Q: If a photon doesn’t experience time, then how can it travel?

Physicist: It’s a little surprising this hasn’t been a post yet.

In order to move from one place to another always takes a little time, no matter how fast you’re traveling.  But “time slows down close to the speed of light”, and indeed at the speed of light no time passes at all.  So how can light get from one place to another?  The short, unenlightening, somewhat irked answer is: look who’s asking.

Time genuinely doesn’t pass from the “perspective” of a photon but, like everything in relativity, the situation isn’t as simple as photons “being in stasis” until they get where they’re going.  Whenever there’s a “time effect” there’s a “distance effect” as well, and in this case we find that infinite time dilation (no time for photons) goes hand in hand with infinite length contraction (there’s no distance to the destination).

At the speed of light there's no time to cover any distance, but there's also no distance to cover.

At the speed of light there’s no time to cover any distance, but there’s also no distance to cover.  Left: regular, sub-light-speed movement.  Right: “movement” at light speed.

The name “relativity” (as in “theory of…”) comes from the central tenet of relativity, that time, distance, velocity, even the order of events (sometimes) are relative.  This takes a few moments of consideration; but when you say that something’s moving, what you really mean is that it’s moving with respect to you.

Everything has its own “coordinate frame”.  Your coordinate frame is how you define where things are.  If you’re on a train, plane, rickshaw, or whatever, and you have something on the seat next to you, you’d say that (in your coordinate frame) that object is stationary.  In your own coordinate frame you’re never moving at all.

How zen is that?

Everything is stationary from its own perspective.  Only other things move.

Everything is stationary from its own perspective.  Movement is something other things do.  When you describe the movement of those other things it’s always in terms of your notion of space and time coordinates.

The last coordinate to consider is time, which is just whatever your clock reads.  One of the very big things that came out of Einstein’s original paper on special relativity is that not only will different perspectives disagree on where things are, and how fast they’re moving, different perspectives will also disagree on what time things happen and even how fast time is passing (following some very fixed rules).

When an object moves past you, you define its velocity by looking at how much of your distance it covers, according to your clock, and this (finally) is the answer to the question.  The movement of a photon (or anything else) is defined entirely from the point of view of anything other than the photon.

One of the terribly clever things about relativity is that we can not only talk about how fast other things are moving through our notion of space, but also “how fast” they’re moving through our notion of time (how fast is their clock ticking compared to mine).


The meditating monk picture is from here.

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197 Responses to Q: If a photon doesn’t experience time, then how can it travel?

  1. Pingback: Q. If you are a Photon, What time is it? | Musea Zine

  2. Russell says:

    If light has traveled across the universe to get to us but experiences no time, then how can we say that any time has elapsed at all? Is it that light has not experienced time and the rest of the universe has?

  3. Orien Rigney says:

    When in doubt about your theory or analysis, use the following.

  4. yoron says:

    “and in this case we find that infinite time dilation (no time for photons) goes hand in hand with infinite length contraction (there’s no distance to the destination).”

    Quite so, brave, very few mathematicians that really dare to have a view of it. Then to get to my view of it you just have to exchange a ‘propagation’ for a ‘timing’, locally defined. then we don’t need time dilations for them, we just need local principles and rules. To it you can add scales, creating a structured local time, and a very weird principle presenting us a ‘common universe’ represented by ‘c’.

  5. Parrish says:

    If time dilation is true and photons have mass then… Every photon is a new moment in time. When a photon is created time stops for the photon until it reacts with something. It is then moved to that point in time. Since movement in time is always observed with photons then this governs our perception of time moving forward.
    What if light isn’t the thing moving? The reason you approach infinite energy as you approach the speed of light is because you are really slowing in moving space.

  6. Tom Hendricks says:

    If I am a photon, what time is it?

  7. Orien Rigney says:

    Your question Tom: If I am a photon, what time is it?

    Let me add just a bit more fuel to that fire Tom.~~~~~~~~~~~~~~~~~~~~~~~~
    Can a photon ever be at rest? If so, with respect (relatively) to what? Again, if so, what must a photon weigh at rest, with respect to what? If everything actually increases in mass (weight) with an increase in speed, what will a photon weigh at C?

