Sean Carroll

Author: Sean Carroll

  • Happy Darwin Day

    darwin-2.jpg Today is Darwin Day, celebrating the 200th anniversary of Charles Darwin’s birth and the 150th anniversary of On the Origin of Species. If you prefer your classics in modern Web 2.0 form, check out John Whitfield’s Blogging the Origin, or Discover‘s own special coverage.

    Darwin Day has a different tenor than Newton Day or Einstein Day would have. The theory of natural selection has an impact on our self-image as human beings in a way that classical mechanics or relativity simply do not. Every great scientist teaches us something about how the world works, but evolution also teaches us something about who we are. (Or, more accurately, is an important part of a wide-ranging set of ideas that teach us something about who we are.) Namely, that we human beings are not separate from the world. We are part of it, subject to the same laws, originating from the same processes, not singled out for some special purpose among the multitude of amazing events within our far-flung universe.

    Too bad for Darwin. It’s nearly impossible to recognize and appreciate his scientific genius without also grappling one way or another with the sad reality that so many people are reluctant to accept the truth of natural selection. We are messy biological creatures, not perfect reasoning machines, and it’s too tempting to view the workings of the world through a lens of our personal preferences. (Ironically, the reason why we are messy biological creatures rather than perfect reasoning machines is that we got to where we are through an unpredictable and historically contingent set of evolutionary steps, rather than being designed from scratch.) We want to be special, we don’t want to be an accident, and in the face of overwhelming evidence we too often simply refuse to accept any other possibility.

    But also, good for Darwin. Because we are part of the universe, every scientific discovery helps us understand who we are; how species evolve is simply a discovery where the connection is all too obvious. Darwin is a scientific hero both for the brilliance of his theory (not to mention his observations as a naturalist), but also for the symbolic role of evolution as a triumph of reality over wishful thinking. If the evidence had indicated that we were designed as part of some Great Plan, the scientifically respectable thing to do would have been to accept that and try to understand it as well as we could. Good science is often disturbing, because the things we don’t yet understand about the world are (pretty much by definition) the things that are difficult and surprising. But reality always wins out.

    So Darwin represents, in a way that even Newton and Einstein and others do not, a triumph of the true human spirit — the drive to get things right and come to terms with how the world really works, regardless of how it all makes us feel in the end. Once we buy into that spirit and appreciate the thrill of honest discovery, of course, we find that it makes us feel pretty good.

  • Guest Post — Kip Thorne on Stephen Hawking

    Most physics fans out there have probably heard of Kip Thorne, author of Black Holes and Time Warps and some other books. If you polled physicists to find out who they thought had been the most influential American scientist doing research in general relativity over the past several decades, Thorne would win hands-down. (Here’s a recent interview in Discover.)

    And if you dropped the delimiter “American” from the question above, the winner would undoubtedly be Stephen Hawking. So we’re very happy to have a guest post from Kip, announcing an upcoming talk by Hawking.

    kip_john_stephen.jpg
    Left to right: John Preskill, Kip Thorne, and Stephen Hawking.

    ————————————————————————————————

    Stephen Hawking is coming to town – to Pasadena, that is.

    Caltech, in Pasadena, California, is Hawking’s home away from home. Since 1991 he has spent roughly a month a year here as our Sherman Fairchild Distinguished Scholar. This year he flies in from his English home at the end of February, then heads off to Texas in early April.

    He arrives with an entourage of five care givers to tend to his physical needs, one or two family members, several graduate students, and a “graduate assistant” who handles logistics and serves as general fixit-person for his computer system and mechanized wheel chair. His current chair is new and sophisticated. At the flick of a switch, its hydraulics can lift him up to a standing person’s eye level or slide him down near ground level for high-speed chases — he has been known to take pleasure from running over the toes of university presidents.

    Hawking’s Pasadena sojourns are rather like Einstein’s in the 1930s. Caltech is an intellectual magnet – a crossroad for ideas about the cosmos and the fundamental laws of nature, which are Hawking’s passion. He contributes mightily to the ferment, and partakes. Our California night life (LA, not Caltech!) is also pretty good; and Hawking, like Einstein, is a party animal, only more so. During his annual month here, my own social life intensifies five-fold just from being his closest California friend. He loves opera, theater, jazz clubs, barbecues that he hosts in the patio of his Pasadena home, and dinners with fine wine – especially an Indian Feast prepared for him by Caltech undergraduates. Yes, we geeks can cook up a storm – well, not me, but the younger generation.

