How much of the universe's energy is tied up as photons?

Question

Is this even a valid question? If a star emits some photons, it has effectively transferred some of it's energy into light right? Now, this energy may spend eons tied up in a photon so as long as it does not hit anything. Does this happen? If so, does this represent a significant ammount of energy?

Answer 1

From John Baez's website:

"We can measure the energy density of the vacuum through astronomical observations that determine the curvature of spacetime. All the measurements that have been done agree that the energy density is VERY CLOSE TO ZERO. In terms of mass density, its absolute value is less than 10-26 kilograms per cubic meter. In terms of energy density, this is about 10-9 joules per cubic meter."

Since we are talking about the energy density of space itself, you can surmize that this density is due to photons, e.g. that space is essentially a photon sea.