  8. Rich B says:

    As time is simply a concept we have constructed with our own brains then it’s true to say that a photon experiences no time. I this is the case then it might help us to understand one of the confusing aspects of quantum physics, whereby atoms (and probably photons) can be everywhere at once.

  9. Orien Rigney says:

    We do take a lot for granted when dealing with Quantum Physics or Mechanics. But time itself is not simply a manifestation of our brain to work out unmanageable or complicated problems, time is real! Yet, even though the “Half Life” of elements have been worked out to a certain degree, it still isn’t an absolute science time wise; but darned close.
    An atom or photon etc. seemingly to be in two places at the same time is probably one of natures tricks much like the double slit particle or wave phenomenon that continues to be questioned.

  10. Peter reid says:

    As I see it, a photon is created as a particle but becomes a wave when it travels at light speed. As time stands virtually still for the photon, it would see itself as a particle even though it’s travelling as a wave at LS. Therefore is it both a wave and a particle simultaneously.????
    Is it possible that all objects travelling at LS will then travel as a wave or does the mass of an object change that?
    Any answers please send to my email, I’m actually interested in finding out!!!!
    peter999@ live.com

  11. Orien Rigney says:

    Some of the sharpest minds of today are just now digging deeply enough into quantum physics and mechanics to begin getting answers allowing them to dig even deeper. Only through due diligence are these people even allowed to work with the equipment needed to do this job. Meanwhile, most of us have to wait, read and listen to what work is in progress. Here is a good take off on it.

  12. Grahame Thorne says:

    The answer given is clear, but I read the question as asking about the photon’s ability to travel in the absence of time, not the observer’s perception of it, so it is largely an answer to a different question!

    Einstein’s Special Relativity tells us that we see the clocks of things moving at speeds (relative to our own frames of reference) running slower, and lengths shorten; both of these phenomena regardless of whether speeds are faster or slower. Therefore, it isn’t too difficult to conceive that a photon travelling at the speed of light appears infinitely contracted in length, more like a particle than a wave, and, as a clock, appears to have frozen time. Conversely, a photon will see the universe through which it passes as infinitely shortened (but only in its direction of travel, excellently illustrated in the diagram above), and time frozen.

    However, in all frames of reference (at all velocities) all clocks within the same reference are observed to run at their proper speed. Presumably this is the same for the photon at the speed of light: a photon will observe its own clock running at its proper speed. If I’ve understood Einstein’s Special Relativity correctly, then it is incorrect to say ‘at the speed of light no time passes at all’, only that ‘(to all observers at any velocity less than the speed of light) time appears to be stationary at the speed of light’.

    At the speed of light, the photon should see the universe as incredibly short (and be intrigued as to how so much can exist such a small, apparently two-dimensional space), it will perceive it’s own speed as very slow (presumably stationary), not because of aberrations in its time, but because its velocity (v=d/t) will tend towards zero as its measure of distance shortens. It also seems likely it would see its own full length extending from its origin through its own ‘present’ in time, more like a wave than a particle.

    I’m not a physicist or a mathematician, so factual corrections or omissions would be welcome.

  13. James Becker says:

    In response to Orien Rigney that time is “real”:

    How are you sure that time is not simply something that humans and possibly other living creatures have thought up to explain things such as distance, aging, etc.? Does time ACTUALLY exist outside of our brains?

    If you refer to external scientific validations, you must admit that even experimental validations are based on human observations of human experiments, which are made to test human theories. All of these things are merely products of lumps of meat called ‘brains’.

    I’d argue that time simply DOES NOT exist outside of our conscious perception. The future is merely probabilistic, and the past is merely deduction-based. All that exists is “this present state”.

  14. Tero Moisio says:

    Agree. Time is measurement we define events to happen. Defined by memory. And compared to other events like earth going around the sun. And then if we think time is always moving forward. Meaning when we measure events, it first starts and then stops. In case of time jump, we would go another way. Event has already happened and we would like to jump to the point event is starting to happen. That would mean all the movement would reverse. Start to move backwards. And without force and energy things just can’t jump to reverse motion.

