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Multiple Universes. What Do We Mean?. Scientific Speculation! Some of these ideas are unproven or controversial But they are taken seriously by at least some scientists What do we mean by multiple Universes?
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Multiple Universes What Do We Mean? • Scientific Speculation! • Some of these ideas are unproven or controversial • But they are taken seriously by at least some scientists • What do we mean by multiple Universes? • The Universe is the totality of existence that we are aware of or can be aware of us • If there are places that are real, but we can’t see them, they are other Universes
Reasons to Believe in Multiple Universes • Universe might be infinite or very large • In a big enough universe, anything can happen • Completely separate universes may appear spontaneously • If our universe came from nothing, why not others? • Many Worlds Interpretation of quantum mechanics • If correct, then everything happens
The Horizon • The Universe has, apparently, a finite age: 13.8 Gy • Nothing moves faster than light • Naively, nothing can affect us more than 13.8 Gly away • Because it was travelling in a smaller universe, it can actually go farther, about 45 Gly • The volume of space withing 45 Gly is our horizon • Sometimes called the visible universe • Effectively, it’s our universe 90 Gly
A Big Universe is Many Universes • Different parts of the Universe are cut off from each other • If the Universe is infinite, there are infinitely many Universes
Spontaneous Creation of the Universe • The universe we see could be created out of nothingness • Quantum Cosmology • The universe could be a bubble of order amidst a Universe of chaos • Chaotic Inflation • Not all bubbles need have thesame properties • Different physical laws • Different numbers ofdimensions?
Quantum Mechanics and Probability • In the everyday world, we think of probability as expressing our ignorance ? 5
Copenhagen Interpretation of Q. M. • Some processes are inherently quantum uncertain • All possibilities actually occur • Until a measurement occurs ? 5
Many Worlds Interpretation of Q. M. • All possibilities actually occur • Even after a measurement occurs • In many cases, the different possibilities become so disconnected, they effectively become separated universes ? • We are only cognizant of one 1 2 3 4 5 6
Do People Take This Seriously? • Many famous physicists, and a lot of obscure ones, believe in the Many Worlds Interpretation Murray Gell-Mann Steven Weinberg Stephen Hawking That One Richard Feynman