Sean Carroll

Author: Sean Carroll

  • Telekinesis and Quantum Field Theory

    In the aftermath of the dispiriting comments following last week’s post on the Parapsychological Association, it seems worth spelling out in detail the claim that parapsychological phenomena are inconsistent with the known laws of physics. The main point here is that, while there are certainly many things that modern science does not understand, there are also many things that it does understand, and those things simply do not allow for telekinesis, telepathy, etc. Which is not to say that we can prove those things aren’t real. We can’t, but that is a completely worthless statement, as science never proves anything; that’s simply not how science works. Rather, it accumulates empirical evidence for or against various hypotheses. If we can show that psychic phenomena are incompatible with the laws of physics we currently understand, then our task is to balance the relative plausibility of “some folks have fallen prey to sloppy research, unreliable testimony, confirmation bias, and wishful thinking” against “the laws of physics that have been tested by an enormous number of rigorous and high-precision experiments over the course of many years are plain wrong in some tangible macroscopic way, and nobody ever noticed.”

    The crucial concept here is that, in the modern framework of fundamental physics, not only do we know certain things, but we have a very precise understanding of the limits of our reliable knowledge. We understand, in other words, that while surprises will undoubtedly arise (as scientists, that’s what we all hope for), there are certain classes of experiments that are guaranteed not to give exciting results — essentially because the same or equivalent experiments have already been performed.

    A simple example is provided by Newton’s law of gravity, the famous inverse-square law. It’s a pretty successful law of physics, good enough to get astronauts to the Moon and back. But it’s certainly not absolutely true; in fact, we already know that it breaks down, due to corrections from general relativity. Nevertheless, there is a regime in which Newtonian gravity is an effective approximation, good at least to a well-defined accuracy. We can say with confidence that if you are interested in the force due to gravity between two objects separated by a certain distance, with certain masses, Newton’s theory gives the right answer to a certain precision. At large distances and high precisions, the domain of validity is formalized by the Parameterized Post-Newtonian formalism. There is a denumerable set of ways in which the motion of test particles can deviate from Newtonian gravity (as well as from general relativity), and we can tell you what the limits are on each of them. At small distances, the inverse-square behavior of the gravitational force law can certainly break down; but we can tell you exactly the scale above which it will not break down (about a tenth of a millimeter). We can also quantify how well this knowledge extends to different kinds of materials; we know very well that Newton’s law works for ordinary matter, but the precision for dark matter is understandably not nearly as good.

    This knowledge has consequences. If we discover a new asteroid headed toward Earth, we can reliably use Newtonian gravity to predict its future orbit. From a rigorous point of view, someone could say “But how do you know that Newtonian gravity works in this particular case? It hasn’t been tested for that specific asteroid!” And that is true, because science never proves anything. But it’s not worth worrying about, and anyone making that suggestion would not be taken seriously.

    As with asteroids, so with human beings. We are creatures of the universe, subject to the same laws of physics as everything else. As everyone knows, there are many things we don’t understand about biology and neuroscience, not to mention the ultimate laws of physics. But there are many things that we do understand, and only the most basic features of quantum field theory suffice to definitively rule out the idea that we can influence objects from a distance through the workings of pure thought.

    The simplest example is telekinesis, the ability to remotely move an object using only psychic powers. For definitiveness, let’s consider the power of spoon-bending, claimed not only by Uri Geller but by author and climate skeptic Michael Crichton.

    What do the laws of physics have to say about spoon-bending? Below the fold, we go through the logic.

    (more…)

  • Wish List

    In case anyone is wondering what to get me for Presidents’ Day, I’d be interested in a nice bottle of 1947 Cheval Blanc. Not necessarily a whole case, or even a magnum; an ordinary bottle would be fine. In Slate, Mike Steinberger explains:

    Cheval Blanc 1947 [T]he ’47 Cheval I drank that night now ranks as the greatest wine of my life, a title I doubt it will relinquish. The moment I lifted the glass to my nose and took in that sweet, spicy, arresting perfume, my notion of excellence in wine, and my understanding of what wine was capable of, was instantly transformed—I could almost hear the scales recalibrating in my head. The ’47 was the warmest, richest, most decadent wine I’d ever encountered. Even more striking than its opulence was its freshness. The flavors were redolent of stewed fruits and dead flowers, yet the wine tasted alive; it bristled with energy and purpose. The ’47s signature flaws—the residual sugar and volatile acidity—were readily apparent, but it was just as Lurton had said: In this wine, the flaws inexplicably became virtues….

