Does expansion of spacetime also stretch amplitude of light waves?

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Discussion Overview

The discussion revolves around the effects of spacetime expansion on light waves, specifically questioning whether the amplitude of light waves is also stretched alongside their wavelengths, and if this would affect the brightness of distant stars.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant suggests that the expansion of spacetime stretches wavelengths and produces redshift, questioning if it also stretches amplitude and makes distant stars appear brighter.
  • Another participant argues that amplitude does not relate to brightness in electromagnetic (EM) waves, stating that intensity depends on the number of photons collected, which is why telescopes are effective.
  • A further reply emphasizes that the intensity of an EM wave is proportional to the square of the amplitude, suggesting a misunderstanding of wave-particle duality in the original question.
  • A participant expresses confusion about the protocol of posting and reiterates the question of whether amplitude gets stretched and if that affects intensity.

Areas of Agreement / Disagreement

Participants do not reach consensus; there are competing views regarding the relationship between amplitude, intensity, and the effects of spacetime expansion on light waves.

Contextual Notes

There is a lack of clarity on how amplitude and intensity are defined in the context of spacetime expansion, and the discussion includes assumptions about wave-particle duality that remain unresolved.

SteveinLondon
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Expansion of spacetime stretches wavelengths and produces the red shift. Does it also stretch the amplitude of the wave, and make distant stars look brighter and therefor nearer?
 
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Amplitude has nothing to do with brightness in an EM wave. Intensity of a light source is dependent on how many photons you are able to collect. This is why telescopes use large mirrors that are able to collect many many times the amount of light than your eye. They then focus this down to a small area, resulting in a visible image.
 
SteveinLondon, you've posted this in two different places: here and https://www.physicsforums.com/showthread.php?t=484699 Please don't do that. It's inconsiderate. I've replied in the other thread.

Drakkith said:
Amplitude has nothing to do with brightness in an EM wave. Intensity of a light source is dependent on how many photons you are able to collect.

The intensity of an EM wave is proportional to the square of the amplitude. I think you're getting confused here by wave-particle duality. The wave stuff doesn't stop being true just because it's also a particle. If you consider a single photon, it has electric and magnetic fields, and the energy density is proportional to their squares.
 
Sorry about the double posting. It's the first time I've posted so not familiar with the protocol.
Does the amplitude get stretched? And therefor the intensity?
 

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