Cosmological Interpretations of Quantum Mechanics

Posted on May 19, 2011 by woit

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…

Update: 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.

Posted in Multiverse Mania | 64 Comments

Particle Theory Job Market 2011

Posted on May 19, 2011 by woit

By now the hiring season for tenure-track jobs is pretty much over, and for the field of particle theory some idea of the results is available at the Theoretical Particle Physics Jobs Rumor Mill. As has been usual for the last few years, most jobs are going to phenomenologists. Remarkably, it seems that no jobs at all are going to string theorists so far this year. The final number of jobs is yet to be determined, with ten people so far getting job offers. It looks like the total number of jobs in the field will remain at the low level typical of the last three years since the recession hit in 2008.

Erich Poppitz has been compiling statistics based on the Rumor Mill data, and has the results through 2010 here. Job numbers rose to a level of 20-25 jobs/year from 2000-2007, from a low level of 10 jobs/year back in the 1990s. This phenomenon is generally attributed to jobs becoming available as the generation that was tenured during the huge expansion of universities in the 1960s finally started to retire. The recession has brought those numbers down to 15 (2008), 9 (2009) and 14 (2010). In recent years (since about 2004) he counts about a fifth of the jobs as going to string theorists. If that number does go to zero this year, that would be the first time this has happened since the numbers became available, and I would guess all the way back to shortly after string theory first became popular in 1984-5.

Posted in Uncategorized | 21 Comments

Hawking and the Google Zeitgeist

Posted on May 16, 2011 by woit

Today is the first day of this year’s Google Zeitgeist gathering of high-powered world leaders and thinkers (described here, it seems that Google either doesn’t believe in having a web presence, or it’s a secret one. Anyway, my attempts to Google it have failed). One of the headline speakers is Stephen Hawking, and the Guardian reports that:

His talk will focus on M-theory, a broad mathematical framework that encompasses string theory, which is regarded by many physicists as the best hope yet of developing a theory of everything.

M-theory demands a universe with 11 dimensions, including a dimension of time and the three familiar spatial dimensions. The rest are curled up too small for us to see.

Evidence in support of M-theory might also come from the Large Hadron Collider (LHC) at Cern, the European particle physics laboratory near Geneva.

One possibility predicted by M-theory is supersymmetry, an idea that says fundamental particles have heavy – and as yet undiscovered – twins, with curious names such as selectrons and squarks.

Confirmation of supersymmetry would be a shot in the arm for M-theory and help physicists explain how each force at work in the universe arose from one super-force at the dawn of time.

They got him to respond to some questions posed in advance, and one of them has the Guardian’s Ian Sample puzzled. Hawking’s answer to “What is the value in knowing “Why are we here?'” was:

The universe is governed by science. But science tells us that we can’t solve the equations, directly in the abstract. We need to use the effective theory of Darwinian natural selection of those societies most likely to survive. We assign them higher value.

Sample’s reaction to this:

On reading it I had one of those familiar, sinking moments of realisation that my brain is so spectacularly inferior to the interviewee’s that all I can do is hold up my hands and say: “Huh?”

At best I might have an inkling of what this means, but I am by no means sure. In this situation, it might take a while to clarify the answer, but other bright minds out there might well be able to unravel it for me and anyone else who might be interested. If you can help, post your thoughts below and put me out of my misery.

To me, it feels as though he is referring to the idea that there are many possible universes and that we can use Darwinian ideas of natural selection to work out which might be most hospitable to life as we know it, and because they are habitable in some sense we value them more highly. That’s my best guess, but I have minimal confidence in it being right.

I will do my best to clarify the answer this week.

My contribution to explaining this is that I see two possibilities:

1. Hawking has signed on to Lee’s Smolin’s ideas about cosmological natural selection.

2. Hawking has realized that once you’ve decided to trade in science for pseudo-science and head down the Multiverse Mania path, there’s no longer any point in worrying about whether what you say makes sense or not, and is behaving appropriately.

Posted in Multiverse Mania | 49 Comments

The Big Bang

Posted on May 15, 2011 by woit

There’s a new film out this weekend with a particle physics theme (no string theory), called The Big Bang, starring Antonio Banderas. I figured that it’s my duty to cover this kind of popular culture use of particle physics, so went to see the film last night. It took some effort to identify the one screen in New York where it was showing, and the theater contained about 10 people at the Saturday night 8:20 show. If it’s showing in your area (only New York and LA I think) and you want to see it on a big screen, better go very soon.

