Many worlds

I just wanted to link to Sean Carroll’s post defending the many-worlds interpretation of quantum mechanics. Sean has a habit of getting this sort of thing right.

He explains that the multiple worlds are not an add-on to the theory but instead are simply what happens naturally when you take the equations of the theory at face value. The standard (“Copenhagen”) interpretation is the one that needs to postulate an ad hoc extra rule. We should simply rename things:

  • The “many-worlds interpretation of quantum mechanics” should henceforth be known as “quantum mechanics.”
  • The Copenhagen interpretation should henceforth be known as “the disappearing-worlds interpretation of quantum mechanics.”

7 Responses to “Many worlds”

  1. Since Sean seems to have become to famous to follow up questions on his own blog, I’ll ask you the same questions:

    Is it your view that the many-worlds interpretation has become more popular in, say, the last 15 years?

    What do you think of the cosmological interpretation of Aguirre and Tegmark?

  2. M Mahin says:

    Lunacy, Ted. Sheer lunacy. You’ve sided with the crazies here.

    We should simply rename the Everett “many worlds” theory as the theory of infinite unnecessary duplication, or the theory of infinite excess baggage.

    There is not now, nor ever could be, the slightest evidence for the existence of a parallel universe. We could never even in theory observe such a thing. The Everett “many worlds” theory is eternally unverifiable nonsense, the most ludicrous theory the mind of man has ever advanced.

    Under the Everett “many worlds” theory, all imaginable absurdities have occurred an infinite number of times. So, according to that theory, there have been an infinite number of times that you or my dog have become the president of the world. The flakiest astrologer never advanced a theory more nutty.

    Do not flatter yourself with the crazy idea that there are an infinite number of you’s. You are the only you.

    http://futureandcosmos.blogspot.com/2013/08/you-are-only-you-no-evidence-for.html

    Is it any wonder that people reject large portions of science (evolution and global warming) when physicists go around endorsing such insane theories?

    Besides being irrational, the many worlds theory is an obvious violation of known physical laws. The universe cannot be constantly splitting into different copies of itself, for that would violate the known law that mass-energy cannot be created or destroyed (the law of the conservation of mass energy).

    The Everett many worlds theory is not science. It is metaphysics — very, very bad metaphysics.

  3. “So, according to that theory, there have been an infinite number of times that you or my dog have become the president of the world.”

    No. At best, any event with finite probability will have occurred an infinite number of times.

  4. Ted Bunn says:

    Phillip –

    I don’t know if the many-worlds interpretation has become more popular. My subjective impression is that it’s been quite popular among cosmologists for a long time. I suspect that it’s much less popular among, say, atomic physicists, but I don’t know of any data to back that up. I’d love to see a survey of some sort of representative sample of physicists, but I don’t think I ever have.

    I haven’t looked at the Tegmark-Aguirre work. I meant to at one point, but then I forgot about it. Maybe I’ll try again.

  5. ” I’d love to see a survey of some sort of representative sample of physicists, but I don’t think I ever have.”

    Penrose said that there are more interpretations of quantum mechanics than there are people who work in the field, but this is not a contradiction since some of them hold more than one interpretation at the same time. :-)

    “I haven’t looked at the Tegmark-Aguirre work. I meant to at one point, but then I forgot about it.”

    Which, in their interpretation, means that, somewhere else in the multiverse, you didn’t forget and did look at it. :-)

    I’ve read Max’s book a couple of times, once in order to transform myself into a superhero and another in order to write a review.

  6. Allen Downey says:

    Carroll’s post is very good; thanks for the pointer (and introduction) to it.

    But I think he is unfair to characterize quantum Bayesianism as a silly objection to Everett; I don’t think it’s silly, and I don’t even think it’s an objection to Everett. Rather, it seems to me like a sensible instrumentalist interpretation of quantum mechanics.

    By claiming that QB denies the existence of reality, he seems to be interpreting it under a strict form of scientific realism that requires us to believe a theory is either true or false, and if true, that all it’s unobservable entities are real. If that view held up to scrutiny, philosophy of science books would be short.

    They are not.

  7. Ted Bunn says:

    I’m not completely sure I understand your last paragraph.

    I don’t know exactly what the advocates of QB claim. Carroll seems to me to be attributing more than just instrumentalism to them. He seems to think that they affirm that there is no deeper underlying reality, and that probabilities of the results of experiments are all there is in nature. If that really is their claim, then it’s something one can reasonably object to.

    If, on the other hand, their claim is “merely” instrumentalist — which I understand to mean that all they care about is making successful predictions and are uninterested in any additional underlying reality — then I agree that it’s a perfectly sound approach, akin to what Mermin calls the “shut up and calculate” interpretation.

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