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The Trouble with Physics 373

SpaceAdmiral writes "You've likely heard of Lee Smolin's book The Trouble with Physics. It has created a lot of controversy because it argues that string theory gets far too much attention and money, despite a complete lack of evidence. It accuses string theorists of groupthink. Smolin has dabbled in string theory from time to time but he's a proponent of the alternative loop quantum gravity. Although irrelevant to this book review, he has also suggested that it is possible that universes reproduce via black holes, making them prone to pressure similar to natural selection (universes that produce a lot of black holes are more successful spawners than those that don't). In The God Delusion, Richard Dawkins quotes Nobel-winner Murray Gell-Mann as once saying, "Smolin? Is he that young guy with those crazy ideas? He may not be wrong."" Read the rest of SpaceAdmiral's review.
The Trouble with Physics
author Lee Smolin
pages 392pp
publisher Houghton Mifflin Company
rating 9
reviewer Fane Henderson
ISBN 0618551050
summary The Rise of String Theory, the Fall of a Science, and What Comes Next


The Trouble with Physics is very unlike most pop-physics books not only in its criticism of string theory, but in its open adulation of Einstein and skepticism of the Copenhagen interpretation of quantum theory. Having said that, it does provide a very decent summary of 20th century physics (including string theory) for laypeople, not unlike more traditional pop-physics books (e.g. by Hawking and Greene).

The book's main criticisms of string theory are that it makes no testable predictions and that some things string theorists take for granted haven't been rigorously proven mathematically. Smolin is highly skeptical of many string theorists' reliance on the Anthropomorphic Principle.

The book becomes most interesting somewhere in the middle where he discuses truly controversial approaches to physics. This includes things like MOND, which, interestingly enough, Smolin is skeptical of.

In case you've forgotten your high-school physics, I'm going to use this paragraph to refresh your memory of special relativity to prepare you for the next couple paragraphs. The basic idea of special relativity is that the speed of light is constant. Pretend that I am shining a light at you while (A) standing still relative to you; (B) moving towards you at half the speed of light, and; (C) moving away from you at half the speed of light. In all three scenarios, I will accurately measure the light moving away from me at 3,000,000 km/s and you will accurately measure the light moving toward you at 3,000,000 km/s. To ensure this result, distances and times will have to be different for me than they are for you, except in case (A).

Now I'll quickly remind you of the Planck length: This is a theoretical limit on how small something can be. According to Smolin, all versions of quantum gravity seem to suggest the Planck length as a limit. But would observers moving relative to each other disagree about the Planck length?

I used to be a big fan of MOND (in a layperson sense) until Smolin introduced me to DSR (doubly special relativity) and DSR II. The basic idea is that it may be possible to modify the theories of relativity such that observers agree not only on a constant speed of light, but also on a constant Planck length. It's not unreasonable to guess that a modification of this sort could solve some of the same problems MOND does (e.g. explain astronomical observations without resorting to dark matter and dark energy). Furthermore, since DSR in its current incarnation predicts that more energetic photons are slightly faster than less energetic photons (only the speed of the least energetic photons is constant in DSR), it could also explain away, for example, inflation in the Big Bang model. (Immediately after the Big Bang, everything was hotter and more energetic, so the average speed of light would have been faster than it is now if DSR is correct.) Although I'm not qualified to judge the actual mathematics of such a theory, I find it very appealing for reasons of consilience.

I was slightly disappointed with the final chapters of Smolin's book since, despite an obvious effort to the contrary, it struck me as awfully bitter and reeked of sour grapes. Leaving physics in favor of sociology, he lambasted the current tenure and peer review systems (particularly in the United States) as favoring Master Craftspeople (like those scientists who developed the standard model of particle physics) over Seers (like Einstein, Bohr, and de Broglie) who look at the deep questions of physics that border on the philosophical rather than the latest technical problem. A few interesting things do emerge in these chapters. One such thing is that Smolin seems to have a soft spot for Paul Feyerabend as a philosopher of science (despite describing himself as a proud Popperazzo in an endnote). Another is that Smolin thinks a scientist who is hated by half his senior colleagues and loved by the other half is likely better than a scientist who is liked by all his senior colleagues. I strongly recommend this book.