    Conversation with Stephen is slow, about 3 words a minute, produced by Stephen moving a muscle in his face (imaged by a lens and photodetector) to control a cursor on his computer screen. It’s slow, but rewarding. You never know, until his sentence is complete, whether it will be a pearl of wisdom or an off-the-wall joke. Faster speeds are on the horizon: computer control via brane waves, without drilling a hole in his head (he’s opposed to that). But he resists changing technology, even without drilling, until forced to. “I can’t believe it’s as good as what I have.” (It actually is; my wife has a friend with ALS who proves it so.)

    Most of Hawking’s Pasadena time is spent thinking, conversing, and working on projects. Jim Hartle drives down from Santa Barbara to continue their decades-long research collaboration on the birth of the Universe. Leonard Mlodinow, a Pasadena-based free-lance writer, toils with him on a book: in the past, A Briefer History of Time; now, their forthcoming The Grand Design. And there are drives to Hollywood to film for Star Trek or the Simpsons or the forthcoming Stephen Hawking’s Beyond the Horizon.

    On each Pasadena visit, Hawking gives a lecture for the general public – always before in Caltech’s limited-seating Beckman Auditorium, but this year in the newly renovated Pasadena Convention Center, at 8PM, Monday March 9. “Why We [the human race] Should Go into Space” is his title. It’s an opportunity to see him in action, be immersed in his mind’s world, and – if last year’s lecture is any indication – participate in a happening. Tickets are available from the Caltech ticket office, (626) 395-4652, at $10 each.

    The last time I saw Hawking speak to such a large audience, thousands, was in a converted railway station in Santiago Chile, soon after General Pinochet’s regime gave way to civilian rule. It was quite a show. Hawking made a grand entrance to rock music and charmed the crowd. The President of Chile and other civilian officials sat on one side of the giant stage, the military brass on the other, with enormous tension between them; they were hardly speaking to each other in those days. Only Hawking could bring them into the same room. His aura works magic. The next day the military flew us to Antarctica: a C130 cargo plane filled with TV cameras, journalists and physicists. It was August, the Antarctic winter, the first flight to Antarctica in more than a month due to winter storms. It was a Hawking Adventure, one among many. He lives life to the fullest. He will fly on a rocket into space soon.

  • Nietzsche: Long Live Physics!

    Henri Poincaré proved his “recurrence theorem” in 1890: in a mechanical system with bound orbits (particles can’t just run off to infinity), any state through which the system passes will be approached (to arbitrary accuracy) an infinite number of times in the future. That was eight years after Friedrich Nietzsche, in The Gay Science, asked us to imagine exactly such a scenario, in his notion of eternal return:

    What if, some day or night, a demon were to steal after you in your loneliest loneliness and say to you: “This life as you now live it and have lived it, you will have to live once more and innumerable times more; and there will be nothing new in it, but every pain and every joy and every thought and sigh and everything unutterably small or great in your life will have to return to you, all in the same succession and sequence—even this spider and this moonlight between the trees, and even this moment and I myself. The eternal hourglass of existence is turned upside down again and again—and you with it, speck of dust!”

    This is the kind of thing you come across when you’re writing a book about time. Nietzsche wanted to suggest that a well-lived life was one you wouldn’t mind knowing would recur throughout eternity, while the prospect would cause gnashing of teeth for most of us. Poincaré’s concerns were somewhat different.

    While looking up this passage, I stumbled across one of my favorite Nietzsche quotes, just a few aphorisms prior:

    Yes, my friends, regarding all the moral chatter of some about others it is time to feel nauseous! Sitting in moral judgment should offend our taste! Let us leave such chatter and such bad taste to those who have nothing else to do but drag the past a few steps further through time and who never live in the present,—which is to say the many, the great majority! We, however, want to become who we are,—the new, unique, incomparable ones, who give themselves their own laws, who create themselves! And to that end we must become the best learners and discoverers of everything that is lawful and necessary in the world: we must become physicists in order to be able to be creators in this sense,—while hitherto all valuations and ideals have been based on ignorance of physics or were constructed so as to contradict it. Therefore: long live physics! And even more so that which compels us to turn to physics,—our honesty!

