are emitted at various frequencies that share the same space time as light. They are not however light. They’re modulated electrons. Modulated photons certainly can be used to carry a vast amount of information a great distance. It cannot do it any faster or better than a radio wave though. Both electrons and photons are mass-less, therefore they both conform to the rules of Special Relativity in the same way. Both travel at the speed of light.

I just don’t understand is it a particle of a wave? It seems like it behaves like wave and sometimes like particle and in some situations is like a what ever you are going to call it.

So, the logical idea would to have formula Photon_influence * weight_for_particle + Wave_influence * weight_for_wave

Make it more compact.

This article is good but the title is bad as by the end we still weren’t told how light travels through space. Also, there are some historical mistakes as already pointed out. Now for my contribution: I think that light and Gravity have a lot in common; for one – an atom’s electrons transmit light and an atom contains the tiny heavy place that knows everything there is to know about gravity, that is, the nucleus. Light and Gravity are both related to the same entity, the atom. Unfortunately, we, still cannot grasp how what’s heavy brings about gravitation. For those of you with a creed for new ideas go to: https://www.academia.edu/10785615/Gravity_is_emergent It’s a hypothesis…

Gravity and light are infinite, like space and time… Mind the concept that there are waves within waves, motions within motion, vibrations within vibration, endless overtones and universal harmony…

From this article, I have “And in the end, the only thing that can truly slow down or arrest the speed of light is gravity”

Doesn’t light slow down in water and glass and other mediums. I was only a Physics minor, but I do remember coivering this though way back in the early 80’s. And in my quick checking online, I found the following.

“Light travels at approximately 300,000 kilometers per second in a vacuum, which has a refractive index of 1.0, but it slows down to 225,000 kilometers per second in water (refractive index = 1.3; see Figure 1) and 200,000 kilometers per second in glass (refractive index of 1.5).”

Were they saying something else here. I did like the article.

Photons are not massless, but their mass is incredibly small even compared to a proton or neutron. So, by Einstein’s E=MC^2, the energy required for a photon to move is greatly reduced, but photons do have mass and are affected by gravity. If photons had no mass at all, then gravity would have no affect on them, but gravity does. Gravity bends light and can change it’s course through space. We see that in the actual test first performed to prove Einstein’s theory buy observing the distorted placement of stars as their light passes near the sun observed during an eclipse. We can also see it through gravitational lensing when viewing deeps space objects. And the fact that there are black holes that are black because light cannot escape it’s gravity. So photons do have mass, be it miniscule, and with that their propagation with light waves through space will eventually run out of energy and stop. but this would probably require distances greater to several widths of our universe to accomplish. Light from the furthest reaches of the universe are not as bright, or as energetic, as they are at anyplace between here and their origins. That reduction in their energy is also attributed to Einstein’s equation and the inverse square law, where the intensity of light is in relation to the inverse square of the distance. That proves that light looses energy the further it travels, but it still moves at the speed of light. As light looses energy, it doesn’t slow the light wave.

It has been proven that more energetic light does in fact travel slightly faster. You can find the experiments done with light that has traveled billions of light years, the more energetic is in fact faster over a number of seconds, around 10 -15 or so. As people encounter this information, they see that many accepted theories can now be debunked.

The point of the article is nothing new; light acts like a particle AND a beam. So when you sit behind a closed door and someone shines a light on the door, the light will engulf the door and wave through and around the edges, the particle does not just bounce straight back. You can focus a beam of light on an object, but it will sneak though the corners and underneath the door, through any opening,. And yes, light travels forever. It is a constant, that cannot be sped up. We can slow it down by focusing it through prisims or crystals. But it still is traveling at 186,000/MPS.and that speed does not change. So, that is why we can see the outer edge of the universe: 13,8B light years away *the time that it takes for light to travel in one year, is one light year. So, it has taken 13,8B light years for the light of other galaxies to get here, so those galaxies could be gone by now, since it took so long to reach us, We are truly looking back in time as we see the light emitted from those galaxies and stars.

It propagates through the quantum mish-mash know as the aether . . .

If light is a particle and particles have mass why does not the mas increase with it speed?

Wow…there are errors in the article, yes…the enthusiasm demonstrated by all the comments is encouraging…but when I read these comments, I am a bit dismayed at the lack of understanding that is evident in most of them…confusing energy and intensity and wavelength…confusing rest mass and inertial mass…not to mention some off-the-wall hypotheses with no experimental evidence to support them. There are some great primers out there…books, documentaries, podcasts (like Astronomy Cast). Good luck!

Precisely correct. Sci-fi rules basic physics, which reflects on the poor education system. Pity.

First time I heard about A. A. and his theory about light I really didn’t like him. Why? Because light was the the fastest thing in the universe and there is no other thing faster than the light. Later, when I have red about angular speed I have asked my self if you have linear and angular speed and both of them are speeds how that will result in the maximum speed. Since then, I have not had a chance to get right answer.

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Is time travel even possible? An astrophysicist explains the science behind the science fiction

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Will it ever be possible for time travel to occur? – Alana C., age 12, Queens, New York

Have you ever dreamed of traveling through time, like characters do in science fiction movies? For centuries, the concept of time travel has captivated people’s imaginations. Time travel is the concept of moving between different points in time, just like you move between different places. In movies, you might have seen characters using special machines, magical devices or even hopping into a futuristic car to travel backward or forward in time.

But is this just a fun idea for movies, or could it really happen?

The question of whether time is reversible remains one of the biggest unresolved questions in science. If the universe follows the laws of thermodynamics , it may not be possible. The second law of thermodynamics states that things in the universe can either remain the same or become more disordered over time.

It’s a bit like saying you can’t unscramble eggs once they’ve been cooked. According to this law, the universe can never go back exactly to how it was before. Time can only go forward, like a one-way street.

Time is relative

However, physicist Albert Einstein’s theory of special relativity suggests that time passes at different rates for different people. Someone speeding along on a spaceship moving close to the speed of light – 671 million miles per hour! – will experience time slower than a person on Earth.

People have yet to build spaceships that can move at speeds anywhere near as fast as light, but astronauts who visit the International Space Station orbit around the Earth at speeds close to 17,500 mph. Astronaut Scott Kelly has spent 520 days at the International Space Station, and as a result has aged a little more slowly than his twin brother – and fellow astronaut – Mark Kelly. Scott used to be 6 minutes younger than his twin brother. Now, because Scott was traveling so much faster than Mark and for so many days, he is 6 minutes and 5 milliseconds younger .

Some scientists are exploring other ideas that could theoretically allow time travel. One concept involves wormholes , or hypothetical tunnels in space that could create shortcuts for journeys across the universe. If someone could build a wormhole and then figure out a way to move one end at close to the speed of light – like the hypothetical spaceship mentioned above – the moving end would age more slowly than the stationary end. Someone who entered the moving end and exited the wormhole through the stationary end would come out in their past.

However, wormholes remain theoretical: Scientists have yet to spot one. It also looks like it would be incredibly challenging to send humans through a wormhole space tunnel.

Paradoxes and failed dinner parties

There are also paradoxes associated with time travel. The famous “ grandfather paradox ” is a hypothetical problem that could arise if someone traveled back in time and accidentally prevented their grandparents from meeting. This would create a paradox where you were never born, which raises the question: How could you have traveled back in time in the first place? It’s a mind-boggling puzzle that adds to the mystery of time travel.

Famously, physicist Stephen Hawking tested the possibility of time travel by throwing a dinner party where invitations noting the date, time and coordinates were not sent out until after it had happened. His hope was that his invitation would be read by someone living in the future, who had capabilities to travel back in time. But no one showed up.

As he pointed out : “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”

Telescopes are time machines

Interestingly, astrophysicists armed with powerful telescopes possess a unique form of time travel. As they peer into the vast expanse of the cosmos, they gaze into the past universe. Light from all galaxies and stars takes time to travel, and these beams of light carry information from the distant past. When astrophysicists observe a star or a galaxy through a telescope, they are not seeing it as it is in the present, but as it existed when the light began its journey to Earth millions to billions of years ago.

NASA’s newest space telescope, the James Webb Space Telescope , is peering at galaxies that were formed at the very beginning of the Big Bang, about 13.7 billion years ago.

While we aren’t likely to have time machines like the ones in movies anytime soon, scientists are actively researching and exploring new ideas. But for now, we’ll have to enjoy the idea of time travel in our favorite books, movies and dreams.

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

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

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

Is time travel possible?

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

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

Learn more: Best travel insurance

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

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

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

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

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

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

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

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

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

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

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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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December 5, 2023

Light Can Travel Backward in Time (Sort Of)

Light can be reflected not only in space but also in time—and researchers exploring such “time reflections” are finding a wealth of delightfully odd and useful effects

By Anna Demming

Ekrem EDALI/Alamy Stock Photo

Can we turn back time? Ask a savvy physicist, and the answer will be “it depends.”

Schemes for retrograde time travel abound but usually involve irreconcilable paradoxes and rely on outlandish theoretical constructs such as wormholes (which may not actually exist). Yet when it comes to simply turning back the clock—akin to stirring a scrambled raw egg and seeing the yolk and white reseparate—a rich and growing subfield of wave physics shows that such “time reversal” is possible.

Reversing time would seem to fundamentally clash with one of the most sacred tenets of physics, the second law of thermodynamics, which essentially states that disorder—more specifically “entropy”—is always increasing, as humbly demonstrated in the incessant work needed to keep things tidy. This inexorable slide toward mess and decay is what tends to make unscrambling eggs impossibly difficult—and what propels time’s arrow on a one-way trip through our day-to-day experiences. And although so far there’s no way to unscramble an egg, in certain carefully controlled scenarios within relatively simple systems, researchers have managed to turn back time.

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The trick is to create a certain kind of reflection. First, imagine a regular spatial reflection, like one you see in a silver-backed glass mirror. Here reflection occurs because for a ray of light, silver is a very different transmission medium than air; the sudden change in optical properties causes the light to bounce back, like a Ping-Pong ball hitting a wall. Now imagine that instead of changing at particular points in space, the optical properties all along the ray’s path change sharply at a specific moment in time. Rather than recoiling in space, the light would recoil in time, precisely retracing its tracks, like the Ping-Pong ball returning to the player who last hit it. This is a “time reflection.”

Time reflections have fascinated theorists for decades but have proved devilishly tricky to pull off in practice because rapidly and sufficiently changing a material’s optical properties is no small task. Now, however, researchers at the City University of New York have demonstrated a breakthrough: the creation of light-based time reflections .

To do so, physicist Andrea Alù and his colleagues devised a “metamaterial” with adjustable optical properties that they could tweak within fractions of a nanosecond to halve or double how quickly light passes through. Metamaterials have properties determined by their structures; many are composed of arrays of microscopic rods or rings that can be tuned to interact with and manipulate light in ways that no natural material can. Bringing their power to bear on time reflections, Alù says, revealed some surprises. “Now we are realizing that [time reflections] can be much richer than we thought because of the way that we implement them,” he adds.

