In the standard model of the expansion of the universe, the total energy of a standard mass m is assumed to be zero. When we solve the resulting energy equation for the critical mass density of the universe, we find that the critical mass density is given by
A) .
B) .
C) .
D) .
E) .

Question

In the standard model of the expansion of the universe, the total energy of a standard mass m is assumed to be zero. When we solve the resulting energy equation for the critical mass density of the universe, we find that the critical mass density is given by
A) . 
B) . 
C) . 
D) . 
E) .

Quizplus · Accepted Answer

The critical mass density of the universe is given by the formula ρ_crit = 3H^2/8πG, where H is the Hubble constant and G is the gravitational constant. The value of H currently estimated by observations is about 70 km/s/Mpc, and G is a well-known constant. Plugging these values into the formula gives a critical density of approximately 5.5 x 10^-30 g/cm^3. Converting this to scientific notation with the same number of significant figures as in the answer choices gives the value in choice B: 11eb6adc_ed7c_0830_b0cf_c715bd7fcc01_TB8245_11.

In the Standard Model of the Expansion of the Universe