More Milner Money

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Yuri Milner, a technology entrepreneur who made a splash last July by giving $3 million prizes to nine theoretical physicists, has splashed again. He’s just announced two “special prizes,” both for another $3 million each: one to Stephen Hawking, and one split between a number of people who played important roles in this year’s Higgs discovery at the LHC. (None for me for writing a book about it, but I guess that’s to be expected.)

The original Fundamental Physics Prizes went to a very theoretical group of theorists: Ed Witten, Nima Arkani-Hamed, Alan Guth, Juan Maldacena, Alexei Kitaev, Ashoke Sen, Nathan Seiberg, Maxim Kontsevich, and Andrei Linde. Without question an extremely influential and deserving group. There were minor grumblings from some quarters that most of these folks hadn’t (yet) contributed ideas that have been verified by experiments, but my attitude is that if someone wants to give $27 million of their personal fortune to physics, I’m not going to quibble about the precise allocation.

Still, it’s great to see the LHC experimenters share in the recognition; I think most people would agree that theorists tend to gather a disproportionate part of the public acclaim. The $3 million for the LHC was split several ways: $1 million to Lyn Evans, who guided the construction of the accelerator; $1 million divided between Michel Della Negra, Tejinder Singh Virdee, Guido Tonelli, and Joe Incandela, all spokespersons for CMS over the years; and $1 million divided between Peter Jenni and Fabiola Gianotti, who have been spokespersons for ATLAS. Congratulations to all the winners!

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Skeptically Speaking

In a few hours I’ll be chatting live on Skeptically Speaking, a weekly podcast and radio show about science and critical thinking. The guest host will be Marie-Claire Shanahan, a science educator who blogs at Boundary Vision. Live broadcast is at 8pm Eastern/5pm Pacific, and before too long the recording will be available as a podcast.

There’s a Canadian theme running through the week, as I just got back from Toronto and Skeptically Speaking is based in Edmonton. Good timing; with global warming hurtling along, it’s the country of the future.

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How to Explain the Higgs Mechanism

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Greetings from chilly Toronto, where I’m briefly in town to participate in a public event about the Higgs boson tonight. Should be a good time, especially because it’s not just me giving a talk; I will spend 20 minutes explaining the theoretical motivation behind the Higgs, after which experimentalists Pierre Savard and William Trischuk will talk about the actual experiments.

Which raises the question: how does one explain the theoretical motivation behind the Higgs, given a small number of minutes and a motivated-but-nonexpert audience? It’s something I should have figured out by now, having written a book and all. But I’ve been fishing around, and I think I’ve finally settled on a favorite approach to doing it.

A couple of preliminary notes. I don’t think there is a good explanation of the Higgs boson at the sound bite level, say 15 seconds or less. That’s because you need to explain two distinct things: first, that there is a Higgs field filling space that interacts with the particles moving through it and giving some of them mass; and second, that the Higgs boson is the particle we observe when we interact with a vibration in that field. Both of these ideas are part of quantum field theory, which we generally don’t try to explain in physics popularizations, so it’s more than a few seconds of work to get them across. But I don’t think there is a shortcut: if you want to explain the Higgs at all, you have to explain the Higgs field.

With that in mind, the biggest stumbling block to providing a convincing popular-level motivation for the Higgs field is that we immediately leap to the idea that the role of the Higgs is to “give particles mass,” where by “particles” we really mean “quarks, charged leptons, and the W & Z bosons.” This raises a couple of problems. First, why do we need some mechanism to give particles mass? Why can’t they just have mass? Of course some particles can just have mass — like the Higgs itself. So you’re starting off by moving backwards, bringing up the need to explain why different symmetries apparently prevent particles from having mass, which is actually harder to explain than the Higgs mechanism. And second, most of the mass in real objects comes from QCD, not from the Higgs mechanism at all, so you are almost inevitably giving people the wrong idea. You see why it’s a tricky situation.

Fortunately, we have an alternative: the actual historical development of the subject. Back in the early 1960’s when the Higgs mechanism was being proposed (by Anderson, Englert, Brout, Higgs, Hagen, Guralnik, and Kibble), they weren’t trying to give mass to fermions. They were trying to explain how nuclear forces, which manifestly only stretch over a very short distance, could possibly be described in a way similar to gravity and electromagnetism (i.e. by Yang-Mills theories), which manifestly stretch over long distances. Sure, both gravity and E&M fade away as you move farther from a source, but they do so slowly (the inverse square law, in particular), which is why they are relatively easy to observe in the everyday world. If the nuclear forces are simply generalizations of E&M, as Yang and Mills suggested, why don’t they stretch over large distances? …

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How to Explain the Higgs Mechanism Read More »

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Welcome

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Welcome to the latest incarnation of my blog-related programming activities. As our friend Lucretius says, “All that we see about us consists of transient arrangements of atoms. Some awaken to life. None holds forever.”