Such structural properties are also found in nature—for example, in the radiant iridescence of a butterfly’s wing. Picking up where nature left off, however, researchers studying metamaterials have engineered structures that can render objects invisible , and applications range from better antennas and earthquake protection to building light-based computers . Now scientists are trading in spatial dimensions of these structural features for temporal ones. “We design metamaterials to do unusual things, and this is one of those unusual things,” says Nader Engheta, a professor at the University of Pennsylvania and a pioneer in metamaterial-modulated wave physics.

Waves Gone Weird

The device Alù and his collaborators developed is essentially a waveguide that channels microwave-frequency light. A densely spaced array of switches along the waveguide connects it to capacitor circuits, which can dynamically add or remove material for the light to encounter. This can radically shift the waveguide’s effective properties, such as how easily it allows light to pass through. “We are not changing the material; we are adding or subtracting material,” Alù says. “That is why the process can be so fast.”

Time reflections come with a range of counterintuitive effects that have been theoretically predicted but never demonstrated with light. For instance, what is at the beginning of the original signal will be at the end of the reflected signal—a situation akin to looking at yourself in a mirror and seeing the back of your head. In addition, whereas a standard reflection alters how light traverses space, a time reflection alters light’s temporal components—that is, its frequencies. As a result, in a time-reflected view, the back of your head is also a different color. Alù and his colleagues observed both of these effects in the team’s device. Together they hold promise for fueling further advances in signal processing and communications—two domains that are vital for the function of, say, your smartphone, which relies on effects such as shifting frequencies.

Just a few months after developing the device, Alù and his colleagues observed more surprising behavior when they tried creating a time reflection in that waveguide while shooting two beams of light at each other inside it . Normally colliding beams of light behave as waves, producing interference patterns where their overlapping peaks and troughs add up or cancel out like ripples on water (in “constructive” or “destructive” interference, respectively). But light can, in fact, act as a pointlike projectile, a photon, as well as a wavelike oscillating field—that is, it has “ wave-particle duality .” Generally a particular scenario will distinctly elicit just one behavior or the other, however. For instance, colliding beams of light don’t bounce off each other like billiard balls! But according to Alù and his team’s experiments, when a time reflection occurs, it seems that they do.

The researchers achieved this curious effect by controlling whether the colliding waves were interfering constructively or destructively—whether they were adding or subtracting from each other—when the time reflection occurred. By controlling the specific instant when the time reflection took place, the scientists demonstrated that the two waves bounce off each other with the same wave amplitudes that they started with, like colliding billiard balls. Alternatively they could end up with less energy, like recoiling spongy balls, or even gain energy, as would be the case for balls at either end of a stretched spring. “We can make these interactions energy-conserving, energy-supplying or energy-suppressing,” Alù says, highlighting how time reflections could provide a new control knob for applications that involve energy conversion and pulse shaping, in which the shape of a wave is changed to optimize a pulse’s signal.

Unscrambling the Physics

Readers who are well versed in the laws of physics can be reassured that Alù’s device does not violate the tenets of thermodynamics. The waveguide does not, for instance, create or destroy energy but simply transforms it efficiently from one form to another—the energy gained or lost by the waves comes from that which is added or subtracted to change the metamaterial’s properties. But what about the inescapable increase of disorder—entropy—over time, as prescribed by thermodynamics? How is a light beam’s time reflection not the equivalent of unscrambling an egg?

As John Pendry, a metamaterial-focused physicist at Imperial College London, explains, however odd reversing a light beam may look, it’s wholly consistent with ironclad thermodynamic principles. The rise of entropy is really a matter of losing information, he says. For instance, line schoolchildren up in alphabetical order, and someone will know exactly where to find each child. But let them loose in the playground, and there’s a vast number of different ways the children could be arranged, which equates to an increase in entropy, and what information you had for locating each child is lost. “If [something is] time-reversible, it means you’re not generating entropy,” Pendry says, even if it looks like you are. Going back to the playground analogy, although the children still run off to play, they know what lines to form to return to class at the bell—so no entropy is generated. “You don’t lose the information,” he says.

Reflection is far from the only optical phenomenon to receive the time-domain treatment. In April Pendry and a team of researchers, including Riccardo Sapienza of Imperial College London, demonstrated a time-domain analogue of a classic experiment from centuries ago that ultimately played a key role in establishing light’s wave-particle duality. First performed by physicist Thomas Young in 1801, the “ double-slit experiment ” provided such irrefutable evidence of light’s wavelike nature that in the face of subsequent evidence for light acting as a particle, scientists could only conclude that both descriptions applied. Send a wave at a barrier with two slits, and waves fanning out from one slit will interfere with those emanating from the other. With light, this constructive and destructive interference shows up on a screen beyond the double slit as multiple bright stripes, or “fringes.” Sapienza, Pendry and their colleagues used indium tin oxide (ITO), a photoreactive substance that can rapidly change from transparent to opaque, to produce “time slits.” They showed that a beam of light interacting with double time slits would produce a corresponding interference pattern in frequency, which was used as a time analogue—that is, there were bright light fringes at different frequencies.

According to Engheta, what motivates experiments that swap time and space in optical effects are the “exciting and novel features we can find in the physics of light-matter interaction.” And there are plenty. Pendry describes with a chuckle how he and his colleagues’ temporal explorations with metamaterials have revealed “some very strange things,” including what he calls a “photonic compressor.” Pendry’s photonic compressor is a metamaterial that is striped with regions of different optical properties that affect the speed at which light propagates. The stripes are adjustable, forming a sort of “metagrating,” and when this metagrating moves through the metamaterial alongside light, it can act to trap and herd the photons together, effectively compressing them. Further investigation has also revealed that this kind of photonic compressor shares characteristics with black holes , potentially providing a more manageable lab-scale analogue for studying those extreme astronomical objects. Having unfurled a whole new time dimension to metamaterials, photon-compressing black hole analogues are just one avenue of curious phenomena to delve into, and the possibilities are legion.

“It’s really assembling a toolbox,” Pendry says, “and then showing this to the world and saying, ‘What can you do with it?’”

MIT Technology Review

• Newsletters

Would you really age more slowly on a spaceship at close to light speed?

• Neel V. Patel archive page

Every week, the readers of our space newsletter, The Airlock , send in their questions for space reporter Neel V. Patel to answer. This week: time dilation during space travel. 

I heard that time dilation affects high-speed space travel and I am wondering the magnitude of that affect. If we were to launch a round-trip flight to a nearby exoplanet—let's say 10 or 50 light-years away––how would that affect time for humans on the spaceship versus humans on Earth? When the space travelers came back, will they be much younger or older relative to people who stayed on Earth? —Serge

Time dilation is a concept that pops up in lots of sci-fi, including Orson Scott Card’s Ender’s Game , where one character ages only eight years in space while 50 years pass on Earth. This is precisely the scenario outlined in the famous thought experiment the Twin Paradox : an astronaut with an identical twin at mission control makes a journey into space on a high-speed rocket and returns home to find that the twin has aged faster.

Time dilation goes back to Einstein’s theory of special relativity, which teaches us that motion through space actually creates alterations in the flow of time. The faster you move through the three dimensions that define physical space, the more slowly you’re moving through the fourth dimension, time––at least relative to another object. Time is measured differently for the twin who moved through space and the twin who stayed on Earth. The clock in motion will tick more slowly than the clocks we’re watching on Earth. If you’re able to travel near the speed of light, the effects are much more pronounced. 

Unlike the Twin Paradox, time dilation isn’t a thought experiment or a hypothetical concept––it’s real. The 1971 Hafele-Keating experiments proved as much, when two atomic clocks were flown on planes traveling in opposite directions. The relative motion actually had a measurable impact and created a time difference between the two clocks. This has also been confirmed in other physics experiments (e.g., fast-moving muon particles take longer to decay ). 

So in your question, an astronaut returning from a space journey at “relativistic speeds” (where the effects of relativity start to manifest—generally at least one-tenth the speed of light ) would, upon return, be younger than same-age friends and family who stayed on Earth. Exactly how much younger depends on exactly how fast the spacecraft had been moving and accelerating, so it’s not something we can readily answer. But if you’re trying to reach an exoplanet 10 to 50 light-years away and still make it home before you yourself die of old age, you’d have to be moving at close to light speed. 

There’s another wrinkle here worth mentioning: time dilation as a result of gravitational effects. You might have seen Christopher Nolan’s movie Interstellar , where the close proximity of a black hole causes time on another planet to slow down tremendously (one hour on that planet is seven Earth years).

This form of time dilation is also real, and it’s because in Einstein’s theory of general relativity, gravity can bend spacetime, and therefore time itself. The closer the clock is to the source of gravitation, the slower time passes; the farther away the clock is from gravity, the faster time will pass. (We can save the details of that explanation for a future Airlock.)

Amplifying space’s potential with quantum

How to safely watch and photograph the total solar eclipse.

The solar eclipse this Monday, April 8, will be visible to millions. Here’s how to make the most of your experience.

• Rhiannon Williams archive page

How scientists are using quantum squeezing to push the limits of their sensors

Fuzziness may rule the quantum realm, but it can be manipulated to our advantage.

• Sophia Chen archive page

The great commercial takeover of low Earth orbit

Axiom Space and other companies are betting they can build private structures to replace the International Space Station.

• David W. Brown archive page

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Chapter 15: Galaxies

Chapter 1 how science works.

