Why doesn't gravity slow the universe's expansion?

[Jack]

As far as I am aware scientists agree that the universe is flat, open or closed. However, if galaxies get further away from each other the gravitational attraction between them would decrease as the universe expands. Why is the universe speeding up not a real possibility?

 

[mathman]

Current theory says the expansion is speeding up. The explanation is not based on weakening gravity, but rather some other effect. Yhere are two theories, called (1)dark energy and (2)quintesscence. The firsts (possibly both) seems to be based on a non-zero cosmological constant in general relativity.

 

[DrChinese]

Originally posted by Jack
As far as I am aware scientists agree that the universe is flat, open or closed. However, if galaxies get further away from each other the gravitational attraction between them would decrease as the universe expands. Why is the universe speeding up not a real possibility?

When gravity decreases, it does not create acceleration of stellar bodies. So it does not speed expansion.

It is possible that an unknown force exists at the large scale of the universe that is causing acceleration of stellar bodies. This is within the range of current observational evidence.