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Clarification on Introductory QM

  1. Mar 24, 2008 #1
    I will apply the same cavaet here that I did to my earlier thread. I have only started taking an introductory QM course, and am still grappling with the subject matter(which is exceptionally counter-intuitive, as I'm sure everyone here would agree) so forgive me if the question seems inane to you experts.

    A person in my class, the TA as a matter of fact, keeps insisting that all interpretations of QM amount to multiverse interpretation involving alternate universes and such. He is an exceptionally strong advocate for MWI, and keeps backing up his claims with random quotes from David Deutsch. I thought MWI was the only multiverse interpretation of QM, and keep on saying the Bohmian mechanics, Copenhagen,and GRW, for example, are single universe views(at least in terms of quantum mechanics is concerned...I understand things like Linde's Bubble Theory could still be applicable). I am not somehow mistaken in asserting this, am I? As an addendum, I have taken the position of instrumentalism in QM until someway of distinguishing between the interpretations is discovered and until a complete theory of quantum gravity is attained. Is this a respectable position, or am I misguided in thinking this? I appreciate whatever help you can give me.
  2. jcsd
  3. Mar 24, 2008 #2


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    QM interpretations have been discussed at length in other threads in the forum. You can locate them using the 'search' menu at the top of the page. There are proponents of every interpretation and the general feeling is that there's no way at present to distinguish them, so it's academic in any case. Those who favour MWI claim that all the mysteries are explained, but it seems to me the cost is to accept something equally weird on faith alone.

    For what it's worth, I take the same view that you do - keeping an open mind.
  4. Mar 24, 2008 #3
    I have tried looking it up...I can find no mention of any other (major) interpretations having any significant multiverse implications, except for MWI. I would like to confirm that I am on firm ground though, and am not overlooking something on account of my unfamiliarity with QM jargon. Frankly, I would like to focus on the physics in my introductory studies and not focus on what seems to belong in the realm of metaphsics and philosophy, but I think I am being given misinformation based on an extremely biased point of view.
  5. Mar 24, 2008 #4
    Donald Knuth once said something along the lines --- when physicists talk to each other about quantum mechanics, they talk about operators and linear spaces; when they talk to other people, out comes all this stuff about waves and particles and uncertainty.

    It doesn't matter which interpretation you choose --- as long as when you do the calculations you end up with the correct numbers. People can (and often do) argue until they're blue in the face, all the whilst agreeing with each other on all the things that are physically observable.
  6. Mar 25, 2008 #5
    Right, I understand this. I'm really not concerned about picking an interpretation, as I think it would be a futile metaphysical excercise, like picking a religion. What does concern me is the possiblity that I'm being given misinformation. So, as far as anyone here knows, is it true or false that the other major interpretations(Copenhagen, Bohm,GRW,etc) all are multiverse interpretations? They seem like single universe QM interpretations by their descriptions, but I'm being emphatically told otherwise by someone.
  7. Mar 25, 2008 #6


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    Please define 'multiverse' as its being used by your informant. As far as I know, MWI is the only interpretation that explicitly invokes alternative universes.
  8. Mar 25, 2008 #7
    They are all "single universe" interpretations. Only MWI considers the idea that that single universe might be divided into an unknown number of multiverse subsets. The principles of each produce the same observable results, MWI was contrived to attempt to explain the non-local and/or unrealistic nature of those results. Nothing short of finding experimental proof can confirm MWI. Some at Fermi Lab are trying see if they can detect surplus gravitons (more than needed for gravity) and watch them disappear into unseen multiverses. But none of the others require MWI to be true, MMI is of course defined to give the same results as the others since that matches observations.
    That in no way retroactively defines all the others to “be MWI”. Your TA is just being a radical advocate for his way of thinking, without proof such advocacy does not make it so. He is just being evangelical with a sincere faith in his chosen religion. Nothing wrong with that belief or even in effort to recruit adherents to the cause. I do have a problem if the TA is condemning those that fail to join that religion. It is little more than a small “r” religious debate.

