Does expansion of spacetime also stretch amplitude of light waves?

In summary, the expansion of spacetime can cause a red shift in wavelengths, but it does not affect the amplitude of the wave. The intensity of a light source is dependent on the number of photons collected, not the amplitude of the wave. Additionally, the wave-particle duality does not change the fact that the energy density is proportional to the square of the amplitude.
  • #1
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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  • #2
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.
 
  • #3
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.
 
  • #4
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?
 
  • #5


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.
 

FAQ: Does expansion of spacetime also stretch amplitude of light waves?

What is spacetime expansion?

Spacetime expansion is a concept in physics that describes the continuous increase in the size of the universe over time. It is believed to have started with the Big Bang and is still ongoing.

How does spacetime expansion affect light waves?

Spacetime expansion does not directly affect light waves. However, it can alter the wavelength and frequency of light waves as they travel through expanding space.

Does spacetime expansion stretch the amplitude of light waves?

No, spacetime expansion does not stretch the amplitude of light waves. The amplitude of a light wave is determined by the energy of the photons, which is not affected by the expansion of spacetime.

Can the expansion of spacetime be observed in light waves?

Yes, the expansion of spacetime can be indirectly observed in light waves. This is known as the redshift effect, where the wavelength of light is stretched due to the expansion of space, resulting in a shift towards the red end of the electromagnetic spectrum.

Is there a limit to how much spacetime can expand?

There is currently no known limit to how much spacetime can expand. It is believed that the expansion of the universe will continue indefinitely, but the rate of expansion may change over time.

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