Time stopped for a photon travelling at the speed of light?

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Discussion Overview

The discussion revolves around the concept of time as experienced by a photon traveling at the speed of light. Participants explore whether it is meaningful to say that time "stops" for a photon and the implications of this for understanding relativistic effects, particularly in relation to different frames of reference.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that from a photon's perspective, it reaches its destination instantly, experiencing zero time and zero distance, which contrasts with the time experienced by observers at rest.
  • Others argue that the concept of time does not apply to a photon, suggesting that the question itself is nonsensical due to the invalidity of a photon's rest frame.
  • A participant mentions that as one approaches the speed of light, the effects of time dilation and length contraction become significant, making the question about photons a limit case.
  • Another participant references an external source to support the idea that discussing time for a photon is not meaningful, reinforcing the notion that valid reference frames are necessary for such discussions.

Areas of Agreement / Disagreement

Participants express disagreement on whether the question of time for a photon is meaningful, with some asserting it is nonsensical while others provide reasoning that suggests a more nuanced view based on relativistic effects.

Contextual Notes

The discussion highlights limitations in understanding time at relativistic speeds and the dependence on valid reference frames, which remain unresolved in the context of the conversation.

mildpiranha
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time "stopped" for a photon traveling at the speed of light?

Is time "stopped" for a photon traveling at the speed of light? Or is this a nonsensical question?
 
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From the photon's point of view, it arrives at its destination immediately after leaving, in zero time. It can travel through the entire universe in no time at all, literally, which is logical since in its frame of reference it also travels zero distance.

From our point of view, obviously, it's just traveling at the speed of light so it may take millions of years to reach its destination.

It's a bit like the space traveler who leaves on a long space trip. As he accelerates to nearly the speed of light, space around him shrinks (in the direction of movement) so that distant galaxies suddenly become so close that he can reach them in a few years. Same thing for the return trip. However, as seen from the earth, he will have been away for millions of years. In fact, the Earth may not even exist anymore when he tries to come back.

The photon is just the same, only it travels AT the speed of light, so lengths are shrunk to zero and travel takes no time at all, in its frame of reference.

If I'm not mistaken, this also means a photon, or any other particle traveling at the speed of light, will never decay since it doesn't have time to do so.
 


This is really a nonsensical question, since the rest frame of a photon is not a valid reference frame.

As the article posted by michelcolman points out, we can ask what happens as we get closer and closer to the speed of light. This question makes sense, since all the reference frames we would be in would be valid.
 

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