    I disagree with your “futile exercise” comment, as to some extent and at some point you will need to choose a religion. Defining "religion" as your beliefs in what fundamental elements make up the true workings and foundation of reality. True it is much like picking a big R Religion, from atheist (Humanism), atheist spirituality (Buddhism) , to theology (Deity Religions). Just not so much family history or pressure, this is more your own choice.

    With or with out a big “R” you will eventually need to pick a small “r” even if by default.
    For example I assume your course work is intended to take you some where.
    If you eventually go with Astrophysics you will likely be most closely associating yourself with a science religion (a fundamental belief in) using the 4 or 5 dimensional warped space and time of GR. That is probably the biggest divide in science with the incompatible Particle Science view of QM and its various doctrines (interpretations) being the other major grouping. Learning and understanding several types will be beneficial, but when you actually do something your approach will define your scientific religion.
  9. Mar 25, 2008 #8
    The bottom line is that your TA is wrong. He may prefer MWI but not all interpretations of QM rely on the concept of a multiverse or of all possible branches of the wavefunction actually occurring.
  10. Mar 25, 2008 #9
    Great, thank you all for your clarification on this issue. It didn't make sense to me that all interpretations involved alternate universes arising from the quantum formalism, because it seems we'd only have variations of MWI, and not seperate interpretations. As I thought, he is only an overzealous MWI advocate presenting an extremely biased viewpoint. Now that that's out of the way, I can focus on the empirical physics, which is what I'm mainly interested in. Thanks again.

    In Response to RandallB: "I disagree with your “futile exercise” comment, as to some extent and at some point you will need to choose a religion. Defining "religion" as your beliefs in what fundamental elements make up the true workings and foundation of reality...Just not so much family history or pressure, this is more your own choice."

    I do agree with you, and I use Zurek's Quantum Darwinism to give me a picture of what's going on. As an evolutionary biology major, this appeals to me intuitively. Perhaps "futile excercise" was a little hyperbolic. But I have no way of knowing what the actual reality of the situation is, so I consider them all to have an equal liklihood of being correct(Bohm a little less so because of the violation of relativity, and MWI I doubt on a visceral level). What I meant was it was futile to be a one-dimensional zealot about one specific approach because we have no way of differentiating them yet.

    RandallB: "Nothing short of finding experimental proof can confirm MWI. Some at Fermi Lab are trying see if they can detect surplus gravitons (more than needed for gravity) and watch them disappear into unseen multiverses."

    That is fascinating, I had no idea such an experiment was even technologically possible. It does seem ambitious however, given we have never detected a graviton. I wonder if they are making any more progress at deteting gravity levels at smaller lengths in attempts to test predictions of string theory...it's applications like this that are making me consider switching from evo. biology to Astrophysics.

    Thank you all again as I struggle to understand this counter-intuitive realm of physics.
    Last edited: Mar 25, 2008
  11. Mar 25, 2008 #10
    They don't say it is possible - only that they were trying to be first to detect it. (Fermi Lab was first to detect a Top Quark - heaviest and last of the quarks)
  12. Mar 26, 2008 #11


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    Do you have a link? I thought there were some proposals that if one of the extra dimensions posed by superstring theory is "large", with our universe being a sort of membrane in this dimension, then this might explain the relative weakness of gravity in terms of gravitons being able to escape the membrane...there were suggestions about how to test the idea of a large extra dimension IIRC (it was talked about in Lisa Randall's book), but I think they involved other particles, not trying to measure gravitons directly. Is this the sort of thing you're talking about? If so, also note that there is really no connection between the other universes of the MWI (which are all supposed to occupy the same physical space) and the extra dimension being postulated by these superstring-inspired theories (even if the extra dimension may be a sort of 'multiverse' in the sense that it can contain other membrane-universes besides our own).
  13. Mar 26, 2008 #12



    Three threads that discuss the issue at length.

    I'd take nobodies word for it atm, I'm wary of MWI advocates, they seem like the new string theorists. Nice idea to get a grip with what is going on, but as to what is really happening? I don't see how it's of any use to science...
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