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The Trouble with Physics

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  • Two sides (Score:2, Insightful)

    by 2.7182 ( 819680 )
    I see two sides to this. Smolin has a point. Most string theory papers are garbage. (True of many fields). But Smolin himself has not been research active in a long time. And it is unlikely that he understands enough mathematics to judge string theory - like most people.
    • Correction (Score:3, Insightful)

      by 2.7182 ( 819680 )
      Smolin is research active, but I seriously doubt he understands what Ed Witten did in the 1990's, for example.
    • actually (Score:5, Informative)

      by giampy ( 592646 ) on Monday January 15, 2007 @04:42PM (#17618482) Homepage
      A quick search on arxiv.org will show you that he is indeed very active, since he is still publishing very technical papers.
      Not only that, Lee Smolin seems one of the very very few physicists who understands BOTH string theory AND other approaches (that is _the_ other approach, loop quantum gravity).

      In any case, it seems that many predictions of loop quantum gravity will be actually tested within the next couple of years trough the GLAST satellite, so, we will get news relatively soon ...
    • Re:Two sides (Score:5, Informative)

      by gardyloo ( 512791 ) on Monday January 15, 2007 @04:44PM (#17618502)
      Smolin himself has not been research active in a long time. And it is unlikely that he understands enough mathematics to judge string theory - like most people.


            Not sure what you mean by "research active". His contributions to xarchiv (many published in hack journals like Physical Review and The Journal of Quantum Gravity) are prolific as recently as 2006 and 2004 (noticeable lack of submissions in 2005). And I would NOT call him mathematically illiterate, even in an "esoteric" field like string theory. (Yes, I am a physicist.)
    • by EmbeddedJanitor ( 597831 ) on Monday January 15, 2007 @04:57PM (#17618702)
      The real problem I see is that there is no real string. Most physics so far has been based on real things: mass, electrons,... Strings are just a modelling tool.

      As physics progresses we seek for something that was hidden from the previous generation of physics. For example we start with observing gravity happen. 100k years ago (or 6k years ago - depending on your worldview) Ogg drops rock, ogg gets sore toe. Then more recently someone figured out it is because of mass/proximity of objects. Then someone figures out a characterising equation. Then someone else figures it is because space is bent. Then strings. No longer are we improving our observations. Now we're coming out with mathematical models of things that don't really exist.

      • by Kandenshi ( 832555 ) on Monday January 15, 2007 @05:22PM (#17619028)
        "It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature." - Niels Bohr

        IMO(and to some other positivists such as Stephen Hawking) it doesn't really matter if something is exactly how that universe IS. It just matters that it allows us to make falsifiable predictions about what we can observe.
        • by nebular ( 76369 )
          I agree, the study of physics is interpreting the universe in ways we can understand.

          Since we are in the universe and thus part of the system, we may not be able to actually view the universe as it actually is, but in terms that make sense to us.
        • Re: (Score:3, Funny)

          by ultracool ( 883965 )
          I must point out String Theory Summarized [xkcd.com] from xkcd.
      • Re: (Score:2, Insightful)

        by eipipuz ( 631495 )
        Your idea of "real object" is very very strange. Mass?? It's just a characteristic of matter. And an electron is as real as quark, and that doesn't exist by itself! Always in couples or triplets. We are improving our observations, it's just that it isn't visible. Call it measurement. If there are strings, they have ways to interact with us. I won't even bite the "mathematical models of things that don't really exist", because physics is by definition a model, a mathematical model. It's a map about reality
        • by Tablizer ( 95088 )
          Your idea of "real object" is very very strange. Mass?? It's just a characteristic of matter.

          Agreed. We cannot tell the difference betwen a "model" and something "real" other than our model of it fitting observations. But fitting observations only tells us how accurate our model is. It says nothing directly about wether something is "real" or not. Wrong models can still fit reality. But perhaps it does not matter. Ideally we would like to have the "correct" model, but a wrong model that produces all the a
      • by MobyDisk ( 75490 )
        Mass is not a real thing either, unless we can find and measure a graviton. Same with quarks. Same with strings. Same with virtual particles. Once you get down to quantum physics, almost everything is "unreal."

        Some of this is perspective. Because of our size, we take gravity for granted as something "real." But it is no different from a string - you can't see it directly. But if you were a proton, a string would seem more "real" to you than gravity, because it would likely affect your daily life.
      • by The_Wilschon ( 782534 ) on Monday January 15, 2007 @07:07PM (#17620692) Homepage
        What do you mean real? Call me back when you see a real electron. Or better yet, when you see a real quark. Superstrings are just as real as either of these. In fact, unless I misunderstand, electrons and quarks would merely be a special case of strings, that is, strings carrying particular vibrational modes.

        Ernst Mach raised precisely this objection against atomic theory. He said that atoms were not real because we could not, and would never be able to, see them. They were just a convenient mathematical model which happened to make reasonable predictions, but they were not actually real. Well, as it turns out, theories which utilize these "unobservable, unreal, mathematical constructs" are often very successful, and, where they have been successful, we have later found ways to observe precisely the objects described.

