Question about the rest frame of a photon

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Discussion Overview

The discussion centers around the concept of the rest frame of a photon and the implications of such a frame on the experience of time and motion. Participants explore theoretical considerations related to Einstein's ideas and the nature of photons in relation to time and acceleration.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that if a photon had a rest frame, it would not experience the flow of time or measurable changes, leading to the idea of a singularity from the photon's perspective.
  • Others argue that it is impossible for an observer to ride along with a photon, as this would imply a rest frame for the photon, which contradicts the definition of a photon traveling at the speed of light in all inertial frames.
  • A participant notes that concepts like "rest frame" and "flow of time" are meaningless for photons, reinforcing the idea that one cannot consider a photon's experience in the same way as an observer moving at less than the speed of light.
  • There is a discussion about the nature of photons being emitted without experiencing acceleration, with some participants confirming that photons travel at the speed of light as soon as they are created.

Areas of Agreement / Disagreement

Participants generally disagree on the implications of a rest frame for photons, with some asserting that such a frame leads to contradictions, while others explore the idea of time and acceleration in relation to photons without reaching a consensus.

Contextual Notes

The discussion involves unresolved assumptions about the nature of time and motion at the speed of light, as well as the definitions of rest frames in the context of special relativity.

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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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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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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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?
 
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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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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Okay and thanks phinds & PeterDonis.
 

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