Monday, May 12, 2003

So, How Many Universes Are There?

About 6 weeks ago I read "Calculating God", by Robert Sawyer. OK read, good concepts, OK writing, but had that "let's wrap it in the last 50 pages deus ex machina" finish that is not uncommon in science fiction. The plot is, aliens show up on earth wanting to do paleontological research because they want to understand why God schedules mass die-outs when he does. They are total theists because their physicists have determined that this is the only universe, and the Anthropic Cosmological Principle then implies that the there must have been intelligent design. (Borrowed from the link: The anthropic cosmological principle asserts that the laws, constants and basic structure of the universe are not completely arbitrary. Instead they are contrained by the requirement that they must allow for the existence of intelligent observers, ourselves.).

I am struck by the converse of this statement. Given that there is no intelligent design, then the anthropic cosmological principle implies that there must be many universes. How many? Oh boy, let's do the math.

If we go with the interpretation of quantum that every quantum event branches a new universe, we could guestimate: 10^80 particles in the universe x 10^10 years (age of universe) x 10^7 seconds/year x 10^22 (? if I remember right) planck times/second = 10^119, call it 10^120 -- a nice round number.

In 1973, P.A.M Dirac gave a talk at MIT. He was I think in his 80's and semi-retired at a university in Florida. He was one of the fathers of quantum physics, popularly credited as having been the predictor of antimatter (the positron). He mostly talked about his theories of large numbers. I think it was that the scale factor of the universe (from the smallest to the largest thing) was 10^40, and the number of elementary particles in the universe was 10^80, so the two must be related in some way. He kind of blew the attending crowd away -- a highly skeptical reaction. What fun, we have the product of his two numbers!

I think multiple universes is highly likely. The big bang as a quantum fluctuation of nothingness or superspace is I think the conventional wisdom. The latest Sky & Telescope has an article on new cosmologies, talking about parallel universes on membranes (branes). These could correspond to the 6 extra tiny dimensions of string threory. And the dark energy, which has seemed like a total kludge to me, is gravity from adjacent branes -- gravity is the only force that crosses branes, which is why it's so weak compared to the other forces (electomagnetic, weak, stong).

So, if there are multiple universes, and there are lots of them, maybe they're not that hard to make -- re Greg Bear "Eon" and lots of others.

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