- #1
fxdung
- 388
- 23
The temperature of expanding Universe is cooler and cooler.The most contribution of energy of background photons(CMB) are of photons having energy ~3kT.Then where have the high energy background photons gone?
Those are way too general questions if you want more than yes/no answers and also off-topic in this thread.fxdung said:What is Dark Matter(and Dark Energy? Does it contribute to Einstein equation or not?Is there any expansion in GR when we consider Dark Matter(and Dark Energy)?
Chronos said:I presume the next queistion is - given energy cannot be created or destroyed, where did it go?
No, this is not true in any way. It is not even clear what would be meant by such a statement in a curved space-time.nikkkom said:In some sense, for the observer who saw them emitted, they still have the same high energy they had when they were emitted - they are just very far away from that observer now.
They did if you consider the comoving frame, which is the one most commonly used. It is a frame dependent issue though. The total energy of the universe is not well defined.nikkkom said:The photons did not lose energy.
You seem to be thinking of Doppler shift. Although it is the same basic idea, you cannot view what happens in a general space time as a Doppler shift due to relative motion of the observer and source other than locally. Also, observations have nothing to do with your choice of coordinate system. Observables are invariants.nikkkom said:They have much lower energy in _our_ coordinate system. IOW: the redshift is an *apparent* loss of energy, caused by photons being observed in constantly changing choice of coordinate system.
High energy background photons are photons with high frequencies and short wavelengths, typically in the X-ray or gamma ray range. They are produced by various astrophysical sources such as black holes, supernovae, and active galactic nuclei.
High energy background photons can come from a variety of sources, including cosmic rays interacting with gas and dust in the interstellar medium, the decay of radioactive elements, and the acceleration of charged particles by magnetic fields in astrophysical objects.
High energy background photons are typically detected using specialized instruments such as X-ray telescopes or gamma ray detectors. These instruments are designed to detect and measure the energy and direction of incoming photons.
When high energy background photons are absorbed, they transfer their energy to the absorbing material, causing it to heat up or produce secondary particles. This process is known as photoelectric effect and is used in X-ray imaging and spectroscopy.
After being absorbed, high energy background photons can either be re-emitted at lower energies or their energy can be dissipated as heat. In some cases, they can also produce secondary particles through the photoelectric effect or pair production.