Travelling (at) the speed of light away from a lightsource

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Discussion Overview

The discussion revolves around a hypothetical scenario where a participant considers the implications of traveling at the speed of light away from a stationary light source, specifically a movie screen. The inquiry focuses on whether the observer would see a still image or a moving picture as they travel away from the screen, while also addressing the constancy of the speed of light in all reference frames.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether they would see a still frame or a moving image while traveling at the speed of light away from a screen, assuming they have massless eyes.
  • Another participant argues that the question is not physically possible and emphasizes the need for a well-defined question within current physical theories.
  • A different participant suggests that if one could observe the photons, they would see a still frame of the image at the time of departure.
  • One post presents a proof by contradiction, stating that the assumption of a massless eye moving at the speed of light leads to a self-contradictory conclusion about the nature of the image observed.
  • A participant reiterates their interest in understanding the implications of the constancy of the speed of light, despite acknowledging the non-physical nature of the scenario.
  • Another participant questions the relevance of the inquiry in a physics forum, pointing out that no reference frame can exist at the speed of light.

Areas of Agreement / Disagreement

Participants express disagreement regarding the physical feasibility of the scenario and the implications of traveling at the speed of light. There is no consensus on the nature of the image that would be observed, as the discussion remains unresolved.

Contextual Notes

The discussion is limited by the non-physical premise of traveling at the speed of light and the assumptions about massless observers. The implications of the constancy of the speed of light in all frames are also not fully explored due to the hypothetical nature of the scenario.

lolcopters
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Hi all,
I was trying to figure out the following:
Say I am standing right in front of a movie playing on a screen. Then, at time t0, I immediately am traveling at the speed of light away from this non-moving screen. Say I looked back while traveling away. Would I see an image (the frame the screen was showing at t0), or would I see a movie, because the speed of light is constant in all frames?

Also, to those who alter the question to "you can't travel at c, now say you were traveling at .99c...", then assume I'm massless, and have working massless eyes, and am traveling at c
 
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lolcopters said:
Also, to those who alter the question to "you can't travel at c, now say you were traveling at .99c...", then assume I'm massless, and have working massless eyes, and am traveling at c
You cannot get around physics by wishing and assuming that it worked differently. You either want an answer to a well defined question within the current working theory or you want a fairy tale.
 
Asking what would happen in circumstances that are not physically possible is a bit of a risk, but I'll have a go at it.
You propose traveling away from the screen at the same velocity as photons are traveling away from it.
Thus if you had any way to observe the photons (which you won't) you would see a still frame picture of what was on the screen at the time of your departure
 
This is an example of proof by contradiction (reductio ad absurdum).

Assumption: there is such a thing as a massless eye moving at ##c##.

Conclusion: As seen by the eye, the movie would be frozen and the movie would not be frozen.

The conclusion cannot be true; it contradicts itself. Therefore the assumption must be false.
 
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I guess what I was trying to get at was: would the result of it being a movie/picture be affected by the fact that the speed of light is constant in all frames? Say that there is no eye. There is just light from the screen traveling through space. From a reference frame moving at speed of light c away from the screen, is it a movie, because c is constant, or is it a picture, because the frame is traveling at the same speed as the light leaving the frame?
I know it's non-physical, but I asked this question because I want to better understand the implications that c is constant in all frames.
 
lolcopters said:
I know it's non-physical, but I asked this question because I want to better understand the implications that c is constant in all frames.
If you know it is non-physical, why do you ask the question in a physics forum? There is no reference frame moving at the speed of light! In fact, no reference frame can be said to have a particular velocity unless it is in relation to another reference frame.

With PAllen's post, I am going to close this thread as it is not going any further.
 

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