IN PHYSICS, the trick is often to ask a question so obvious no one else would have thought of posing it. Apples have fallen to the ground since time immemorial. It took the genius of Sir Isaac Newton to ask why. Of course, it helps if you have the mental clout to work out the answer. Fortunately, Newton did.

It was in this spirit, almost 50 years ago, that a few insightful physicists asked themselves where mass comes from. Like the tendency of apples to fall to the ground, the existence of mass is so quotidian that the idea it needs a formal explanation would never occur to most people. But it did occur to Peter Higgs, then a young researcher at Edinburgh University, and to five other scientists whom the quirks of celebrity have not treated so kindly. They, too, had the necessary mental clout. They got out their pencils and papers and scribbled down equations whose upshot was a prediction.

The reason that fundamental particles have mass, the researchers calculated, is their interaction with a previously unknown field that permeates space. This field came to be named (with no disrespect to the losers in the celebrity race) the Higgs field. Technically, it is needed to explain a phenomenon called electroweak symmetry breaking, which divides two of the fundamental forces of nature, electromagnetism and the weak nuclear force. When that division happens, a bit of leftover mathematics manifests itself as a particle. This putative particle has become known as the Higgs boson, whose possible discovery was announced to the world on December 13th (see article).

Physicists demand a level of proof that would in any other human activity (including other scientific ones) be seen as ludicrously high—that a result has only one chance in 3.5m of being wrong. The new results—from experiments done at CERN, the world's premier particle-physics laboratory, using its multi-billion-dollar Large Hadron Collider, the LHC—do not individually come close to that threshold. What has excited physicists, though, is that they have got essentially identical results from two experiments attached to the LHC, which work in completely different ways. This coincidence makes it much more likely that they have discovered the real deal.

If they have, it would be a wonderful thing, and not just for science. Though nations no longer tremble at the feet of particle physicists—the men, and a few women, who once delivered the destructive power of the atom bomb—physics still has the power to produce awe in another way, by revealing the basic truths that underpin reality.

Model behaviour

Finding the Higgs would mark the closing of one chapter in this story. The elusive boson rounds off what has become known as the Standard Model of physics—an explanation that relies on 17 fundamental particles and three physical forces (though it stubbornly refuses to accommodate a fourth force, gravity, which is separately explained by Albert Einstein's general theory of relativity). Much more intriguingly, the Higgs also opens another chapter of physics.

The physicists' plan is to use the Standard Model as the foundation of a larger and more beautiful edifice called Supersymmetry. This predicts a further set of particles, the heavier partners of those already found. How much heavier, though, depends on how heavy the Higgs itself is. The results just announced suggest it is light enough for some of the predicted supersymmetric particles to be made in the LHC too.

That is a great relief to those at CERN. If the Higgs had proved much heavier than this week's announcement implies they might have found themselves with a lot of redundant kit on their hands. Now they can start looking for the bricks of Supersymmetry, to see if it, too, resembles the physicists' predictions. In particular, in a crossover between particle physics and cosmology, they will be trying to find out if (as the maths suggest) the lightest of the supersymmetric partner particles are the stuff of the hitherto mysterious “dark matter” whose gravity holds galaxies together.

A critique of pure reason

One of the most extraordinary things about the universe is this predictability—that it is possible to write down equations which describe what is seen, and extrapolate from them to the unseen. Newton was able to go from the behaviour of bodies falling to Earth to the mechanism that holds planets in orbit. James Clerk Maxwell's equations of electromagnetism, derived in the mid-19th century, predicted the existence of radio waves. The atom bomb began with Einstein's famous equation, E=mc{+2}, which was a result derived by asking how objects would behave when travelling near the speed of light. The search for antimatter, that staple of science fiction, was the consequence of an equation about electrons which has two sets of solutions, one positive and one negative.

Eugene Wigner, one of the physicists responsible for showing, in the 1920s, the importance of symmetry to the universe (and who was thus a progenitor of Supersymmetry), described this as the “unreasonable effectiveness of mathematics”. Not all such predictions come true, of course. But the predictive power of mathematical physics—as opposed to the after-the-fact explanatory power of maths in other fields—is still extraordinary.

Some might see the hand of God in such predictability. The Higgs boson is, indeed, known to headline writers as the God particle (though the sobriquet was actually first given by a bowdlerising editor, who shortened an author's reference to “that goddamn particle”). Others will prefer to stand in awe of a universe that they suspect began as a quantum fluctuation in pre-existing nothingness. And yes, there are calculations explaining how that could have happened, too.

Both sides, though, should be in awe not merely of the universe, but also of the men and women who have stripped, and continue to strip, that universe of its mystery—and do so without diminishing the wonder of it all. So, at a time when the future of human affairs seems particularly uncertain, a Christmas toast to the predictability of physics.