    Again how we see far away events is interesting. There we discuss more how information from events is travelling long distances. And even short distances. Meaning everything we observe is history. Nothing we see or hear happens right now. It has already happened. But when we see events happening we know how events will proceed. As we can make observations faster then events are proceeding. Example car is coming towards. We see car all the time and memory is keeping information that car seems to come toward us. As mass is moving in speed we can estimate with observions.

    So of we think time is actually speed and direction of events, time would have always one direction. Forward. And with high speed meaning event is as fast as information we can observe, we have difficulties to define time.

  15. Orien Rigney says:

    Not to get mushy James, but this my best way of describing time.
    Time may not be the best or only way to mark the progression of events as we record them. But, unless an occasion is thought of as a metaphorical or transcendental philosophy, time is probably the best method we will ever have in discussing events. A celestial body orbiting another is one way to look at time inanimately. Water standing still in a swamp or running down stream is another. Animatedly, living plants such as trees and grasses grow leaves in the spring and produce seeds and fruit during the summer and autumn, only to shed their greenery and lie dormant during the winter. Bears and a few other animals and reptiles sleep nearly half their lives away in order to preserve what they feel is the best of their life cycle. Humans stay awake most of the time figuring out ways to screw someone else out of a nickel. Whether real or metaphysically, time is likely the best method nature has of conditioning everything in its realm to use accordingly.

  16. Let’s put some ideas together.
    1. photons left the big bang at the speed of light
    2. at the speed of light, no time passes.
    That would suggest there is no time between the big bang and now for a photon. In other words the big bang is happening now for the photon?

    More combinations.
    1. Photons were all concentrated in the big bang.
    2. Were they all entangled with each other?
    Then, are all photons from the big bang entangled together? And if there is no time for a photon, then are all photons entangled now as they were at the big bang?

  17. Tero Moisio says:

    I don’t believe big bang but as idea, photons born in big bang would be still in big bang time. But so far away we would not reach them (if travelling all the time). We experience only photons born in materia around us. So photon does not experience time when moving from point a to point b. This is my best understanding so far..

  18. Orien Rigney says:

    We really don’t know that much about photons other than they were ‘supposedly’ created a few seconds or minutes after the BB occurred. Throughout the universe photons are produced daily, to die instantly under certain conditions. Black bodies absorb them while others reflect them. Photons are a celestial phenomena we simply must accept as fact.

  19. I don’t see any problem with the fact that à photon expériences a “no distance” and “no time” universe. In fact this would solve a few problems regarding the exchange of information between photons in disregard of the distance. We could say that the actual universe is one big photon.

    We then would expérience distance and time simply because our motion is slower than the speed of light.

    The real problem occurs when I consider the time of traveling of the photon that started from 380,000 years after “time zéro”, and just reached Planck satellite so it could make its picture of the universe of that “far away” time. It took him 13,8 billions years to get here.

    If the answer is that the span of time of travel for the photon is relative to my perspective, than the “reality” should be given to the photon and since he doesn’t travel at all, there is no real unobservable universe behind the picture of the satellite Planck.

  20. The other problem is there’s no real obervable universe either. So …

  21. Samantha says:

    If photons don’t experience time does this mean their waves propagate infinitely? And, a somewhat off-topic thought: if we could step outside of our universe and look at it, would all we see be light? Would we be able to differentiate anything at all?

  22. Orien Rigney says:

    If our present standard model, “LambdaCDM” is correct; stepping outside the parameters of this space and time bubble of a universe we live in would be impossible because? “There is no outside” to it. But, if our universe is expanding in an “endless continuum” with no such parameters? yes; we could step beyond the expansion and look back on it.

  23. Jason says:

    @Samantha, “If photons don’t experience time does this mean their waves propagate infinitely?”, no because there is nothing moving. No change in time means no change of position. Their creation and destruction have to be at the same time and place.

  24. But doesn’t that suggest that all photons at the big bang are still there concentrated in one point?

  25. Orien Rigney says:

    If the entire universe is moving (exponentially?), at a given speed; why shouldn’t photons not be doing likewise? Perhaps we should refer to them as mythons?

  26. James Becker says:

    @Tom Hendricks, I’m not a professional physicist, but from my understanding, the phrase “still there” is time-space related. “Still” is a time-related word meaning they were there before, and they’re there now. “There” is a space-related word that refers to specific location in three dimensions. You have to remember that the words you’re using are constructs of the English language and can’t necessarily apply to quandaries that involve constructs which lie outside of space-time as we humans understand it.

