# Many-Worlds Theory

1. ### Emanresu56

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?

2. ### Fredrik

10,536
Staff Emeritus
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).

3. ### DaveC426913

16,371
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).

4. ### Emanresu56

13
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. :)

Last edited: Feb 10, 2009
5. ### DaveC426913

16,371
This isn't a sentence; it is missing a verb. I don't understand what you are asking. Can you rephrase?

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.

6. ### Emanresu56

13
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.

7. ### Tac-Tics

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.

18,041
Staff Emeritus
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.

9. ### The Dagda

266
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.

10. ### ThomasT

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.

11. ### Cyrus

I believe in Many-Worlds Theory because I am the center of all of them!

12. ### Dmitry67

I am happy that more and more people abandon Copenhagen I. and accept MWI

13. ### math_04

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.

14. ### Phrak

What is the principle of MWT?

15. ### The Dagda

266
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

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. :tongue2:

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.

Last edited: Feb 12, 2009

17. ### The Dagda

266
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.

18. ### Dmitry67

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!

19. ### Dmitry67

MWI is very logical.

1. We take QM in its purest form, without all weird and magic 'observers', 'measurements', 'our knowledge' etc.
2. We make an experiment with a Schodienger cat, and based on the calculations there are 2 cats, dead and alive!
3. But we make another calculations (described in the Quantum decoherence article) and we find out these these 2 cats do not interact with each other, and it explains why we see only one of them
4. However, we need to conclude that the symmetry is preserved, and all other outcomes do exist.

Very often people try to eliminate MWI using Occams razor. But it is a logical mistake: you percieve only one world, so you think that MWI suggests something EXTRA: another worlds. Then you try to cut these extra worlds using Occams razor or falifiability blah blah blah.

But in fact, it is CI (and other interpretations) which adds something extra: it adds a symmetry-breaking mechanism (called 'randomness') to explain why some cats are real and why some are not.

Imagine that we talk about an infinite flat space. The claim that it is infiniteis simpler then a claim that 'it ends somewhere'. because if it ends somewhere then there is a strange object called 'end of space', it has shape etc. So the claim 'all outcome exist' is simpler, then 'only one outcome exists'

20. ### The Dagda

266
What does visiting an inferred phenomena we really know nothing directly about have to do with the interpretation of QM? You seem to be avoiding the issues, they are laid out in a previous post.

Occam's razor in this case makes the two the same, which means MWI gets eliminated by the laws of theory.

A theory must distinguish itself from any preceding theory. If its just to all observable purposes just the same as CI then it is CI with extra philosophical nugat to make philosophers all hot.

There aren't two cats in this case there is every probable decay in a radioactive isotope, which may lead to the cat being dead or alive.

You can't appeal to randomness as a deal breaker just because you don't like the implications, this is physics not philosophy, if you want to make a claim it has to be experimentally verifiable or distinguishable, or it is just arm waving away things you personally think should be wrong in your own particular world. If we can do that then we might as well just become String Theorists and abandon experiment altogether.

Last edited: Feb 12, 2009