Speed of light between a source and target moving wrt to each other

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Discussion Overview

The discussion revolves around the experimental evidence regarding the constancy of the speed of light (c) between a source and a target that are in relative motion. It explores theoretical implications, historical theories, and potential variations in the speed of light based on the source's velocity.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the amount of experimental evidence supporting the idea that the speed of light remains constant (c) between moving sources and targets.
  • Another participant asserts that there is no evidence for this claim.
  • A third participant references the Alvager experiment, which tested emission theory by measuring the speed of photons from decaying neutral pions, concluding that their speed was within 10-4 of c.
  • Further discussion raises the possibility that emission theory may be an over-generalization, suggesting that there could be other theories where the source's velocity affects the local speed of light without simply adding to c.
  • Some participants propose that if such effects are reciprocal at the target, they might cancel out, resulting in a perceived speed of light equal to c, indicating potential gaps in physics modeling.

Areas of Agreement / Disagreement

Participants express differing views on the evidence for the constancy of the speed of light and the implications of emission theory. The discussion remains unresolved with multiple competing perspectives presented.

Contextual Notes

Limitations include the lack of consensus on the interpretation of experimental results and the definitions of theories discussed, particularly regarding emission theory and its implications for the speed of light.

Passionflower
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How much experimental evidence is there that the speed of light stays c between a source and target moving wrt to each other?
 
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The idea that the speed of light might depend on the velocity of the source was known as emission theory. It was tested by the Alvager experiment, in which 6 GeV neutral pions were allowed to decay in flight: π0 → γ + γ. The photons were then timed over a flight path of about 30 m, and the result was that the velocity of the photons was within 10-4 of c.
 
Bill_K said:
The idea that the speed of light might depend on the velocity of the source was known as emission theory.

I'm wondering if that might be an over-generalization. Won't emission theory specifically be the case where the velocity of the emitting particle is added to the nominal propagation velocity?

Other theories might exist where the velocity of the source affects the local speed of light without necessarily adding linearly to the nominal propagation velocity c. If such effects are reciprocal in the sink then they may cancel leaving a perceived velocity c (which could indicate a deficiency for physics modeling the perceived effects in comparison to physics modeling the underlying effects).
 

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