Science

I’ll take this opportunity to offer one of my occasional plugs for Caltech’s Quantum Frontiers blog. They publish posts by various members of the Institute for Quantum Information and Matter. Remarkably, the posts manage to exhibit considerable personality, rather than being perfunctory mentions of recent papers or talks. Much credit should go to Spiros Michalakis for getting the thing off the ground.

A lot of credit should also go to John Preskill, who is very well-known for his work in particle physics and quantum field theory as well as his second career as a quantum information. Who knew there was an entertaining blogger lurking inside the facade of a respectable scientist? (Third career?) John’s posts invariably manage to be enjoyable as well as informative. Now he’s put up a couple of hour-long videos, lectures that he gave at the 12th Canadian Summer School on Quantum Information. Two hours is a good length: enough time to actually convey useful information, without demanding the commitment of a full-semester course.

That’s the first video; click over for the second. And for an entertaining story about noisy hotel rooms and the exciting, thrill-a-minute life of the academic lecturer.

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!

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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To celebrate the publication of The Particle at the End of the Universe, here’s a cheat sheet for you: mind-bending facts about the Higgs boson you can use to impress friends and prospective romantic entanglements.

1. It’s not the “God particle.” Sure, people call it the God particle, because that’s the name Leon Lederman attached to it in a book of the same name. Marketing genius, but wildly inaccurate. (Aren’t they all God’s little particles?) As Lederman and his co-author Dick Teresi explain in the first chapter of their book, “the publisher wouldn’t let us call it the Goddamn Particle, though that might be a more appropriate title, given its villainous nature and the expense it is causing.”

2. Nobel prizes are coming. But we don’t know to whom. The idea behind the Higgs boson arose in a number of papers in 1963 and 1964. One by Philip Anderson, one by Francois Englert and Robert Brout (now deceased), two by Peter Higgs, and one by Gerald Guralnik, Richard Hagen, and Tom Kibble. By tradition, the Nobel in Physics is given to three people or fewer in any one year, so there are hard choices to be made. (Read Chapter 11!) The experimental discovery is certainly Nobel-worthy as well, but that involves something like 7,000 people spread over two experimental collaborations, so it’s even more difficult. It’s possible someone associated with the actual construction of the Large Hadron Collider could win the prize. Or someone could convince the Nobel committee to ditch the antiquated three-person rule, and that person could be awarded the Peace Prize.

3. We’ve probably discovered the Higgs, but we’re not completely sure. We’ve discovered something — there’s a new particle, no doubt about that. But like any new discovery, it takes time (and in this case, more data) to be absolutely sure you understand what you’ve found. A major task over the next few years will be to pin down the properties of the new particle, and test whether it really is the Higgs that was predicted almost five decades ago. It’s better if it’s not, of course; that means there’s new and exciting physics to be learned. So far it looks like it is the Higgs boson, so it’s okay to talk as if that’s what we’ve discovered, at least until contrary evidence comes in.

4. The Large Hadron Collider is outrageously impressive. The LHC, the machine in Geneva, Switzerland, that discovered the Higgs, is the most complicated machine ever built. (Chapter 5.) It’s a ring of magnets and experimental detectors, buried 100 meters underground, 27 kilometers in circumference. It takes protons, 100 trillion at a time, and accelerates them to 99.999999% the speed of light, then smashes them together over 100 million times per second. The beam pipe through which the protons travel is evacuated so that its density is lower than you would experience standing on the Moon, and the surrounding superconducting magnets are cooled to a temperature lower than that of intergalactic space. The total kinetic energy of the protons moving around the ring is comparable to that of a speeding freight train. To pick one of countless astonishing numbers out of a hat, if you laid all the electrical cable in the LHC end-to-end it would stretch for about 275,000 kilometers, enough to wrap the Earth almost seven times.

5. The LHC was never going to destroy the world. Remember that bit of scaremongering? People were worried that the LHC would create a black hole that would swallow the Earth, and we would all die. (It was never quite explained why the physicists who built the machine would be willing to sacrifice their own lives so readily.) This was silly, mostly because there’s nothing going on inside the LHC that doesn’t happen out there in space all the time. There was a real setback on September 19, 2008, when a magnet kind of exploded, but nobody was hurt. The current casualty list from the LHC mostly consists of people’s favorite theories of new physics, which are continually being constrained as new data comes in.

6. The Higgs boson isn’t really all that important. The boson is just some particle. What’s important is something called the Higgs mechanism. What really gets people excited is the Higgs field, from which the particle arises. Modern physics — in particular, quantum field theory — tells us that all particles are just vibrations in one field or another. The photon is a vibration in the electromagnetic field, the electron is a vibration in the electron field, and so on. (That’s why all electrons have the same mass and charge — they’re just different vibrations in the same underlying field that fills the universe.) It’s the Higgs field, lurking out there in empty space, that makes the universe interesting. Finding the boson is exciting because it means the field is really there. This is why it’s hard to explain the importance of the Higgs in just a few words — you first have to explain field theory!

7. The Higgs mechanism makes the universe interesting. If it weren’t for the Higgs field (or something else that would do the same trick), the elementary particles of nature like electrons and quarks would all be massless. The laws of physics tell us that the size of an atom depends on the mass of the electrons that are attached to it — the lighter the electrons are, the bigger the atom would be. Massless electrons imply atoms as big as the universe — in other words, not atoms at all, really. So without the Higgs, there wouldn’t be atoms, there wouldn’t be chemistry, there wouldn’t be life as we know it. It’s a pretty big deal.

8. Your own mass doesn’t come from the Higgs. We were careful in the previous point to attribute the mass of “elementary” particles to the Higgs mechanism. But most of the mass in your body comes from protons and neutrons, which are not elementary particles at all. They are collections of quarks held together by gluons. Most of their mass comes from the interaction energies of those quarks and gluons, and would be essentially unchanged if the Higgs weren’t there at all. So without the Higgs, we could still have massive protons and neutrons, although their properties would be very different.

9. There will be no jet packs. People sometimes think that since the Higgs has something to do with “mass,” it’s somehow connected to gravity, and that by learning to control it we might be able to turn gravity on and off. Sadly not true. As above, most of your mass doesn’t come from the Higgs field at all. But even putting that aside, there’s no realistic prospect of “controlling the Higgs field.” Think of it this way: it costs energy to change the value of the Higgs field in any region of space, and energy implies mass (through Einstein’s famous E = mc²). If you were to take a region of space the size of a golf ball and turn the Higgs field off inside of it, you would end up with an amount of mass larger than that of the Earth, and create a black hole in the process. Not a feasible plan. We haven’t been looking for the Higgs because of the promise of future technological applications — it’s because we want to understand how the world works.

10. The easy part is over. The discovery of the Higgs completes the Standard Model; the laws of physics underlying everyday life are completely understood. That’s pretty impressive; it’s a project that we, as a species, have been working on for at least 2,500 years, since Democritus first suggested atoms back in ancient Greece. This leaves plenty of physics that we don’t yet understand, from dark matter to the origin of the universe, not to mention complicated problems like turbulence and neuroscience and politics. Indeed, we’re hoping that studying the Higgs might provide new clues about dark matter and other puzzles. But we do now understand the basic building blocks of the world we immediately see around us. It’s a triumph for human beings; the future history of physics will be divided into the pre-Higgs era and the post-Higgs era. Here’s to the new era!