    Remember that space and time are an inseparable object. We can conceive of bidirectional travel in space, but it’s difficult for us to conceive of bidirectional travel in time. We as humans are always tempted to order things chronologically, but according to physics, that’s not actually how photons experience reality.

    Yes, those photons are “still there”! —But they’re there in a time which you and I perceive as being in the “past”—merely another word which is a construct and doesn’t necessarily exist outside of our cognition (which we may well share with all sentient life—but not with photons). If you get outside consciousness, yes, the photons are still there—they “always” “were”, and “always” “will be”.

  27. Perhaps best to say my question this way, from the photons point of view, it’s still the big bang, the photons have not aged and they are still in a single point.

  28. Orien Rigney says:

    To: J. Baker
    James, I would like to interject a thought. If photons must travel in straight lines, or Give the impression of being stationary since they (photons) are already at max speed, how can gravitational lensing make sense?


  29. James Becker says:

    @Tom Hendricks, Keeping in mind that the universe is nonlocal, correct. The photons are still in one single point, and they are also everywhere at once.

    From my understanding, when we “observe” photons, we are actually creating our own observations. If one were to actually be able to “observe” photons without human-created instruments, which are bound to space and time, then one would realize that every photon is in actuality every-where and every-time at once.

  30. James Becker says:

    @Orien Rigney, I’m not sure what you mean. Photons are not always particles which travel in straight lines. They are only this way when observed. Sans observation, they manifest more generally waves which are everywhere at once and exist only probabilistically until their location is observed. Since space-time is curved, the photons themselves may appear to us observers to be traveling in curved lines, but they are eternally traveling in straight lines in their own plane of existence. It is only the universe around them which, from their perspective, would appear to be curving.

  31. This leads to strange ideas – could we have just one photon that is everywhere at the same time? Or could we say that all photons are entangled still?

    This makes Alice look like she is in no wonder land in comparison.

  32. Orien Rigney says:

    Tom, I am definitely not a physicist, so what I say likely doesn’t matter at all. But, if a flashlight is turned on, no matter how bright or dim the beam, where do photons come from creating that light? And space/time warping? With mathematics, one can come to any conclusion they desire.

  33. Orien Rigney, Good points. Flashlight seems to be a way to add new photons.

  34. James Becker says:

    To God/an outside observer, the universe is but an inch across…

  35. Samantha says:

    My question has led me to be more confused about photons. Can’t wait for the day I fully grasp them! Thanks everyone for the responses. Really interesting stuff

  36. Orien Rigney says:

    Tsk-tsk! James. Let us not get lugubrious and religious simultaneously. I’d normally say, “expound” on such a statement, but this is viewed as scientific discussion and not a supernatural investigation.
    Photons are created in as any ways as there are objects in this universe that can create a spark, which is light (photons). Electrical (lightening) storms here on planet earth alone should be enough to convince one that light emitted from such is not eternal. A flash, a boom and the light is dissipated along with the boom. Laser light, used to etch, engrave and do surgery, is it part of this idea that light goes on forever?

  37. But Orien Rigney aren’t you contradicting yourself? If a photon is going the speed of light, it is outside time, how can it not be eternal? The time is on our side not the side of the photon – right?
    This is why this is so difficult to grasp.

  38. James Becker says:

    @Samantha, no one really grasps photons. No one. They are a mystery. So don’t feel alone. Keep on trying, though!

    @Orian Rigney, let’s not suffocate honest scientific and philosophical inquiry (and yes, at a certain point in scientific inquiry, philosophy DEMANDS its place—science and the scientific method alone cannot stand, as needs no explaining) with political correctness. Besides, I said God/an outside observer, which would seem to be rather inclusive no matter which side of the fence you stand on. And if you wish, you can interpret God as “consciousness” or “source” or whatever you like.

    As far as your interpretations of photons, you’re still stuck inside the human notion of cause-and-effect. It’s an easy place to be stuck, being a human, isn’t it? Unfortunately, cause-and-effect breaks down at the quantum level—the level at which photons exist.