    A quote which engenders, as you might imagine, swift elaborations on the part of Nietzsche scholars that he certainly wasn’t talking about what we ordinarily mean by “physics.” But I’m not so sure. The substance of physics (experimental results, theoretical understandings) is of no help whatsoever in leading a moral life. But the method of physics — open-minded hypothesis testing and scrupulous honesty in confronting what Nature has to tell us — is a pretty good model for other aspects of our lives.

    Not that physicists are, as a matter of empirical fact, any better at being good human beings on average than anyone else. Even we physicists could learn to be better physicists.

  • Blue Yodel No. 9

    Louis Armstrong and Johnny Cash. Forty years after Armstrong first recorded this song with Jimmie Rogers, the father of country music. Via Marginal Revolution.

    This is a clip from the Johnny Cash show in 1970, less than a year before Armstrong died. It’s great to see these two performers together, but Armstrong’s playing is pretty restrained. Here he is with Dizzie Gillespie, doing “Umbrella Man.”

    I presume there is no video recording of Armstrong back in the 1930’s with the Hot Fives or Hot Sevens?

  • Big Surprises

    I got to have dinner last night with Robin Hanson, who blogs at Overcoming Bias. Robin is a creative big-picture thinker, who took a twisting career path from physics through philosophy of science and artificial intelligence research to become a tenured professor of economics. He posed a question, which he just re-posed at his blog: what is the most surprising thing we’ve learned about the universe?

    Obviously the right answer depends on a set of expectations; surprising to whom? I originally suggested quantum mechanics, and in particular the fact that the outcomes of experiments are not perfectly predictable even in principle. I think that was the most surprising thing to the people who actually discovered it, in the context of what they thought they understood. But what about the most surprising thing to our pre-scientific hunter-gather ancestors? I suggested the fact that the same set of rules govern living beings and inanimate matter, but if you have any better ideas feel free to chime in.

    But we can ask the complementary question: what is the most surprising thing about the universe that we haven’t yet discovered, but plausibly could? Something that is not already reasonably excluded by experiments that we’ve done, but also wouldn’t be readily accommodated by a theoretical model. So “string theory is right” certainly wouldn’t count, but neither would “the proton is heavier than the neutron.”

    I once discussed this with Bill Wimsatt on an episode of Odyssey (RealPlayer). I went with “reproducible violations of the Second Law of Thermodynamics.” But there are plenty of other good possibilities; what if we discovered tachyons, or that there really was an Intelligent Designer? Suggestions welcome.

  • Looking for Dark Matter in All the Wrong Places

    res.pngDavid Harris at symmetry breaking points to a paper and accompanying commentary on the search for high-energy cosmic antiprotons by the PAMELA satellite experiment. (What one defines as “high-energy” depends on one’s upbringing; we’re talking about energies of up to 100 times the mass of the proton.) The impression is given that this is a brand-new result casting doubt on the earlier claims that PAMELA might have detected evidence for dark matter; that’s not really a correct impression, so it’s worth getting it all straight.

    The PAMELA satellite, an Italian/Russian/German/Swedish collaboration, looks at high-energy cosmic rays from orbit, and pays particular attention to the presence of antimatter — basically, positrons (anti-electrons) and anti-protons. Part of the idea is that a high-energy matter particle can simply be a particle that had been lying around for a while and was accelerated to large velocities by magnetic fields or other astrophysical processes, whereas you need some pretty high energies to produce antiparticles in the first place. Say, for example, from the annihilation of dark matter particles with each other. There are certainly some high-energy collisions in the ordinary non-dark-matter world, so you expect to see a certain fraction of antimatter, but that fraction should noticeably diminish as you get to higher and higher energies.

    So in October the experiment released two papers back to back:

    A new measurement of the antiproton-to-proton flux ratio up to 100 GeV in the cosmic radiation
    Authors: O. Adriani et al.
    arXiv:0810.4994

    Observation of an anomalous positron abundance in the cosmic radiation
    Authors: O. Adriani et al.
    arXiv:0810.4995

    If you look closely, you’ll notice the second paper has 10 trackbacks to its abstract on arxiv, while the first doesn’t have any (until now!). The reason is clear: the second paper has the word “anomalous” in the title. The PAMELA measurements of positrons deviate significantly from the theoretical expectation, while the measurements of anti-protons reported in the first paper are exactly what you might have predicted. Who wants to write about observations that fit theories we already have?