        So, I would say that strings, if the theory turns out to produce useful, accurate, precise results, are just as real as photons, atoms, rocks, and stars.

        That's not to say I like string theory. I hope string theory doesn't win. I think that it would put us in actually a worse position than the Standard Model has us in right now. The standard model has umpteen different parameters which must be fine tuned by experiment. This is generally regarded as a serious shortcoming, as the values of those parameters ought to be predicted by a good theory. String theory is "parameterless". This is a wonderful thing, until you consider that those extra spacial dimensions can be wrapped up around each other in an enormous number of ways, and each way produces a completely different set of particles and natural laws. So now, rather than measuring a few values, we must instead investigate every possible way of wrapping up the extra dimensions, until we find one which matches our own universe. So, in short, the topology of space is the parameters of string theory, and a much nastier parameter space than for the standard model it is.
        • IBM (Score:3, Informative)

          Ernst Mach raised precisely this objection against atomic theory. He said that atoms were not real because we could not, and would never be able to, see them.
          IBM disagrees [bbc.co.uk].
  • by roman_mir ( 125474 ) on Monday January 15, 2007 @04:30PM (#17618262) Homepage Journal
    Nothing for you to see here. Please move along.

    Although irrelevant to this book review, he has also suggested that it is possible that universes reproduce via black holes, making them prone to pressure similar to natural selection (universes that produce a lot of black holes are more successful spawners than those that don't). doesn't the same despite a complete lack of evidence quote apply to this just as well?
  • by tylersoze ( 789256 ) on Monday January 15, 2007 @04:39PM (#17618392)
    Really? I didn't realize giving human characteristics to subatomic particles was a part of any current mainstream physics theory. :) I'm assume you mean the *anthropic* principle.
  • Accurate? (Score:5, Informative)

    by Whalou ( 721698 ) on Monday January 15, 2007 @04:40PM (#17618422)
    In all three scenarios, I will accurately measure the light moving away from me at 3,000,000 km/s and you will accurately measure the light moving toward you at 3,000,000 km/s.

    Not very accurate. It should be 300,000 km/s. Or 299,792.458 km/s to be precise.
    • by Jamu ( 852752 )
      Strictly you can't measure the speed of light in km/s. SI units define the value for good reasons. One of which is that the speed of light (in Relativity) is a fundamental limit for any velocity. Saying that more energetic photons have a higher velocity is not a simple thing.
  • Is there really an Anthropomorphic principle or should that have read Anthropic Principle?

    I'd be interested to know what the Anthropomorphic principle was... the laws of the universe are structured such that man-shaped being have to exist, perhaps?

  • by zappepcs ( 820751 ) on Monday January 15, 2007 @04:41PM (#17618440) Journal
    did he write this book using 12 sided dice and a lot of caffeine?

  • by olclops ( 591840 ) on Monday January 15, 2007 @04:41PM (#17618442)
    Smolin is highly skeptical of many string theorists' reliance on the Anthropomorphic Principle.
    That's the Anthropic Principle: the idea that the constants we observe in this universe which are ostensibly crucial for the formation of life, are that way because if they were any other way we wouldn't be here to observe them.
    • by flyingsquid ( 813711 ) on Monday January 15, 2007 @04:52PM (#17618626)
      Hrm, is their a Misanthropic Principle? That the physical constants of the universe are the way they are to make our lives miserable?
      • by HTH NE1 ( 675604 )
        "You know, I used to think it was awful that life was so unfair. Then I thought, wouldn't it be much worse if life were fair, and all the terrible things that happen to us come because we actually deserve them? So now I take great comfort in the general hostility and unfairness of the universe." -- Ranger Marcus Cole
      • Oddly enough, this has already been reported on. It turns out that the physical constants of our Universe are such that it is inevitable that toast will tend to fall butter-side down. See Tumbling toast, Murphy's Law and the fundamental constants [iop.org] by R. A. J. Matthews in the European Journal of Physics.