    I realized that it was silly even to try to place the ’47 in the context of other wines; it defied comparison, a point underscored when I tasted another legend, the 1945 Château Latour, later that night (yeah, it was a nice evening). The Latour was stunning—probably the second-best wine I’ve ever had—but it at least fell within my frame of reference: It was a classically proportioned Bordeaux that just happened to be achingly good. The ’47 Cheval, by contrast, was an otherworldly wine—a claret from another planet. And it was amazing.

    What is the sound of scales recalibrating? I’d like to find out.

  • Respect Mah Authoritah

    Actual footage of U.S. Senator Arlen Specter questioning National Football League commissioner Roger Goodell as part of an inquiry into whether or not the New England Patriots sneakily videotaped their opponent’s sidelines. An issue, we can all agree, of world-historical importance.

  • American Association for the Advancement of PseudoScience

    What’s wrong with this list?

    Seems at first glance like a list of scientific professional organizations, or at least the subset of such a list beginning with the letter “P.” And indeed it is — it’s an excerpt from the list of Affiliates of the American Association for the Advancement of Science.

    But take a look at that second entry — the Parapsychological Association? Is that what it sounds like? Indeed it is — “the international professional organization of scientists and scholars engaged in the study of ‘psi’’ (or ‘psychic’) experiences, such as telepathy, clairvoyance, psychokinesis, psychic healing, and precognition (“parapsychology”).”

    The only problem is, parapsychology is not science. It’s pseudoscience. From a completely blank-slate perspective, one can certainly pose scientific questions about whether the human mind can tell the future or read minds or move objects around without touching them. The thing is, we know the answer: no. The possibilities have been investigated and found wanting; more straightforwardly, they would violate the known laws of physics. Alchemy was science once, but it’s not any more. Not all hypotheses are equally worthy of our respect and attention; sometimes we learn that a particular idea doesn’t work, and move on with our lives.

    So what in the world is the Parapsychological Association doing as part of the AAAS? Benefiting from the implication of respectability, is the obvious answer. Note that “Affiliate of the AAAS” is displayed prominently on the PA homepage — an endorsement that, say, the Paleontological Society or the Phycological Society of America (not misspelled, I swear) didn’t deem worth of such prominent display.

    Apparently the PA was founded by J.B. Rhine in 1957, and became affiliated with the AAAS in 1969 thanks to the advocacy of then-AAAS-president Margaret Mead. In 1979 John Wheeler campaigned to have it kicked out, but his effort failed.

    The AAAS is a useful organization, and it’s a shame to see them associate their good name with pseudoscience. Their annual meeting begins to day in Boston, and it’s always a fun event, a great way to catch up with some of the major themes in all areas of science. None of those themes should involve reading people’s thoughts or bending spoons with one’s mind. I hope the AAAS can gently extract itself from this relationship.

  • Signaling

    Brad DeLong disentangles the messages that a (male) professor sends by wearing a tie. (Inspired by this sad little diatribe, properly mocked here.)

    I have found that wearing a suit and tie is very effective if done occasionally with non-math-oriented students. It tells them that I care because it shows that I have taken sufficient time to prepare and teach the class even though I am a busy person whose schedule requires meetings with:

    • some powerful political figure,
    • some powerful economic figure,
    • some powerful university administrative figure, or
    • some TV interviewer

    With math-oriented students, however, a tie tells them that I spend too little time thinking about isomorphisms

    Cf. Focus. Professors were once students.

  • No Check to my Genius from Beginning to End

    3quarksdaily points to a mildly amusing piece at McSweeney’s: Famous Authors Predict the Winner of Super Bowl XLII. Ayn Rand, for example:

    When he saw Bill Belichick in the hallway before the press conference, Tom Coughlin’s face contorted into a whine. “It isn’t fair!” he shrieked. “You have all the best players!” he whimpered. “What happened to helping your fellow man?!” he mewled. “You … all you care about is winning!” he sniveled.

    The muscular coach set his prominent jaw, and his hard, handsome eyes glistened. “Why, Tom,” he asked with a smile, “isn’t winning what the NFL is all about?”

    Sadly, the author went completely off the rails when it came time to write in the style of Jane Austen. Here is what we get:

    Hyacinth and amethyst adorned the landscape of her heart, betrothed to fragrant oakmoss and blazing scarlet within the amorous lovestrokes of an incandescent horizon. In the shade of the gray branches, she put pen to paper. “I love you, Tom Brady,” it began. “Though others call you wicked.”

    Um, what? Are there a large number of educated people out there, writing satirical pieces for hip web zines, who think that Jane Austen wrote some sort of Harlequin romances, presumably because she was female?

