Why Does Light Lose Energy with Universe Expansion?

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Discussion Overview

The discussion centers around the phenomenon of light losing energy as the universe expands, exploring the physical reasons behind this observation. Participants delve into the implications of cosmological expansion on light waves, including concepts related to wavelength and energy. The scope includes theoretical explanations and conceptual clarifications.

Discussion Character

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

Main Points Raised

  • Some participants propose that the expansion of the universe stretches light waves, resulting in longer wavelengths that correspond to lower energy.
  • Others challenge this explanation, questioning the validity of equating wavelength expansion with the universe's expansion, noting that wavelength is defined as distance per cycle and does not follow Lorentz length contraction.
  • It is mentioned that cosmological expansion can be described in terms of both kinematic Doppler shifts and as a result of the expansion of space, suggesting multiple perspectives on the phenomenon.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between wavelength expansion and the universe's expansion, indicating that the discussion remains unresolved with competing interpretations present.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about wavelength and its relationship to cosmological expansion, as well as the implications of different interpretations of Doppler shifts.

sancharsharma
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Can anyone please explain the physical reason of why is light losing energy as universe is expanding?
 
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Can you give a reference to that statement?
 
sancharsharma said:
Can anyone please explain the physical reason of why is light losing energy as universe is expanding?
A simple way to look at is that the expansion is stretching the light waves. Longer wavelength is equivalent to lower energy.
 
@mathman,
But the wavelength of light is not merely a distance between two points. As a support it doesn't follow lorentz length contraction. It is distance per cycle.
So are you sure that it is a valid argument to say that wavelength expands as universe expands?
 
sancharsharma said:
@mathman,
But the wavelength of light is not merely a distance between two points. As a support it doesn't follow lorentz length contraction. It is distance per cycle.

Cosmological expansion isn't the same thing as Lorentz contraction.

sancharsharma said:
So are you sure that it is a valid argument to say that wavelength expands as universe expands?

It is valid to describe cosmological Doppler shifts verbally as kinematic Doppler shifts, and it is also valid to describe them verbally as being due to the expansion of space. These are just two different ways of talking about the mathematics of general relativity.
 

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