        Abstract. We investigate the dynamics of toast tumbling from a table to the floor. Popular opinion is that the final state is usually butter-side down, and constitutes prima facie evidence of Murphy's Law

      • Re: (Score:3, Funny)

        How about a lycanthropic principal? That if the physical constants were changed we would transform into something else?
    • Re: (Score:2, Funny)

      by hehman ( 448117 )
      No, he did indeed mean the Anthropomorphic Principle, the one where strings act like people. Smolin is right to be highly skeptical of string theorists' reliance on yarn finger puppets to do serious research.
  • by Baldrson ( 78598 ) * on Monday January 15, 2007 @04:42PM (#17618460) Homepage Journal
    An hypothesized (meta)algorithm running our universe [idsia.ch] has been proposed in "The New AI: General & Sound & Relevant for Physics [idsia.ch]" by Jürgen Schmidhuber [idsia.ch] of Dalle Molle Institute for Artificial Intelligence [idsia.ch]:
    "Systematically create and execute all programs for a universal computer, such as a Turing machine or a CA; the first program is run for one instruction every second step on average, the next for one instruction every second of the remaining steps on average, and so on."
    This actually computes all universes -- not just ours. It also computes what might be thought of as nested universes, giving rise to the idea promoted by Smolin that some universes might be more prolific than others. Among the consequences of this hypothesis is:
    "Large scale quantum computation will not work well, essentially because it would require too many exponentially growing computational resources in interfering 'parallel universes'".
    Prof. Schmidhuber's post-doc student, Marcus Hutter [wikipedia.org], of Hutter Prize for Lossless Compression of Human Knowledge [slashdot.org] fame came up with some of the key breakthroughs in "The New AI" [hutter1.net] upon which Schmidhuber's hypothesis is based.
  • by nhavar ( 115351 ) on Monday January 15, 2007 @04:42PM (#17618484) Homepage
    What does this have to do with the book, string theory, or anything else for that matter?

    In The God Delusion, Richard Dawkins quotes Nobel-winner Murray Gell-Mann as once saying, "Smolin? Is he that young guy with those crazy ideas? He may not be wrong."


    Why is it that suddenly people are working out ways to mention Dawkins in as many articles as they can that have little if nothing to do with him? Are we playing a six-degrees-to-Richard-Dawkins game here?
    • Re: (Score:3, Funny)

      by samoverton ( 253101 )
      In nhavar's quote, nhavar quotes slashdot editors who posted a story, in which Richard Dawkins was quoted as writing that Nobel-winner Murray Gell-Mann once said, "Smolin? Is he that young guy with those crazy ideas? He may not be wrong."
    • Re: (Score:3, Funny)

      by nizo ( 81281 ) *
      Smolin? Is he that young guy with those crazy ideas? He may not be wrong.


      I think the point being made here is that todays nutjob is often tomorrows nobel winner. Besides you don't get to hear much from Richard ever since he left Family Feud.


      (Yeah I am just kidding, I know it is Richard Dawson [wikipedia.org] who is of Family Feud fame)

      • by plopez ( 54068 )
        Game show host by day, brilliant theorectical physicist by night....
      • "I think the point being made here is that todays nutjob is often tomorrows nobel winner."

        I don't recall too many Nobel winners being called nutjobs in their early days. I think that is a myth propogated by bitter nutjobs.

        "He may not be wrong." ...and he may not be right!
    • The point is that Gell-Mann hasn't written off Smolin, which may lend some degree of credence to him. The only reason Dawkins is mentioned is to properly attribute the quote. I understand your confusion though; proper attribution is so rare on the InterWebs these days.
  • Fan of Heim, myself (Score:3, Interesting)

    by Valdrax ( 32670 ) on Monday January 15, 2007 @04:43PM (#17618486)
    I used to be a big fan of MOND (in a layperson sense) until Smolin introduced me to DSR (doubly special relativity) and DSR II.

    Personally, I've been a fan of Heim theory, not necessarily because I think it's definitely true even though it makes nice predictions about particle mass, but because I just really want a space drive to be possible.
  • by SpinyNorman ( 33776 ) on Monday January 15, 2007 @04:49PM (#17618574)
    There's an interesting article in the last issue of New Scientist, discussing work by physicist Gerard 't Hooft in refining his theory of a determanistic level of reality below quantum physiscs, from which the apparent randomness and Copenhagen state collape of quantum physics appears.

    http://www.newscientist.com/channel/fundamentals/m g19025504.000 [newscientist.com]

    Maybe Einstein was right that "God doesn't play dice" (a rather misunderstood statement given that Einstein was an ardent aetheist).

    Presumably efforts such as string theory to unite general relativity & quantum mechanics may be quite shaken up if this new theory is correct.

    • by Aladrin ( 926209 )
      As one of those who 'misunderstood' that statement for years, and just looked it up, allow me to explain to everyone what the real meaning is:

      Einstein was not saying anything about Fate or God or Free-will. He referring to Heisenberg's Uncertainty Principle, which basically says that events at the "microphysical" level happen 'by pure chance' or 'without any cause'. Einstein maintained that it wasn't without cause, we were simply unable to make measurements that fine and could not predict the movements.
      • by jonatha ( 204526 )
        The Bell inequality rules out the "hidden parameter" explanation.