    You might remember the PAMELA positron result as the one that created a stir when they gave a talk before submitting their paper, and theorists in the audience snapped pictures of the data with their cell phone cameras and proceeded to write papers about it. Those wacky theorists.

    Here is the relevant positron plot, from paper 2 above:

    PAMELA positron fraction

    The vertical axis is the fraction of positrons in the total sample of electrons+positrons, plotted against energy. The red dots are the data, and the black curve is the theoretical prediction from ordinary astrophysical processes. Not the best fit, eh? At low energies that is not a surprise, as “weather” effects such as solar activity can get in the way of observing low-energy positrons. But at high energies the prediction should be more robust, and that’s where it’s the worst. Indeed, it’s pretty clear that the fraction of positrons is increasing with energy, which is pretty baffling, but could conceivably come from dark matter annihilations. See Resonaances for more discussion.

    And here is the version for antiprotons, from paper 1 above:

    PAMELA antiproton fraction

    Now that’s what we call a fit to the data; again, fraction of antiprotons plotted versus energy, and the data go up and down just as predicted.

    What happened is that the PAMELA collaboration submitted their second paper (anomalous positrons) to Nature, and their first paper (well-behaved antiprotons) to Physical Review Letters. The latter paper has just now appeared in print, which is why Simon Swordy’s commentary in Physics appeared, etc. Although the idea behind Physics (expert-level commentary on recently published articles) is a good one, it’s sponsored by the American Physical Society, and therefore pretends that the only interesting articles are those that appear in journals published by the American Physical Society. Which Nature is most surely not.

    So one might get the impression that the antiproton result is a blow against the idea that we are seeing dark-matter annihilations. Which it is; if you didn’t know any better, you would certainly expect to see an excess of antiprotons in dark-matter annihilations just as surely as you would expect to see an excess of positrons. But it’s not a new blow; the papers appeared on arxiv (which is what really matters) at the same time!

    And it’s not a blow that can’t be recovered from. All you have to do is declare that your dark matter candidate is “hadrophobic,” and likes to annihilate into electrons and positrons rather than protons and antiprotons. Not an easy task, but that’s why theorists get paid the exorbitant salaries we do. (Without ready access to champagne and caviar, we can hardly be expected to justify unusual branching ratios in WIMP annihilations.) The favorite model out there right now belongs to Arkani-Hamed, Finkbeiner, Slatyer, and Weiner, featuring a new gauge force that is broken at relatively low energies. But there are various models on the market, and the number is only going to grow.

    Most likely the PAMELA positron excess is coming from something that can be fit quite nicely into the Standard Model of particle physics, like pulsars. That’s my guess, anyway. Happily, there’s all sorts of data coming down the pike that will help us sort it out.

  • I’m Pretty Sure This Is What That Official at NSF Was Watching

    20090202.jpg

    I will just mention that this guy doesn’t really look like Brian Greene. And that I’m disappointed the word “heterotic” couldn’t be worked in there somewhere.

    And also that ordinary one-dimensional strings don’t form knots in higher dimensions of space, so extra-dimensional bondage requires extended objects. So really the guy in the cartoon should probably be “Dr. Polchinski.”

  • The Numbers Behind NUMB3RS

    If you’re like me, all too often while relaxing and watching a good procedural drama on TV you find yourself wondering, “How did they solve that differential equation so quickly?” That’s why we need more hit prime-time TV shows with web pages that explain the mathematical content underpinning each episode.

    As far as I know, the only show that rises to this challenge is NUMB3RS, the CBS drama featuring Charlie Epps, a math professor at a suspiciously Caltech-esque university who teams up with his FBI-agent brother to solve crimes. The shows creators, Nicolas Falacci and Cheryl Heuton, had a goal from the beginning of creating an entertaining hour of television that would involve science in an intimate way. (I suppose math is almost as good.) As part of the effort, they’ve partnered with Wolfram Research to follow each episode with a web page delving into the various mathematical concepts that were discussed, including Mathematica notebooks to illustrate the various ideas:

    The Math Behind NUMB3RS

    Episode 11 this year was entitled “The Arrow of Time.” Here’s the opening:

    You can see the full episode here; the math page is here. This stuff would make a great topic for a book.

