Speed of light relative to universe expansion?

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Discussion Overview

The discussion centers around the relationship between the speed of light and the expansion of the universe. Participants explore whether the speed of light is affected by universal expansion, the implications of such a relationship, and the nature of measurements of light speed in various contexts.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that the speed of light could be relative to the expansion of the universe, suggesting it might act as a barrier to escaping the universe.
  • Others argue that the speed of light is a constant 'c', independent of the universe's size or expansion, and that it remains fixed regardless of the observer's motion.
  • A participant mentions that the speed of light is measured as 'c' only over short distances using local clocks and rulers, with discrepancies in cosmological contexts attributed to space-time curvature.
  • Concerns are raised about whether the motion of the Earth and other celestial bodies affects measurements of light speed, with some suggesting that our rulers and clocks might be changing alongside the universe.
  • There is mention of a theory proposing a variable speed of light, but it is noted that this view is not widely accepted in the cosmology community and lacks strong evidence.
  • One participant discusses the Hubble sphere and the cosmological principle, suggesting that any observer perceives themselves at the center of expansion, which could imply a relationship between local light speed and global universe properties.
  • Another participant explains that while gravitational fields have minimal effects on light speed measurements, the speed of light remains constant when measured over short distances.

Areas of Agreement / Disagreement

Participants express differing views on whether the speed of light is influenced by the expansion of the universe. While some assert that it remains constant, others raise questions about the implications of universal expansion on measurements of light speed. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants highlight the importance of defining standards of distance and time when measuring the speed of light. There are unresolved questions regarding the effects of cosmic motion and gravitational fields on these measurements.

  • #31
pervect said:
Do you have a reference that calls this the sagnac effect? I have some doubts that the term is being used properly - it seems to me that you are talking about simple doppler shift and calling it the "sagnac effect". AFAIK the sagnac effect only occurs in rotating systems. As I said, if you have a reference for this I'd like to see it.

pervect - I am citing these not for content, but for nomenclature

http://arxiv.org/ftp/physics/papers/0609/0609202.pdf

Http://www.geocities.com/mail0110261847/npa/npa2007y.pdf

I will recheck that last link - may not be correct
 
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  • #32
pervect - The link seems to work - take a look at page 8 for how this guy views the Sagnac phase shift as actually a translational affect.

I don't have a reference for the rectangle with the source/receiver moving with uniform velocity v along one leg - but by analogy with the rotation of the entire frame about some center point of the mirror system, the same phase shift should occur for v = wr and v = dx/dt so long as v is measured relative to the at rest lab frame. If you need more on the one way Sagnac - you might google one way Sagnac effect in GPS
 
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