Physics has a well-deserved reputation for being horrendously complicated, but sometimes it's the simplest questions that lead to truly profound insights. When Einstein asked himself, What would happen if you could ride on a beam of light?, for example, the answer led him to the special theory of relativity.
For the past few decades, particle physicists have been wrestling with another deceptively simple question: Why does anything have mass? You might wonder, Why not? But according to modern physics, you can't get away that easily. The existence of mass the property of matter that gives gravity something to pull on needs an explanation.
Now, say two independent teams of scientists who revealed their results at a symposium in Switzerland Tuesday morning, Dec. 13, there are experimental signs of an elusive particle formally known as the Higgs boson and informally known as the God particle. If the Higgs is really there, the existence of mass has finally been explained and a Scottish physicist named Peter Higgs is a lock for a Nobel Prize.
It's a big if, though, and nobody is making an actual claim. Indeed, Fabiola Gianotti, a member of one of the teams, said at the symposium, "We cannot conclude anything at this stage."
But that hardly means there's nothing to say. The gathering took place in a packed auditorium at the CERN laboratory outside Geneva the home of the mammoth Large Hadron Collider. The LHC, the world's most powerful particle accelerator, works by taking subatomic protons, sending them racing in opposite directions through a 17-mile (27 km) oval-shaped tunnel, then letting them smash together head-on at nearly the speed of light. The impact is powerful enough to vaporize the particles into tiny fireballs of pure energy, re-creating the conditions in the first moments after the Big Bang. Then, just as in the early universe, the energy recondenses into particles. Among them may be the elusive Higgs.
That's what physicists have been hoping for, anyway, since long before the LHC was built. It was way back in the 1960s that Peter Higgs of the University of Edinburgh proposed what came to be known as the Higgs mechanism. (Others came up with similar ideas, but his is the name that stuck.) The way it works is ... no, let's not go there. Suffice it to say that there's a sort of energy field that pervades the universe and that when particles like protons, neutrons, quarks and the rest interact with the Higgs field, they're rewarded with mass. The Higgs boson helps broker the transaction.
When the Higgs condenses out of particle collisions, it immediately decays into other particles, so physicists can't see it directly; they can only reconstruct its existence from the debris, like a CSI unit reconstructing what a bomb must have looked like from its fragments. And since each miniBig Bang creates so many particles that decay into so many other particles, the reconstruction is incredibly difficult. The good news is that the new hints of a Higgs in all that particle debris come from not one but two entirely different detectors at the LHC the ATLAS (short for "A Toroidal LHC ApparatuS") and the CMS (for Compact Muon Solenoid). The two operate in different ways, as a sort of mutual cross-check.
Both detectors have seen evidence of the Higgs which is big news and was the reason for both the symposium and all the speculation that attended its announcement. But the less good news is that in statistical terms, that evidence weighs in at what is known as the three-sigma confidence level. No need to go into too much detail here either, except to say you'd need to get to the five-sigma stage to claim an actual discovery. "It's too early to draw a definite conclusion," said Gianotti. "We need four times as much data."
Getting sufficient data requires many thousands of fireballs, and the LHC accelerator will need another year or more to crank all of them out and allow Gianotti and her colleagues to announce that they've indeed discovered the Higgs boson. Or not. "The number of sub-three-sigma discoveries that have turned out to be wrong," says Princeton astrophysicist Michael Strauss, "is reasonably large."
You'd think that if the hunt for the Higgs comes to nothing, it would be a big disappointment for physicists. But that's not necessarily so. Finding the Higgs would add a key missing brick to the edifice of the standard model of particle physics, which would be important but also just a bit dull.
"The great irony," Harvard theorist Lisa Randall told the New York Times recently, "is that not finding a Higgs boson would be spectacular from the point of view of particle physics, pointing to something more interesting than the simple Higgs model." For physicists, it turns out, "be careful what you wish for," especially if you're wishing for a Higgs, may be truer than it seems.