### Multiple Universes

Here are a few questions:

a) Do multiple universes exist?

b) If they do how did they begin?

c) was there a single "big bang"?

d) how can we detect other universes?

a) Do multiple universes exist?

b) If they do how did they begin?

c) was there a single "big bang"?

d) how can we detect other universes?

## 1 Comments:

According to Max Tegmark, the existence of other universes are a direct implication of cosmological observations. In an article entitled "Parallel Universes" in the May 2003 issue of Scientific American, he presents a clear and comprehensive picture of the idea of parallel universes. Tegmark describes the set of related concepts which share the notion that there are universes beyond the familiar observable one. He goes on to provide a taxonomy of parallel universes organized by levels.

Level I: (Open multiverse) A generic prediction of cosmic inflation is an infinite ergodic universe, which contains Hubble volumes realizing all initial conditions - including an identical copy of you about meters away.

Level II: (Andre Linde's bubble theory) In chaotic inflation, other thermalized regions may have different effective physical constants, dimensionality and particle content. Surprisingly this level includes Wheeler's oscillating universe theory as well.

Level III: (Hugh Everett III's many-worlds interpretation) An interpretation of quantum mechanics that proposes the existence of multiple universes, all of which are identical, but exist in possibly different states. It is widely believed that Everett's interpretation considered as a formal theory is a conservative extension of standard quantum mechanics, that is, as far as results expressible in the language of ordinary quantum mechanics is concerned, it leads to no new results. According to Tegmark "This is ironic given that this level has historically been the most controversial".

Level IV: (The ultimate "Ensemble theory" of Tegmark) Other mathematical structures give different fundamental equations of physics. M-theory would be placed here. Since this subsumes all other ensembles, it therefore brings closure to the hierarchy of multiverses: there cannot be a Level V.

For more details refer:

http://en.wikipedia.org/wiki/Multiverse

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