    Here is a representative scene from an actual book written by Jane Austen — Darcy’s proposal to Elizabeth, from Pride and Prejudice:

    After a silence of several minutes, he came towards her in an agitated manner, and thus began,

    “In vain have I struggled. It will not do. My feelings will not be repressed. You must allow me to tell you how ardently I admire and love you.”

    Elizabeth’s astonishment was beyond expression. She stared, coloured, doubted, and was silent. This he considered sufficient encouragement, and the avowal of all that he felt and had long felt for her immediately followed. He spoke well, but there were feelings besides those of the heart to be detailed, and he was not more eloquent on the subject of tenderness than of pride. His sense of her inferiority — of its being a degradation — of the family obstacles which judgment had always opposed to inclination, were dwelt on with a warmth which seemed due to the consequence he was wounding, but was very unlikely to recommend his suit.

    In spite of her deeply-rooted dislike, she could not be insensible to the compliment of such a man’s affection, and though her intentions did not vary for an instant, she was at first sorry for the pain he was to receive; till, roused to resentment by his subsequent language, she lost all compassion in anger. She tried, however, to compose herself to answer him with patience, when he should have done. He concluded with representing to her the strength of that attachment which, in spite of all his endeavours, he had found impossible to conquer; and with expressing his hope that it would now be rewarded by her acceptance of his hand. As he said this, she could easily see that he had no doubt of a favourable answer. He spoke of apprehension and anxiety, but his countenance expressed real security. Such a circumstance could only exasperate farther, and when he ceased, the colour rose into her cheeks, and she said,

    “In such cases as this, it is, I believe, the established mode to express a sense of obligation for the sentiments avowed, however unequally they may be returned. It is natural that obligation should be felt, and if I could feel gratitude, I would now thank you. But I cannot — I have never desired your good opinion, and you have certainly bestowed it most unwillingly. I am sorry to have occasioned pain to any one. It has been most unconsciously done, however, and I hope will be of short duration. The feelings which, you tell me, have long prevented the acknowledgment of your regard, can have little difficulty in overcoming it after this explanation.”

    Dude, you have just been pwned. As the kids say. Jane Austen may have been many things, but a portrayer of hyacinth-adorned heart landscapes was not one of them. Next time, if you are going to parody a famous author, try reading one of their books first.

    Austen lounging

    Context for post title here.

  • Headsabloggin’

    I’ve done Bloggingheads — where people who are more comfortable behind a keyboard than in front of a camera pick up the phone to talk about things they’d be too lazy to type about — before, but never with someone I was married to. But some marketing wizard thought it would be fun to have a special Valentine’s Day edition of Science Saturday. Say it together: Awwwwwww. So here I am with Jennifer, talking about brains and movies and whiteboards.


    bheads2.jpg

    Don’t worry, it doesn’t get mushy.

  • Aether Compactification

    Even in an election year, physics marches on. Physics is forever.

    In this case it’s a fun little paper by Heywood Tam (a grad student here at Caltech) and me, arXiv:0802.0521:

    We propose a new way to hide large extra dimensions without invoking branes, based on Lorentz-violating tensor fields with expectation values along the extra directions. We investigate the case of a single vector “aether” field on a compact circle. In such a background, interactions of other fields with the aether can lead to modified dispersion relations, increasing the mass of the Kaluza-Klein excitations. The mass scale characterizing each Kaluza-Klein tower can be chosen independently for each species of scalar, fermion, or gauge boson. No small-scale deviations from the inverse square law for gravity are predicted, although light graviton modes may exist.

    This harkens back to the idea of a vector field that violates Lorentz invariance (which Ted Jacobson and friends have dubbed “aether,” appropriately enough), and in particular a vector that picks out a preferred direction in space. I explored this possibility last year in a paper with Lotty Ackerman and Mark Wise, and Mark recently wrote a followup with Tim Dulaney and Moira Gresham. (Our paper was detailed in the “anatomy of a paper” series, 1 2 3.)

    There is an obvious problem with the notion of a vector field that violates rotational invariance by picking out a preferred direction through all of space — we don’t see any evidence for it! Physics as we have thus far experienced it seems pretty darn rotationally invariant. In my paper with Lotty and Mark, we sidestepped this issue by imagining that the vector was important in the early universe, and subsequently decayed away.

    But there’s another way to sidestep the issue, pretty obvious in retrospect: have the vector point in a direction we don’t see! Extra dimensions are of course a popular theoretical construct, and once you make that leap you can ask what would happen if an unseen extra dimension contained a constant vector field. That would leave good old four-dimensional Lorentz invariance completely unbothered, so it’s not immediately constrained by any well-known experimental bounds.