        At least that's what "Quantum Reality" [amazon.com] says...
        • Re: (Score:3, Informative)

          by Deviant Q ( 801293 )
          The Bell Inequality rules out local counterfactually definite hidden variable theories. Nonlocal theories in particular are quite doable, and David Bohm worked on those for a long time before he died. I've been reading some of his books (but not scientific papers), and they seem fairly reasonable; however, I think they fall in to the "not mainstream enough to take seriously" category.

          I don't know what 't Hooft's theory is though.

          On another note, I've written a paper on why the Bell Inequality does not falsi
      • Re: (Score:3, Informative)

        by 2short ( 466733 )

        Heisenberg's Uncertainty Principle says it's impossible to know both the position and velocity of a particle; and particularly that increasing the precision whith which you know one will decrease the precision with which you know the other. It is related to, but not quite the same as, the assertion of quantum mechanics that at the smallest scales, reality is not deterministic.

        Einstein thought this risiculous, as expressed in the famous quote, but most physicists now beleive he was wrong.

        Either position is
        • Re: (Score:3, Insightful)

          by kestasjk ( 933987 ) *
          The quote you're referring to is "God does not roll dice" - Einstein, but your mention of God worries me because Einstein wasn't referring to a supernatural God but using God as a label for the way the universe ticks. (This was discussed at length in Dawkin's book mentioned above actually)
  • by ranton ( 36917 ) on Monday January 15, 2007 @04:50PM (#17618576)
    A big problem amongst educated people is to think that scientists are not prone to the same illogical behavior as average people. We think that they are immune to "following the flock" or otherwise being influenced by their peers.

    While scientists are in general better than average people at being objective, they still tend to have their own biases. Spending you life working on a particular theory makes it hard to give it up even when the evidence disproves it. Even an objective scientist is going to have problems throwing away their life's work.

    --
    • by rho ( 6063 ) on Monday January 15, 2007 @06:32PM (#17620116) Homepage Journal

      For example, the quote from Gell-Mann in the review's summary. It's an interesting bit of personal history, but has nothing to do with any physics. What Gell-Mann thinks about anybody's physics is utterly irrelevant. By definition the only thing of interest in science is what can be proven. But scientists, being people, will put more weight on one person's opinion over another's for unscientific reasons.

      The scientific method is very good for getting at the reasons behind something, but once you start to worship science as an abstract, you've lost perspective.

    • Re: (Score:3, Insightful)

      by Keebler71 ( 520908 )
      Excellent points... funny how when I raise the same points in a global warming discussion (not that it isn't occurring, just that scientists are human and have biases) ... I get modded down...
  • Vilenkin says... (Score:4, Informative)

    by Cally ( 10873 ) on Monday January 15, 2007 @04:50PM (#17618600) Homepage
    Vilenkin has published an interesting paper [physicsforums.com] which suggests a problem with Smolin's "natural selection of life-friendly universes via black holes" theory; OTOH Smolin strikes back [physicsforums.com]! Ahhh, I love it when cosmologists attack ;)
  • by Gromius ( 677157 ) on Monday January 15, 2007 @04:51PM (#17618620)
    Because theres not a lot else in fundamental theoretical particle physics to spend it on. Basically we've reached the point where everything we can test right now is tested and understood and there hasnt been any significant surprises in the last 30 years. Basically the cludge that is the Standard Model works far too well and its completely theoretically worked out. And the theorists are just screwing around with silly things now because they are waiting for experiment to catch up with theory. We hope that this will happen when the Large Hadron Collider (LHC) turns on and that we will find something unexpected. This will give us the clue what to try next theoretically. And as soon as that happens, the theorists interest in string theory will disappear as they will (hopefully) have something new to work on to explain (hopefully) very strange experimental results. Particle physics is either about to go through a golden age in two years time or its going to wither and die.
    • by Animats ( 122034 )

      There's still the basic problem that general relativity and quantum mechanics are inconsistent. Until that's resolved, it's clear that there's some basic physics we don't understand yet. String theory was developed to try to resolve that issue.

