# Many-Worlds Theory

by Emanresu56
Tags: manyworlds, theory
 P: 13 I'm not a huge fan of many-worlds theory, but I do think that multiple Universes can exist. My only problem is that if there's an infinite number of Universes, why hasn't a Universe collided with our own yet? Are there other Universes somehow keeping that Universe from colliding with ours? And does it go on like that ad infinitum?
 Emeritus Sci Advisor PF Gold P: 9,403 The "worlds" in the MWI aren't flying around like the molecules of the air. They don't occupy locations in some kind of space, and it isn't possible to make sense of such ideas as the ones you have in mind ("a world's position in space", "the distance between two worlds", etc).
 P: 15,319 As Fredrik points out, the universes in WMI aren't out there, they're right here - overlapping. They just don't interact with us (because of some as-yet unexplained reason).
P: 13
Many-Worlds Theory

 Quote by DaveC426913 As Fredrik points out, the universes in WMI aren't out there, they're right here - overlapping. They just don't interact with us (because of some as-yet unexplained reason).
Regardless of the infinite possibilities in an infinite multiverse where the "overlapping" doesn't matter? Sorry if I seem hostile, I just have this nagging intuition that Many-Worlds does not work. :)
P: 15,319
 Quote by Emanresu56 Regardless of the infinite possibilities in an infinite multiverse where the "overlapping" doesn't matter?
This isn't a sentence; it is missing a verb. I don't understand what you are asking. Can you rephrase?

 Quote by Emanresu56 I just have this nagging intuition that Many-Worlds does not work. :)
Intuition and its brother "common sense" are as useful as teats on a snake when it comes to the mathematical nature of the universe. Don't use them.
P: 13
 Quote by DaveC426913 This isn't a sentence; it is missing a verb. I don't understand what you are asking. Can you rephrase?
Basically, I've been having this nagging idea that an infinite multiverse leads to an infinite regress - and, while there might not be any problems with an infinite regress existing, there's still the feeling that Many-Worlds is simply a cop-out. I use "feeling" in the intuitive sense, not the personal sense.
 P: 810 What would it even mean for a universe to "collide" with another? What would it matter if there were infinitely many universes versus a finite number? From what I've seen, MWI is just a complicated way physicists use to explain how randomness appears. That instead of requiring a "choice" to ever be made, the universe simply permutes through all possible choices.
Mentor
P: 16,356
 Quote by DaveC426913 As Fredrik points out, the universes in WMI aren't out there, they're right here - overlapping.
Sidney Coleman used to say "In Many-Worlds, there are not many worlds. There is only one world." His point was that in MWI, the wave function does not collapse, but in all measurements it appears as if it does.

It may also be worth pointing out that MWI is an interpretation, not a theory. It makes exactly the same predictions as Copenhagen: there is no test possible, even in theory, that distinguishes them.
P: 266
 Quote by Emanresu56 Basically, I've been having this nagging idea that an infinite multiverse leads to an infinite regress - and, while there might not be any problems with an infinite regress existing, there's still the feeling that Many-Worlds is simply a cop-out. I use "feeling" in the intuitive sense, not the personal sense.
Cop outs are all the rage atm, it reflects some rather annoying limitations in physics, mind you cop out $\neq$ worthless.

Me I object to MWI on the basic principle I object to anything in science, and that is the show me the money factor. It's arbitrary and no one gets out of it for long.

Intuition isn't useless in physics, physics just doesn't care what you think should happen or should be, only what does in fact happen and is and that is a fish that is hard to catch.
P: 1,414
 Quote by Emanresu56 Basically, I've been having this nagging idea that an infinite multiverse leads to an infinite regress - and, while there might not be any problems with an infinite regress existing, there's still the feeling that Many-Worlds is simply a cop-out. I use "feeling" in the intuitive sense, not the personal sense.
There are intuitive as well as mathematical physics bases for multiverse. And, it seems that there's always going to be room for something beyond any description that mankind will be able to produce.
 P: 4,777 I believe in Many-Worlds Theory because I am the center of all of them!
 P: 2,456 I am happy that more and more people abandon Copenhagen I. and accept MWI
 P: 104 The Copenhagen interpretation is also flawed because it treats the observer as an outside 'God' when in fact, we the observers should also be treated within the same quantum mechanical framework.
 P: 4,512 What is the principle of MWT?
P: 266
 Quote by Phrak What is the principle of MWT?
The wave function resolves itself in every possible form in other realities/worlds, the measurement is discernibly identical to CI, thus it's indistinguishible from CI, and probably always will be, which has lead some people to cry *cough cop out*. This theory is deterministic.

http://en.wikipedia.org/wiki/Many-worlds_interpretation

 * There is circularity in Everett's measurement theory. Under the assumptions made by Everett, there are no 'good observations' as defined by him, and since his analysis of the observational process depends on the latter, it is void of any meaning. The concept of a 'good observation' is the projection postulate in disguise and Everett's analysis simply derives this postulate by having assumed it, without any discussion.[23] Talk of probability in Everett presumes the existence of a preferred basis to identify measurement outcomes for the probabilities to range over. But the existence of a preferred basis can only be established by the process of decoherence, which is itself probabilistic.[24] MWI response: Everett's treatment of observations / measurements covers both idealised good measurements and the more general bad or approximate cases.[25] Thus it is legitimate to analyse probability in terms of measurement; no circularity is present.
What I might call the magic bullet that kills it and others might hand wave away. Even the answer here does not rid us of a priori assumptions that cannot ever be verified, and in fact it's high order hand waving/philosophy in its purest sense. Which leads a lot of people to say, so what's the point? There are 1001 possible alternatives to CI already, why do we have to invent ones that can potentially never be verified; my answer is to ask the String Theorists, they've been getting away with it for years quite successfully.

Undeniably MWI is interesting but is it anything like what really happens or just more wishful thinking to explain away our doubts?

By the way this isn't exactly my position but it certainly has a good point.
 P: 2,456 I dont know what is a concept of 'good observations' [25], 1956 (!!!!!!!!!) But now all problems are solved: http://en.wikipedia.org/wiki/Quantum_decoherence
P: 266
 Quote by Dmitry67 I dont know what is a concept of 'good observations' [25], 1956 (!!!!!!!!!) But now all problems are solved: http://en.wikipedia.org/wiki/Quantum_decoherence
They are? How exactly? Have you visited these many worlds to in act verify the results of their experiments? Good observation just means being able to measure something you haven't just assumed before you started the experiment. In that sense MWI is axiomatic.
P: 2,456
 Quote by The Dagda 1. They are? How exactly? 2. Have you visited these many worlds to in act verify the results of their experiments? Good observation just means being able to measure something you haven't just assumed before you started the experiment. In that sense MWI is axiomatic.
1. Name the problems first :)
2. Have you even visited the interior of the black holes to speculate about the Schwarzschild/Kerr solution? You just believe that if GR works outside there are no reasons to believe that it does not work inside!

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