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Problems with Many Worlds Interpretation 
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#1
Aug1911, 08:46 AM

P: 19

Hello,
While the majority of physicists embrace the Many Worlds interpretation of quantum decoherence, I am holding out hope for the Copenhagen interpretation or better yet, a undiscovered interpretation. Please allow me to pose three problems I have with the MW interpretation. 1) There is a nonzero prob of me spontaneously becoming a miniature sun. Let me elaborate. Since I am made of atoms, there is a nonzero prob that all of the subatomic particles comprising each of the nuclei of my atoms are all one kilometer away except for a single proton and single electron in each atom. I.e. I am now spontaneously comprised of only hydrogen atoms. Now let's say that since even the exact position of these hydrogen atoms is uncertain they are close enough that gravity overpowers all and nuclear fusion takes place. I.e. I have become a miniature sun. The probability of this happening is obviously miniscule, but nonzero. With the CI interpretation this will never happen because the probability is so small that the universe is not old enough for such a low probability to have been realized. However with MWi since the probability is nonzero, it has happened. Moreover it has been happening every second of every day since the minute I was born in some parallel universe. 2) My second problem with MW intepretation is how can an interference pattern result in a double slit experiment if the particle is actually traveling through a different slit in separate universes. Shouldn't the interference only occur if the particle is travelling through both slits simultaneously in the same universe? 3) My third problem with MW is that it really does away with the concept of probability although many quantum experiments have shown that the concept does exist. For example, take a weighted coin which is 99% more likely to flip heads, than tails. CI predicts that a 100 flips would yield 99 heads and 1 tail. With a single flip, one is much more likely to get a head than a tail. However with MW, one flip will result in head in one universe, tail in another so therefore 5050 probability. Can someone help me to understand these issues any better? Thanks! 


#2
Aug1911, 09:06 AM

P: 882

1) Philosophically : I agree with you. Physically  you should take better example, as scattering away your nuclei would require lots of energy, which had to be provided somehow, hard to make it "realistic" even in Many Words.
2) simple ;) if you consider a pattern of 1000 particles made with a resolution of 0.1mm on 10 cm wide screen, you must consider [itex]100^{1000}[/itex] worlds, of which vast majority exhibit patters. 3) That's a clou of Everett's idea. To replace (Bayesian) probability in one World with a number of possible worlds, and your consciouness present in just one of them. Is that convincing? Up to your metaphysical taste. Not for me... (don't try quantum suicide experiment, unless you truly believe MWI!!!) EDIT>>> I recommend Max Tegmark's "MANY WORLDS OR MANY WORDS?", (as a book chapter, "Fundamental Problems in Quantum Theory", 1997), free copy: http://arxiv.org/abs/quantph/9709032v1 


#3
Aug1911, 10:33 AM

P: 400




#4
Aug1911, 10:44 AM

P: 19

Problems with Many Worlds Interpretation
Thanks xts for your reply.
With point #1, I agree I was being facetious to make a point, but you have to agree it's still a nonzero probability which means it is occurring all the time in some parallel universe. With point #2, why should any of the 100^{1000} worlds show an intereference pattern, since there is only one point particle in each world. I can see why splitting occurs in an CI universe where a single particles probability wave travels through multiple slits simultaneously. But with MW, only one particle traveled through each slit and so no interference should occur? 


#5
Aug1911, 10:56 AM

P: 882

#2) nope, you misunderstood the idea. The world splits not when electron goes through 1st or 2nd slit, but when you notice a flash on the screen. Your world splits to 100 as you record the first particle. Then it splits to 10,000 as you record the second one. After recording 1000 particles, you'll have [itex]100^{1000}[/itex] worlds, each of them containing some pattern consisting of 1000 flashes. Vast majority of those will be well known fringe patters.



#6
Aug1911, 11:04 AM

P: 19

Thanks JeffKoch for your reply.
I understand that MW does not change predictions about quantum mechanical experiments, however, I would argue that the distinction is not purely philosophical. Which interpretation you agree with will change the way you think about physics problems which can affect future theories and experiments. I am equipped with only undergraduate level physics exposure. I have been reading on MW vs CI for past 3 years and the three questions I posed have not been answered in any of my readings thus far. Do you have any particular suggestions? 