• The Scientific Method
• Measurements
• Units and the Metric System
• Measurement Errors
• Mass, Length, and Time
• Observations and Uncertainty
• Precision and Significant Figures
• Errors and Statistics
• Scientific Notation
• Ways of Representing Data
• Mathematics
• Testing a Hypothesis
• Case Study of Life on Mars
• Systems of Knowledge
• The Culture of Science
• Computer Simulations
• Modern Scientific Research
• The Scope of Astronomy
• Astronomy as a Science
• A Scale Model of Space
• A Scale Model of Time

Chapter 2 Early Astronomy

• The Night Sky
• Motions in the Sky
• Constellations and Seasons
• Cause of the Seasons
• The Magnitude System
• Angular Size and Linear Size
• Phases of the Moon
• Dividing Time
• Solar and Lunar Calendars
• History of Astronomy
• Ancient Observatories
• Counting and Measurement
• Greek Astronomy
• Aristotle and Geocentric Cosmology
• Aristarchus and Heliocentric Cosmology
• The Dark Ages
• Arab Astronomy
• Indian Astronomy
• Chinese Astronomy
• Mayan Astronomy

Chapter 3 The Copernican Revolution

• Ptolemy and the Geocentric Model
• The Renaissance
• Copernicus and the Heliocentric Model
• Tycho Brahe
• Johannes Kepler
• Elliptical Orbits
• Kepler's Laws
• Galileo Galilei
• The Trial of Galileo
• Isaac Newton
• Newton's Law of Gravity
• The Plurality of Worlds
• The Birth of Modern Science
• Layout of the Solar System
• Scale of the Solar System
• The Idea of Space Exploration
• History of Space Exploration
• Moon Landings
• International Space Station
• Manned versus Robotic Missions
• Commercial Space Flight
• Future of Space Exploration
• Living in Space
• Moon, Mars, and Beyond
• Societies in Space

Chapter 4 Matter and Energy in the Universe

• Matter and Energy
• Rutherford and Atomic Structure
• Early Greek Physics
• Dalton and Atoms
• The Periodic Table
• Structure of the Atom
• Heat and Temperature
• Potential and Kinetic Energy
• Conservation of Energy
• Velocity of Gas Particles
• States of Matter
• Thermodynamics
• Laws of Thermodynamics
• Heat Transfer
• Thermal Radiation
• Radiation from Planets and Stars
• Internal Heat in Planets and Stars
• Periodic Processes
• Random Processes

Chapter 5 The Earth-Moon System

• Earth and Moon
• Early Estimates of Earth's Age
• How the Earth Cooled
• Ages Using Radioactivity
• Radioactive Half-Life
• Ages of the Earth and Moon
• Geological Activity
• Internal Structure of the Earth and Moon
• Basic Rock Types
• Layers of the Earth and Moon
• Origin of Water on Earth
• The Evolving Earth
• Plate Tectonics
• Geological Processes
• Impact Craters
• The Geological Timescale
• Mass Extinctions
• Evolution and the Cosmic Environment
• Earth's Atmosphere and Oceans
• Weather Circulation
• Environmental Change on Earth
• The Earth-Moon System
• Geological History of the Moon
• Tidal Forces
• Effects of Tidal Forces
• Historical Studies of the Moon
• Lunar Surface
• Ice on the Moon
• Origin of the Moon
• Humans on the Moon

Chapter 6 The Terrestrial Planets

• Studying Other Planets
• The Planets
• The Terrestrial Planets
• Mercury's Orbit
• Mercury's Surface
• Volcanism on Venus
• Venus and the Greenhouse Effect
• Tectonics on Venus
• Exploring Venus
• Mars in Myth and Legend
• Early Studies of Mars
• Mars Close-Up
• Modern Views of Mars
• Missions to Mars
• Geology of Mars
• Water on Mars
• Polar Caps of Mars
• Climate Change on Mars
• Terraforming Mars
• Life on Mars
• The Moons of Mars
• Martian Meteorites
• Comparative Planetology
• Incidence of Craters
• Counting Craters
• Counting Statistics
• Internal Heat and Geological Activity
• Magnetic Fields of the Terrestrial Planets
• Mountains and Rifts
• Radar Studies of Planetary Surfaces
• Laser Ranging and Altimetry
• Gravity and Atmospheres
• Normal Atmospheric Composition
• The Significance of Oxygen

Chapter 7 The Giant Planets and Their Moons

• The Gas Giant Planets
• Atmospheres of the Gas Giant Planets
• Clouds and Weather on Gas Giant Planets
• Internal Structure of the Gas Giant Planets
• Thermal Radiation from Gas Giant Planets
• Life on Gas Giant Planets?
• Why Giant Planets are Giant
• Ring Systems of the Giant Planets
• Structure Within Ring Systems
• The Origin of Ring Particles
• The Roche Limit
• Resonance and Harmonics
• Tidal Forces in the Solar System
• Moons of Gas Giant Planets
• Geology of Large Moons
• The Voyager Missions
• Jupiter's Galilean Moons
• Jupiter's Ganymede
• Jupiter's Europa
• Jupiter's Callisto
• Jupiter's Io
• Volcanoes on Io
• Cassini Mission to Saturn
• Saturn's Titan
• Saturn's Enceladus
• Discovery of Uranus and Neptune
• Uranus' Miranda
• Neptune's Triton
• The Discovery of Pluto
• Pluto as a Dwarf Planet
• Dwarf Planets

Chapter 8 Interplanetary Bodies

• Interplanetary Bodies
• Early Observations of Comets
• Structure of the Comet Nucleus
• Comet Chemistry
• Oort Cloud and Kuiper Belt
• Kuiper Belt
• Comet Orbits
• Life Story of Comets
• The Largest Kuiper Belt Objects
• Meteors and Meteor Showers
• Gravitational Perturbations
• Surveys for Earth Crossing Asteroids
• Asteroid Shapes
• Composition of Asteroids
• Introduction to Meteorites
• Origin of Meteorites
• Types of Meteorites
• The Tunguska Event
• The Threat from Space
• Probability and Impacts
• Impact on Jupiter
• Interplanetary Opportunity

Chapter 9 Planet Formation and Exoplanets

• Formation of the Solar System
• Early History of the Solar System
• Conservation of Angular Momentum
• Angular Momentum in a Collapsing Cloud
• Helmholtz Contraction
• Safronov and Planet Formation
• Collapse of the Solar Nebula
• Why the Solar System Collapsed
• From Planetesimals to Planets
• Accretion and Solar System Bodies
• Differentiation
• Planetary Magnetic Fields
• The Origin of Satellites
• Solar System Debris and Formation
• Gradual Evolution and a Few Catastrophies
• Chaos and Determinism
• Extrasolar Planets
• Discoveries of Exoplanets
• Doppler Detection of Exoplanets
• Transit Detection of Exoplanets
• The Kepler Mission
• Direct Detection of Exoplanets
• Properties of Exoplanets
• Implications of Exoplanet Surveys
• Future Detection of Exoplanets

Chapter 10 Detecting Radiation from Space

• Observing the Universe
• Radiation and the Universe
• The Nature of Light
• The Electromagnetic Spectrum
• Properties of Waves
• Waves and Particles
• How Radiation Travels
• Properties of Electromagnetic Radiation
• The Doppler Effect
• Invisible Radiation
• Thermal Spectra
• The Quantum Theory
• The Uncertainty Principle
• Spectral Lines
• Emission Lines and Bands
• Absorption and Emission Spectra
• Kirchoff's Laws
• Astronomical Detection of Radiation
• The Telescope
• Optical Telescopes
• Optical Detectors
• Adaptive Optics
• Image Processing
• Digital Information
• Radio Telescopes
• Telescopes in Space
• Hubble Space Telescope
• Interferometry
• Collecting Area and Resolution
• Frontier Observatories

Chapter 11 Our Sun: The Nearest Star

• The Nearest Star
• Properties of the Sun
• Kelvin and the Sun's Age
• The Sun's Composition
• Energy From Atomic Nuclei
• Mass-Energy Conversion
• Examples of Mass-Energy Conversion
• Energy From Nuclear Fission
• Energy From Nuclear Fusion
• Nuclear Reactions in the Sun
• The Sun's Interior
• Energy Flow in the Sun
• Collisions and Opacity
• Solar Neutrinos
• Solar Oscillations
• The Sun's Atmosphere
• Solar Chromosphere and Corona
• The Solar Cycle
• The Solar Wind
• Effects of the Sun on the Earth
• Cosmic Energy Sources

Chapter 12 Properties of Stars

• Star Properties
• The Distance to Stars
• Apparent Brightness
• Absolute Brightness
• Measuring Star Distances
• Stellar Parallax
• Spectra of Stars
• Spectral Classification
• Temperature and Spectral Class
• Stellar Composition
• Stellar Motion
• Stellar Luminosity
• The Size of Stars
• Stefan-Boltzmann Law
• Stellar Mass
• Hydrostatic Equilibrium
• Stellar Classification
• The Hertzsprung-Russell Diagram
• Volume and Brightness Selected Samples
• Stars of Different Sizes
• Understanding the Main Sequence
• Stellar Structure
• Stellar Evolution

Chapter 13 Star Birth and Death

• Star Birth and Death
• Understanding Star Birth and Death
• Cosmic Abundance of Elements
• Star Formation
• Molecular Clouds
• Young Stars
• T Tauri Stars
• Mass Limits for Stars
• Brown Dwarfs
• Young Star Clusters
• Cauldron of the Elements
• Main Sequence Stars
• Nuclear Reactions in Main Sequence Stars
• Main Sequence Lifetimes
• Evolved Stars
• Cycles of Star Life and Death
• The Creation of Heavy Elements
• Horizontal Branch and Asymptotic Giant Branch Stars
• Variable Stars
• Magnetic Stars
• Stellar Mass Loss
• White Dwarfs
• Seeing the Death of a Star
• Supernova 1987A
• Neutron Stars and Pulsars
• Special Theory of Relativity
• General Theory of Relativity
• Black Holes
• Properties of Black Holes

Chapter 14 The Milky Way

• The Distribution of Stars in Space
• Stellar Companions
• Binary Star Systems
• Binary and Multiple Stars
• Mass Transfer in Binaries
• Binaries and Stellar Mass
• Nova and Supernova
• Exotic Binary Systems
• Gamma Ray Bursts
• How Multiple Stars Form
• Environments of Stars
• The Interstellar Medium
• Effects of Interstellar Material on Starlight
• Structure of the Interstellar Medium
• Dust Extinction and Reddening
• Groups of Stars
• Open Star Clusters
• Globular Star Clusters
• Distances to Groups of Stars
• Ages of Groups of Stars
• Layout of the Milky Way
• William Herschel
• Isotropy and Anisotropy
• Mapping the Milky Way

Chapter 15 Galaxies

• The Milky Way Galaxy
• Mapping the Galaxy Disk
• Spiral Structure in Galaxies
• Mass of the Milky Way
• Dark Matter in the Milky Way
• Galaxy Mass
• The Galactic Center
• Black Hole in the Galactic Center
• Stellar Populations
• Formation of the Milky Way
• The Shapley-Curtis Debate
• Edwin Hubble
• Distances to Galaxies
• Classifying Galaxies
• Spiral Galaxies
• Elliptical Galaxies
• Lenticular Galaxies
• Dwarf and Irregular Galaxies
• Overview of Galaxy Structures
• The Local Group

Light Travel Time

• Galaxy Size and Luminosity
• Mass to Light Ratios
• Dark Matter in Galaxies
• Gravity of Many Bodies
• Galaxy Evolution
• Galaxy Interactions
• Galaxy Formation

Chapter 16 The Expanding Universe

• Galaxy Redshifts
• The Expanding Universe
• Cosmological Redshifts
• The Hubble Relation
• Relating Redshift and Distance
• Galaxy Distance Indicators
• Size and Age of the Universe
• The Hubble Constant
• Large Scale Structure
• Galaxy Clustering
• Clusters of Galaxies
• Overview of Large Scale Structure
• Dark Matter on the Largest Scales
• The Most Distant Galaxies
• Black Holes in Nearby Galaxies
• Active Galaxies
• Radio Galaxies
• The Discovery of Quasars
• Types of Gravitational Lensing
• Properties of Quasars
• The Quasar Power Source
• Quasars as Probes of the Universe
• Star Formation History of the Universe
• Expansion History of the Universe