I was going to write a review, and mention as many as possible of the various physics inside jokes that appear, but this has been done better here, where the film is aptly described as belonging to the genre “nerd noir”, with a “particle physics fetish” sex scene. The film features an LHC-lookalike built underground in New Mexico, designed to search for the Higgs (God Particle). The sex scene mentioned in the review pairs Banderas with a woman with a bubble chamber event and uncertainty principle tatoos. In the throes of passion she discusses Heisenberg uncertainty, entanglement, and the Standard Model.

There’s more about the film here, and Lubos has his take here. Rex Reed really didn’t like it, and it’s hard to disagree, unless you’re a great fan of particle physics camp in movies.

Presumably this will be going more or less straight to DVD in a rather short time.

Posted in Film Reviews | 13 Comments

Recent NSF Grants

Posted on May 11, 2011 by woit

In responding to a comment on the previous posting, I was curious if one could easily get some data on relative sizes of grants in mathematics and physics, so started to do a quick search on nsf.gov. Among the first few NSF grants that turned up, I noticed a couple rather odd things:

  • Award 1056580 for a postdoc in “Dark Energy, Fine-Tuning, and the Multiverse: Testing Theories in Modern Cosmology” drew my eye, since my impression was that NSF physics panels weren’t so likely to support Multiverse Mania research. Taking a look at the details of the award gave the explanation: this one is being funded not by the physics division (PHY) at NSF, but by the sociologists (SES, Division of Social and Economic Studies). So, now it seems that multiverse studies are part of sociology, which is much more appropriate than physics, and has the added advantage of opening up new funding opportunities.
  • Trying to pick a typical theory group grant, I took a look at Award 0969020, for the string theorists at UT Austin. I was pleased to see that blogging is now a selling point on NSF grants:

    Professor Distler authors a blog which discusses and elucidates many of the important research papers which appear on the daily arXiv listings, and he plans to continue his activity.

    The abstract was the usual sort of string theory promotional verbiage, beginning:

    For the past two decades, string theory has been one of the most intensely investigated areas of theoretical high-energy physics. This is true chiefly because string theory offers what is currently the most successful method of unifying gravity with the other fundamental forces (strong, weak, and electromagnetic).

    The next one I took a look at was Award 1001296 to theorists at UPenn, whose abstract sounded kind of familiar, beginning:

    For the past two decades, string theory has been one of the most intensely investigated areas of theoretical high-energy physics. This is true chiefly because string theory offers what is currently the most successful method of unifying gravity with the other fundamental forces (strong, weak, and electromagnetic).

    • Posted in Multiverse Mania | 29 Comments

    Pricey Strings

    Posted on May 11, 2011 by woit

    In recent years most of the conferences I’ve attended have been mathematics and mathematical physics ones, and I had noticed that, while modest registration fees were often a feature many years ago, these days most such conferences, especially in the US, have no registration fee at all. It seems that mathematicians tend to organize conferences at rather modest cost, and mathematics research is very well supported by the NSF, universities and private foundations. This morning I’d been idly considering the idea of taking a day-trip down to Philadelphia next month to visit friends and maybe attend a couple talks at String-Math 2011, which has a promising list of speakers, but not yet a schedule of talks. I noticed though that registration is $200, which is a bit high as a price to attend a couple talks, whatever source I might find to pay for it.

    As one moves from mathematics topics to physics ones, it seems that things get a lot pricier. You might think that string theory not working out as hoped would lead to the availability and market-value of string theory talks heading downwards, but the opposite seems to be true. The big string theory conference this summer is Strings 2011 in Uppsala, where registration will cost you 5625 Swedish Krona (about \$900) [Organizer Joe Minahan points out that this is the on-site cost for faculty, for whom the pre-May 19 price is 4375 Swedish Krona = \$700, post-May 19 5000 Swedish Krona = \$800. Costs for students are lower]. For that you get the talks, coffee, lunch and a reception. If you want to go to the conference dinner, that’s \$112 extra. The conference series is advertised as “gathering more than 500 researchers in string theory”, although in recent years, attendance at Strings 20XX conferences has been a bit lower. Last year’s was anomalous, held in March (when academics often can’t travel) in College Station, Texas (not exactly a major tourist destination), it attracted only 193 participants, despite a relatively low registration fee of only $350. For Strings 2011, they’ve got 208 people registered already. The list of speakers is here. There’s an associated program of Public Lectures which seem likely to have little to do with string theory, instead concentrating on “mind-boggling questions” about the multiverse and the Big Bang. Those at least seem to be free.

