What does it mean to say that the universe is expanding?
Is the space around us expanding?
The space immediately surrounding us is not expanding
because the gravitational effects of nearby bodies such as the Earth, Sun,
and our entire galaxy have halted the local expansion of space. However
our galactic cluster is expanding and it is also moving away from other galaxies.
How can the expansion have no center?
The universe is expanding from no central point because the universe
has no center. It is analogous to the two dimensional surface of a
balloon (see video below). As it is blown up every point on it's surface
moves away from every other point at a speed proportional to their distance
apart, however the expansion of the balloon has no center contained within
its two dimensional surface (Kolb). Another analogy is
that of a loaf of bread with raisins in it. As the bread rises all
the raisins get further from each other by an amount proportional to their
distance from each other.
Balloon Demo Video
(must have Quicktime to play .mov file)
Video from:
UMN Physics Demos
External Links:
www.anzwers.org/free/universe/ bigbang.html
Background from:
http://www.chemsoc.org/timeline/pages/1997_exu.html