Chapter 17 Cosmology

• Early Cosmologies
• Relativity and Cosmology
• The Big Bang Model
• The Cosmological Principle
• Universal Expansion
• Cosmic Nucleosynthesis
• Cosmic Microwave Background Radiation
• Discovery of the Microwave Background Radiation
• Measuring Space Curvature
• Cosmic Evolution
• Evolution of Structure
• Mean Cosmic Density
• Critical Density
• Dark Matter and Dark Energy
• Age of the Universe
• Precision Cosmology
• The Future of the Contents of the Universe
• Fate of the Universe
• Alternatives to the Big Bang Model
• Particles and Radiation
• The Very Early Universe
• Mass and Energy in the Early Universe
• Matter and Antimatter
• The Forces of Nature
• Fine-Tuning in Cosmology
• The Anthropic Principle in Cosmology
• String Theory and Cosmology
• The Multiverse
• The Limits of Knowledge

Chapter 18 Life On Earth

• Nature of Life
• Chemistry of Life
• Molecules of Life
• The Origin of Life on Earth
• Origin of Complex Molecules
• Miller-Urey Experiment
• Pre-RNA World
• From Molecules to Cells
• Extremophiles
• Thermophiles
• Psychrophiles
• Acidophiles
• Alkaliphiles
• Radiation Resistant Biology
• Importance of Water for Life
• Hydrothermal Systems
• Silicon Versus Carbon
• DNA and Heredity
• Life as Digital Information
• Synthetic Biology
• Life in a Computer
• Natural Selection
• Tree Of Life
• Evolution and Intelligence
• Culture and Technology
• The Gaia Hypothesis
• Life and the Cosmic Environment

Chapter 19 Life in the Universe

• Life in the Universe
• Astrobiology
• Life Beyond Earth
• Sites for Life
• Complex Molecules in Space
• Life in the Solar System
• Lowell and Canals on Mars
• Implications of Life on Mars
• Extreme Environments in the Solar System
• Rare Earth Hypothesis
• Are We Alone?
• Unidentified Flying Objects or UFOs
• The Search for Extraterrestrial Intelligence
• The Drake Equation
• The History of SETI
• Recent SETI Projects
• Recognizing a Message
• The Best Way to Communicate
• The Fermi Question
• The Anthropic Principle
• Where Are They?

In the everyday world, as perceived by the human senses, light seems to travel instantaneously from one place to another. In fact, the speed of light is not infinite, and light doesn't instantly jump from your ceiling light to your desk and then to your eye. We perceive light as moving instantly because its actual velocity is almost unimaginably high; light travels at 300,000 km/s, denoted c. Using the equation Rate × Time = Distance, you can divide any distance by this number to figure out the time it would take light to cross that distance. In this way, we can see that light takes 1.5 × 10 8 / 3 × 10 5 = 500 seconds to reach Earth from the Sun, or just over 8 minutes. It takes light about 40 times longer ( Pluto at a distance of 39.4 A.U.) to leave the Solar System or about 5 hours.

The speed of light is a built-in quality of our universe . All evidence to date indicates that light has always traveled at this speed, that the speed is exact, and that the same speed is observed for all observers. The vast size of the universe, coupled with the finite (albeit large) speed of light, means that as we look out in space, we look back in time. Distant light is old light.

The 5 hours it takes light to travel across our Solar System may seem like a short period to cross such a large distance, but we have to think about scale. While distances within the Solar System are large to us, they are dwarfed by the distances between the stars. Considering larger regions of the Milky Way, a natural distance unit is the distance light travels in one year. This is called a light year. We can easily calculate the size of this unit by remembering that distance has the units of velocity times time. So:

D ly = vt = c x 1 year = 3 × 10 5 x (3600 × 24 × 365) = 9.5 × 10 12 km

A light year is the typical distance between stars in the neighborhood of the Sun. It is nearly 10 trillion kilometers or 6 trillion miles! The fundamental unit of distance defined by geometry is the 13 km; defined as the distance corresponding to a parallax of 1 second of arc.">parsec , equal to 3.1 × 10 13 km. This is described in more detail in the article on parallax . Geometrically, one parsec is the height of a right triangle with an angle of 1 arcsec describing its apex , and a distance of 1 AU describing its base. The units are related by a small numerical constant D ly = 3.26 D pc . So to roughly convert from parsecs to light years, multiply by 3.3.

The following list gives the distance to various points within the Milky Way and beyond, both in terms of parsecs and the light travel time in years (which is also the distance in light years or 3.3 times the distance in parsecs). To fully appreciate how isolated we are in space, remember that light is the fastest thing we know of. The fastest spacecraft can not reach 1% of the speed of light. So you would have to multiply the numbers on the right-hand side of the table by at least 100 to estimate how long it would take to send a probe through the Milky Way and into the Local Group with current technology.

• Nearest star (α Centauri) - 1.3 pc, 4.2 years • Sirius - 2.7 pc, 8.8 years • Vega - 8.1 pc, 26 years • Hyades cluster - 42 pc, 134 years • Pleiades cluster - 125 pc, 411 years • Orion nebula - 460 pc, 1500 years • Nearest spiral arm - 1200 pc, 3900 years • Center of the 8 to 10 13 solar masses.">galaxy - 8500 pc, 29,000 years • Far edge of the galaxy - 24,000 pc, 78,000 years • Large Magellanic Cloud - 50,000 pc, 163,000 years • Andromeda galaxy (M31) - 670,000 pc, 2.2 million years

What does Andromeda look like now? Nobody knows. Since nothing travels faster than light (and this applies to all the colors of light across the electromagnetic spectrum ), there is no quicker way to send information from one place to another. We are stuck with collecting and measuring "old" light. While this seems like a limitation, scientists actually find that it turns out that light travel time is a wonderful tool. By looking further out in space we look further back in time. In this way, astronomers get to explore the earlier stages of the universe seeing firsthand (with a delay) what the early universe looked like.

Light Year Calculator

What is light year, how to calculate light years.

With this light year calculator, we aim to help you calculate the distance that light can travel in a certain amount of time . You can also check out our speed of light calculator to understand more about this topic.

We have written this article to help you understand what a light year is and how to calculate a light year using the light year formula . We will also demonstrate some examples to help you understand the light year calculation.

A light year is a unit of measurement used in astronomy to describe the distance that light travels in one year . Since light travels at a speed of approximately 186,282 miles per second (299,792,458 meters per second), a light year is a significant distance — about 5.88 trillion miles (9.46 trillion km) . Please check out our distance calculator to understand more about this topic.

The concept of a light year is important for understanding the distances involved in space exploration. Since the universe is so vast, it's often difficult to conceptualize the distances involved in astronomical measurements. However, by using a light year as a unit of measurement, scientists and astronomers can more easily compare distances between objects in space.

As the light year is a unit of measure for the distance light can travel in a year , this concept can help us to calculate the distance that light can travel in a certain time period. Hence, let's have a look at the following example:

• Source: Light
• Speed of light: 299,792,458 m/s
• Time traveled: 2 years

You can perform the calculation in three steps:

Determine the speed of light.

The speed of light is the fastest speed in the universe, and it is always a constant in a vacuum. Hence, the speed of light is 299,792,458 m/s , which is 9.46×10¹² km/year .

Compute the time that the light has traveled.

The subsequent stage involves determining the duration of time taken by the light to travel. Since we are interested in light years, we will be measuring the time in years.

To facilitate this calculation, you may use our time lapse calculator . In this specific scenario, the light has traveled for a duration of 2 years.

Calculate the distance that the light has traveled.

The final step is to calculate the total distance that the light has traveled within the time . You can calculate this answer using the speed of light formula:

distance = speed of light × time

Thus, the distance that the light can travel in 100 seconds is 9.46×10¹² km/year × 2 years = 1.892×10¹³ km

How do I calculate the distance that light travels?

You can calculate the distance light travels in three steps:

Determine the light speed .

Determine the time the light has traveled.

Apply the light year formula :

distance = light speed × time

How far light can travel in 1 second?

The light can travel 186,282 miles, or 299,792,458 meters, in 1 second . That means light can go around the Earth just over 7 times in 1 second.

Why is the concept of a light year important in astronomy?

The concept of a light year is important in astronomy because it helps scientists and astronomers more easily compare distances between objects in space and understand the vastness of the universe .

Can light years be used to measure time?

No , despite the name, you cannot use light years to measure time. They only measure distance .

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Helmholtz resonator, radiation pressure, secretary problem (valentine's day).

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What Is Daylight Saving Time, and When Does the Time Change in 2024?

Daylight saving time starts on the second Sunday of March and ends on the first Sunday of November. This means we’ll be “springing forward,” causing many of us to lose an hour of sleep during the transition (but able to experience later sunsets and more sunshine outdoors!). Then in the fall, we’ll be back to gaining an extra hour of sleep (excellent!), with the trade-off being earlier sunsets (bummer!). Though there is a movement to end daylight saving time , this twice-annual tradition is currently observed by more than 70 countries around the world, including the United States, save for two states .

But what is daylight saving time , exactly, and what is the point of it? Read on to find out.

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What is daylight saving time?

To start off, its daylight saving, not savings, as it is commonly called. Daylight saving time, also known as DST, is a practice where we advance the clocks by one hour on the second Sunday of March and set them back by one hour on the first Sunday of November, at 2 a.m. The goal of DST is to make better use of the varying daylight hours caused by the Earth tilting at different points during its orbit.

Since the Earth tilts at different times of the year, this gives us our Northern Hemisphere seasons (and reverses them in the Southern Hemisphere). It also contributes to the shortening and lengthening of daylight hours. By moving the clocks forward an hour in sun-rich spring, shortly before the spring equinox , the intention is that the majority of the day will be lived under full daylight hours, until the time changes again in fall.

When does daylight saving time start in 2024?

Daylight saving time always starts and ends at 2 a.m. in the United States. This years daylight saving time starts on Sunday, March 10, and ends on Sunday, Nov. 3.

Here are the future start and end dates for 2025 and beyond:

• 2025: Sunday, March 9, to Sunday, Nov. 2
• 2026: Sunday, March 8, to Sunday, Nov. 1
• 2027: Sunday, March 13, to Sunday, Nov. 7
• 2028: Sunday, March 12, to Sunday, Nov. 5

Why do we have daylight saving time?

There are several stories about the origins of the DST concept. You might have heard that the idea stemmed from Benjamin Franklin, but that’s not strictly true. He did write a satirical letter to The Journal of Paris (where he was living in 1784) suggesting that the city would save 64 million pounds of candle wax if only its citizens would rise with the sun, but he also included a recommendation that they get the people on schedule by firing cannons in every street as a citywide alarm clock. We’re grateful for Franklin’s other inventions but glad this particular one did not catch on.

It wasnt until 1908 that Thunder Bay, Canada, became the first city to implement daylight saving time. Its purpose: to preserve daylight hours in the winter months. Then, in 1916, Germany and Austria became the first countries to implement DST, to save money on energy costs during World War I.

