Does expansion of spacetime also stretch amplitude of light waves?

AI Thread Summary
The expansion of spacetime stretches wavelengths, causing redshift, but does not affect the amplitude of light waves, which is unrelated to brightness. Brightness is determined by the intensity of light, which depends on the number of photons collected, not the amplitude. The intensity of an electromagnetic wave is proportional to the square of its amplitude, but this does not imply that amplitude stretching increases brightness. Telescopes enhance visibility by collecting more photons, allowing for clearer images. The discussion clarifies that while amplitude and intensity are related, the expansion of spacetime does not change amplitude or brightness.
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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