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Multiverse: The theories of multiple universes - Part 2
Before we proceed, let´s talk about Martin Bojowald of Pennsylvania State University. Physics World points that in a series of important papers, Bojowald has shown that one can study quantum states that are exact solutions of the full theory of quantum gravity and have the observed symmetries of our universe. In particular, Bojowald has discovered that there is never an initial singularity (i. e. a point where the curvature of space-time becomes infinite) and therefore no first moment to time, as Alex Vilenken and others have hypothesized. Nor is there any excursion into a domain in which the universe has a boundary in "imaginary time", as hypothesized by Jim Hartle, Stephen Hawking and others. Instead, the universe continues back before the moment classical cosmology predicts that it began, to a phase where it was previously expanding. This behavior has been called a "bounce"; it suggests that the Big Bang arose from an event in a previous universe (any previous universe?), either through the collapse of a black hole in that universe or from the collapse of the whole universe. This is all in conjunction with an approach to Quantum Mechanics called "The Many Worlds Interpretation". At every instant when a quantum measurement is made that has more than one possible outcome, the universe splits into two or more universes, each corresponding to a possible future. Everything that can happen at each juncture happens. Time is no longer linear. It is a rapidly branching tree: the number of separate universes increases at a prodigious rate. As de Witt wrote: "I still recall vividly the shock I experienced on first encountering the multiworld concept. The idea of 100^100+ slightly imperfect copies of oneself all splitting into further copies, which ultimately become unrecognizable, is not easy to reconcile with common sense. This is schizophrenia with a vengeance!" Bryce de Witt is talking about the theory that was first advanced by Hugh Everett III in 1956 in a Princeton doctoral thesis: what divides scientists nowadays is this: other worlds are physically real or just abstractions? Scientist David Deutsch belongs to the first team: "I may feel subjectively that I am distinguished among the copies as the ´tangible´ one, because I can directly perceive myself and not the others, but I must come to terms with the fact that all the others feel the same about themselves. Many of those Davids are at this moment writing these very words. Some are putting it better. Others have gone to a cup of tea". The Many Worlds Interpretation is different from the multiverse proposed by Andrei Linde, backed by Martin Rees. Says Martin Gardner: "Linde´s multiverse goes like this. Every now and then, whatever that means, a quantum fluctuation precipitates a Big Bang. A universe with its own space-time springs into existence randomly selected values for its constants. In most of these universes those values will not permit the formation of stars and life. They simply drift aimlessly down their rivers of time. However, in a very small set of universes the constants will be just right to allow creatures like you and me to evolve. We are here not because of any overhead intelligent planning, but simply because we happen by chance to be one of the universes properly tuned to allow life to get started". Ending this presentation, we now come to the multiverse
of David Lewis, from Princeton University. He maintains
that every logical possible universe - that is, one with
no logical contradictions such as square circles - is
somewhere out there. Says Gardner again: "The notion
of logical possible worlds, by the way, goes back to Leibniz´s
Theodicy. He speculated that God considered all logically
possible worlds, then created the one He deemed best for
His purposes". Gardner considers this one the wildest
of the three multiverse theories so far presented, and
states bluntly his judgement about all of them: "In
my opinion, they are all frivolous fantasies". Note: this article drew heavily on Martin Gardner´s article Notes of a Fringe-Watcher. |
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