A thought experiment with theory of relativity.

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Discussion Overview

The discussion revolves around a thought experiment related to the theory of relativity, specifically addressing the implications of traveling at the speed of light and the nature of time and space in such scenarios. Participants explore concepts of time dilation, the experience of a hypothetical observer traveling at light speed, and the meaning of time for massless particles like photons.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant proposes a thought experiment involving a fly on a photon, suggesting that from the fly's perspective, time would be zero as it travels at the speed of light.
  • Another participant counters that time is meaningless for objects traveling at the speed of light, indicating that the concept of time does not apply to photons.
  • A different participant highlights the impossibility of a fly traveling at the speed of light due to its mass, emphasizing that there is no inertial rest frame for photons.
  • One participant notes that the question raised is common and refers to existing resources in the forum that address similar inquiries, suggesting that the term "meaningless" is more appropriate than "nothing" in this context.

Areas of Agreement / Disagreement

Participants express differing views on the implications of traveling at the speed of light, particularly regarding the nature of time and the feasibility of a fly existing on a photon. There is no consensus on the validity of the thought experiment or the interpretation of time for massless particles.

Contextual Notes

Participants reference the limitations of discussing time from the perspective of photons, noting the violation of fundamental principles of relativity if such a frame were to exist.

Supreethsj
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Hi,
I had a question on theory of relativity. It is more of a thought experiment.

As per the theory of relativity, as the speed of an object increases time slows down. If any particle travels faster than the speed of light, theoretically it has to travel back in time. So from this we can deduce that when a particle is exactly at the speed of light t=0.

Thought experiment- let's say a fly sits on a photon that is emitted by the sun. We know that from out standpoint of time, the photon takes approximately 8min 20 sec to reach earth. But let's say that the fly has a stopwatch and it starts the watch when it leaves the sun. As the photon and the fly are traveling at the speed of light, t=0, hence the fly clocks 0 seconds confirms that the photon traveled instantly from sun to earth. Concurring from this, even if the photon travels across the universe, the result i.e t=0 stands same.

Also according to Einstin's theory, time and space are considered to be a single diminution called 'Time Space'. So as the speed of a particle tends towards the the speed of light, it is not just that time slows down but also space has to contract, eventually at exactly the speed of light space also become 0 (null). This brings us to Nothing.

I am a novice. I would love your comments on the same. Thank you.
 
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The contradiction you've thought up is the reason why particles can't go the speed of light and why it makes no sense to talk about what "time" a photon sees.

Time is meaningless to objects that travel at the speed of light.
 
Well, never seen fly sitting on a photon, and there are good reasons for that. First, flies like rotten meat, not photons. Second, they have mass, which means that there exists no frame of reference in which they can move at the speed of light.
However, you can ask how does world looks like from the rest frame of the photon. And answer is, in relativity photons don't have inertial rest frame. It would violate very important postulate that speed of light is the same in any rest frame.
 
Your question is asked frequently. That is why it is covered in the FAQ section. There you will find that instead of your word "Nothing", the word "meaningless" is applied (as Pengwuino) pointed out. You can find a lot more threads on this subject by searching this forum for "meaningless". Lots and lots. And now there is one more.
 

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