When did daylight saving time start in the United States?

While the World War Iera changes in Germany and Austria launched a daylight saving practice that was followed by most of Europe, the United States didnt follow suit until March 19, 1918, when the Standard Time Act was signed into law. (This law also established our five time zones.) But the story doesn’t end there. After World War I, the DST federal law was repealed, before being resurrected during World War II with the intent of saving money on energy costs. After the war, DST was made optional, which led to absolute chaos when traveling. A 35-mile bus journey from Moundsville, West Virginia, to Steubenville, Ohio, meant going through seven different time changes!

Finally, in 1966, Congress passed the Uniform Time Act, standardizing DST for the six months from April to October. It was extended to seven months in 1986, and finally to eight months in 2005, leaving us with the MarchNovember DST we have todayin 48 states, at least.

What U.S. states dont do daylight saving time?

There are only two U.S. states that dont observe daylight saving time: Hawaii and Arizona (except the Navajo Nation, in northeastern Arizona). Perhaps because both those states get plenty of sunshine year-round, they dont feel the need to hoard it.

Do other countries practice daylight saving?

Only about a third of the worlds countries practice daylight saving timemost in Europe, with Egypt being the only African nation that observes it.

In the U.K. and other European countries, where daylight saving is known as summer time, DST begins on the last Sunday of March and ends on the last Sunday of October. Another interesting fact ? The only European countries that dont currently follow the practice are Armenia, Azerbaijan, Georgia, Belarus, Iceland, Russia and Turkey.

Will daylight saving be eliminated in the United States?

As of now, no! However, Sen. Marco Rubio’s Sunshine Protection Act was reintroduced in March 2023. If enacted, the bill would end “falling back” in November, allowing us to keep a full year of DST. Progress has yet to be made, so as of now, daylight saving time is here to stay.

Why trust us

At Readers Digest , were committed to producing high-quality content by writers with expertise and experience in their field in consultation with relevant, qualified experts. We rely on reputable primary sources, including government and professional organizations and academic institutions as well as our writers personal experience where appropriate . We verify all facts and data, back them with credible sourcing, and revisit them over time to ensure they remain accurate and up to date. Read more about our team , our contributors and our editorial policies .

• Time and Date : “Daylight Saving Time Statistics”
• U.S. Department of Defense : Daylight Saving Time Once Known as ‘War Time'”
• Pew Research Center : Most Countries Dont Observe Daylight Saving Time
• Press release from Sen. Marco Rubio : Rubio Reintroduces Bill to Make Daylight Saving Time Permanent

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The post What Is Daylight Saving Time, and When Does the Time Change in 2024? appeared first on Reader's Digest .

Protect Your Trip »

The 18 best places to see the northern lights.

Check the aurora borealis off your bucket list.

The Best Places for the Northern Lights

Getty Images

The northern lights, known as the aurora borealis, are a spectacular natural light show visible at certain times of the year in the Northern Hemisphere. They occur when electrically charged particles from the sun collide with gases in the Earth's atmosphere, creating vibrant streaks of blue, green, pink and violet dancing across the night sky. 2024 and 2025 are an excellent time to catch the northern lights: Solar activity will be at a peak, making for a more impressive experience, if you're in the right place.

The best places to see the aurora borealis have little light pollution, clear skies and no precipitation. The lights are only visible at northern latitudes when it's dark outside, so the months from September to April are best for seeing the aurora. There's also a Southern Hemisphere counterpart, the aurora australis; there are fewer easy spots from which to view this phenomenon, but if you're lucky, it can be equally brilliant.

For more information on the northern lights, scroll down to the FAQ section at the bottom of this page. Read on to discover the top destinations where you can see the kaleidoscopic northern and southern lights.

Fairbanks, Alaska

Fairbanks is by far one of the best places in the world to view the northern lights, as it's located directly under the auroral oval. This ring-shaped zone sits around the Earth's geomagnetic North Pole and is generally associated with the most vibrant aurora sightings. Visitors can expect to see the lights on an average of four out of five clear nights during aurora season, which lasts from late August to late April.

You can book a northern lights tour to see the aurora from the springs and tubs at Chena Hot Springs Resort. This excursion includes round-trip transportation to the resort from town, a soak in the hot springs, a visit to the Fairbanks Aurora Ice Museum and an aurora viewing tour; dinner and drinks centered around Alaska produce are an option extra with hot drinks supplied.

There's more to Fairbanks than just the northern lights: If you visit in late summer, consider family-friendly activities like a ride on the Riverboat Discovery or gold panning. For a festive holiday experience in the winter, head around 15 miles out of Fairbanks to visit the Santa Claus House in the city of North Pole. Travelers can also see ice sculptures in February and March at the impressive World Ice Art Championships or take a dog-sledding or snowmobiling tour .

Where to stay: For excellent chances of aurora viewing, book a private igloo at Borealis Basecamp, a top glamping resort located on 100 remote acres of boreal forest about 25 miles from Fairbanks. With activities like dog-sledding on top of aurora viewing, past visitors regularly describe it as a once-in-a-lifetime experience.

Tromsø, Norway

Located about 220 miles above the Arctic Circle, Tromsø is one of several top spots to view the northern lights in Norway. At the darkest point of the aurora season – which runs from September to early April – the sun doesn't rise in this northern part of the country, although there is twilight during the day. With this level of darkness, there are more opportunities to see the aurora.

Tromsø itself is a small but lively city, so there's plenty to see and do when you're not looking up at the sky, including a visit to the beautiful Arctic Cathedral. In late January to early February, the city hosts the Northern Lights Festival, a 10-day music and performing arts event featuring a variety of musical genres.

Aurora chasers can view the lights on their own while in town, but to get a better view, it's recommended to head away from the city lights. Arctic Circle Tours is one company offering guided trips, with small groups for a more personal vibe. Alternatively, adventure-seekers can embark on an exhilarating husky trekking expedition in the Arctic wilderness.

Where to stay: For accommodations with harbor views, look no further than the Scandic Ishavshotel – guests love it for its convenient central location in the city, as well as its plus-sized breakfast buffet with plenty of choices.

Luosto and Rovaniemi (Lapland), Finland

Lapland is located within the Arctic Circle in the northernmost part of Finland. The northern lights are most visible here between the end of August and April – and approximately 200 times a year – so there are many opportunities for aurora spotting. Finnish Lapland is also known as home to the Sámi people (the only recognized Indigenous group in the European Union region), some 200,000 reindeer and Santa Claus – who can be visited in the town of Rovaniemi, the region's largest city and a great base for your aurora expedition.

Consider venturing roughly 70 miles north of Rovaniemi to the resort town of Luosto, set among the picturesque and hilly landscape of Pyhä-Luosto National Park. Here, you can also spend a magical evening outdoors under star-filled skies during a reindeer-drawn sleigh ride through the snow-covered forests. Jaakkola Reindeer Farm offers a reindeer sleigh tour to spot the aurora once weekly; it includes a stop to warm up at a bonfire camp with snacks, hot beverages and local fireside stories.

Where to stay: For a bucket list experience, watch the impressive light show from a glass igloo at Santa's Hotel Aurora & Igloos in Luosto. Past visitors love the cozy atmosphere here, boosted by amenities like saunas and log fireplaces. If you're sticking to Rovaniemi, the Arctic TreeHouse Hotel is a stunning choice, with designer cabins perched among the snow-covered taiga forest.

Orkney, Scotland

This group of captivating (and mostly uninhabited) islands, located about 10 miles off Scotland's remote northern coast, is one of the best places to see the northern nights in the U.K. Fall and winter are the best seasons to witness the aurora, also known in local Shetland dialect as the "Mirrie Dancers," with fall bringing the highest proportion of clear nights. A few places to see the spectacular light show include along the coast at Birsay or the Broch of Gurness, an archaeological ruin on a sweeping and dramatic coastline.

In addition to the aurora, Orkney is home to breathtaking coastal landscapes and more sheep than you can count (try some local lamb, if you can). Travelers can also visit the Heart of Neolithic Orkney, a UNESCO World Heritage Site with several monuments dating back 5,000 years.

Where to stay: During your visit, plan to stay in the historic town of Kirkwall, the capital of the Orkney Islands: The no-fuss Ayre Hotel offers harbor views, and past visitors compliment the hearty meals in the hotel restaurant. Spot the aurora close to town at Inganess Bay and Wideford Hill.

Yellowknife, Canada

Yellowknife, the capital of Canada 's Northwest Territories, dubs itself the "Aurora Capital of the World." Thanks to its position in the middle of the auroral oval, the city puts on one of the world's most awe-inspiring light shows. The period from mid-November to the beginning of April is the recommended time to spot the aurora, but it's also possible to see the aurora during more hospitable weather from late summer to early fall as the lights are visible up to 240 days a year.

Located on the northern shore of Great Slave Lake, Yellowknife boasts winter sports such as ice fishing and cross-country skiing. If you visit in March, plan to attend the monthlong Snowkings' Winter Festival, which features events and activities like a snow-carving competition, a snow castle, live music and more.

For a unique experience, book a tour through Aurora Village to view the lights. The property will pick you up from your hotel and take you to its site, where you can stay warm in a tent while sipping hot beverages. The Aboriginal-owned Aurora Village also offers activities such as dog-sledding or snowshoeing excursions.

Where to stay: Warm up in the fireside lounge at The Explorer Hotel in Yellowknife. Previous visitors note the warm and helpful staff as a strength here.

Jukkasjärvi, Sweden

The optimal time for seeing the illuminated skies in the northern part of Sweden, known as Swedish Lapland, is between early September and late March. The small Swedish village of Jukkasjärvi sits around 125 miles above the Arctic Circle on the Torne River and is an ideal locale for aurora viewing. You'll fly to the nearby Kiruna Airport to get here. With the village's origins dating back to the 17th century, you can still find some of the original homesteads, including an old timber cottage. Today the village boasts 800 residents – and more than 1,000 dogs.

Where to stay: If you're up for a chilly overnight adventure, reserve accommodations at the world's first permanent ice hotel, the aptly named Icehotel 365. Each of its artist-designed suites is sculpted from ice with a unique theme and maintains temperatures around minus 5 degrees Celsius (about 23 degrees Fahrenheit). The rooms also feature beds with reindeer hides and thermal sleeping bags so you can bundle up during the night. While you're at the property, take advantage of the guided "Northern Lights Safari on Snowmobile" or embark on the "Moose Safari on Horseback" atop an Icelandic horse.

Reykjavik, Iceland

October through March is the best time to chase the aurora borealis in Iceland . There are numerous natural parks and attractions throughout the country where you can view the show during the long and dark winter, but the capital city of Reykjavik also offers many options for accommodations, restaurants, tours and other activities for your visit. For optimum aurora viewing in the city away from the light pollution, head to Öskjuhlið. This wooded and hilly area in Reykjavik sits at 200 feet above sea level and has walkways and paths where you can see the nighttime show.

