Question about photons traveling on same path

  • Context: Undergrad 
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Discussion Overview

The discussion revolves around the behavior of photons traveling along the same path, particularly in relation to their speed and the motion of their sources. Participants explore concepts from relativity, including the invariance of the speed of light and how it is perceived by different observers. The scope includes theoretical implications and conceptual clarifications regarding the nature of light and motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that if photons are traveling on the same path, they cannot pass each other because they all travel at the speed of light, c.
  • Others argue that the speed of light remains c relative to all observers, regardless of the motion of the sources emitting the light.
  • A participant questions how the speed of photons can be perceived differently by observers moving relative to the source, suggesting that the rate of change of separation between the source and emitted light could be perceived as c-v.
  • Another participant clarifies that the speed of light is always measured as c by any observer, regardless of their relative motion to the source.
  • Some participants discuss the implications of the Principle of Relativity, asserting that there is no difference in the behavior of light from moving or stationary sources.
  • There is a mention of the relativistic velocity addition formula, which indicates that the speed of light remains c even when considering the relative speeds of different observers.
  • One participant expresses confusion about how light can be perceived at c for all observers, prompting a reference to the Michelson-Morley experiment as an example of light's behavior in motion.

Areas of Agreement / Disagreement

Participants generally agree that the speed of light is invariant and remains c for all observers. However, there are competing views regarding how this invariance is perceived in relation to moving sources and the implications of relative motion, indicating that the discussion remains unresolved on certain nuances.

Contextual Notes

Some statements reflect assumptions about the nature of light and motion that may not be universally accepted, and there are unresolved questions regarding the interpretation of speed in different reference frames.

  • #31
PAllen said:
There are no implications, because we can't tell anything except if we assume isotropy (for clock synchronization and in all our laws of physics), we get the simplest equations. Personally, I take this as a definiiton of physically meaningful isotropy. If our universe was observably anisotropic, that would mean that assuming isotropy leads to excess complications. Note, isotropy of two way light speed is measurable, so if you assume anisotropy it has to be of a very special type.
I understand your last sentence.
Einstein was complaining about the math complexity for general relativity. perhaps math simplicity can be a false prophet? I don't use math much and I feel more at ease with anisotropy than isotropy with regard to light speeds, as it seems closer to a pre-SR way of seeing. what really puzzles me is time dilation, mass increase and length contraction and what makes them real. maybe I'll look into it some time.

Anyway, I don't have enough time for physics. Thanks for everyones help.
 

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