I'm looking at a question to a practice exam. It states the following.(adsbygoogle = window.adsbygoogle || []).push({});

Imagine the universe is a spherical cavity at a temperature of 3K. Using this assumption, estimate the total number of photons in the universe.

Notes: integral[0->infinity,{x^2dx/(e^x-1)*dx}=2.4

black body energy density:

u = h_/(pi^2*c^3)*w^3/(e^((h_w/(kT))-1)

I need to find out the number of photons per unit volume (N/V). Once I have that, I can find what I'm looking for.

Any ideas on how to solve this?

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# Homework Help: Total number of photons in universe

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