    I haven’t added up the total cost, but if you’ve got significant funds available from a grant, university research support, or private wealth, you can spend pretty much the entire summer attending not just string theory talks, but even string phenomenology talks (see a list here). There’s the String Vacuum Project meeting in Philadelphia starting May 23, from which one could head to String Phenomenology at Nordita from May 30 to June 25, then Strings 2011 in Uppsala until July 2, a workshop and conference in Spain from July 3-29, Les Houches for most of August, then String Phenomenology in Madison August 22-26 and SUSY11 at Fermilab keeping you busy until Labor Day.

    Update: The hot topic these days is not string theory, but gauge theory amplitudes, using twistors. If you can’t afford strings, the price of the twistor talks is still low: a correspondent points out to me that for a registration fee of 15 pounds, you can attend Twistors, Geometry and Physics, a meeting this summer in honor of Penrose’s 80th birthday.

    Posted in Uncategorized | 35 Comments

    This Week’s Hype

    Posted on May 8, 2011 by woit

    Philip Gibbs points to an impressive piece of string theory hype from British Channel 4 news.

    If you watch the clip, you get the latest news about string theory and the LHC: people were getting discouraged about string theory, but now some of its predictions are being confirmed by the LHC. For the extra dimensions to appear, we may have to wait a couple years for when the machine runs at design energy.

    Not clear at all where they got this nonsense from.

    Update: The source for this seems to be a story by Jonathan Leake in The Sunday Times, entitled Stand by, we may soon enter a new universe (subscription required, but a syndicated version is freely available here). The story has David Evans of Alice trying to promote his experiment with:

    The Alice experiment may soon be able to make experimental measurements which, for the first time, can be modelled using the techniques of string theory.

    Although the experimental results will not prove string theory to be correct, an accurate prediction would certainly show that the techniques work, could distinguish between different versions of the theory, and perhaps even show whether the theory is going in the right direction.

    Given this kind of quote, one can see why the writer completely mixes up string theory unification and string theory as approximate calculational method in heavy-ion physics:

    The researchers, at Cern, the European centre for particle physics near Geneva, say results from the Large Hadron Collider suggest it could offer the first experimental test for some aspects of string theory.

    Formulated in the 1960s, this theory attempts to describe how all the fundamental forces of nature, such as gravity and electromagnetism, interact with matter.

    On paper, the theory has been highly successful, resolving many mathematical problems.

    In practice, however, there is no experimental evidence to support its predictions, including the idea that there could be as many as 11 dimensions – the three physical dimensions, time and seven others as yet undiscovered.

    At Cern, there are now hopes the LHC may be able to break this impasse.

    Then, as usual, the headline writer takes things a step further:

    SCIENTISTS have devised the first experiment capable of giving insight into one of the universe’s greatest mysteries: could there be more dimensions than we know about?

    So, out-of-control promotional efforts for ALICE are at the bottom of this one.

    Posted in This Week's Hype | 21 Comments

    Not a Leak

    Posted on May 8, 2011 by woit

    ATLAS this weekend has finally released their latest analysis of the gamma-gamma invariant mass spectrum, carried out in response to claims from within their collaboration that a 4 sigma Higgs signal had been observed in this channel. The result? Nada:

    The dominant background components are measured and found to be in agreement with the Standard Model predictions, both in terms of overall yield and invariant mass distribution. No excess is observed.

    Posted in Experimental HEP News | 2 Comments

    This Week’s Leak

    Posted on May 4, 2011 by woit

    Recently there was a bit of a kerfuffle triggered by someone leaking here the abstract of an internal ATLAS document claiming to have found a Higgs signal as a bump in the gamma-gamma invariant mass distribution. After some initial discussion of this, I wrote:

    Best guess seems to be that this is either a hoax, or something that will disappear on further analysis.

