Cosmological Redshift: Where Has the Energy Gone?

In summary, as the Universe expands and the photons stretch to longer wavelengths, the energy of the photons is reduced and becomes negligible in the current state of the universe due to the lack of global energy conservation in general relativity.
  • #1
Glenn G
113
12
As the Universe expands and the photons stretch to longer wavelengths (say from UV photons to the CMBR now) where has the energy gone since longer wavelength photons have less energy?
Regards,
G.
 
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  • #2
It is gone.

There is no global energy conservation in general relativity.
 
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Likes Glenn G
  • #3
mfb said:
It is gone.

There is no global energy conservation in general relativity.

I'm surprised it's just gone mfb.
I was wondering if there's a type of gravitational potential it goes but for photons instead of matter.
I suppose then that in total that's quite a bit of energy that's gone if all photons get stretched this way.
G.
 
  • #4
Today the energy density of the radiation is negligible, but in the early universe it was relevant.
 

Related to Cosmological Redshift: Where Has the Energy Gone?

1. What is cosmological redshift?

Cosmological redshift is a phenomenon in which light from distant galaxies appears to be shifted towards the red end of the electromagnetic spectrum. This is due to the expansion of the universe, which stretches the wavelengths of the light as it travels through space.

2. How is energy affected by cosmological redshift?

The energy of light is directly proportional to its frequency, so as the wavelength of light is stretched by cosmological redshift, its frequency decreases and therefore its energy decreases as well. This means that the light from distant galaxies appears redder and less energetic than it would if there were no cosmological redshift.

3. Where does the energy go when light is redshifted?

The energy is not actually "lost" in the traditional sense. It is simply spread out over a larger distance as the universe expands. This is similar to how the energy from a spring is spread out over a larger distance as it is stretched.

4. How is cosmological redshift measured?

Cosmological redshift is measured using a unit called redshift z, which is calculated by comparing the observed wavelength of a distant object to its known rest wavelength. The higher the value of z, the greater the redshift and the farther away the object is from us.

5. What does cosmological redshift tell us about the universe?

Cosmological redshift is one of the key pieces of evidence for the expanding universe and the Big Bang theory. It also allows us to measure the distances and velocities of distant galaxies, which helps us understand the structure and evolution of the universe.

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