Cosmological Interpretations of Quantum Mechanics

It seems that there’s now a new burgeoning field bringing together multiverse studies and interpretational issues in quantum mechanics. Last year Aguirre, Tegmark and Layzer came out with with Born in an Infinite Universe: a Cosmological Interpretation of Quantum Mechanics, which claimed:

This analysis unifies the classical and quantum levels of parallel universes that have been discussed in the literature, and has implications for several issues in quantum measurement theory… the analysis suggests a “cosmological interpretation” of quantum theory in which the wave function describes the actual spatial collection of identical quantum systems, and quantum uncertainty is attributable to the observer’s inability to self-locate in this collection.

Last month there was Nomura’s Physical Theories, Eternal Inflation, and Quantum Universe where “a picture that the entire multiverse is a fluctuation in the stationary, fractal “mega-multiverse,” in which an infinite sequence of multiverse productions occurs” is invoked and:

Our framework provides a fully unified treatment of quantum measurement processes and the multiverse. We conclude that the eternally inflating multiverse and many worlds in quantum mechanics are the same.

Most recently, tonight’s arXiv listing has Bousso and Susskind’s The Multiverse Interpretation of Quantum Mechanics:

We argue that the many-worlds of quantum mechanics and the many worlds of the multiverse are the same thing, and that the multiverse is necessary to give exact operational meaning to probabilistic predictions from quantum mechanics.

I confess that I’m having trouble making sense of any of these papers. According to Bousso and Susskind, if I want to understand how quantum mechanics describes some simple, local physical system and what happens when I do measurements of it, I need to sign on to the theory of eternal inflation and the multiverse:

We will offer some principles that we believe are necessary for a consistent interpretation of quantum mechanics, and we will argue that eternal inflation is the only cosmology which satisfies those principles.

In the case of many string theory papers, one’s problems understanding their claims could often be attributed to the highly complex and sophisticated mathematical framework involved. These papers are mostly long sections of verbiage, sometimes with pictures. My inability to make sense of them must have some other source…

: Lubos has an explanation of the Bousso-Susskind paper: “they’re on crack”.

Update: I suppose one could have guessed that Sean Carroll would be a fan of this. In his book he argues that the way to understand the second law of thermodynamics and the arrow of time is to invoke cosmology and the multiverse, now he seems happy to do the same thing with the interpretation of quantum mechanics. The ideas seems to be that to understand some local quantum mechanical phenomenon, you need to use cosmology and think about the horizon that is part of the deSitter geometry. I don’t find this argument any more plausible than the arrow of time one.

It does seem like this is now being promoted as the hot topic in theoretical physics, with Sean and others organizing a conference partially devoted to this at Perimeter this summer.

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64 Responses to Cosmological Interpretations of Quantum Mechanics

  1. edm says:

    The paper is really about a measurement (or upper limit) of the electric dipole moment (EDM) of the electron. (There seem to be many ongoing or proposed EDM searches.) Many BSM theories yield much larger values for the EDM than the SM value. (Indeed the SM is almost unique in yielding very small values for EDMs of elementary particles.) Many theories of CP violation yield much larger values for EDMs than the SM, and many models were ruled out in the 1982 review by Norman Ramsey

    So almost 30 years later, the search for EDMs continues, and the ruling out of BSM models continues. Of course, for SUSY one can tweak the SUSY parameters. But that will also constrain other things (sparticle masses?).

  2. edm says:

    A more precise statement is that the SM is almost unique in that it predicts nonzero CP violation and also small values for EDMs of fundamental particles. Most other models of CP violation also yield much larger EDMs. Experimental searches for nonzero EDMs have ruled out many such models.

  3. Bernhard says:

    I spent my morning trying to digest Sean’s post. Seems the universe is an inverse black-hole like place where light far away can not reach us (or whatever place you take as “central”) and that defines a cosmological horizon. With this you define a notion of “in and out” of this say pocket universe and just like in a black hole to have a complete description you need to know what’s actually inside the observable universe and this has to includes an amplitude for being in various possible states. Now why and how this possible states becomes the many worlds of quantum mechanics I have no idea. He then asks what the consequences are for cosmological initial conditions and the arrow of time. What I on the other hand would like to know is what would be the consequences of this for experimental cosmology, if any. A pure philosophical discussion with very little chances of becoming a discussion of physics.

  4. somebody says:

    “A pure philosophical discussion with very little chances of becoming a discussion of physics.”

    The point however is that these are the ONLY chances we have for making progress in fundamental physics. So I would take them, even if they are slim.

    Since this seems to be a popular objection to a lot of what goes for as high energy physics (including string theory), let me just clarify a point that I have often seen the proverbial “layman” to miss. This is not necessarily addressed to the author of the quote.

