Cosmological Redshift: Where Has the Energy Gone?

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SUMMARY

The discussion centers on the concept of energy conservation in the context of cosmological redshift, specifically addressing the fate of energy as the Universe expands. It is established that there is no global energy conservation in general relativity, meaning that the energy associated with photons is effectively "gone" as they stretch to longer wavelengths, such as from ultraviolet (UV) to cosmic microwave background radiation (CMBR). Participants noted that while the energy density of radiation was significant in the early Universe, it has become negligible in the present day.

PREREQUISITES
  • Understanding of general relativity principles
  • Familiarity with cosmological redshift concepts
  • Knowledge of photon energy and wavelength relationships
  • Awareness of the cosmic microwave background radiation (CMBR)
NEXT STEPS
  • Research the implications of general relativity on energy conservation
  • Explore the physics of cosmological redshift in detail
  • Study the early Universe's energy density and its evolution
  • Investigate the properties and significance of cosmic microwave background radiation (CMBR)
USEFUL FOR

Astronomers, physicists, and students of cosmology who are interested in the implications of general relativity on energy conservation and the evolution of the Universe.

Glenn G
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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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It is gone.

There is no global energy conservation in general relativity.
 
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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.
 
Today the energy density of the radiation is negligible, but in the early universe it was relevant.
 

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