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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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