Question about the rest frame of a photon

In summary, Einstein considered the concept of an observer riding along with a photon and realized it was not possible. This means that concepts like a "rest frame" and "flow of time" are meaningless for photons. Additionally, photons are created at the speed of light, so they do not experience any acceleration.
  • #1
member 342489
[Mentors’ note: this thread was split from the FAQ at https://www.physicsforums.com/threads/rest-frame-of-a-photon.511170/]

I am not an expert!

As I understand it, Einstein considered, what a guy standing in a photon will experience if he look at his watch.

My understanding says, that the guy, and the photon does not experience the flow of time, and also no other measurable change.

If my understanding is correct, should the universe then not be a singularity, when experienced from a photon?
 
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  • #2
Brian E said:
Einstein considered, what a guy standing in a photon will experience if he look at his watch.

No, that's not what Einstein considered. He considered whether it was even possible for someone to be riding along with a photon. And he realized that it was not possible to do that, because someone riding along with a photon would see it as a standing wave, oscillating in space but not in time; but there is no solution of Maxwell's Equations in free space that describes a standing wave. There are only solutions describing waves traveling at ##c##.

Brian E said:
My understanding says, that the guy, and the photon does not experience the flow of time, and also no other measurable change.

No, that's not correct. The correct understanding is that it is impossible for an observer to ride along with a photon, and concepts like "rest frame" and "flow of time" are meaningless for photons.
 
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  • #3
Brian E said:
[Mentors’ note: this thread was split from the FAQ at https://www.physicsforums.com/threads/rest-frame-of-a-photon.511170/]

I am not an expert!

As I understand it, Einstein considered, what a guy standing in a photon will experience if he look at his watch.

My understanding says, that the guy, and the photon does not experience the flow of time, and also no other measurable change.

If my understanding is correct, should the universe then not be a singularity, when experienced from a photon?
The problem with your analysis is this: A guy riding on a photon would be a rest relative to the photon. This would mean that there is an inertial frame in which a photon is at rest. But by definition, a photon travels at c in all inertial frames. Thus you have posited a frame in which a photon is BOTH at rest and traveling at c. Makes no sense.

All I've done is just say the same thing the thread you linked to
 
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  • #4
PeterDonis & phinds Thank you both.

I think I understand better now.
I actually were told years ago, that photons travel at c relative to any observer, but now I get it (I think )

but that must make photons able to beeing emitted without experiencing any acceleration?
 
  • #5
Brian E said:
but that must make photons able to beeing emitted without experiencing any acceleration?
Yeah, I had a little trouble with that when I first learned about this, but yep, that's the way it is. They travel at c as soon as they are created.
 
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  • #6
Brian E said:
that must make photons able to beeing emitted without experiencing any acceleration?

Photons are created when they are emitted, and they are already moving at ##c## when they are created. So they don't need to accelerate.
 
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  • #7
Okay and thanks phinds & PeterDonis.
 

Related to Question about the rest frame of a photon

1. What is the rest frame of a photon?

The rest frame of a photon is a theoretical concept that describes the state of a photon when it is not in motion. Since photons always travel at the speed of light, they do not have a rest frame in the traditional sense. However, the concept is still useful in understanding the behavior of photons in different reference frames.

2. Why is the rest frame of a photon important?

The rest frame of a photon is important because it helps us understand the behavior of light in different reference frames. It allows us to make predictions about how light will behave in different situations, such as when it is moving at different speeds or when it is interacting with matter.

3. How is the rest frame of a photon different from other particles?

The rest frame of a photon is different from other particles because photons always travel at the speed of light, while other particles have varying speeds. This means that photons do not have a rest frame in the traditional sense, but rather a frame of reference in which they are not moving.

4. Can the rest frame of a photon be observed?

No, the rest frame of a photon cannot be observed directly. Since photons always travel at the speed of light, they do not experience time or distance in the same way that we do. This means that we cannot measure their rest frame in the same way that we can measure the rest frame of other particles.

5. How does the rest frame of a photon relate to the theory of relativity?

The rest frame of a photon is an important concept in the theory of relativity. It helps us understand how light behaves in different reference frames and how it is affected by the principles of relativity, such as time dilation and length contraction. The theory of relativity also explains why the rest frame of a photon cannot be observed directly.

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