Friday
November 28, 2014

Homework Help: Physics help

Posted by SOmebody on Thursday, May 23, 2013 at 11:26pm.

The galaxies in the universe are all flying away from each other. The speeds of nearby galaxies are proportional to the distance the galaxy is away from us. This relation, v=Hd is known as Hubble's law and the constant H is known as Hubble's constant. The evolution of our universe is determined by general relativity and the amount of matter, dark matter, and dark energy in our universe. If we ignore dark energy (pretend there is none) one can determine the "critical density" of the universe. If the universe is more dense than the critical density of the universe, the universe will eventually crash back together, whereas if the density is less than the critical density, the universe will fly apart forever. This was a big question up until the discovery of dark energy.

Interestingly enough, one can determine the critical density through Newtonian physics. Consider a galaxy a distance d away from us, moving radially away with a velocity given by Hubble's law. If the galaxy is not to escape to infinity, what is the critical density in # atoms of hydrogen per cubic meter?

Note: enter your answer to the nearest hundredth.

Details and assumptions
The Hubble constant is 68 km/s/Megaparsec.
Assume that all the matter is uniformly distributed throughout space.
Newton's gravitational constant is 6.6710−11 Nm2/kg2.

Answer this Question

First Name:
School Subject:
Answer:

Related Questions

physics - The galaxies in the universe are all flying away from each other. The ...
Science - The galaxies in the universe are all flying away from each other. The ...
Science-Repost-Universe&Stars - What does it mean by the Local Group of galaxies...
astronomy - Imagine that you live in a distant galaxy far far away. This galaxy ...
unsolved mysteries astrophysics - Q3.2 COLLAPSE TIMESCALE (5 points possible) ...
Science need help ?????/// - An astronomer observes two galaxies, A and B, which...
Astronomy - help! - Imagine that you have obtained spectra for several galaxies ...
Astrophysics - The Earth formed at a redshift of z∼0.53. That means that ...
Astronomy - The apparent brightness of a Cepheid variable star in a far-away ...
Cosmology - What observations were used by Edwin Hubble to show that the ...

Search
Members