#7
Aug1911, 11:06 AM

P: 19

Thanks again xts for that clarification as well as the article link. I guess point #2 is now eliminated from my list of problems.



#9
Aug1911, 03:44 PM

P: 19

from: http://www.anthropicprinciple.com/p...anyworlds.html "Political scientist" L David Raub reports a poll of 72 of the "leading cosmologists and other quantum field theorists" about the "ManyWorlds Interpretation" and gives the following response breakdown [T]. 1) "Yes, I think MWI is true" 58% 2) "No, I don't accept MWI" 18% 3) "Maybe it's true but I'm not yet convinced" 13% 4) "I have no opinion one way or the other" 11% Amongst the "Yes, I think MWI is true" crowd listed are Stephen Hawking and Nobel Laureates Murray GellMann and Richard Feynman. GellMann and Hawking recorded reservations with the name "manyworlds", but not with the theory's content. Nobel Laureate Steven Weinberg is also mentioned as a manyworlder, although the suggestion is not when the poll was conducted, presumably before 1988 (when Feynman died). The only "No, I don't accept MWI" named is Penrose. 


#10
Aug1911, 07:34 PM

Sci Advisor
P: 2,470

MWI and Copenhagen are absolutely equivalent as far as predictions of any observable in any experiment. As such, saying that you don't like one or the other is silly. Physically, they are the same. The rest is philosophy and does not belong on a physics forum.



#11
Aug1911, 09:01 PM

P: 269




#12
Aug2011, 09:36 AM

P: 90

I think the MWI is not required at all. Better is to view a particle  in superposition  as not in spacetime physically. Sure, it gives a result when colocated with another particle's wave function. Those 'results' are what we interpret as real physical objects. But they are only values retrieved from the HUP.
Furthermore  MWI seems to appeal to some people's spiritual side and that is why they support it. Nobody in this forum, though, I am sure. Trying not to be rude about MWI...... 


#13
Aug2011, 09:42 AM

P: 400




#14
Aug2011, 06:39 PM

P: 172

@Threadstarter:
No, it is not embraced by the majority, it's still a very much minority position. That poll you mention isn't even right, Hawking is on record denying MWI etc. and Weinberg just said earlier this year that none of the interpretations are satisfying. @The guy who thought he had solved the problem of probability in MWI, sorry but that just doesn't work. 


#15
Aug2011, 07:18 PM

P: 400

So, this would seem to be an exceptionally unreliable quote and reference upon which to base a foundation for the claim that most physicists support MW. In fact in the absence of any direct evidence for the statement, which I failed to find despite looking around for, I would call it worthless. 


#16
Aug2111, 03:43 AM

P: 882

Max Tegmark made a poll on preferred interpretation of QM during a conference Fundamental Problems in Quantum Theory, 1997, and got:
Copenhagen 13 Many Worlds 8 Bohm 4 Consistent Histories 4 Modified dynamics (GRW/DRM) 1 None of the above/undecided 18 http://arxiv.org/abs/quantph/9709032v1 


#17
Aug2111, 04:21 AM

HW Helper
P: 3,440

JeffKoch and K^2 are right, there has been no experiment so far to distinguish between manyworlds and copenhagen.
(Which is why they are still two possible interpretations of QM. If one of them was not, then it would be discarded). So at the moment we can only speculate, using our intuition. And unfortunately, QM has always been very nonintuitive, which is why it is difficult to guess which interpretation is the best (if any). If I had to guess, I reckon experiments into wavefunction collapse (if indeed it does collapse) will probably bring about some new extension to QM theory that is neither CI nor manyworlds. 


#18
Aug2111, 04:43 AM

Sci Advisor
P: 2,470

It's not just that there is no experiment to distinguish. There can't be. The predictions from the two interpretations are identical. There could be an experiment that would show both interpretations wrong, and it might be easier to fix one than the other, but as they are now, they cannot be experimentally distinguished.
For example, if we find that underlying field theory is actually nonlinear, which is entirely possible giving nonlinearity of General Relativity, both Copenhagen and MWI would be demonstrated wrong. But the results of experiments showing nonlinearity in the field theory might be easier to relate to one interpretation than the other. 


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