  • Guest Post: Michael Peskin on John Updike

    Michael Peskin One of our guiding principles here at CV has always been that disciplinary barriers are meant to be leapt across. So, to mark the passing of an influential writer of fiction, who better than an influential writer of quantum field theory textbooks? We’re happy to have Michael Peskin contribute a guest post on the passing of John Updike.

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    John Updike (1932-2009)

    John Updike, one of the great American writers, died on Tuesday. The Cosmic Variance bloggers might seem to write incessantly, but they had nothing on him. Updike produced 26 novels, 9 poetry collections, and, it seemed, a short story in the New Yorker every other week. There was no aspect of culture that he did not know. Yesterday, I saw him celebrated on the sports page of the San Francisco Chronicle for his classic on Ted Williams’ last at bat, “Hub Fans Bid Kid Adieu”. We scientists should also acknowledge our gratitude and send our friends out to read his work.

    Every particle physicist knows Updike’s poem “Cosmic Gall,” the number one popularization of neutrinos:

    At night, they enter at Nepal
    and pierce the lover and his lass
    From underneath the bed …

    Readers of Cosmic Variance will find much more interesting his 1986 novel Roger’s Version. In Chapter One, the scruffy fundamentalist computer science graduate student Dale Kohler walks into the office of the comfortably middle-aged Harvard professor of divinity Roger Lambert and shatters his worldview by explaining that new discoveries in physics and cosmology require intelligent design. The characters in the story that follows personify all points of view in the science versus religion debate, until — but I shouldn’t ruin the surprise.

    John Updike People who are serious about literature claim that these works have merely intellectual interest. If you are in that group, there are also Updike novels that will move you with the depth of his empathy. His masterwork is the set of four Rabbit Angstrom novels, a thousand pages in all, one novel every ten years from 1960 to 1990. The greatest moments of Harry “Rabbit” Angstrom’s life came in high school, when he was a star basketball player in his small town in upstate Pennsylvania. When the first novel opens, that part of his life is already over. He has an uninspiring job, a tiny apartment, and a baby who dies in the first few pages. Harry has no introspection. The glow that surrounded him on the basketball court brings him women, and, one after another, they push him into all varieties of trouble. Harry’s wife Janice is tougher and recognizes that the two are stronger together than apart, but she cannot control his whims. In Rabbit, Run, he wanders in and out of his new marriage and an affair with a girl from the town. In Rabbit, Redux, he takes in a runaway teen and her drug habit. In Rabbit is Rich, he inherits his father-in-law’s Toyota dealership and samples the country-club life. In Rabbit at Rest, he tries to retire to Florida, but the bad choices of the past three books — and one astonishing new one — follow him. Harry also seduces his readers. We stay one step ahead of him in anticipating the next catastrophe, but we also watch through his eyes the panorama of America in Updike’s era.

    If this is too heavy to carry, you could pick up the short, early novel The Centaur. A father, a high school science teacher, sacrifices himself for his son. It is a brief story, told with great pathos. But also, magically, just under the surface, the story unfolds as a Greek myth, and, in the end, the father, Updike’s father, ascends to the heavens.

    It may not be true for those who blog, but those who put pen to paper will always be with us. Enjoy!

    John Updike Image (c) Michael Mundy

  • The Sacred

    Over at Reality Base, Melissa has invited Adam Frank to contribute a series of guest posts related to his new book: The Constant Fire: Beyond the Science vs. Religion Debate. Adam is an astrophysicist at Rochester, a smart guy, and a great science writer; he interviewed me for this story in Discover, and it was the most conscientious bit of science journalism I’ve been involved with.

    There is a copy of Adam’s book lying around here somewhere, but I can’t find it right now; I’ve looked through it, but admittedly haven’t read it closely. You can get some feeling for where he’s coming from by checking out his blog devoted to the book. Roughly: “Sure, simple-minded creationism and a naively interventionist deity is crazy. But there is something valuable in notions of the sacred and spiritual endeavor that captures something important about being human, and it’s a mistake to simply dismiss it all under the same umbrella.” There is a family resemblance to the argument made (in very different words) by Stuart Kauffman in his recent book Reinventing the Sacred: A New View of Science, Reason, and Religion. Kauffman points out an indisputably true fact: there is such a large number of possible configurations of the genetic material in a complex organism that we will never come anywhere close to exploring every possible arrangement. Therefore (he leaps), we have to look beyond simple determinism to understand our world. There is (he bravely continues) a radical contingency in the way life actually plays itself out, and it makes sense to grapple with this contingency by turning to concepts such as “the sacred.”

