Measuring the Speed of Light from Distant Sources: How Do We Know It's Constant?

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Discussion Overview

The discussion revolves around the measurement of the speed of light from distant sources, particularly addressing the question of whether the speed of light remains constant regardless of the source's location. The scope includes theoretical considerations and experimental evidence related to this topic.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how the speed of light from sources outside the galaxy is measured and whether it is indeed constant.
  • Another participant asserts that the speed of light is constant, regardless of the distance of the light source, citing examples from nearby and distant sources.
  • A third participant acknowledges the initial question and mentions that various experiments have tested the constancy of the speed of light from different objects at great distances, indicating no measurable difference in 'c'.
  • References to recent experiments exploring this question are offered, with a request for further information.
  • A link to a resource discussing the speed of light from very distant objects is provided, with a personal endorsement of its validity.

Areas of Agreement / Disagreement

Participants express differing views on the initial question regarding the measurement of the speed of light from distant sources. While some assert its constancy, the discussion remains open to further exploration and evidence.

Contextual Notes

Some assumptions about the constancy of the speed of light and the methods of measurement are not fully explored, and the discussion references ongoing experiments without detailing their methodologies or results.

Prometheus
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Does anyone know how the speed of light from sources outside the galaxy is measured, such that we are able to recognize that even from these sources the speed of light is constant?
 
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Why would you think the speed of light would depend on the location of the light source? As far as we can tell, whether the light source is a flashlight sitting two feet away from you or the sun 93 million miles away, the speed of light is c.
 
Gza, you skipped past the question right into the assumption you thought was behind it [I am guilty of that all too often!] Prometheus: That proposition has been tested by examining light sources from different objects at great distances, using mirrors and interferometers, then comparing them to local sources. There is no measurable diffence in 'c'. A number of experiments, some very recent, have been performed to explore your very good question. I will give references if you like.
 
Chronos said:
A number of experiments, some very recent, have been performed to explore your very good question. I will give references if you like.
I would appreciate references.
 
http://www.student.oulu.fi/~ktikkane/c-const.html of speed of light from very distant objects. The proceedure looks valid to me.

Keep on chuggin !

Vern
 

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