The existence of parallel universes may seem like something cooked up by science fiction writers, with little relevance to modern theoretical physics. But the idea that we live in a “multiverse” made up of an infinite number of parallel universes has long been considered a scientific possibility – although it is still a matter of vigorous debate among physicists. The race is now on to find a way to test the theory, including searching the sky for signs of collisions with other universes.
It is important to keep in mind that the multiverse view is not actually a theory, it is rather a consequence of our current understanding of theoretical physics. This distinction is crucial. We have not waved our hands and said: “Let there be a multiverse”. Instead the idea that the universe is perhaps one of infinitely many is derived from current theories like quantum mechanics and string theory.
The universes predicted by string theory and inflation live in the same physical space (unlike the many universes of quantum mechanics which live in a mathematical space), they can overlap or collide. Indeed, they inevitably must collide, leaving possible signatures in the cosmic sky which we can try to search for.
Whether we will ever be able to prove their existence is hard to predict. But given the massive implications of such a finding it should definitely be worth the search.
(Score: 2) by c0lo on Friday September 04 2015, @12:17AM
Or not... you'll never know until you hear them, but suddenly you won't understand then. Or maybe you'd understand them, but you may never hear them.
Alive or not, that cat be damn'd.
(Score: 2) by HiThere on Friday September 04 2015, @10:02PM
You're misunderstanding. *If* the "eternal inflation" model is correct, what it's saying is that the universe is so large that sections of it large enough to form a light cone must be identical. Identical, as in indistinguishable by any test, were it possible to make such tests. (There will, of course, also be extremely many more sections that are different.) And that's why it's called a multiworld theory. They exist in separated regions that originated with the same "big bang" that started off the part that we live in. The quantum indeterminacy multiworld (i.e. the Everett-Graham-Wheeler one) is the one that depends on the cat being dead or alive. And, neither of those is the m-brane multiworld theory which is what it sounds as if this is searching for evidence of.
(Score: 2) by c0lo on Monday September 07 2015, @01:04AM
And no, I didn't misunderstood.
First, what you say implies that the many universes would have the same number of (multidimensional) states - (e.g. necessary the same number of particles/energy); which isn't necessary true - see the Hilbert's Grand Hotel [wikipedia.org]
Second: this is a pure academic exercise (and, for the moment, so is string theory); in practical sense, there's nothing to be gained if a second identical universe exists: if these universes are identical, any attempt to contact them would look like a monologue in the mirror. If the symmetry is broken and you'd actually have a dialogue with your counterpart, they will cease to be identical and they'll diverge exponentially (or faster) - therefore my play on the Schroedinger’s cat, the very act of the contact will kill the "identity cat"