# Problems with Many Worlds Interpretation

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 50-50 probability.

Can someone help me to understand these issues any better? Thanks!

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xts
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 $100^{1000}$ 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/quant-ph/9709032v1

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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 50-50 probability.

Can someone help me to understand these issues any better? Thanks!
I don't think you understand the MW point of view, which is really philosophical until there are experiments to guide the way - it does not change any predictions about outcomes of slit interference, coin flips, or spontaneous combustion experiments. If you read and begin to understand it, you'll have answered your own questions.

With point #1, I agree I was being facetious to make a point, but you have to agree it's still a non-zero probability which means it is occurring all the time in some parallel universe.

With point #2, why should any of the 1001000 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?

xts
#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 $100^{1000}$ worlds, each of them containing some pattern consisting of 1000 flashes. Vast majority of those will be well known fringe patters.

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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?

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

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jtbell
Mentor
While the majority of physicists embrace the Many Worlds interpretation of quantum decoherence,
Can you cite a survey to back up this statement?

Can you cite a survey to back up this statement?
Hi jtbell,

from: http://www.anthropic-principle.com/preprints/manyworlds.html

"Political scientist" L David Raub reports a poll of 72 of the "leading
cosmologists and other quantum field theorists" about the "Many-Worlds
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 Gell-Mann and Richard Feynman. Gell-Mann and
Hawking recorded reservations with the name "many-worlds", but not with
the theory's content. Nobel Laureate Steven Weinberg is also mentioned
as a many-worlder, 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.

K^2
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.

However with MW, one flip will result in head in one universe, tail in another so therefore 50-50 probability.
50-50 conclusion is incorrect. Instead the multiverse (or rather that part of it in contact with the coin) quickly evolves into two separate regions, one where things are generally consistent with the heads and another with tails. The ratio of volumes of these regions (in whatever Hilbert space they inhabit) would be 99:1 and the boundaries are somewhat fuzzy. IMHO.

I think the MWI is not required at all. Better is to view a particle - in superposition - as not in space-time physically. Sure, it gives a result when co-located 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......

Nobody in this forum, though, I am sure..
Are you?

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.

from: http://www.anthropic-principle.com/preprints/manyworlds.html

"Political scientist" L David Raub reports a poll of 72 of the "leading
cosmologists and other quantum field theorists" about the "Many-Worlds
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%
Funny, if I try to find the source of this quote by digging around with Google, I get hundreds of hits to the same phrase - repeated over and over and over again, usually verbatim, often by new-agey/occult/crackpot types who appear to include the supposed original source of the statement, Tipler, an advocate of multiple crackpot theories including "intelligent design" and a writer about the "physics of christianity". No link to any original work by someone named L. David Raub, with or without the quotes around "political scientist".

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.

xts
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/quant-ph/9709032v1

BruceW
Homework Helper
JeffKoch and K^2 are right, there has been no experiment so far to distinguish between many-worlds 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 non-intuitive, 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 many-worlds.

K^2
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 non-linear, which is entirely possible giving non-linearity of General Relativity, both Copenhagen and MWI would be demonstrated wrong. But the results of experiments showing non-linearity in the field theory might be easier to relate to one interpretation than the other.

Brian Greene in his book the Hidden Reality claims that in fact MWI and CI may actually make different predictions, although I must admit I do not really understand his example or explanation.

Greene argues that in Many Worlds, the wave-function have multiple spikes, corresponding to different possible outcomes. He reasons that these "spiked waves" might interfere, causing an observable interference pattern, which would disagree with Copenhagen wave function collapse.

IMO non-local hidden variables explains it better than MW (which is weird) and Copenhagen (which requires some degree of "shut up and calculate"--hardly an explanation), because non-local hidden variables seems an inevitable side-effect of Mach's principle, for one thing. Why do the vast majority of scientists seem to consider Mach's principle only a quaint product of yesteryear rather than the inevitable (and profoundly fundamental) trait of reality that it is?

BruceW
Homework Helper
Mach's principle doesn't mean information can travel faster than the speed of light, if that is what you're suggesting.

Mach's principle doesn't mean information can travel faster than the speed of light, if that is what you're suggesting.
The same could be asked of someone defending the existence of entanglement. The problem, here, is that we keep applying concepts we learned solely from observing classical mechanics (the large-scale behavior of many QM events) to the behavior of QM events. Those concepts work to a point but eventually they must be modified or maybe dropped altogether.

Its like someone observing a swarm of bees from a distance and concluding that "all objects look like clouds, can change shape, and make a rushing sound". Then when that person gets the opportunity to walk closer to study a single bee, they insist that the bee is yet another type of cloudy thing that can change shape and makes a sort-of rushing sound.

Likewise we learned the details of the concepts of continuum (real numbers), dimension, time, space, speed, etc. solely from observing the "average" behavior of a lot of particles, but we continue to insist those concept will also be axioms in our understanding of particle-particle interactions. Now I'm not saying those concepts have no part in QM. Obviously they are very useful. but we must be leery of assuming they are axioms.

For all we know, everything is entangled, and that is Mach's principle. (And who is the observer that decohere's that entaglement?)

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xts
Why do the vast majority of scientists seem to consider Mach's principle only a quaint product of yesteryear rather than the inevitable (and profoundly fundamental) trait of reality that it is?
[...] The same could be asked of someone defending the existence of entanglement.
[...] For all we know, everything is entangled, and that is Mach's principle.
Because vast majority of scientists are Occamian conservatists.
Bell+Aspect convinced most of us that non-locality is unevitable. That was painful (esp. for Einstein) but to stay honest we had to adopt that into our Weltanschauung. But we definitely prefer view with just two entangled particles over the spaghetti plate of whole Universe entangled.

K^2
MWI is the spaghetti view. Clearly, a big fraction, if not majority, do prefer to view the universe as fully entangled. Problem is that it doesn't help with GR vs Mach's Principle. It makes it worse, if anything.

We either need a linear theory that explains gravity or a non-linear theory that linearizes to RQFT. Former is preferable, but later is far more likely.

J 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 many-worlds.
right and nonlinear quantum mechanics (unlike standard quantum mechanics, a linear one).

.