    Also, you may want to look up the word “lugubrious” in a dictionary.

    @Tom Hendricks, precisely. All photons are eternal, because time does not exist for them. They are either eternal, or they don’t exist at all. There is no other interpretation.

  39. Orien Rigney says:

    James, My comments weren’t to make light of the debate on photons, just to say; not all of the balloting is in on understanding them. Thought this link might shed some light on the argument. And Lugubrious! Perhaps I should have used melancholy?


  40. John says:

    I am reading the posts for a while and my brain is about to explode.:-) Like the b. B. !

    Also I would like to say that where there is a start and an end, between this start and end some time is passing. So when I switch on the light there should be some time passing when the light is travelling even if this time is very very close to zero. I mean when light is travelling from me to the opposite wall. Even if this seems to me to be instant travel of the light to the wall in reality it is maybe not.

    I am not an exert on these things, so what I say is maybe wrong

  41. David Roberts says:

    And then there is the problem of something traveling faster than light travels in vacuum.
    Does it get there before it begins the journey, and what does the distance become?
    Remember that subatomic particles can travel faster than light in a medium such as water. Look up Cherenkov Radiation.

  42. Jay VanSant says:

    A photon is emitted somewhere, and its location is spread out traveling as a wave-front over the electromagnetic field as long as it is not detected or absorbed by some other particle (like an electron shell of an atom). The quanta of energy that it transfers at the end-point is then fully transferred at that position in space-time, and it is suddenly not available anywhere else along the wave-front. How this happens is not understood yet, but the fact that the photon itself experiences no passage of time and no distance in space means that its absorption at the end-point happens simultaneously with its emission. Is it possible that the change of state properties at the absorption point can instantaneously affect the state of the emitted photon (and so affect the entire wave-front where ever it has reached)? Specifically it might change the property of being able to be absorbed so it becomes effectively non-existent everywhere else along the wave front. This still wouldn’t explain how the energy of the photon spread out all over the wave front can suddenly be available at the single end-point. Perhaps what is carried by the photon-wave is just a trigger that causes a local transfer of a quantum of energy from the vacuum (or the Higgs Field).

    I find it interesting that there have not been scientific papers published dealing with the relativistic and quantum field theory implications of the photon moving at light speed. The story is told about how the young Einstein imagined what it would be like to be on the front of a flashlight beam when it was turned on. After he subsequently published his 1905 papers on the quantum-particle-nature of photons and the General Theory of Relativity, why didn’t he (or someone else) work out and publish the implications of his
    discoveries on the same imagined flashlight thought experiment? Have I just missed some published article? I’ve been reading about developments in physics for more than 40 years (mostly in Scientific American and in layman level books), and I don’t remember seeing anything that discussed this.

  43. richard taylor says:

    if time stand still for a photon would not all created photons exist and arrive at there destination at the same time according to a photons perception of time ? and just out of interest do photons travel in a straight wave or a corkscrew motion

  44. Samantha says:

    Okay, so a somewhat off topic question/thought that I feel could get answers and spark some discussion here. I was thinking the other day that if humans could learn to propagate gravitational waves themselves that we could use them like sonar to get information on distant galaxies. This would be practical because gravitational waves can travel faster than the speed of light, correct? They don’t disobey the laws of physics since they are spacetime itself so they can move faster is my understanding. Could be totally wrong. Thoughts anyone?

  45. Time says:

    Your idea of quote on quote time-is relative disassociates the lack of view into perspective of real time which was fabricated by theories which have been created by an imperfect being which can only live in the now. We remember the past and use past learnings to think about the future. To refute this is a waste of time. No?

  46. Orien Rigney says:

    The following link gives you a look at light from many perspectives. But then, at best this information only leads to more questions without answers. A person blind from birth can probably give a better description of what light is all about, perhaps even better than the most noted scientists.

  47. John Smith says:

    I’m going to tell my boss that I’m like a photon. He thinks I’m taking a longer lunch and not doing anything, but actually I created a copy/paste program to do some extra work for me so I can take the longer lunch. It may seem that I’m not doing anything, but I’m actually moving pretty far along. I suppose it seems that way to him, because he moves so slow compared to a photon.

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