      Wikipeida has a reasonably decent article on this. [wikipedia.org]

    • Because theres not a lot else in fundamental theoretical particle physics to spend it on.
      No. The whole point of Smolin's book is that there's a variety of approaches to quantum gravity, and that the extreme focus on string theory (in terms of funding, tenured positions,...) is wrong, given that the theory has arguably been a failure.
      • If string theory is a failure, then alternatives such as loop quantum gravity are far more than that. They also have not been testable yet, and are not obviously any more predictive than string theory, given the infinitude of quantization ambiguities that plague other approaches. Loop quantum gravity also uses non-standard quantization rules with no experimental justification and is not yet even well defined. String theory is much better defined, at least as much so as quantum field theory is, and has a
        • String theory is much better defined, at least as much so as quantum field theory is, and has a demonstrable low-energy limit which recovers QFT+GR
          I'm not so sure about the GR part, since the spacetime background is assumed to be static. One of Smolin's big points in favor of loop quantum gravity is formulated in way that's manifestly consistent with the basic principles of GR (background independence), whereas string theory isn't. Also, it's now been shown that an asymptotically flat spacetime is a solu
          • I'm not so sure about the GR part, since the spacetime background is assumed to be static.

            The background spacetime in string theory is unobservable; it receives dynamical corrections from string interactions which render it observationally equivalent to GR (+ high energy corrections).

            One of Smolin's big points in favor of loop quantum gravity is formulated in way that's manifestly consistent with the basic principles of GR (background independence), whereas string theory isn't.

            That's a nice philosophical goal, but it's not a physical objection. Furthermore, string theory does have background-independent formulations (via matrix compactification, AdS/CFT and various dualities, etc.)

            Also, it's now been shown that an asymptotically flat spacetime is a solution to loop quantum gravity.

            I don't regard that to be as formally well established as Smolin does, especially since in the presence o

    • Nah, particle physics aren't going to die due to a lack of a breakthrough in two years. The field is not dominated by some sort of "nutcases" thinking up crazy theories either, that's just a fraction of them, and their presence should be valued, as their abscene would do much worse for possibilities of scientific breakthroughs.

      Basically we've reached the point where everything we can test right now is tested and understood

      No, this sounds really wrong -- we can test theories of gravity and get results from o
  • Look how much money the pr0n industry makes.


    ...wait a minute! THAT string theory ... oops!
  • by Anonymous Coward on Monday January 15, 2007 @05:00PM (#17618770)
    As a layman, I'll wait until the mod points are assigned on this article's comments. Then I'll have a reliable introduction to theoretical physics.
  • Below is the text of an email I sent Dr. Smolin late one night as I was reading the subject book. Ne never answered; if anyone can clarify I would greatly appreciate it...

    Sir -

    A friend of mine lent me a copy of "The Life of the Cosmos" and I have just reached the point at which you introduce the hypothesis that the observed values of certain of the parameters in the standard model may have arisen in an evolutionary fashion.

    It is now four in the morning and I am sending you this letter because I don't think
  • because it argues that string theory gets far too much attention and money

    Yes, physicists need to spend more time and money on other more worthwhile goals. My zero-g flying car isn't going to invent itself. I was promised we'd have flying cars by now.

  • by Animats ( 122034 ) on Monday January 15, 2007 @05:11PM (#17618890) Homepage

    "Science is prediction, not explanation" - Fred Hoyle

    The serious problem with string theory is that it doesn't yield falsifiable predictions. Theories which don't yield falsifiable predictions are not useful - you can't check them by experiment, you can't effectively choose between them, and you can't develop engineering based on them.

    This matters. From subatomic physics we got nuclear power. From quantum electrodynamics we got semiconductors and lasers. From string theory we got nothing. If you can't make predictions, you can't do engineering design.

    With string theory, you can create pretty mathematical objects, but it's not clear that there's any connection to the real world. Smolin says that's bad physics, and he's probably right.

    There's real progress in physics, but it's mostly at the low-energy, low temperature end. Seemingly impossible objects like Bose-Einstein condensates and materials with negative indices of refraction have both been demonstrated. Quantum computing is hard to do, but real. That's progress. But the high energy physicists and the cosmologists have been stuck for a while.

    It's possible for an entire field to take a wrong turn like this. Artificial intelligence did, back in the 1980s, when the expert systems people were claiming that strong AI was just around the corner. Then came the "AI winter". Twenty years later, AI is moving again, but with new approaches (more statistics, less formal logic) and new people.

    • Re: (Score:2, Interesting)

      by Anonymous Coward
      the high energy physicists . have been stuck for a while.
      It's possible for an entire field to take a wrong turn like this.


      I think discontinuing the http://en.wikipedia.org/wiki/Superconducting_Super _Collider [wikipedia.org] had a large bearing on that outcome.
    • Re: (Score:3, Informative)

      by bcrowell ( 177657 )
      The serious problem with string theory is that it doesn't yield falsifiable predictions.
      One of Smolin's arguments is that string theory has yielded falsifiable predictions, at those predictions were later disproved. For instance, one of the early predictions of string theory was that the cosmological constant had to be less than or equal to zero; there seemed to be no reasonable way to make the theory produce a positive value. Then it turned out that the cosmological constant was nonzero and positive. The
    • Re: (Score:3, Insightful)

      by fermion ( 181285 )
      Prediction is engineering, that is the application of known rules to know what will work and what will not work. Prediction is also what some theoretical physicist do, you know the swine that get hit on the head when they find a truffle.