    These questions are only “purlely philosophical” in as far as we are NOT able to do experiemnts/observations at high enough energies like the GUT or Planck scale. If we could (for example) do direct observations of gravitational waves from before big bang many of these questions/theories/models will have immediate answers. Even including things like multiverse. So these are possibly physical, yet at the current time technologically inaccessible (at least if we don’t get lucky), questions. You might be not interested in this distinction, but they do exist. If we had a Planck scale collider of course, these questions are DEFINITELY physical questions, but building one is likely technologically impossible at ANY time.

    Finally, ANY fundamental question that we are puzzled by at this point in history, is BOUND to be open to this criticism. We understand the understood Universe amazingly well (this is lost oftenh on many people), so what is to be understood is going to quite difficult to experimentally reach! Despite the statements made on this blog, I am not sure there is a much better way to go about unraveling the remaining mysteris of the Universe than our current ones. We are all a bit frustrated we are not living in the haydays of quantum field theory in the late sixties or so when experiments were still accessible, but we got to keep trying.

    Our best shot after LHC (Last High-energy Collider?) will be cosmology.

  5. Bernhard says:


    I agree with the fact that such discussions have have a certain value, but I repeat that as of today they remain a philosophical discussion, and there is nothing wrong with that. This fact could change and multiverses could even become part of physics, but more than having the experimental apparatus would be needed in order to change this. The problem is not how crazy or not this all sounds. I’m sure when Einstein started to talk about curved space this was taken as crakpot talk by many. The difference is that GR made genuine predictions that could be tested. It’s up to the proponents of a theory to suggest how can be tested or falsified.

    I ask, even with the galactic collider or even with cosmology, how would anything Susskind and Bousso claim be falsifiable and become as you say a physical discussion? I cannot see how this would be possible, but maybe a just missed it. I’m open to hear the contrary and I it would be exciting to be wrong.

    Also, I disagree with you that this is the only way to make progress. Progess will be made by people collecting data, making plots and theorists struggling to understand it. The hope is of course to see some real SM deviations at the LHC and this would be real progress in fundamental theory. I understand some people just can’t wait for experiments to reach they favorite physics scenario but with no predictions, no experiments or even suggestions of a test, it remains a discussion beyond physics. The some physics can potentially emerge from this someday, I can’t deny, but right now, this is something entirely different.

  6. Christine says:

    There is a simple, but fundamental detail. It is called the “scientifc method”. 

    As a method, it consists of several items to proceed. One of them is experimental verification. The scientist should provide concrete statements on how to prove that a proposed theory will correctly describe observed data or predict certain phenomena. If that is so, the theory can be regarded as a scientific one. Otherwise, it is not a scientific theory. It is called “speculation”. The end.

    Now, there are only 2 possibilities: 1- people deliberately want to dismiss the scientific method altogether in order to promote their speculative endeavors as some kind of new “science”. 2- They do not know what the scientific method is.

    Either possibility is disturbing. Specially if they teach to the younger generation.

  7. Anon says:

    It is clear that Bousso and Susskind do not understand the relative state (many-worlds) interpretation. They do not appear to understand the purpose of it, and they /clearly/ do not understand its technicalities. I doubt they even bothered to read the original Everett paper.

  8. Christian Takacs says:

    May I propose that the problem with the Bousso and Susskind (known hereafter as B.S.) model is not of a philosophical kind, it is actually of a logical nature. By demonstration ; A is true because of B. B is not measureable, testible, or predictable until C. C is when a miracle occurs OR some unknown discovery at some unknown time allows B to be measureable, OR when pigs fly. Logic clearly shows that the B.S. model suffers from premature speculation without any kind of verification, and should be given the sniff test before further consideration.

  9. Anon says:

    Are we sure this paper is not a parody? It reminds me of this classic paper by V. Gates et al., maybe from 1985:

  10. Peter Woit says:


    It’s more like this one:

    I’m pretty sure though that these papers are not parodies. For one thing, they’re not funny…

  11. Jeffrey Dunham says: – is this missing matter that is not part of dark matter, or is it saying they found the matter that dark matter was suppose to account for?

  12. Peter Woit says:

    As far as I know this has nothing to do with dark matter. But you really should consult an astrophysicist, not me.

  13. Cosmonut says:

    This seems to be part of a general pseudoscience principle:
    X can’t be observed/explained, neither can Y.

    Hence, X is the same as Y, or X explains Y.

    I hereby propose that the multiverse is the same as the many worlds of QM which is also the same as the various spirit worlds proposed by the religions of the world.

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