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Probably been answered but couldn't find the answer.

From the perspective of a photon: - For the photon to travel from body A to body B would take 0 secs. - The universe would be one point in "something" and the lifespan of a photon would be 0 secs. - But photons are created and "die" all the time, did they exist? - There is no such thing as time(?).

Singularity but what falls apart, if the photon exists?

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    $\begingroup$ Photons have a finite speed $c$ and it takes them a finite amount of time to get from A to B. $\endgroup$
    – Gert
    Commented Nov 25, 2015 at 20:24
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    $\begingroup$ You cannot go to frame of a photon, since in its frame (if it existed) the photon would be at rest and no massless particle can ever be at rest in any frame. $\endgroup$
    – Prahar
    Commented Nov 25, 2015 at 20:36
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    $\begingroup$ In other words, photon exists, but the "frame of a photon" doesn't exist. $\endgroup$
    – Prahar
    Commented Nov 25, 2015 at 20:37
  • $\begingroup$ why this Pavlov answering each time everywhere, while you could harmlessly transform the question by an electron going to near-c speed ? $\endgroup$
    – Fabrice NEYRET
    Commented Nov 26, 2015 at 7:32
  • $\begingroup$ Possible duplicate of Would time freeze if you could travel at the speed of light? $\endgroup$
    – jinawee
    Commented Nov 26, 2015 at 11:13

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From the perspective of a photon:

There is no such perspective.

I was trying get an understanding of the universe from the photons perspective.

There is no such perspective.

Consider the following excerpt from I am driving my car at the speed of light and I turn on my headlights. What do I see?:

Sometimes people persist: What would the world look like in the reference frame of a photon?

What does a photon experience?

Does space contract to two dimensions at the speed of light?

Does time stop for a photon?. . .

It is really not possible to make sense of such questions and any attempt to do so is bound to lead to paradoxes.

There are no inertial reference frames in which the photon is at rest so it is hopeless to try to imagine what it would be like in one.

Photons do not have experiences.

There is no sense in saying that time stops when you go at the speed of light.

This is not a failing of the theory of relativity. There are no inconsistencies revealed by these questions. They just don't make sense.

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    $\begingroup$ This is a common but unsatisfying answer: one can surely imagine an observer who is made out of photons. Therefore the repetition "there is no such perspective" is incomplete. The reason such observers don't constitute a valid reference frame is because of the subtle fact that the notion of a reference frame is only valid for bodies whose observational interactions to a good approximation do not affect their motion. Generally speaking, for photons any observational interaction non-negligibly affects its direction of motion (though one can imagine interactions that only change its frequency). $\endgroup$
    – user1247
    Commented Jan 21, 2016 at 19:09
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    $\begingroup$ It is instructive to go through the motions of calculating what the perspective of a scientist made out of parallel-moving photons would look like, and to find the root of the inconsistency. Hint: parallel-moving photons have zero invariant mass and therefore have zero interaction cross-section. $\endgroup$
    – user1247
    Commented Jan 21, 2016 at 19:11
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Imagining that "you are the photon" is an ill-posed question.

The problem is this: There is a strict distinction between massive and massless particles. For massive ($m\neq0$) particles, you can always find a reference frame where the particle is stationary. For massless ($m=0$) particles this is impossible. This means there is no reference frame in which the photon perceives itself as "at rest" while cruising through the universe.

An illuminating way of thinking is in terms of what is happening at simultaneous time (see image bellow). For a stationary observer (green), space and time are orthogonal, as seen by all other stationary observers. The faster the relative speed between observers (purple), the more the time- and space axis tilt towards each other.

When a particle is traveling at the speed of light (orange, which means $m=0$), then the time axis and the space axis are parallel. This means that all events along the trajectory of the photon take place at the same time (for the photon).

In this sense, the lifetime of a photon is $t=0$ seconds. On the other hand, you may imagine the photon as frozen in time, so these $t=0$ seconds are not "noticed" by the photon.

enter image description here

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  • $\begingroup$ "is that you simply cant" that sounds too much like religion to me. Its fine to say "we don't know" from time to time. We don't know what the world would look like to a photon, and that's good because that means that we have still much to learn about the Universe. $\endgroup$
    – Nuke
    Commented Aug 9, 2022 at 17:05
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    $\begingroup$ @Nuke I may have been a bit vague with what i meant. I hope you will enjoy the edited explanation with a corresponding spacetime diagram. $\endgroup$
    – Mikael Fremling
    Commented Aug 20, 2022 at 12:16
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It means that for ultra near-c-speed particles, the closest to c the less time and space exist. For instance, transactionalists consider the emission then absorption of a photon by distant electronic layers as a simple handshake between them (the photon jumping instantaneously from one to the other in his "frame"). This also gives some clue about the pre-bigbang universe, before particules be coupled with mass: this univers could mostly be considered as a network of interactions without such notion on clock and lengths. Which does not mean particles and interaction don't "exist". Plus it does not mean that c-speed particles won't have length and duration for an exterior observer.

Now, take care about the photon being a particle, like a kind of small marble. Would you say a wave travelling on top of the ocean is an object ? that "exist" ? ;-)

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