ajl1989
Apr6-09, 09:57 PM
1. The problem statement, all variables and given/known data
Estimate the rate of continuous creation required to keep the density of the universe constant at 10-29 g/cm3
Assume Hubble's constant Ho=70 km/s/Mpc
2. Relevant equations
I'm not sure if these are relevant, but for spherical shells: dV=4*(pi)*r2dr and N=4*(pi)*r2ndr, where N is the total number of particles in the shell and n is the density (#/unit volume)
Hubble's law: v=Hd or dr/dt=H*r
3. The attempt at a solution
So, given the mass of a proton, the density is approximately 6*109 protons/km3.
I also converted Hubble's constant to 2.2*109 km/year/Mpc.
I'm kind of stuck after that... I feel like there should be some easy way to figure out how much a volume changes per year, but that depends on how many Mpc away we are.
I feel like there's some simple equation that I'm missing...
Estimate the rate of continuous creation required to keep the density of the universe constant at 10-29 g/cm3
Assume Hubble's constant Ho=70 km/s/Mpc
2. Relevant equations
I'm not sure if these are relevant, but for spherical shells: dV=4*(pi)*r2dr and N=4*(pi)*r2ndr, where N is the total number of particles in the shell and n is the density (#/unit volume)
Hubble's law: v=Hd or dr/dt=H*r
3. The attempt at a solution
So, given the mass of a proton, the density is approximately 6*109 protons/km3.
I also converted Hubble's constant to 2.2*109 km/year/Mpc.
I'm kind of stuck after that... I feel like there should be some easy way to figure out how much a volume changes per year, but that depends on how many Mpc away we are.
I feel like there's some simple equation that I'm missing...