# Are we living in a black hole?

## Main Question or Discussion Point

If the universe is all there is then it can't be radiating light to anywhere else. Thus light must be trapped inside it like light is trapped inside a black hole.

If we carry this analogy further then maybe the size and mass of the universe is given by the expression for the Schwarzschild radius of a black hole:

2 * G * M / R = c^2

where M is the mass of the universe and R is the size of the universe.

If you put this expression into the Friedmann equations for the universe, together with the assumption of a flat spacetime, you find:

R = c * t

where R is the size of the universe and t is the age of the universe.

Also one finds a dark energy term such the the density (rho) of dark energy is given by:

rho = (1 / 8 pi G) * 1 / t^2.

This model gives the present density of dark energy rho_0 as

rho_0 = H_0^2 / 8 pi G

Putting in the present Hubble constant H_0 one finds a value of rho_0 which is a few proton masses per m^3.