    It quickly became clear this was not a hoax, but now there’s a new leak, this one from CMS to New Scientist, which indicates that “disappear on further analysis” is where this is going:

    Now physicists working on the LHC’s other main detector, CMS, have come up empty in an initial search for a similar bump in their data, according to a document shown to New Scientist. So ATLAS’s bump may not be due to Higgs particles, after all, but instead down to something mundane, such as an error in the analysis.

    The internal CMS document has not been released to the public, so the result is still preliminary, as was the news of the original ATLAS bump, for that matter, which was leaked before it was reviewed or endorsed by the ATLAS collaboration.

    Well, maybe first news of the Higgs won’t show up on a blog, but at a more standard journalistic outlet…

    Update: Curiouser and curiouser. It seems that there are questions about the existence of the supposed CMS document leaked to New Scientist. In other rumors floating around, while there may not be such a CMS document shooting down this signal, there really is an ATLAS one, soon to see the light of day. In any case, there are no rumors I’m aware of that there’s any confirmation of the original signal.

    Posted in Experimental HEP News | 19 Comments

    This Week’s Hype

    Posted on April 28, 2011 by woit

    This week’s hype comes from an unusual source, John Baez and his ex-student John Huerta, who have a new article in Scientific American entitled The Strangest Numbers in String Theory.

    The expository article about octonions by John (Baez) that appeared in the AMS Bulletin (copy here, a web-site here) is one of the best pieces of mathematical exposition that I have ever seen. The octonions can be thought of as a system of numbers generalizing the quaternions. As with the quaternions, multiplication does not commute, and things are even worse, it’s not associative either. So, probably best not to try and think of these as “numbers”, but they do give a very remarkable exotic algebraic structure, one that explains all sorts of other exotic structures occurring in different areas of mathematics. The article beautifully explains a lot of the intricate story of how octonions connect up surprising phenomena in algebra, geometry, group theory and topology.

    If you’re a mathematical physics mystic like myself, you’re susceptible to the belief that anything this mathematically deep, showing up in seemingly unrelated places, must somehow have something to do with physics. The story of octonions is closely related to the story of Clifford algebras, which are definitely a crucial part of physics, but it seems to me we’re still a long ways from truly understanding the role in physics of Clifford algebras, much less the more esoteric octonions. One thing that is fairly well understood is that the sequence of division algebras explains some of the structure of low-dimensional spin groups in Minkowski signature, through the isomorphisms:
    SL(2,R)=Spin(2,1)
    SL(2,C)=Spin(3,1)
    SL(2,H)=Spin(5,1)
    The octonion story is supposed to be the next in line, involving Spin(9,1), but made much trickier by the fact that SL(2,O) doesn’t really exist, since the octonions are non-associative.

    Back in 1982, a very nice paper by Kugo and Townsend, Supersymmetry and the Division Algebras, explained some of this, ending up with some comments on the relation of octonions to d=10 super Yang-Mills and d=11 super-gravity. Baez and Huerta in 2009 wrote the very clear Division Algebras and Supersymmetry I, which explains how the existence of supersymmetry relies on algebraic identities that follow from the existence of the division algebras. Kugo-Townsend don’t mention string theory at all, and Baez-Huerta refers to superstrings just in passing, only really discussing supersymmetric QFT. There’s also Division Algebras and Supersymmetry II by Baez and Huerta from last year, with intriguing speculation about Lie n-algebras and what these might have to do with relations between octonions and 10 and 11 dimensional supergravity. For a nice expository paper about this stuff, see their An Invitation to Higher Gauge Theory.

    In contrast to the tenuous or highly-speculative connections to string theory that appear in these sources, the Scientific American article engages in the all-too-familiar hype pattern. The headline argument is that octonions are important and interesting because they’re “The Strangest Numbers in String Theory”, even though they play only a minor role in the subject. It wouldn’t surprise me at all if octonions someday do end up playing an important role in a unified theory, but the rather obscure connection to the calculation of the critical dimension of the superstring that seems to be the main point of the Scientific American article isn’t a very convincing argument for such a role.

    Somehow I suspect that those string theorists who were upset by Scientific American’s decision to publish speculation by Garrett Lisi about E8 and wrote in to complain, won’t be similarly upset to find this highly speculative material about the octonions appearing in the magazine.

    Posted in This Week's Hype | 27 Comments