It is possible that multiple parallel universes can co-exist, but they must be linked in a very tight fashion, because the existing laws constrain things pretty tightly. In particular, the basic laws of the universe are _reversible_ -- i.e., information-conserving -- so any interaction with a parallel universe must interchange the same number of bits in both universes. E.g., when a quantum state is "measured" in one universe, other universes measure the same state, but the result of the measurement will be different. Quantum states that are entangled in one universe will necessarily be entangled in the other universe, and so on. This is the essence of the Everett-Wheeler model. At 06:01 AM 4/18/03 -0400, Ken Roberts wrote:

...

From: Helger Lipmaa <helger@saturn.tcs.hut.fi> Subject: [math-fun] Parallel Universes

http://www.sciam.com/article.cfm?articleID=000F1EDD-B48A-1E90-8EA5809EC58800...

"In infinite space, even the most unlikely events must take place somewhere."

A nice article but that "infinite" word jars a bit. I wish the Cantor diagonalization process had been discussed. I suppose it is considered in with-math version of the article, but that article is so long that it could not be fit within the 2^N size of an issue of SciAm or the 2^M size of a reader's mind.