Astronomy Posting

When I was young, my main scientific interest was in astronomy, and to prove it there’s a very geeky picture of me with my telescope on display in my apartment, causing much amusement to my guests (no way will I ever allow it to be digitized, I must ensure that it never appears on the web). By the time I got to college, my interests had shifted to physics, and since that time I’ve hardly at all kept up with what is going on in astronomy. Like everyone, I’m still fascinated by the amazing pictures coming out of the field, and like most particle physicists, I’m deeply jealous of astronomers for the fact that they have a wealth of exciting new data to work with, together with promising prospects of lots more to come.

This week there’s a big meeting of the American Astronomical Society going on in Seattle, producing lots of astronomy news. Many bloggers are in attendance, including Rob Knop, Steinn Sigurdsson, Phil Plait, and C.C. Petersen. Rumors that celebrity couple Sean Carroll and Jennifer Ouellette were there turned out to be partially unfounded. Lots of press releases are being generated, including one from the University of Washington full of the usual overhyped claims about cosmic superstrings.

This week’s Science has a special issue on particle astrophysics, with lots of articles worth reading, including a nice summary of the exciting things happening in the field by Adrian Cho. He reports that many experimental particle physicists have moved into the field, partly because of the opportunities there, partly because of the difficult situation of experimental particle physics, especially in the U.S. Michael Turner is quoted explaining that the particle physicists have brought to the field some ambitious ideas, due to their habit of “thinking big”:

These are not people who are afraid to ask for big things, and they’re used to people saying yes.

An example of this is the IceCube neutrino experiment being put together under the ice in Antarctica, employing 400 researchers and costing $271 million.

Turner also has an article summarizing the situation in cosmology, where he notes that many string theorists are now pinning their hopes on making some connection to the real world in this context:

Nowhere in particle physics are the stakes higher than for string theory. If string theory is to live up to its billing as “the theory of everything” rather than, as some say, a theory of nothing, it needs a home run. Because most of its current predictions exceed the reach of terrestrial laboratories, many string theorists are pinning their hopes on a cosmological home run, such as a fundamental understanding of inflation (or a more attractive alternative), a solution to the puzzle of cosmic acceleration, or insight into the nature of the Big Bang itself.

For something truly bizarre, check out the cover story of the February issue of Astronomy magazine, entitled “What if string theory is wrong?” (mentioned earlier here). It confirms me in my opinion that I shouldn’t write about things I don’t know much about, like astronomy, since it’s by an astronomer who clearly knows very little about particle physics, especially about supersymmetry:

Supersymmetry is a mathematical principle that allows force-carrying particles, such as photons and gluons, to transform into one another. It also allows the unification of gravity with other forces because its particle, which some call the graviton, can transform into one of the other force-carriers…. If extra dimensions don’t exist, then supersymmetry doesn’t either… Without supersymmetry, some physicists have proven that the energy of empty space would be so enormous the universe would instantly collapse. Only by understanding physics beyond the standard model can we hope to understand how the vacuum works and the universe’s dark side. And only string theory appears able to serve as a reliable mathematical guide to that larger universe.

Lenny Susskind provides the usual over-the-top outrageous quote:

It is hard to find a serious paper about particle phenomenology that doesn’t in some way use the tools of superstring theory.

The author seems to believe that there’s some sort of experimental evidence of string theory and that it is just like general relativity:

While string theory is sparse on experimental validation, the situation is not so different from general relativity in its early days, when difficult mathematics made calculating a prediction extremely challenging.

and somehow thinks that string theory is the only hope for the future of physics:

Without superstring theory, we’d lose the intriguing prospects for the multiverse, with its infinite and eternal creativity in spawning new universes… More immediately, dark matter and dark energy would remain imponderable enigmas, shorn of any clues about where they come from. Astronomers can live without knowing the quantum properties of gravity. But to learn that 96 percent of the cosmos is unknowable would be a bitter pill to swallow. It would be even worse for physicists. Without a logical framework in which to pose and answer questions, our inquiries into the fundamental aspects of the physical world would devolve into semantic quibbles.

Some days I think that there’s definitely a more realistic view of string theory out there, other days I’m not so sure…

Update: It seems that Edward Witten is attending the AAS meeting, although not speaking there. See the comment from David Cobden, and Steins Sigurdsson’s blog entry from the conference Trendspotting, where he reports:

On a completely unrelated note, Ed Witten was spotted wandering the halls…
Now there is always some cosmic string or quantum cosmo thingy going on here, but what we ask (and, yes, I did actually ask), was he doing in the extrasolar planet session?

