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6 of 15 people found the following review helpful
4.0 out of 5 stars Useful but not convinced, 23 Feb. 2013
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This review is from: Emergent Multiverse: Quantum Theory According to the Everett Interpretation (Hardcover)
This is probably the first textbook account of the Many Worlds interpretation that has appeared in the literature. In that sense it performs a useful guide for those who want to know more about this particular interpretation. Wallace along with his colleague Simon Saunders have done much to develop the interpretation over the past 15 years or so. However whilst it is useful I remain totally unconvinced by the intepretation or its motivation.

The first chapter tries to motivate it by claiming that there is a problem with the standard interpretation of quantum mechanics and an outline of the measurement problem. It is curious that most physicists are not really concerned with the measurement problem and it certainly does not prevent them from using the formalism of quantum mechanics to make ever more predictions about the quantum world. This activity is relatively independent of any interpretation and one would think that is telling us something about quantum mechanics.

The so called foundational issues seems to have been left to philosophers whilst physicists get on with the job of explaining the properties of solids, cosmology, astrophysics and particle physics.

For my part I see nothing wrong with the minimalist view that the so called wave function is a complex probability state vector whos modulus squared gives rise to a probability density function via the Born Rule. Indeed it is quite instructive to recast the language of classical physics in the language of quantum physics. One can write down a wave function for a dice and by application of the Born rule one will get the correct probabilities. Ok in quantum physics one needs to extend classical probability to include complex numbers whose modulus squared gives rise to the probabilities relevant to the situation.

Such a pragmatic viewpoint does not seem to satisfy people like Dave Wallace who wish to give the wavefunction some sort of physical meaning. One way of doing this is via the Everrett interpretation which implies the generation of a whole new universe every time a measurement is made. This view borders on science fiction and seems to stem from a perspective which wishes to associate every mathematical concept with something out there. Yes if you wish to take the wavefunction as corresponding to some element of reality you will probably end up with something like the Everrett interpretation but the price is to high. One can't test the existence of other universes. I dare any one who is tempted by the Everrett interpetation to play quantum suicide because in one of the many branches it is alleged that you will still be alive.

On a more constructive note it is useful to have in one book a fairly definitive account of the interpretation. On the other hand it would seem to paraphrase Bernard Shaw those who can do physics do physics those who cant interpret it.
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Showing 1-6 of 6 posts in this discussion
Initial post: 8 Feb 2014 14:07:41 GMT
Rory says:
The personal jibe at the end is cheap, particularly as Wallace does hold a phD in Physics from Oxford, and many other well-qualified philosophers and philosophers of physics also champion the Everett interpretation. Moving away from claims of authority, however, I don't understand the force of your objection. You say that the price of associating 'every mathematical concept with something out there is to [sic] high', yet you don't explain why. Is it just that the theory is counter-intuitive?

In reply to an earlier post on 8 Feb 2014 14:51:25 GMT
It is

a) By definition we can't test the existence of other universes as by definition there is no communication between them. I belong to a school of thought which says that if you can't falsify a hypothesis then it isn't science.

b) A much simpler way is to see the solution of Schrodinger's equation as a complex probability amplitude who's modulus squared gives rise to
a probability density function. Which is essnentally what the Born rule
states. There is no need to postulate wave function collapse as a probability density function by definition refers to an ensemble of particles and not a single one. All the so called wavefunction is is a means of generating the correct probabilities for a given situation.

The problem with those who advocate a realist understanding of the so called wavefunction is that they either have to invoke a scarcely credible many universe theory as Wallace does. Or the reality of a 3N+1 dimensional configuration space where N is the number of particles and to which our three dimensional world is an illusion.

Of course denying the reality of the wavefunction doesn't mean denying the reality of particles or their interactions. The reason being that whilst the uncertainty principle applies to canonically conjugate properties such as spin components or momentum and position, It does not apply to properties which commute such as mass and charge.

So the simplest way to interpret quantum mechanics with out invoking other universes or the reality of configurartion space is to take the Born rule seriously. Admttedly that means extending our notion of probabilty to embrace complex probability amplitudes but once that is done then the rest follows

Confronted with a choice of a modest extension of our notions of probability to embrace complex numbers as opposed to a fantastical notion of a universe being created every time a measurement is made I know which one I prefer.

In reply to an earlier post on 10 Feb 2014 12:26:06 GMT
Last edited by the author on 10 Feb 2014 12:26:56 GMT
muggleson says:
The point of an Amazon review is to give an idea of the quality of the product as what it claims to be, not to criticise the whole idea of producing the product in the first place. If I'm interested in this book then by definition I take the Everett view seriously. What I want to know from a review is whether this book is a good presentation of that view. Your review does not do this.

In reply to an earlier post on 11 Feb 2014 13:42:43 GMT
Last edited by the author on 11 Feb 2014 13:43:31 GMT
| said it was a good account of the Everrett theory however If I disagree with it I'm entitled to express my opinion and expalin why.
You will find that many reviewers on Amazon do this.

In reply to an earlier post on 15 Mar 2016 14:15:21 GMT
First, the MWI is testable, see

http://arxiv.org/abs/1508.02048.

Second, you have greatly underrated the difficulty of your proposal. The theory your propose would have to be both non-local and non-Lorentz invariant, as shown by John Bell and Lucien Hardy respectively, see http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.68.2981.

As a result your proposal would require discarding all of modern quantum field theory and the special and general theories of relativity.

Also, your proposal is ad hoc and doesn't make determinate predictions as it doesn't explain the collapse process.

In reply to an earlier post on 15 Mar 2016 18:18:28 GMT
So are you claiming that the Born Interpretation is incorrect if so that would surprise many practicing physicists

Where are these other universes and what is the point if we can't access them.

It is well known that the Standard Interpretation of quantum mechanics sees the solution to Schrodinger's equation as a probability amplitude the modulus squared of which gives rise to a probability density function.
Modern quantum field theory does not challenge that. As for discarding all of general relativity we don't have a quantum theory of general relativity so eventually it will be discarded. Of course for modelling and the prediction of experimental results it is fine. To some extent the fact that it is incompatible with quantum mechanics is irrelevant.

As for the collapse process if the solution to Schrodinger-s equation is effectively the square root of a probability density function (something the book refuses to acknowledge) then it isn't real and doesn't collapse.

If you want to claim the solution to Schrodinger's equation is something akin to a real field you either have to accept the reality of 3N+1 dimensional configuration space where N is the number of particles or the reality of many universes.

Finally I can't see how you can claim on the MWI you have explained the collapse process all you say is that one of the many branches have been realised in the universe which you are currently experiencing. You don't explain why the branch you are on is the one that you are experiencing and not others. It seems to confuse possibility with actuality.

I'll stick to the Born Interpretation thank you.
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