      The base of physics, shared equally by experimental and theoretical physicist, is the collection and concise modeling and classification of data in such a way that is self consistant and is amenable to simple 'laws' that can be used to make predictions. The predictions a

      • by Rich0 ( 548339 ) on Monday January 15, 2007 @08:17PM (#17621652) Homepage
        Well, to the average layman most of Einstein's theoretical work seems meaningless. But, when you build a photocopier anybody can see that there is something to it.

        Ditto for everything else that physics has discovered. The value of the discoveries is appreciated when it is seen how these discoveries apply to the real world.

        The issue with string theory is that while it is self-consistent, it seems like nobody is able to actually do anything useful with it, and to me that makes it an inadequate theory, because the proof is in the ability to apply the theory.

        I can plot my movements for the entire day and fit them to a 47-degree polynomial with a decent level of error, and then wax philisophical about the general theory of human locomotion. And that would last about as long as it takes somebody to realize that five minutes after I publish the theory fails to account for my subsequent activities.

        Given a complex enough equation you can fit any set of data. And given enough time you can even make that equation look "beautiful". What I want to know is how well it holds up six months from now without constant tweaking...
  • by Ambitwistor ( 1041236 ) on Monday January 15, 2007 @05:16PM (#17618964)
    Below I'd like to repost something I once wrote trying to explain why string theorists think string theory is an important approach, to counter the inevitable "it's not science" claims I see on string-related threads.

    (I would like to note first that Smolin himself has written string theory papers, and historically has advocated combining string theory with loop quantum gravity, so even he doesn't think string theory is nonsense — he just would like to see it mesh with his own theories and doesn't like the attention it gets relative to them.)

    Anyway, my two cents on string theory and its justification and testability:

    First, string theory could certainly be tested if we could probe the Planck scale. We will never be able to build an accelerator to do
    that directly. There is some chance we might eventually do it indirectly by measuring fluctuations in the cosmic gravitational wave
    background. In addition, string theory encompasses many scenarios in which the string scale could be probed at much lower energies, but nobody is very confident that those scenarios are likely to be correct.

    That being said, there is a serious possibility that string theory might not be testable in practice, at least in the foreseeable future. I don't believe that puts string theory totally outside the realm of science altogether. String theory does at least make predictions, even if we can't test them. But that is a weak argument. More strongly, string theory is motivated by reason of consistency with known physics. Gravity has to be reconciled with quantum theory somehow. There are strong reasons to believe that string theory overcomes obstacles to quantizing gravity in a unique way that all other approaches can't duplicate, although this can't be proven. That is one of the main reasons why string theory is taken so seriously despite its experimental shortcomings (which are not surpassed by its alternatives, either).

    Here are a couple of arguments in favor of string theory put forth by string theorists which I have begun to agree with:

    In particle physics, it has been possible to write down theories of the non-gravitational forces while being ignorant of high energy
    Planck scale physics. This is essentially due to the Applequist-Carrazone "decoupling" theorem, which uses renormalization
    group arguments to show that low-energy physics can be made independent of high energy physics, because at sufficiently low
    energies you can't excite the higher-energy modes; therefore, their contribution is irrelevant.

    This decoupling breaks down for gravity. Because gravity is a universal interaction, it couples to everything (because everything
    has mass-energy); the low energy effects of quantum gravity are never independent of high-energy physics. So you can't write down a theory of quantum gravity unless you purport to know everything about particle physics up to arbitrarily high energies — which of course you can't possibly say, unless you can do experiments at the Planck scale.

    This is a criticism that string theorists level against loop quantum gravity. LQG is usually attempted ignoring all realistic particle
    physics, and even if that approach succeeded, you'd have to write down a different LQG theory to take into account real particles, which might work completely differently than a vacuum LQG theory. LQGers respond by saying that they want to start by just proving it's possible to quantize *any* kind of gravity using this approach, and then worry about "realistic gravity".

    String theory, on the other hand, evades the whole problem. It has a very unique mathematical structure which provides "mysterious" exact cancellations at all orders, rendering low energy physics decoupled from high energy physics despite the universal coupling of gravity.
    Thus, it can make predictions about high energy physics even without our being able to make measurements at that scale. No other approach to quantum gravity has shown any signs of being abl
    • Below I'd like to repost something I once wrote trying to explain why string theorists think string theory is an important approach, to counter the inevitable "it's not science" claims I see on string-related threads.

      rimshot

      Thank you, I'll be here all week.
    • Nice write-up.

