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The Question
(Submitted September 02, 2001)
It has been said that because our universe creates its own "space and
time" it is expanding into pure nothing. Is there a possibility that this
"nothings"' main attribute is that of a perfect vacuum pulling the
universe apart like a balloon inside a bell jar when the air is removed?
The Answer
Interesting idea, which may help explain why the universe appears to be
expanding at an ever increasing rate. If I can extend your logic - an
infinitely dense point of matter appears in an otherwise perfect vacuum
state. An event of some sort causes that point to begin to expand very
rapidly, overcoming whatever initial gravitation pull would keep the point
of mass together. As the new universe continues to expand, there is less
and less gravitational pull to bring all of this mass back to its origin.
If the pulling force outward is constant and the gravitational pull
continues to decrease, the expansion rate will continue to increase. This
is a valid line of thought, however, let's say one inserts a puff of gas
into an evacuated bell jar. The gas will quickly expand, but the more
volume it fills, the slower the expansion rate (at least in terms of the
radius of the expansion; maybe the change in volume per unit time is
constant or increases?).
Apart from that potentially damaging argument, there is the issue of the
definition of "universe." Or universe, by one definition, is everything.
There is nothing beyond or outside of it, not even the empty space-time we
can conceive of as perfect space, so there would be no vacuum into which
the universe could expand. This may seem a bit of a paradox, as we can
always imagine something outside of our house or our solar system, but then
it really becomes a question of philosophy as much as science.
Thanks for the question, and keep reading and thinking,
Scott & Laura
for Ask an Astrophysicist
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