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Name: Sherryl
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Two years ago at the Aspen Physics Institute, Dr. Hawking gave a lecture on the end of the universe. It needs a certain amount of matter to contract; else it will expand. We see (or measure) 1% of the critical mass. We infer 10% more from relative motion of galaxies (Newton's laws). Then he says there may be enough matter. So where does he get this extra factor of 10 to jump from 10% to 100%? I have been wondering about this for 2 years; I think I must have missed something very important, but the numbers do not make sense to me.

He gets it from pure conjecture. Many physicists think that if they were creating the universe, then they would give it mass exactly equal to the critical value. The present universe may or may not accord with this prejudice. The matter is very much in doubt, because even the present rate of expansion of the universe is not very well measured yet. One of my colleagues is fond of pointing out that there are a number of dark matter "problems", and these vary according to the scale on which one views the universe. The point? There is a lot of esthetics that motivates physics (and astronomy).

J Lu

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