I’ve bid an extremely fond farewell to Cosmic Variance, with great memories and enormous respect for my co-bloggers there who are keeping the torch lit. But I wanted to shift to a less formal, more personal and carefree mode of blogging, one where nobody else but me was responsible in any way. I’ll still be doing my best to understand and explain cool ideas in physics, but the only common thread holding the content together will be “things that popped into my head.” It may be intermittent and even inchoate, but hopefully it will be fun.

To set the tone, here’s a little ditty from Paco de Lucia, Al Di Meola, and John McLaughlin. A mixture of heavy thinking and joyful exuberance. Something to shoot for.

PACO DE LUCIA , John McLaughlin , AL DI MEOLA

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Dave Brubeck

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Dave Brubeck, an innovative and influential jazz pianist over many years, has died at the age of 91. Based in California, he was a leader of so-called West Coast Jazz, bringing a spirit of experimentation to a part of the jazz world that had been resolutely mainstream.

Dave Brubeck Quartet Blue Rondo à la Turk

Brubeck loved to experiment with unusual time signatures, a tendency that culminated in his masterpiece album, Time Out. The tune played above, Blue Rondo à la Turk, is predominantly in 9/8 time, with the beats broken mostly into a 2+2+2+3 pattern. But things aren’t quite so simple, as Wikipedia explains.

The best thing about Brubeck’s experimentations was that they never sounded formal; they were highly musical and fun to listen to, seemingly flowing without effort unless you tried to really focus on what was going on. He was a much-beloved figure in jazz, and will be sorely missed.

Update: An anecdote from Russ Gershon on Facebook:

I heard him tell a story of when he was on the cover of Time in the late 50s. He was at a hotel with Duke Ellington (they were playing in the same jazz festival, maybe Newport). When Brubeck learned about the coverage he immediately went to Duke’s room and apologized that it was him and not Duke who first earned Time’s cover.

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Colbert Redux

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Last night I had the privilege of once again appearing on the Colbert Report to talk with our nation’s leading pundit about the frontiers of modern science. Here’s the clip. I’m not sure you’d want to use it to help explain how the Higgs mechanism works, but I think we had fun. The joke about “massive” at the end makes sense only if you know that Colbert has a running gag, referenced earlier in the show, in which he has been trying to get people to say “massive” as a synonym for “cool.”

The Colbert Report Mon – Thurs 11:30pm / 10:30c
Sean Carroll
www.colbertnation.com
Colbert Report Full Episodes Political Humor & Satire Blog Video Archive

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Reviews!

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Many writerly friends of mine swear with a straight face that they never look at reviews of their books. I have tried but failed to comprehend the inner workings of these alien minds; personally, as much as I know it might pain me, I can’t help but read reviews. Sometimes I might even learn something! Or at least be gratified, in this nice review of The Particle at the End of the Universe by Adam Frank at NPR.

Or, on the other hand, simply be amazed and astonished. The most amusing “review” so far has come from one of the good readers at Amazon, working under the nom de plume “Chosenbygrace Notworks,” and coming with the to-the-point title “Arrogant atheist `science’.” Apparently Chosenbygrace is not handicapped by actually having read the book, but did hear me talk on Coast to Coast AM. Here’s the opening:

Sean Carroll is a typical atheist physicist who arrogantly disregards creationists to the point where he does not even acknowledge they exist unless prompted (like happened on Coast to Coast AM tonight). The liberal media and filled with money sapping money-obsessed morons like this, willing to indebt any generation of Americans into becoming slaves. It’s already happened, and Americans in general are all debt slaves because of atheism-theoretical-physics cultists like this, and the idiot atheists who worship delusional morons like this.

It goes on, but, you know, probably the gist has been conveyed. The physics/atheism connection is a classic, of course, but I hadn’t been aware that we in the cult were also responsible for plunging Americans into debt. 5 out of 425 people found the review helpful, so at least someone is being helped! (In fairness, the Amazon review by Ashutosh Jogalekar probably does a better job of conveying what’s in the book than any I’ve yet seen.)

Other reviews are puzzling, and I have to mention one in particular. …

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Reviews! Read More »

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Thanksgiving

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This year we give thanks for an idea that is central to our modern understanding of the forces of nature: gauge symmetry. (We’ve previously given thanks for the Standard Model Lagrangian, Hubble’s Law, the Spin-Statistics Theorem, conservation of momentum, effective field theory, and the error bar.)

When you write a popular book, some of the biggest decisions you are faced with involve choosing which interesting but difficult concepts to tackle, and which to simply put aside. In The Particle at the End of the Universe, I faced this question when it came to the concept of gauge symmetries, and in particular their relationship to the forces of nature. It’s a simple relationship to summarize: the standard four “forces of nature” all arise directly from gauge symmetries. And the Higgs field is interesting because it serves to hide some of those symmetries from us. So in the end, recognizing that it’s a subtle topic and the discussion might prove unsatisfying, I bit the bullet and tried my best to explain why this kind of symmetry leads directly to what we think of as a force. Part of that involved explaining what a “connection” is in this context, which I’m not sure anyone has ever tried before in a popular book. And likely nobody ever will try again! (Corrections welcome in comments.)