    Let’s get the agreement out of the way first. There is certainly no question that the techniques of fundamental physics are not sufficient for dealing with getting us through our everyday lives. Even if we are hard-core determinists, and think that every particle and quantum field does nothing but march to the tune of the universal Schrödinger equation, that fact isn’t very helpful when it comes to fixing the economy or listening to music. We deal with complicated human experiences, and a different set of concepts and vocabulary is required, even if it’s nothing but the laws of physics underlying it all. And it would indeed be nice if atheist/materialist thinkers spent more time putting forward a positive agenda of living human life, in addition to their undoubtedly successful programs of understanding the natural world and highlighting the inadequacy of traditional religious belief.

    So I’m very happy to have creative and intelligent people like Frank and Kauffman address these hard issues from the perspective of someone who takes the laws of nature seriously. However, I continue to be baffled about why they would ever think it was a good idea to invoke words like “spiritual” or “sacred” as part of that endeavor.

    The problem is, words have meanings. When you start talking about “spirituality,” people are going to take you to mean something that goes beyond the laws of nature, in the sense of being incompatible with them, not just “hard to understand in terms of them” — something supernatural. Now, you may not want them to make that association; that might not be a connotation you wish to invite. (Or maybe it is, in which case I’ve completely misunderstood.) And you are free, as was Humpty Dumpty, to insist that words mean whatever you say they mean. But it’s a very good strategy for guaranteeing that people will misunderstand you.

    The puzzles of human life, and our mutual sense of wonder, and a feeling of awe when confronted with the cosmos, are all perfectly respectable topics for discussion. And there exists perfectly respectable vocabularies for discussing them, that don’t come laden with unfortunate supernatural overtones: literature, anthropology, psychology, the arts, and so on. There is a huge disadvantage to throwing around words like “sacred” and “spiritual,” in that you will very frequently be understood (misunderstood, one hopes) to be talking about the supernatural. So if you really want to rehabilitate those words in the eyes of a cheerful naturalist such as myself, your task is clear: give very specific examples and contexts in which we gain some sort of understanding by using that vocabulary that we would not gain by sticking to words without those unfortunate connotations. I’m happy to admit that such a context might be possible, but I haven’t seen anything close to a persuasive argument, so I’ll remain extremely skeptical until one comes along.

    And then, one can’t leave this territory without bringing up Richard Dawkins for some good bashing. Here is where Adam has a go. “Dawkins only addresses a naive and simplistic view of religion,” etc. We’ve talked before about how “sophisticated” approaches to religion are not any better, and how Dawkins has served an extremely valuable rhetorical purpose. But there is a deeper point, which is consistently missed by the gentle-minded/accommodationist/agnostic/liberal-religious/sophisticated-theology segment of the debate: It’s Not About You. Richard Dawkins was not addressing this kind of touchy-feely non-interventionist religion, for the excellent reason that it doesn’t match up with what the overwhelming majority of religious believers actually believe.

    Dawkins was, rather, addressing the kind of religion professed by Congressman Paul Broun (R-GA). Rep. Broun is shown here, accompanied by two ministers, anointing a doorway in the U.S. Capitol building with oil. It was the doorway that Barack Obama would walk through on the way to his inauguration, and these well-meaning gentlemen understood that a carefully placed dab of oil might make God look more charitably on the new President.

    Obama Anointing Prayer for Walkway to Inaugural Stage

    This is what Richard Dawkins was arguing against. This is a member of the U.S. Congress, who in fact is a member of the House Committee on Science and Technology, who believes that some sort of esoteric rite is going to curry favor with an omnipotent being. Dawkins is worried about them, not about people who are occasionally impressed with the grandeur of the cosmos. If the oil-anointers were a tiny minority of religious believers rather than the vast majority, I suspect Dawkins would spend his time worrying about other things.