Ed likes exoplanets!
Dood.

Update: Science a Gogo has an article about this, String Theory? Knot!, which uses my characterization of Susskind’s quote as “over-the-top”, but then uses the wrong quote, using something from the Astronomy magazine article which wasn’t written by Susskind.

Update: The University of Washington press release on cosmic superstrings, based upon a poster presented at the AAS meeting, has made it to Fox News (via Lubos).

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69 Responses to Astronomy Posting

  1. wow says:

    Actually, gauge theory (and field theory as a whole) was criticized in much the same way as you are criticizing string theory, for about 20 years following the original Yang-Mills paper. This culminated in the bootstrap/S-matrix movement where the irrelevant technical “rube goldberg” details of field theory, which was itself not unique and far from well defined, could be swept under the rug.

    Of course this was badly misleading. Field theory is difficult and nonunique. It is also deep, beautiful, and correct. My guess is that this is true of string theory as well. A difference seems to be that string theory is unique, but has many solutions, while field theory is fundamentally non-unique. But this is not an important difference.

  2. D R Lunsford says:

    Peter,

    Like you I started with astronomy and dropped it in college. Recently I acquired a good 10″ telescope and let me tell you, the thrill is still there! You’ll enjoy having one, I recommend it. It’s also more fun now that I understand light and the universe a lot better than I used to.

    -drl

  3. D R Lunsford says:

    Tommaso,

    “Astronomy” has always been a miserable sensationalist rag. It also had the bad effect of debasing Sky&Telescope by forcing them to compete on a more glossy level. In a sense it annihilated with the old S&T and they both disappeared in a burst of advertising dollars.

    -drl

  4. woit says:

    wow,

    The difference between QFT and string theory has nothing do with questions about uniqueness. The simplest QFT in the class of gauge theories (QED) accurately describes nature to absurd precision, makes an infinite number of non-trivial predictions, all of which turn out to work when you test them. This remains true of the only slightly more complicated non-abelian gauge theories and the standard model.

    People did not argue against QFT that is was untestable, they were testing it all the time. They argued that it couldn’t describe the strong interactions, and that appeared to be the case until the discovery of asymptotic freedom. There has never been any time when people studying QFT were claiming that it was impossible to get predictions out of it because there were too many QFTs.

    If you want to make an argument that string theory will someday triumph the way QFT did, you could try and claim that someday we’ll better understand string theory, and realize that it has some surprising property like asymptotic freedom that will make its current problems describing nature go away. Maybe, but there’s no evidence for that now.

  5. woit says:

    drl,

    I still have an old 8″ telescope, don’t get to use it very much in New York City though…

  6. wow says:

    The history of qft is not as you say. There were two periods of significant “discouragement” due to people who thought the structure should be easier and more unique than it is.

    If you read about QED (see Dysons many accounts), it is clear that by the mid 40s, after 15-20 years of worrying about relativistic quantum mechanics, most of the old heroes of qm (Dirac, Schrodinger,…) Thought a fundamentally new structure to replace qm (not QED) was needed. It was the new generation (feynmanm schwinger etc) that saw that the old complicated theory, could indeed be made to work. They needed rube goldberg contraptions to explain loop effects and it took 25 years before the correct wilsonian understanding of renormalization was attained.

    Then, later, the chicken littles appeared when the theory of strong interactions required novel features of qft.

    The analogy is quite clear. Understood poorly, qft is very difficult, nonuniqe, and even seems ambiguous (due to misunderstandings of renormalization). The aesthetic worries were irrelevant (science doesn’t demand uniqueness, just that one avatar of the theory be a good approximation of nature).

  7. Thomas Larsson says:

    Wow: Funny, I used exactly this summary of the history of QFT in the introduction to my contribution to this book. However, I don’t see how it can be construed to support string theory. Adding tons of unconfirmed (and increasingly unlikely) “new physics”, like susy, extra-dimensions, fundamental extended objects, 496 gauge bosons, or 10^500 universes is more like the new physics that Oppenheimer and others thought was necessary to cure the infinities of QED.

  8. Peter Woit says:

    Wow,

    I have read a bit about the history of QFT… Earlier I was referring to the post 40s history of the subject, but I don’t think your interpretation of the earlier history holds water.