Atop this hill sits Perlan, which houses the only planetarium in the country and a museum featuring exhibits about Iceland. Perlan is also home to the world's first indoor ice cave and glacier exploratorium. During your visit, don't miss the panoramic views of the city from the building's fourth-floor observation deck. From this vantage point, you'll be able to see the Snæfellsjökull glacier; Keilir, a volcanic mountain; and Esja, the mountain of Reykjavik.

Where to stay: While in Reykjavik, splurge on an overnight tour with Buubble Tours. This experience includes breathtaking sightseeing spots and a night spent under the magical northern skies in a transparent bubble at the 5 Million Star Hotel. For longer stays, consider the eco-friendly Eyja Guldsmeden Hotel, with sweeping views of the city – guests love it for its cozy yet chic Scandinavian design.

Southern Iceland

While Reykjavik is a great aurora-viewing spot if you like having amenities close by, consider getting out into Iceland's stunning, otherworldly countryside for a unique backdrop for the northern lights. One unique place to see them is the black sand beach at Reynisfjara (but watch out for the dangerous waves here). Alternatively, head to Jökulsárlón, a glacial lagoon and seal habitat, where the aurora's reflections in the icy water are truly beautiful.

There's no shortage of tours that will stop by these locations and more for possible aurora sightings. Consider a 10- or 13-day tour around the country with Fun Travel, or a four-day option from Arctic Adventures. If you want to do things at your own place, it's also possible to self-drive – just know that road conditions can be icy, particularly in the depths of winter (although Icelandic roads are generally well-maintained).

Where to stay: Hotel Rangá is a formidable option for aurora-spotting. It offers a variety of special amenities, such as aurora wake-up calls, a lookout deck and snowsuits to keep you warm if you're outside viewing the lights. Past visitors praise Rangá for being a comfortable yet luxurious place to relax, be it in the outdoor hot tubs or the cozy and sociable bar.

Kangerlussuaq, Greenland

Greenland may not be the most accessible place to travel for viewing the northern lights, with limited flight options (mostly via Iceland), but those who make it here will be thrilled they did. The tundra of Kalaallit Nunaat – the Greenlandic name for the country – is one of the best places on the globe to see the aurora from September to early April.

For the more adventurous aurora seekers, head to the top of the Greenland Ice Cap for spectacular views of the lights. This impressive glacier covers 80% of the country and is accessible via the tiny town of Kangerlussuaq. Located on a fjord right along the Arctic Circle, the town, often described as a gateway to Greenland, was a former U.S. Air Force base and is now home to Greenland's main airport. The town is known for having clear skies on some 300 nights per year, so chances of a sighting are particularly good here.

Tour company Guide to Greenland offers various tours, from two-hour aurora-viewing trips to a tough but rewarding multi-night dog-sledding expedition across the ice. For a less strenuous experience, companies like Nordic Saga Tours offer cruises through the Arctic landscapes around Kangerlussuaq.

Viking cruise along Norway's coast

Courtesy of Viking

Embrace the winter and set sail for the Arctic Circle to experience the aurora in northern Norway. The 13-day "In Search of the Northern Lights" cruise itinerary with Viking departs from London for the North Sea with stops in ports of call that are top aurora-viewing locales, including Tromsø, Alta and Narvik, plus a stop in Amsterdam en route. The cruise ends in Bergen, Norway.

While on land, take in the natural beauty of the snow-blanketed landscapes and book bucket list excursions like a night spent in an igloo or a reindeer sledding adventure. You can also chase the lights into the wilderness by snowmobile, take a dog sled ride under the stars or view them from a Sámi tent atop the mountain Pæska in Alta. This Viking Ocean Cruises itinerary is offered with departure dates from mid-January to mid-March.

Headlands International Dark Sky Park, Michigan

Regarded as one of the top spots in the U.S. to see the aurora outside Alaska, Headlands International Dark Sky Park sits at the top of Michigan 's lower peninsula, less than 5 miles from Mackinaw City. While the northern lights are less common here due to the relatively southern location, the best time to catch a glimpse of this phenomenon is typically during the spring and fall – and appearances can usually be predicted a couple of days in advance. The park even maintains an online Clear Sky Chart so you can check the weather forecast before you go.

There are also other stargazing opportunities throughout the year at Headlands. During the summer months the Milky Way is visible across the sky, and late summer evenings entertain visitors with meteor showers.

Where to stay: If you're visiting between late April and the end of October, splurge on a stay at Mission Point Resort on Mackinac Island, where the aurora should also be visible. Guests describe this iconic property situated along the shoreline of Lake Huron as positively charming, thanks to its historic nature and manicured grounds. The resort also offers a host of outdoor activities from bike rentals to swimming.

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Voyageurs National Park, Minnesota

Martha Shuff | Courtesy of Voyageurs National Park

Located on the international border between Minnesota and Ontario, Voyageurs National Park is an approximately 218,000-acre labyrinth of boreal forests, lakes and streams. Voyageurs is Minnesota's only national park; it's also unique in that the park's interior is accessible only by boat, unless you visit by snowmobile in winter. As a certified International Dark Sky Park , Voyageurs provides opportunities to view the Milky Way on clear evenings, especially in the summer. Year-round aurora viewing is also possible on evenings with clear dark skies, but chances are better during the winter, when it's dark for longer.

For a guided stargazing tour – including the Milky Way, the constellations and (if you're lucky) the northern lights – book with Voyageurs Outfitters. If you're on your own, park officials note that almost any campsite is a good spot for northern lights viewing and stargazing. You can also check out the boat launch areas around Ash River, Kabetogama Lake and the Rainy Lake Visitor Center for top-notch views.

Where to stay: Those who prefer to sleep in a warm, cozy bed instead of camping under the stars can make reservations at the Cantilever Distillery + Hotel, a boutique Trademark Collection by Wyndham property in the nearby town of Ranier, Minnesota. Visitors report that there's a lot to like here, from the industrial-chic rooms to friendly staff to top-notch cocktails in the active distillery on the premises.

Abisko National Park, Sweden

Given its Arctic location, Sweden is one of the prime spots for aurora viewing in the Northern Hemisphere, with Swedish Lapland at the top of the list. The fall and winter months (from September to March) offer the best opportunities to witness the spectacle, as there is more darkness than light during the days.

If you're up for the Arctic adventure, December is an ideal month to visit Abisko National Park, which some regard as one of the best places on Earth to see the lights dance across the sky. The park's mountainous terrain and clear dark skies offer dramatic front-row seats for viewing the northern lights. The Aurora Sky Station is one of the best vantage points to see the aurora in the park. Join one of the expert presentations to learn about the science behind this fascinating phenomenon.

If you'd prefer to chase the lights with a curated tour, professional photographers and aurora-chasing guides at Visit Abisko lead three- to four-hour tours throughout the fall and winter. If you can, try to join the tours in fall, as this time of year offers a unique opportunity to view the lights both in the sky and reflected in the lakes and rivers, which you won't see in the winter months.

Where to stay: For cozy Nordic vibes, stay at Abisko Mountain Lodge, which also offers activities like ice climbing and snowmobile tours in winter. Guests love the excellent restaurant here, which offers Swedish specialties ranging from salmon to moose.

Nellim, Finland

Courtesy of Wilderness Hotels

Located a stone's throw from the Russian border in Finnish Lapland, this remote Arctic destination is a top-rated locale to view the northern lights due to the lack of light pollution. You'll be seriously out of the way of any built-up areas, as there's not even a paved road into Nellim. The best time to visit is between December and early April. This village is a great place to hunker down in a lodge and relax while enjoying a slice of life in the Finnish wilderness.

Where to stay: The Nellim Wilderness Hotel offers a perfect base with year-round activities, including aurora-chasing tours by car, snowmobile or on snowshoes. You can even take a sleigh ride through the snow to a campsite on Lake Inari to spot the aurora in pristine nature.

Beyond standard rooms, the Wilderness Hotel also offers glass-roofed cabins, as well as classic log cabins and bubble-shaped accommodations for two where guests can watch the dancing lights through the glass roof above your warm, cozy bed. When you're not chasing the lights, enjoy other Arctic activities like a husky safari, ice fishing, snowmobiling or a day in the snow meeting the local reindeer.

Saariselkä and Kakslauttanen, Finland

These two towns are around 150 miles above the Arctic Circle, with a prime location under the auroral oval, allowing as many as 200 opportunities per year to see the northern lights (weather permitting, of course). This area in Finnish Lapland is known for its stunning scenery, Sámi culture, cross-country and downhill skiing, and Urho Kekkonen National Park – one of Finland's largest.

Ski enthusiasts can roll two trips into one by hitting the slopes by day in Saariselkä and aurora spotting by night at Finland's northernmost ski resort. March into early April is the best time to view the aurora, as the Finnish Meteorological Institute notes that the weather is usually clearer at this time of year. But it's possible to see the northern lights at any time during the season from late August to early or mid-April.

Where to stay: Seven miles south of Saariselkä sits the village of Kakslauttanen, where you can book two- or four-person Glass Igloos at the Kakslauttanen Arctic Resort. The new Kelo-Glass Igloos, which sleep up to six, mix the comforts of a log chalet with the visibility of the glass roof; enjoy a private sauna, a fireplace and more. There's also an impressive selection of year-round tours and activities at this resort, including northern lights excursions on snowmobiles or by horse-drawn carriage.

Stewart Island, New Zealand

Courtesy of RealNZ

Although they may be isolated, some far-south destinations offer the chance to see the aurora australis – or southern lights. While you might be able to see them year-round in some locations (just as with the northern lights), certain months are better for aurora viewing in the Southern Hemisphere. Stewart Island is regarded as one of the top spots to see the brilliant display in New Zealand , with 85% of the island encompassed by Rakiura National Park, so there are few people and virtually no light pollution. You can reach Stewart Island by flying in from Invercargill or taking a ferry from Bluff.

New Zealand's winter months – June to August – are the best time to see the southern lights; spring and fall are also not bad times to spot them. The brighter summer months, between December and February, make it more difficult to spot the aurora, but there's still a chance you'll catch a glimpse between midnight and 4 a.m.

Where to stay: Consider reserving a room with at Stewart Island Lodge, an intimate bed-and-breakfast. This beautiful property is just minutes by foot from the village of Oban, and the property will pick you up at the ferry terminal for your stay. Past visitors rave about the spectacular views of Halfmoon Bay and the Foveaux Strait from both the rooms and lodge terrace.

Tasmania sits approximately 150 miles south of mainland Australia. This mountainous island is one of relatively few places on the planet where it's theoretically possible to see the aurora 365 days a year due to its latitude, which allows for full darkness even on summer nights. The capital city of Hobart is the easiest point of entry: It's home to Tasmania's largest airport and serves as a convenient base. The city's burgeoning food and cultural scenes will also give you plenty to see and do.