      I am a layman on string theory, as well as on General and Special Relativity, Quantum Theory, etc., etc., etc. (like no doubt 99.999999% of the people on the planet). Still, I enjoy reading about it and generally do hear about any new ideas out there.

      If I remember right, the basic eureka moment behind string theory came from the realization that a zero dimensional object (a point) cannot physically exist in our multi-dimensional universe. A lot of special relativity math, taken to it
      • If I remember right, the basic eureka moment behind string theory came from the realization that a zero dimensional object (a point) cannot physically exist in our multi-dimensional universe.

        I suppose that's one way of putting it. One dimensional strings soften the ultraviolet divergences that plague zero dimensional point particle theories (quantum field theory). At at a very crude level, it's because particles can interact at a point, but strings don't have a well-defined point of intersection; they come together smoothly. This "fuzzing out" of the interaction has mathematical consequences for the renormalizability of the theory.

        (This is not, however, the original motivation that led to t

  • They're simply not science. When we find some way to test them, then they'll become science, physics. Until then, they're just philosophy.

     
    • You can say the same about quantum field theory. QFT is a framework; you can write down specific models in it, some of which (such as the Standard Model) are testable, and some of which are not (e.g., models with all the masses up near the Planck scale). You can do the same in string theory: there are testable string models, and others that are not testable. String theory isn't developed enough to tell us which of those models may be correct, but then again, QFT doesn't tell us which model is correct ei
  • by Anonymous Coward
    One thing I like about this debate is the cool quotes :):

    http://en.wikipedia.org/wiki/Feynman [wikipedia.org]

    Feynman, "I don't like that they're not calculating anything. I don't like that they don't check their ideas. I don't like that for anything that disagrees with an experiment, they cook up an explanation - a fix-up to say, 'Well, it still might be true.'"

    http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/ 03/14/MNGRMBOURE1.DTL [sfgate.com]

    Another Nobel Prize winner, Robert Laughlin considers string theory to be physic's version
  • For those of you interested in the social process of doing science, you may want to check out Kuhn's Structure of Scientific Revolutions. It is a rigorous account of how communities of scientists frequently stick to tribalism (e.g. "the string theory camp" or "the Heliocentric camp" or "the natural selection camp") and how this tribalism structures how science is done. Kuhn's story seems to be reflected in this slashdot story.

    (Kuhn didn't use the term tribalism, that's just how I think of it)
  • Sour Grapes (Score:2, Interesting)

    by mdsolar ( 1045926 )
    The review of the final chapter seems to me to downplay a pretty valid point:

    If you have ever refereed a paper, you know that you can't much help approching it like a term paper. You look for places to take points off. Visionary papers are almost always unfinished and so get poor reviews. Perfectionist papers that confirm what everyone thinks any way are harder to ding for points. (And are more likely to be fraudulant.)

    Smolin has urged at least one frind of mine to just publish a visionary work to
  • by Fujisawa Sensei ( 207127 ) on Monday January 15, 2007 @06:26PM (#17620028) Journal

    The 90s called, they want their theory back.

  • MOND (Score:4, Informative)

    by soliptic ( 665417 ) on Monday January 15, 2007 @06:39PM (#17620252) Journal
    Was I the only one to think it wouldn't have hurt to have spelled out what MOND is the first time it is used?

    Before you say, "Well, anyone who knows ANYTHING about physics knows that, you retard, this book is not for you..." - well, I did think this was supposed to be a layperson's book. So, I clicked to read this review despite having an effectively non-existent knowledge of physics.

    Well, anyway, here's your answer, at least according to Wikipedia (obviously, not being my field, I can't vouch for its accuracy):

    In physics, Modified Newtonian Dynamics (MOND) is a theory that explains the galaxy rotation problem without assuming the existence of dark matter. Currently, the most widely accepted galactic rotation theory assumes that a halo of dark matter surrounds each galaxy, causing all the stars in the galaxy disc to orbit with the same velocity. When this uniform velocity was first observed it was unexpected because the Newtonian theory of gravity predicted that objects that are farther out will have lower velocities. For example, planets in our Solar System orbit with velocities that decrease as their distance from the Sun increases.

    MOND was proposed by Mordehai Milgrom in 1981 to model the observed uniform velocity data without the dark matter assumption. His key insight was that Newton's Second Law ( F = ma ) for gravitational force has only been verified when gravitational acceleration is large.
    Source: http://en.wikipedia.org/wiki/MOND [wikipedia.org]

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