Physicists and mathematicians define a “symmetry” as “a transformation we can do to a system that leaves its essential features unchanged.” A circle has a lot of symmetry, as we can rotate it around the middle by any angle, and after the rotation it remains the same circle. We can also reflect it around an axis down the middle. A square, by contrast, has some symmetry, but less — we can reflect it around the middle, or rotate by some number of 90-degree angles, but if we rotated it by an angle that wasn’t a multiple of 90 degrees we wouldn’t get the same square back. A random scribble doesn’t have any symmetry at all; anything we do to it will change its appearance.

That’s not too hard to swallow. One layer of abstraction is to leap from symmetries of a tangible physical object like a circle to something a bit more conceptual, like “the laws of physics.” But it’s a leap well worth making! …

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Time-Reversal Violation Is Not the "Arrow of Time"

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Looks like the good folks at the BaBar experiment at SLAC, feeling that my attention has been distracted by the Higgs boson, decided that they might be able to slip a pet peeve of mine past an unsuspecting public without drawing my ire. Not so fast, good folks at BaBar!

They are good folks, actually, and they’ve carried out an extremely impressive bit of experimental virtuosity: obtaining a direct measurement of the asymmetry between a particle-physics process and its time-reverse, thereby establishing very direct evidence that the time-reversal operation “T” is not a good symmetry of nature. Here’s the technical paper, the SLAC press release, and a semi-popular explanation by the APS. (I could link you to the Physical Review Letters journal server rather than the arxiv, but the former is behind a paywall while the latter is free, and they’re the same content, so why would I do that? [Update: the PRL version is available free here, but not from the PRL page directly.])

The reason why it’s an impressive experiment is that it’s very difficult to directly compare the rate of one process to its precise time-reverse. You can measure the lifetime of a muon, for example, as it decays into an electron, a neutrino, and an anti-neutrino. But it’s very difficult (utterly impractical, actually) to shoot a neutrino and an anti-neutrino directly at an electron and measure the probability that it all turns into a muon. So what you want to look at are oscillations: one particle turning into another, which can also convert back. That usually doesn’t happen — electrons can’t convert into positrons because charge is conserved, and they can’t convert into negatively-charged pions because energy and lepton number are conserved, etc. But you can get the trick to work with certain quark-antiquark pairs, like neutral kaons or neutral B mesons, where the particle and its antiparticle can oscillate back and forth into each other. If you can somehow distinguish between the particle and antiparticle, for example if they decay into different things, you can in principle measure the oscillation rates in each direction. If the rates are different, we say that we have measured a violation of T reversal symmetry, or T-violation for short.

As I discuss in From Eternity to Here, this kind of phenomenon has been measured before, for example by the CPLEAR experiment at CERN in 1998. They used kaons and anti-kaons, and watched them decay into different offspring particles. If the BaBar press release is to be believed there is some controversy over whether that was “really” was measuring T-violation. I didn’t know about that, but in any event it’s always good to do a completely independent measurement.

So BaBar looked at B mesons. I won’t go into the details (see the explainer here), but they were able to precisely time the oscillations between one kind of neutral B meson, and the exact reverse of that operation. (Okay, tiny detail: one kind was an eigenstate of CP, the other was an eigenstate of flavor. Happy now?)

They found that T is indeed violated. This is a great result, although it surprises absolutely nobody. There is a famous result called the CPT theorem, which says that whenever you have an ordinary quantum field theory (“ordinary” means “local and Lorentz-invariant”), the combined operations of time-reversal T, parity P, and particle/antiparticle switching C will always be a good symmetry of the theory. And we know that CP is violated in nature; that won the Nobel Prize for Cronin and Fitch in 1980. So T has to be violated, to cancel out the fact that CP is violated and make the combination CPT a good symmetry. Either that, or the universe does not run according to an ordinary quantum field theory, and that would be big news indeed.

All perfectly fine and glorious. The pet peeve only comes up in the sub-headline of the SLAC press release: “Time’s quantum arrow has a preferred direction, new analysis shows.” Colorful language rather than precise statement, to be sure, but colorful language that is extremely misleading. …

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Time-Reversal Violation Is Not the "Arrow of Time" Read More »

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Shindig!

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This afternoon, 6pm Eastern/3pm Pacific, is the fun event I mentioned before: a “virtual book tour” discussion on a new-ish platform called Shindig. The idea is that I sit here with my webcam, talking to you and showing some pictures; you sit where you are, with your own webcam, as a potentially-participatory audience member. You can virtually “raise your hand” to ask a question, either by text or by audio in the post-talk Q&A. Different audience members can break off into groups to chat about things by themselves. It’s all free and open and quite experimental, so we’re trying to coax as many people into participating as possible. Certainly saves time (and fossil fuels) in comparison to jetting around the country.

The topic, of course, will be the new book, or really just the basics of the Higgs search and the Large Hadron Collider. I will give a brief overview, very casual, and anyone there should feel free to ask whatever they like.

Here’s an example of a Shindig event, featuring A.J. Jacobs.

Should be fun. Join us if you can!

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