Does expansion of spacetime also stretch amplitude of light waves?

[SteveinLondon]

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?

 

[Drakkith]

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.

 

[bcrowell]

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.

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.

 

[SteveinLondon]

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?

 

[sardar]

The expansion of spacetime does not directly affect the amplitude of light waves. The stretching of wavelengths and the resulting red shift is due to the stretching of space itself, which causes the light to travel a longer distance and therefore appear to have a longer wavelength. This does not change the amplitude of the wave, which is a measure of its intensity or brightness. While distant stars may appear brighter due to the red shift, this is not because their amplitude has been stretched, but rather because their light has been spread out over a larger area. This does not necessarily make them appear closer, as the distance to these stars is still determined by their red shift and not their apparent brightness.