The discussion revolves around estimating the number of Cosmic Microwave Background (CMB) photons in a volume of 0.25 liters. Participants explore theoretical approaches and mathematical relationships related to blackbody radiation and photon density.
Participants express varying levels of understanding and approaches to the problem, with no consensus on the method to derive the number of CMB photons. Confusion remains regarding the necessary steps and formulas.
Some participants highlight the need for specific assumptions regarding temperature and frequency, as well as the potential complexity of deriving the number density from first principles.
Frimus said:I recommend a textbook by Barbara Ryden https://www.amazon.com/dp/1107154839/?tag=pfamazon01-20. In section "2.5 Cosmic Microwave Background" she makes calculations you are asking about and comes to a conclusion that "...there are about 411 CMB photons per cubic centimeter of the universe at the present day."
Chalnoth said:This link might help:
https://en.m.wikipedia.org/wiki/Photon_gas
If you want to drive the result yourself, use E=hv for the energy of a photon of a given frequency to do the appropriate integral.
I'm not sure what level the question is being asked. The photon gas wiki page has the number of photons per volume as a function of temperature directly. You could just use that formula and get the answer straight away.rano jojo said:Thank you, but i how i can get the frequency and then how i can find the number of the photons? just i am confused
Use E=mc^2 n another relation in which uses T of this relation~rano jojo said:i know that the total energy density of a blackbody radiation is
E= 4 segma/C * T^4
so how i can use this to find the number of the CMB photons in 0.25 litre?