From here you'll be able to reach several great viewing locations with unobstructed and open views of the sea along the southern and southeast coastlines, like Goat Bluff and Tinderbox Bay. When you're not staring at the night sky, splurge on a once-in-a-lifetime helicopter flight with Tasmanian Air Tours. Depending on your whims, your private pilot can whisk you away to soar over the sea cliffs; stop at a local winery to sample local vintages; or head south to the UNESCO World Heritage Site of Port Arthur , Tasmania 's historic and most notorious prison.

Where to stay: Reserve accommodations at The Tasman, a Luxury Collection Hotel, Hobart. The historic luxury property is situated along the lively waterfront area with harbor views. Past guests admired the historic building housing the hotel and loved the heritage rooms featuring gas fireplaces for those cold Tasmanian nights.

Expedition cruise to Antarctica

If you're one of the lucky few people on the planet to travel to the southernmost continent on Earth, it may be pricey, but you'll have an adventure of a lifetime in Antarctica, especially if the aurora illuminates the sky. The southern lights are most visible in the winter months (between March and October), but due to weather conditions, only researchers brave the Antarctic winter – and they mostly stay indoors.

However, all hope is not lost if you seek to view the aurora australis in Antarctica. Late-season expedition cruises to this continent offered in March also bring the opportunity to view the southern lights and enjoy the end of Antarctica's fleeting summer. As the days shorten in length, you may encounter light snow across the extreme landscape and ice starting to form on the water's surface.

When it comes to wildlife viewing, humpback whale sightings are abundant, and you'll still see penguin colonies – including king and gentoo penguins. You can also keep your eyes peeled for elephant seals, leopard seals, wandering albatross and other species of birds. When night falls on clear evenings, look for the light show in the southern sky. Companies that offer March voyages include Swoop Antarctica, Atlas Ocean Voyages, Silversea Cruises , Aurora Expeditions and Hurtigruten Expeditions.

Frequently Asked Questions

There's no one location that's widely accepted as the best place to see the northern lights. However, the strongest light displays are within what's called the "auroral oval": a rough circle around the Earth's magnetic northern pole that tends to occur around 60 to 70 degrees of latitude. The oval's exact size expands and contracts (some more southerly destinations can fall under it when the aurora is particularly strong), but there are certain locations that generally fall within the oval most of the time.

These places include:

• Central and northern Alaska
• Large areas of Yukon, the Northwest Territories and northern Quebec in Canada
• Southern Greenland
• Far northern Norway, Sweden and Finland

Within these areas, it could be argued that Iceland is the best place to see the aurora as it experiences much milder temperatures than some other areas within the oval. But this is subjective, and some travelers may prefer a location like Yellowknife in Canada for a full-on, very cold Arctic experience.

The northern lights are only visible when it's dark out. Since many of the best places to see them are so far north that they experience near-constant daylight in the summer, you'll generally want to schedule a trip between late August and early April. However, within this time period, there's some debate about the best time to catch the lights. For example, the aurora tends to be more active around the September and March equinoxes due to stronger solar winds – but on the other hand, your chances of seeing them may be higher in the depths of winter, since there's longer nights and therefore a longer window in which they might appear.

In more southern locations like Minnesota, it may be possible to see the light show in the summer months, but it's still advisable to go at a time when the nights are longer. It can also be worth trying to schedule your northern lights trip when there's a new moon: While the aurora can shine through moonlight, it may be harder to see if there's a full moon.

Of course, cloudy weather can block the aurora even if you go at the right time of year. So, it may be wise to research the local weather patterns at your chosen destination to find out if there's a month where you can expect clearer skies. In many cases, though, there's a little luck involved.

These two countries can offer excellent views of the northern lights, since both are directly under the typical auroral oval. Yet there are some differences to be aware of.

In Norway, you'll need to head to the north of the country to catch the aurora: While they have been sighted in Oslo , the capital and largest city, it's too far south to be a reliable vantage point. Cities like Tromsø are popular spots, but direct flights there are only possible from some European cities, so North Americans will have to take connecting flights. On the other hand, Iceland is generally easier to reach, with direct flights to its capital, Reykjavik, from a large number of U.S. destinations (particularly from the East Coast) with no further connection required.

Since clear skies are key for seeing the northern lights, weather is another factor to consider. In November, December and March, Reykjavik has statistically slightly more frequent clear skies, while in January and February, Tromsø is a little better, but the difference isn't big: Both places have clear skies only around 25 to 30% of the time in these months. Reykjavik has slightly warmer weather, though, so between that and the ease of access, it has a slight edge over Norway for seeing the northern lights.

Alaska and Iceland are known for stellar aurora light shows, so deciding between them may depend on which destination you find more convenient and more to your tastes. In Alaska , the city of Fairbanks is considered a great spot to catch the northern lights. (They can still be seen elsewhere in the state – for example, in Anchorage, although they're not so common in more southern locations like Juneau). The advantage of Fairbanks is that you won't need a passport , yet there aren't many direct flights from the lower 48 states. Despite being an international destination, Iceland may be more accessible (particularly from the eastern U.S.), thanks to fairly regular flights to Reykjavik from numerous American cities.

Fairbanks does offer statistically better weather for aurora viewing: It has clear skies more often than Reykjavik, particularly in March when the Alaska city experiences them around 45% of the time (compared to about 25% for Reykjavik). But you'll have to be able to tolerate the cold. While temperatures in Reykjavik hover around freezing in midwinter, Fairbanks is a veritable deep freeze, with average highs around 5 degrees Fahrenheit down to lows colder than minus 5 in December.

Why Trust U.S. News Travel

Timothy Forster , as a Canadian who has traveled from coast to coast in that sprawling country, knows all about travel in the cold northern reaches of the world. Forster used his extensive traveling background along with research expertise to curate this article.

You might also be interested in:

• The Top Waterfalls in Iceland
• The World's Top Treehouse Hotels
• The Most Beautiful Beaches in the World
• The Best Travel Insurance Companies

Most Beautiful Landscapes in the World

Tags: Travel , Vacation Ideas

World's Best Places To Visit

• # 1 South Island, New Zealand
• # 4 Bora Bora

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April 22, 2024

Making history: brightline west breaks ground on america’s first high-speed rail project connecting las vegas to southern california  , officials hammer the first spike commemorating the groundbreaking for brightline west.

LAS VEGAS (April 22, 2024)  – Today, Brightline West officially broke ground on the nation's first true high-speed rail system which will connect Las Vegas to Southern California. The 218-mile system will be constructed in the middle of the I-15 and is based on Brightline’s vision to connect city pairs that are too short to fly and too far to drive. Hailed as the greenest form of transportation in the world, Brightline West will run zero emission, fully electric trains capable of speeds of 200 miles per hour. Brightline West is a watershed project for high-speed rail in America and will establish the foundation for the creation of a new industry and supply chain. The project was recently awarded $3 billion in funding from President Biden’s Bipartisan Infrastructure Bill. The rest of the project will be privately funded and has received a total allocation of $3.5 billion in private activity bonds from USDOT.

The groundbreaking included remarks from U.S. Transportation Secretary Pete Buttigieg, Brightline Founder Wes Edens, Nevada Gov. Joe Lombardo, Sen. Catherine Cortez Masto, Sen. Jacky Rosen, Senior Advisor to President Biden Steve Benjamin and Vince Saavedra of the Southern Nevada Building Trades. In addition, Nevada Reps. Dina Titus, Susie Lee and Steve Horsford and California Reps. Pete Aguilar and Norma Torres made remarks and joined the celebration. More than 600 people, including union representatives, project supporters and other state and local officials from California and Nevada, attended the event.

“People have been dreaming of high-speed rail in America for decades – and now, with billions of dollars of support made possible by President Biden’s historic infrastructure law, it’s finally happening,” said Secretary Buttigieg. “Partnering with state leaders and Brightline West, we’re writing a new chapter in our country’s transportation story that includes thousands of union jobs, new connections to better economic opportunity, less congestion on the roads, and less pollution in the air.”

“This is a historic project and a proud moment where we break ground on America’s first high-speed rail system and lay the foundation for a new industry,” said Wes Edens, Brightline founder. “Today is long overdue, but the blueprint we’ve created with Brightline will allow us to repeat this model in other city pairs around the country.”

CONSTRUCTION OF BRIGHTLINE WEST

Brightline West's rail system will span 218 miles and reach speeds of 200 mph. The route, which has full environmental clearance, will run within the median of the I-15 highway with zero grade crossings. The system will have stops in Las Vegas, Nev., as well as Victor Valley, Hesperia and Rancho Cucamonga, Calif.

The privately led infrastructure project is one of the largest in the nation and will be constructed and operated by union labor. It will use 700,000 concrete rail ties, 2.2 million tons of ballast, and 63,000 tons of 100% American steel rail during construction. Upon completion, it will include 322 miles of overhead lines to power the trains and will include 3.4 million square feet of retaining walls. The project covers more than 160 structures including viaducts and bridges. Brightline West will be fully Buy America Compliant.

STATIONS AND FACILITIES

Brightline West will connect Southern California and Las Vegas in two hours or almost half the time as driving. The Las Vegas Station will be located near the iconic Las Vegas Strip, on a 110-acre property north of Blue Diamond Road between I-15 and Las Vegas Boulevard. The site provides convenient access to the Harry Reid International Airport, the Las Vegas Convention Center and the Raiders’ Allegiant Stadium. The station is approximately 80,000 square feet plus parking.

The Victor Valley Station in Apple Valley will be located on a 300-acre parcel southeast of Dale Evans Parkway and the I-15 interchange. The station is intended to offer a future connection to the High Desert Corridor and California High Speed Rail. The Victor Valley Station is approximately 20,000 square feet plus parking.

The Rancho Cucamonga Station will be located on a 5-acre property at the northwest corner of Milliken Avenue and Azusa Court near Ontario International Airport. The station will be co-located with existing multi-modal transportation options including California Metrolink, for seamless connectivity to Downtown Los Angeles and other locations in Los Angeles, Orange, San Bernardino and Riverside Counties. The Rancho Cucamonga Station is approximately 80,000 square feet plus parking.

The Hesperia Station will be located within the I-15 median at the I-15/Joshua Street interchange and will function primarily as a local rail service for residents in the High Desert on select southbound morning and northbound evening weekday trains.

The Vehicle Maintenance Facility (VMF) is a 200,000-square-foot building located on 238 acres in Sloan, Nev., and will be the base for daily maintenance and staging of trains. This site will also serve as one of two hubs for the maintenance of way operations and the operations control center. More than 100 permanent employees will report on a daily basis once operations begin and will serve as train crews, corridor maintenance crews, or operations control center teammates. A second maintenance of way facility will be located adjacent to the Apple Valley station.

The Las Vegas and Southern California travel market is one of the nation’s most attractive corridors with over 50 million trips between the region each year. Additionally, Las Vegas continues to attract visitors from around the world, with 4.7 million international travelers flying into the destination. The city dubs itself on being the world’s No. 1 meeting destination, welcoming nearly 6 million people to the Las Vegas Convention Center last year.