    So, beyond being fun and not ruled out, is it good for anything? The answer is: quite possibly. Heywood and I calculated what the influence of such a vector would be on other fields that propagated in a single extra dimension. In good old-fashioned Kaluza-Klein theory, momentum in the extra dimension can only take on discrete values (it’s quantized, in other words), and each kind of field breaks into an infinite “tower” of particles of different masses. The separation between different mass levels is just the inverse of the size of the extra dimension in natural units. What’s that? You insist upon seeing the equation? Okay, if the original mass of the field is m and the size of the extra dimension is R, we have a series of masses indexed by n:

    displaystyle m_n^2 = m^2 + left(frac{hbar n}{cR}right)^2,.

    Here, hbar is Planck’s constant, c is the speed of light, and n is just a whole number that can be anything from 0 to infinity. So the effect of the compact fifth dimension is to give us an infinite set of four-dimensional particles, indexed by n, each with a different mass. Not a very big mass, unless the extra dimension is pretty small; separating the levels by about 1 electron volt requires a dimension that is about 1 micrometer across. We would certainly have noticed all those new particles unless the extra dimensions were considerably smaller than a Fermi (10-15 meters).

    The interesting thing that Heywood and I discovered is that the effect of an aether field pointing in the extra dimension is to boost all of the mass levels in the Kaluza-Klein tower. There is a new set of coupling constants, αi for every kind of particle i, that tells us how strongly that particle interacts with the aether. The mass formula is modified to read

    displaystyle m_n^2 = m^2 + left(alpha_ifrac{hbar n}{cR}right)^2,.

    So if αi is huge, you could have a huge mass splitting even with an extra dimension that was pretty large. This gives a new way to hide extra dimensions — not just make them invisibly small (the old-school Kaluza-Klein method) or confine us to some thin brane (the new-school ’90s style), but to boost the effective masses associated with momentum in the new direction. And there is an obvious experimental test, if you were to find all of these new particles: unlike plain vanilla compactification, where the towers associated with each kind of field have the same mass splittings, here the splittings could be completely different for every kind of particle, just by choosing different αi‘s.

    To be fair, this idea does not by itself suggest any reason why the extra dimensions should be large. To allow for a millimeter-sized dimension, the coupling αi has to be at least 1015, which any particle physicist will tell you is an unnaturally big number. But the aether at least allows for the possibility, which I think is worth exploring. Who knows, some clever young graduate student out there might figure out how to use this idea to solve the hierarchy problem and the cosmological constant problem, then we would discover aetherized extra dimensions at the LHC, and everyone would become famous.

  • Chaos at the Polling Station!

    Not the arguably-good kind of chaos — unruly throngs of new voters, eager to participate in the thrills of the electoral process, overwhelm a sleepy polling station. Democracy whiskey sexy! No, this was the certainly-bad kind of chaos: incompetent bureaucracy renders voting experience difficult to impossible.

    So I show up at my decidedly non-thronged voting place — five machines, three or four workers, a handful of voters, no more than one or two hundred square feet in total. But my name is not on the list of registered voters. The volunteer worker seems not at all surprised; did I register recently, he asks? Well, it was some time in December — I’ve been receiving sample ballots and all that in the mail, so I know that my registration successfully went through. Ah, he explains, your name is probably on the “supplemental voter list.” Which, apparently, they don’t currently have. But it’s coming! They’ve sent another volunteer over to fetch it (from someone’s house, apparently — I didn’t pry), shouldn’t be more than another ten minutes.

    So I wandered over to Starbucks to have a coffee and peer at the internets through my iPhone, and came back about fifteen minutes later. Now it was approaching lunchtime, and something of a throng was indeed gathering — fifteen or twenty would-be voters were squeezed into the tiny space. But there wasn’t that much voting going on. More than half of the people who showed up were, for some reason or another, not on the list of registered voters. They were now encouraging people to cast “provisional ballots” — you could vote, but it wouldn’t be immediately counted. Someone would later check to see if you were really registered, and if you were, then it would be added to the total. Did I trust the finely-tuned machine I saw before me to successfully check on my registration status? No, I did not. Besides, I wanted my vote to be included on the totals to be shown later tonight on CNN. But almost everyone affected did end up casting provisional ballots, amidst much grumbling and requests for the phone number of the Board of Elections.

