posted on Aug, 18 2004 @ 12:25 AM
Originally posted by websurfer
If the universe is expanding, what would slow it down? Hawkings seems to predict a big crunch following the big bang but space is frictionless.
The big crunch
I'm looking at it like this: Throwing a stone in the air, speed decreases to zero(stops), and falls back down to ground.
The density of the universe determines its fate and its geometry.
If the density of the universe exceeds the critical density
, the geometry of the
universe is closed
, positively curved like a sphere. In that case, there is enough mass/gravity to overcome the expansion, and a big crunch
If the density of the universe is less than the critical density, the geometry of the universe is open
, negatively curved. In that case, there
is not enough mass to overcome the expansion, thus the universe expands forever.
If the densiity of the universe is equal to the critical density, the geometry of the universe is flat
, like a sheet of paper. In that case,
the universe will also expand forever, however the expansion will gradually slow down, but will not end.
According to the latest measurements of WMAP
(WILKINSON MICROWAVE ANISOTROPY PROBE), the
universe is flat. So no big crunch!
"The matter of which we are made is only a small portion of the Universe, 4%. 23% is an exotic type of material known as "cold dark matter". And
73% is an even more exotic "dark energy". One possibility for the dark energy was introduced by Albert Einstein, a so called "cosmological
constant...The geometry of the Universe is flat."
[edit on 18-8-2004 by jp1111]