In California, approximately 17 million Southern California residents are within 25 miles of the Brightline West station sites. Studies show that one out of every three visits to Las Vegas come from Southern California.

ECONOMIC & ENVIRONMENTAL BENEFITS

Brightline West's $12 billion infrastructure investment will create over $10 billion in economic impact for Nevada and California and will generate more than 35,000 jobs, including 10,000 direct union construction roles and 1,000 permanent operations and maintenance positions. The investment also includes over $800 million in improvements to the I-15 corridor and involves agreements with several unions for skilled labor. The project supports Nevada and California's climate goals by offering a no-emission mobility option that reduces greenhouse gasses by over 400,000 tons of CO2 annually – reducing vehicle miles traveled by more than 700 million each year and the equivalent of 16,000 short-haul flights. The company will also construct three wildlife overpasses, in partnership with the California Department of Fish and Wildlife and Caltrans for the safe passage of native species, primarily the bighorn sheep.

BRIGHTLINE FLORIDA

Brightline’s first rail system in Florida connecting Miami to Orlando began initial service between its South Florida stations in 2018. In September 2023, Brightline’s Orlando station opened at Orlando International Airport, connecting South Florida to Central Florida. The company has plans to expand its system with future stops in Tampa, Florida’s Space Coast in Cocoa and the Treasure Coast in Stuart.

BRIGHTLINE WEST

ABOUT BRIGHTLINE WEST

Brightline is the only private provider of modern, eco-friendly, intercity passenger rail service in America – offering a guest-first experience designed to reinvent train travel and take cars off the road by connecting city pairs and congested corridors that are too short to fly and too long to drive. Brightline West will connect Las Vegas and Southern California with the first true high-speed passenger rail system in the nation. The 218-mile, all-electric rail service will include a flagship station in Las Vegas, with additional stations in Victor Valley and Rancho Cucamonga. At speeds up to 200 miles per hour, trains will take passengers from Las Vegas to Rancho Cucamonga in about two hours, twice as fast as the normal drive time.

Brightline is currently operating its first passenger rail system connecting Central and South Florida with stations in Miami, Aventura, Fort Lauderdale, Boca Raton, West Palm Beach, and Orlando, with future stations coming to Stuart and Cocoa. For more information, visit  www.brightlinewest.com  and follow on  LinkedIn ,  X ,  Instagram  and  Facebook .

QUOTE SHEET

“Through this visionary partnership, we are going to create thousands of jobs, bring critical transportation infrastructure to the West, and create an innovative, fast, and sustainable transportation solution. Nevada looks forward to partnering with Brightline on this historic project.”  - Governor Joe Lombardo, Nevada

“Today, not only are we breaking ground on a historic high-speed rail project here in Nevada, we are breaking ground on thousands of good paying American jobs, union jobs.”  - Steve Benjamin, Senior Advisor to the President and Director of the White House Office of Public Engagement

“For decades, Nevadans heard about the promise of high-speed rail in our state, and I’m proud to have led the charge to secure the funding to make it a reality. Today’s groundbreaking is the beginning of a new era for southern Nevada -- creating thousands of good-paying union jobs, bringing in billions of dollars of economic development, enhancing tourism to the state, reducing traffic, and creating a more efficient and cleaner way to travel. This is a monumental step, and I’m glad to have worked across the aisle to make this project come true.”  - Senator Jacky Rosen (D-NV)

“Having high-speed rail in Las Vegas will electrify our economy in Southern Nevada, and I’m thrilled to celebrate this milestone today. This project is on track to create tens of thousands of good-paying union jobs while cutting down traffic on I-15, and I’ll keep working with the Biden Administration to get this done as quickly as possible and continue delivering easier and cleaner transportation options for everyone in Nevada.”  - Senator Catherine Cortez Masto (D-NV)

“Today’s groundbreaking is a historic step in modernizing rail service in the United States. Californians driving between the Los Angeles region and Las Vegas often face heavy traffic, causing emissions that pollute the air in surrounding communities. The Brightline West Project will provide travelers with more options—helping Californians and visitors alike get to their final destination without facing gridlock on the road.”  - Senator Alex Padilla (D-Calif.)

"High-speed rail in the Southwest has been a dream as far back as the nineties when Governor Bob Miller appointed me to the California-Nevada Super Speed Train Commission. As a senior Member of the House Transportation & Infrastructure Committee, I am honored to have helped write the Bipartisan Infrastructure Law and secure $3 billion to turn that dream into a reality which will generate millions of dollars in tax revenue, reduce carbon emissions by easing traffic on Interstate 15, and create thousands of good-paying union jobs. I am proud to stand with advocates and transportation leaders as we break ground on the Brightline West project and look forward to welcoming high-speed passenger rail to Southern Nevada."  - Congresswoman Dina Titus (NV-1)

“For decades, high-speed rail was just a dream in southern Nevada – but now, I’m beyond proud that we finally made it a reality. I worked across the aisle to help negotiate, craft, and ultimately pass the Bipartisan Infrastructure Law because I knew it would kickstart transformative projects like Brightline West that will stand the test of time. Together, we’re cutting down on traffic, boosting our tourism economy, and creating thousands of good-paying union jobs.”  - Congresswoman Susie Lee (NV-3)

“I am proud to join Brightline West for the groundbreaking of this monumental project for Southern Nevada and the southwestern United States. By connecting Las Vegas to Southern California via high-speed rail, we will boost tourism, reduce congestion on the I-15 corridor, and create jobs. The impact on our local economy and the people of the Silver State will be tremendous. In my conversations with Secretary Buttigieg, Brightline West, and our Nevada labor leaders, I know that local workers and our Nevada small businesses will benefit from this transformational investment. This will be the nation's first true high-speed rail system, blazing a new path forward for our nation’s rail infrastructure, and we hope it will serve as a blueprint for fostering greater regional connections for many other cities across the country.  - Congressman Steven Horsford (NV-4)

“Brightline West’s groundbreaking today marks the construction of a dynamic high-speed rail system that will link Las Vegas, Hesperia, and Apple Valley to Rancho Cucamonga’s Metrolink Station, creating new jobs and fostering economic growth in California’s 23rd Congressional District. This convenient alternative to driving will reduce the number of cars on the road, decreasing emissions and reducing congestion in our High Desert communities. This is an exciting step and I look forward to the completion of this project.”  - Congressman Jay Obernolte (CA-23)

"Today's groundbreaking on the Brightline West high-speed rail project marks an incredible milestone in the Biden-Harris Administration's commitment to fulfilling the promise of high-speed rail and emissions-free transportation across the country. As a longtime supporter of this project, I helped pass the Bipartisan Infrastructure Law, which has already invested over $3 billion to support the completion of this project. By increasing transportation options, spurring job creation and new economic opportunities, and improving our environment through cutting over 400,000 tons of carbon pollution each year, this project will be transformative to my district and all of Southern California for generations—particularly in and around the last stop in Rancho Cucamonga. With the goal of being operational in time for Los Angeles to host the Summer Olympic Games in 2028, I look forward to Brightline West facilitating travel for the millions visiting our region and elevating our 21st-century connectivity on the global stage."  - Congresswoman Judy Chu (CA-28)

"As the Member of Congress that represents the City of Rancho Cucamonga and a member of the House Appropriations Subcommittee on Transportation, Housing, and Urban Development, it is my honor to participate in breaking ground on one of the most highly anticipated high-speed rail projects in the country. We gathered today thanks to the Biden Administration's leadership, which enacted the Bipartisan Infrastructure Law and the Inflation Reduction Act to fund vital projects like this and transform our economy. The Brightline project is a stellar illustration of the power of successful public-private partnerships. Thanks to all the labor unions, Tribes, and wildlife advocates for their hard work, which brought this project to life. The bright line is fully electric and has zero emissions, which is excellent for our environment. I am eagerly anticipating the completion of this project in my district and look forward to seeing everyone there."  - Congresswoman Norma J. Torres (CA-35)

Media Contact

Vanessa Alfonso [email protected]

• Puget Sound
• Traffic Lab

Your how-to guide for the new Eastside light rail line

The East Link Starter Line, also called the 2 Line, begins service 11 a.m. Saturday with eight stops in Bellevue and Redmond. If you’re a newcomer to Sound Transit light rail, here’s what to know.

Hours: Eastside trains are scheduled to arrive every 10 minutes, seven days a week from 5:30 a.m. to 9:30 p.m.

Travel time: A ride on the 6-mile line, end to end, lasts 20 minutes.

Capacity: Two-car trains are intended to carry 300 people, when half are seated and half standing.

Locations: At the south end is South Bellevue Station. From there, trains head northeast to East Main, Bellevue Downtown, Wilburton, Spring District, BelRed, Overlake Village and the last stop, Redmond Technology Station. Free park-and-ride space is available at South Bellevue (1,500 stalls), BelRed (300), Overlake Village (203 stalls, four blocks away) and Redmond Technology (300). The other four stations include passenger drop-off sites and connecting bus stops.

Fares: Standard adult fares are $2.25 to $2.50 depending on distance. Link light rail charges $1 for 65+, disabled and low-income passengers holding a discounted ORCA fare card. People 18 and younger ride transit free throughout Washington state. Fares will be collected opening weekend.

How to pay: Fares are paid before entering trains. Most people use a regional ORCA fare card, tapping it on a yellow detector near the station entrance. Tap again when leaving a station to avoid overcharges. See orcacard.com to order fare cards online or find in-person sites . ORCA cards are available at many QFC and Fred Meyer stores. Paper single-trip and all-day tickets are sold in station vending machines, which accept cash or credit/debit cards. If you’re taking more than a couple of rides, it’s simpler to buy an ORCA fare card directly from the ticket machine. You pay $3 for the card, then load it with funds. Or download the Transit Go app .

Station entry: There are no turnstiles. “Fare ambassadors” canvass some trains to check for proof of payment and help people navigate. They issue advice or warnings and can cite repeat evaders for $50 or more. Pedestrians should look all ways for trains next to station platforms and at grade crossings around BelRed Station.

Bicycles: Bikes are allowed onboard light rail, hanging from a hook in a nook that doubles as luggage space.

Restrooms: There are no public restrooms in the eight stations.

Buses: The primary train-bus connections are I-90 routes that swing by South Bellevue Station; Highway 520 routes next to Redmond Technology Station; and I-405 buses that converge at Bellevue Downtown Station. Metro’s B Line bus links the Crossroads neighborhood to multiple train stops including Wilburton.

Traffic Lab | Eastside Light Rail

• Eastside’s light rail wait is almost over with ‘Starter Line’
• Map: Eastside’s first light rail stations open April 27
• Timeline: Eastside light rail has been a long time coming
• Eastside tech workers, we want to hear from you about your commute

Traffic Lab reporter Mike Lindblom is taking questions for an upcoming story. Email him at [email protected]

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The opinions expressed in reader comments are those of the author only and do not reflect the opinions of The Seattle Times.

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