Not being very mathematically inclined, I'm stumped with this one. Can anyone help?(adsbygoogle = window.adsbygoogle || []).push({});

Imagine a toy “closed” universe in the form of a very large box (say the size of our universe) with perfectly rigid and reflecting walls. The box is static in size (neither expanding nor contracting) and is uniformly filled with electromagnetic radiation, with an average energy density Rho, and nothing else.

The electromagnetic radiation will exert mutual gravitational attraction (vie E=mc^2).

At low values of Rho, we would expect to see no gravitational clumping of this radiation, in other words the toy universe would be stable with a uniform distribution of radiation.

Q1) What value of Rho is required before we observe gravitational clumping of the radiation (if at all)?

Q2) What value of Rho is required before we observe black holes forming?

Q3) If it is possible to spontaneously form black holes at high values of Rho, what would be the equilibrium mix of black holes vs background radiation as a function of Rho (taking into account the fact that black holes emit Hawking radiation)?

Best Regards

MF

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Radiation Universe

**Physics Forums | Science Articles, Homework Help, Discussion**