    I inquired about the status of the mysterious supplemental list. Well, it was explained, it was not successfully fetched. But now it is being faxed right here! So I settled back to observe the voting. (About five Democrats for every one Republican, but that shouldn’t be a surprise in Downtown LA). After about ten minutes I inquired again — still being faxed! That seemed like an awfully slow fax machine. So, to clarify, I asked whether it was actually emerging from the fax machine at present. Ah, no, but there were definite plans in the works to fax it! Soon.

    At that point I gave up and left, although I plan to go back tonight and give it another shot — the polling stations are open until 8 p.m. (Sorry, East Coasters — California will be reporting late tonight.)

    And then, of course, I walked back to my car in time to see an officer drop a parking ticket on my windshield. I had put (just to be safe!) about 36 minutes on the meter, but the whole affair took about forty minutes total. Our Board of Elections may make the Three Stooges look like the Kirov Ballet, but Parking Enforcement is a marvel of ruthless efficiency!

    What an embarrassment.

    Update: So I went back, inquired about the supplemental voter list, and happily it had arrived. (Not, evidently, by fax, but I was too polite to press the issue.) Sadly, my name wasn’t on it. I toyed briefly with the notion of flying into a Hulk-like rage, upending the table piled high with paperwork and generally inflicting even more chaos on the already-disordered polling station. But I decided that wouldn’t be productive.

    So I filled out a provisional ballot, and whiled away the extra time in line commiserating with the others who were in the same predicament. It seemed to be a common occurrence, and the volunteers verified this casual impression. I suspect that my poor little ballot will never see the light of day, and the state of California will find itself bereft of my opinion that it’s okay to let the Indian casinos install more slot machines. (A weighty decision, the kind that the Golden State simply won’t entrust to its legislature, preferring instead to decide via the exciting mechanism of Direct Democracy.)

    The much worse problem seems to be the hidden button that independent voters must push (on an already unwieldy butterfly ballot) to indicate that yes, not only are they expressing a preference for a candidate in the Democratic primary, but they would also prefer if their vote actually counted! Being a proud Democrat myself, I didn’t have to jump through the tiny little extra hoop.

    I understand that the United States is slowly and painfully making it way toward becoming a functioning modern technological society, and wish it all the best during the difficult transition.

  • The Statistical Mechanics of Political Change

    It’s Super Tuesday, and I’m about to go cast my vote for Barack Obama. Although both he and Hillary would be enormously better for the country than anyone the Republicans have to offer, I (along with my fellow political elites) think he offers the best chance to break away from a certain kind of corrosive political mindset that characterizes our present system. As just a single example, see this post by Katherine at Obsidian Wings, about Hillary’s proud assertion that “Anybody who committed a crime in this country or in the country they came from has to be deported immediately, with no legal process,” to great applause. I suppose that it sounds good to deport people who commit crimes. But how precisely can we be sure that they really did commit a crime, if there is no legal process? It’s not a thoughtful policy — it’s just a cheap trick to take advantage of some anti-immigrant sentiment, since that’s what seems to be riling up people in the heartland this year. I would like to get past that.

    Nevertheless! I’m writing this post to get on the record my annoyance with Obama’s main theme, one beloved of politicians since back in Athens: “Change.” It was, of course, the same theme that Bill Clinton ran on in 1992. And for good reason: after eight years of George W. Bush, almost everyone outside the die-hard 27% wants change of some sort. Including me, that’s for sure.

    Still, as a physicist it bugs me. I can’t hear the motto without thinking: change in what direction? The reason why this is such a great political slogan is because anyone can project onto it whatever kind of “change” they most prefer. But it’s highly unlikely that generic change would be a good thing. In the phase space of political configurations, one must imagine that the subspace of “good” configurations (however you want to define them) is one of fairly low-entropy — there are far more ways to have an ineffective or actively dangerous government than to have a good one.

    Political Phase Space

    If that’s true, and you just adopt “change” as your motto, you are far more likely to make things worse than to make them better. It’s just the Second Law of Political Dynamics, people.

    Of course, reasoning along these lines is just what brings some people to become conservative (in the true and essentially-abandoned meaning of the term) — there are too many ways to make things worse, so let’s keep it as it is so as to not mess stuff up. And it would be a terrible way of thinking if that’s as far as you went, as it would shut off any opportunities for future progress.

    The key is that you want to have directed change, not generic change. The way that you change things really does matter! And I think, electioneering slogans notwithstanding, that the kind of change Obama represents is a good one: toward a more sensible diplomacy, a less confrontational politics, and a more compassionate society here at home. It won’t be easy, of course — you can lower the entropy of an open system, but only by doing work.

    All of which reminds us why politicians so rarely have physicists in their inner circle of advisors.