    From the very beginning in the late 1920s, QED had a huge amount of experimental backing. First-order perturbation theory was well-defined, and gave extremely accurate, testable predictions of a huge variety of experimentally measurable effects. The problems with higher order perturbation theory were a matter of principle, but practically of little significance. The measurement of the Lamb shift made clear that higher-order effects were real and the theory had to explain them, which was rather quickly done.

    It’s true it took 15-20 years to sort out the problems of how to renormalize QED, but for a large chunk of this period, most physicists were either trying to save their skins or working on war-related projects. People were worried that QED might very well be inconsistent, but I don’t know of anyone who was worrying that it was consistent, but experimentally untestable.

    And the reason people took seriously Feynman and Schwinger’s renormalization methods, whether or not they found them to be of a “Rube Goldberg” nature, was that these methods gave extremely accurate and experimentally confirmed predictions for things like the anomalous magnetic moment of the electron. If Feynman and Schwinger had been doing higher order perturbation theory calculations using complicated methods, but getting no predictions out of them, just a bunch of excuses for why QED couldn’t make predictions, absolutely no one would have taken them seriously.

  9. wow says:

    I haven’t actually heard any string theorists say the theory will not lead to predictions, once (by whatever fortuitous experiment) the correct class of solutions is found. I have heard you say this many times, but apparently the rather large community of technical experts on string theory, does not believe your statement. To me, this looks like what critics of field theory would have been saying in the 30s and 60s. And the response of the string theorists, is similar to what the wise folks who kept working in the natural extension of existing theory (QFT) did.

    The absence of data at the relevant energy scale is indeed different. This is not a problem of string theory, and has haunted
    beyond SM physics for 20 years. To attack string theorists and not the huge number of phenomenologists who worked on supersymmetry, technicolor, large extra dimensions, randall sundrum scenarios, little higgs models, or whatever, seems silly to me. One could just as easily make ad hominem remarks about the 10s of thousands of papers there with no experimental confirmation of the ideas. And these remarks would be just as silly: the goal of the endeavor is to divide up the space of models so * when interesting signatures are SEEN *, one will know what this means about where we live in theory space.

    String theorists do the same thing with their framework. If Smolin had a framework I imagine he would also do this, though I have never understood in what sense he does have one.

  10. Peter Woit says:

    wow,

    I’m sure people working on string theory hope that it will some day lead to predictions, but there aren’t any now, and the problem is that at this point there’s not a plausible scenario for how this is going to happen. You seem to be saying that you believe in a “fortuitous experiment” that will indicate that the string theory landscape picture is correct by providing evidence for a certain class of string theory solutions. That’s logically possible, but I don’t see any evidence for this scenario other than wishful thinking based upon a firm conviction that string theory has to be true. Yes, this judgement about the plausibility of your scenario is a personal one, but I’m pretty sure that it is shared by a large fraction of particle theorists who are not string theorists.

    Beyond the standard model particle phenomenology has, like string theory, had very little success over the last 20 years. With no experimental guidance, it’s a very hard problem. Like string theory, some ideas about particle phenomenology are overhyped by their enthusiasts. But I just don’t see the same unhealthy domination of the subject by a single idea that is not working. Phenomenologists are at least trying lots of different ideas (even if none of them are especially promising). The idea of getting beyond the standard model physics out of some kind of string/M theory on a 10/11 space has not just failed to work out the way people hoped, but it continues to dominate a large fraction of particle theory research. Given the lack of any other successful ideas, there’s no reason some people shouldn’t work on it, but people who do so should acknowledge that things are not going well, and that probably other quite different ideas are needed.

    The day technicolor models are pursued by large groups of theorists who create institutes devoted their study, won’t hire people who don’t work on these models, write books and TV shows about the glories of technicolor, and start up blogs devoted to calling anyone who doesn’t believe in technicolor an imbecile, I’ll start writing postings pointing out the problems with what they are doing.

  11. Thomas Larsson says:

    To me, this looks like what critics of field theory would have been saying in the 30s and 60s. And the response of the string theorists, is similar to what the wise folks who kept working in the natural extension of existing theory (QFT) did.

    “The critics are right. We have no single prediction of string theory that is verified by observation. Even worse, we don’t know how to use string theory to make predictions. Even worse than that, we don’t really know what string theory is.”
    -Steven Weinberg

  12. anonymous says:

    “and start up blogs devoted to calling anyone who doesn’t believe in technicolor an imbecile”

    Hey, I bet Ken Lane can be persuaded to do that!

