Dark Matter and Expanding Universe

Most recent answer: 09/23/2014

Q:
How is the universe moving apart if the universe is 95% dark matter? All matter has mass even dark matter. Matter creates gravity so; dark matter has the most gravity of all. The universe should be pulling together because the gravity of dark matter.
- Randy (age 40)
Knoxville TN USA
A:

You are right, Randy, that dark matter has mass and it attracts other masses both regular and dark through the gravitational interaction.  In fact dark matter was "discovered" due its effect on the shape and rotational properties of galaxies.  I say "discovered" in the sense that we have never really "seen" a dark matter particle in spite of many ongoing experiments.   What would really convince us that it actually exists would be if some of the dark matter particles would interact in one of the detectors in various laboratories, usually deep underground in order to shield against ordinary cosmic rays.  If you Google "Dark matter searches" you will find a raft of information about ongoing searchs.     Also there is a nice Wikipedia article on the "discovery" of dark matter by astronomers by observing anomalous rotation curves of many galaxies. 

That said, back to your original problem "Why is the Universe expanding?"   The answer is we don't know.  We do know, however, that an expanding universe is consistant with the Theory of General Relativity and is one of many possible solutions.    Why this particular one?   I wish I knew.

 

LeeH

 

 

 

 


(published on 09/23/2014)