## Wednesday, June 3, 2015

### cosmology and chemistry

can you estimate how many stars there are in the observable universe and give your answer in units of Avogadro's number?

2. thanks a lot for your reply, Phillip! my estimate would be very similar, by computing the mass in the Hubble volume $M=4\pi/3\rho_\mathrm{crit}\chi_H^3$ with the Hubble length $\chi_H$. that's roughy $10^{52}~$kg, resulting in $10^{22}$ stars of the mass of the Sun, which is $10^{30}~$kg. concerning your question: if I didn't make a mistake, the ball should be as large as the Sun, which would be surprising!