    “But I just don’t see the same unhealthy domination of the subject by a single idea that is not working. Phenomenologists are at least trying lots of different ideas (even if none of them are especially promising).”

    Wah? I guess by one idea you mean “the right theory is a string theory.” At the same level of generality phenomenologists generally go from the idea “the right theory is a QFT for which the SM is a low-energy effective theory.” There is of course lots of diversity in what phenomenologists do, but at the same time there is diversity in stringy model-building (intersecting brane models, flux compactifications, etc.). I don’t see what you’re doing as an apples-to-apples comparison.

  13. M says:

    wow, many phenomenologists are interested in if/which new physics keeps the weak scale naturally small (supersymmetry or technicolor or…?) because colliders are now exploring physics at the weak scale. This is not only an important issue, it also is an issue that will be clarified, probably soon at LHC. The present attempts could be right, or could be wrong, but cannot be not-even-wrong.

  14. wow says:

    M:

    Many of the things explored by model builders (including the most influential ideas of the past decade or so) were either directly
    or indirectly but obviously influenced/inspired by string theory
    ideas. I am not saying this as “an arrogant adherent of string theory” — this is a fact that the originators of the models would freely admit. It is true of the Randall/Sundrum works on warping and anomaly mediation; it is true of the large dimensions works which not coincidentally blossomed right after D-brane gauge theories became a topic of interest; it is true of new ideas in SUSY model building which took off from Seiberg’s classic works, which in turn were inspired in part by thinking precisely about string theory moduli spaces. It is true of the recent resurgence of interest by cosmic string theorists, who see the reasonable motivation for new possibilities of strings with smaller tension that play a very subleading role in structure formation. It is true of most attempts to build models relevant for Planck, that would show measurable non-Gaussianity or gravitational waves (specially the former; ideas about the latter go back to the origin of inflation, but have been considerably influenced by theoretical considerations of quantum gravity more recently).

    So, M, even the things that you say are defensible because in some very short term they are “relevant” to near term experiments, have a history that shows the value of the more formal research going on in particle/string theory.

  15. Chris W. says:

    The aesthetic worries were irrelevant (science doesn’t demand uniqueness, just that one avatar of the theory be a good approximation of nature). (- wow)

    Right, I got it; that’s good. So, one should make sure that one’s theory has as many “avatars” as possible, with as much diversity as possible, to maximize the likelihood that one of the them will be a good approximation of nature. After all, nature can be anything at all, and science is fundamentally trial and error, so we want to make sure the options available for those trials really cover the bases. Works for me. It looks like string theory and its offshoots are doing a heckuva job then.

    (Karl Popper used to talk about how important it was for a theory to restrict the observations that one might anticipate making. Man, what a crock of s*** that was…)

    [ :) ]

  16. M says:

    wow, what you say about extra dimensions is true, and probably their connection with strings also is the main reason why these ideas attracted so much attention. Experiments will tell if it was worthy.

    I prefer to look at physics rather than at physicists: recent decades will be likely remembered for the following fundamental discoveries: the cosmological constant, inflationary cosmology and structure formation, solar neutrino oscillations, atmospheric neutrino oscillations. Strings played no role there.

  17. Kyrie says:

    recent decades will be likely remembered for the following fundamental discoveries: the cosmological constant, inflationary cosmology and structure formation, solar neutrino oscillations, atmospheric neutrino oscillations

    I would add to this list the definitive observational proof of the existence of dark matter. And maybe also the experimental proof of the CKM model of CP violation.

  18. M says:

    I hope that next years will be the crucial ones for both topics.
    Dark Matter could be seen in direct detection experiments and produced at LHC.
    The second topic you suggest could be part of a more general issue: since 30 years theorists think that the SM must be replaced at the weak scale by some new physics that solves the hierarchy problem, but since 30 years experiments (colliders, CP,…) fail to find it. If this negative trend continues at LHC, I would consider it as a fundamental discovery, more fundamental than e.g. supersymmetry. But I don’t know how this could be explained to funding agencies…

  19. Ari Heikkinen says:

    “cosmic superstrings”

    So any “fluctuation” whatsoever on whatever measuring device and it’s evidence for cosmic superstrings? Come on, even Hoagland would have more reasoning for his theories than that.. :)