I recently asked myself the question "If all the stars in the universe condensed together to form a black hole how big would that black hole be?" Using the information from http://en.wikipedia.org/wiki/Observable_universe I got the approximate mass to be 3x10^52kg. After that it was just a matter of finding the Schwarzschild Radius. So... 2GM/c^2 = 2(6.67300x10^-11)(3x10^52)/8.98755x10^16 = 4.45482918x10^25m Is this right? I feel like this number is too large since the overall size of the observable universe is ~4.3x10^26. It seems strange that the radius of this black hole would take up this much space since the universe is mostly empty already. Am I not taking something in to account? Am I just doing the math wrong? Or am I right and that's just how the universe is?