Question:
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.
Replies:
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).
NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.
