Higgs Boson Born of Physicists’ Love of Metaphor: Mark Buchanan
It’s an iconic image: the professor of physics, wild hair, Einstein-like, standing before a chalkboard covered with arcane equations. It could be Einstein himself, the scribbled mathematics describing his theory of relativity and the link between mass and energy, E=MC2.
Or, later, Paul Dirac, the English physicist who, seeking mathematical elegance, forged bonds between Einstein’s relativity and the quantum theory, and set the stage for physics today.
The tentative discovery at CERN’s Large Hadron Collider of the Higgs boson -- among the key missing links in our fundamental theories of matter -- again shows the surprising power of mathematics to illuminate nature’s secrets. But the discovery also points to the value of scientific metaphor, of guessing that things we know nothing about might turn out to be surprisingly similar to things we’re familiar with. Indeed, the theory behind the Higgs boson owes as much to what’s already known about mundane things like iron magnets and metals as it does to exotic mathematics.
In 1895, French physicist Pierre Curie showed in extensive experiments that magnets made of iron (and many other materials) abruptly lose their magnetic power when they get too hot. Below about 770 degrees Celsius, a temperature easily achieved in a wood fire, an iron magnet will tug on nails, but it loses this power at higher temperatures, and regains it again if cooled. This is a “phase transition” -- an abrupt change in the properties of a material, akin to ice melting into liquid.
Something From Nothing
I suspect that Plato might have found this phenomenon fascinating, as it’s an indisputable example of something coming directly from nothing. After all, a piece of iron above 770 C lacks magnetism, has no north or south poles, no orientation in space whatsoever. All directions are equal. Yet, on cooling, the iron suddenly points as a magnet in just one direction.
Physicists refer to this kind of thing as spontaneous symmetry breaking, because the initially equal and symmetric status of all directions in space spontaneously crumbles. One direction gets chosen as special, and magnetism appears where there was none before.
It’s the power of such examples that really drives physics, and science more generally. Seeing a something-from-nothing phenomenon in one place, it’s natural to wonder whether it might happen elsewhere, too. It was this idea, with further inspiration from the behavior of ordinary metals, that led scientists to predict the existence of the Higgs boson.
A metal like tin or aluminum will also undergo various phase transitions with changing temperature. Above about 232 degrees Celsius, tin melts. Below about -269 C (4 degrees Kelvin), it becomes superconducting. That is, it conducts electricity with absolutely zero resistance. And, more profoundly, it refuses to let any magnetic field penetrate to its interior. Put some tin in a magnetic field, then cool it to make it superconducting, and the field inside will be readily expelled.
The onset of superconductivity is another example of spontaneous symmetry breaking. In this case, the symmetry involved is a little more abstract -- it’s what physicists call gauge invariance -- but what’s important is that something very new emerges in the superconductor, and it has surprising consequences.
Physicists constructed a complete theory to explain superconductivity in 1957, and this theory showed that what emerges inside the metal to make it superconducting is a kind of supersensitive liquid of electrons. This supersensitive liquid responds strongly to any applied fields, such as those from a magnet brought close, by stirring up currents that cancel out fields in the superconductor’s interior. This is the essence of superconductivity, and it causes a total change in the way electricity and magnetism work on the inside of the material.
Suddenly There’s Mass
Most important, this changes the very character of the photon -- the quantum particle of light. In empty space, photons have no mass, and this lack of mass is closely related to the ability of magnetic fields to penetrate matter and extend over long distances. But inside a superconductor, where no fields can penetrate, photons effectively acquire a mass. The details of all this are quite complicated, but the implications are not: Superconductivity clearly demonstrates how a particle with no mass can suddenly come to have mass. In essence, its free movement becomes impeded by the abrupt appearance of an engulfing substance with which it interacts very strongly.
If any of this rings a bell from recent stories about the Higgs boson, it is no accident. Early work on the Higgs field -- a hypothetical field that fills all space and gives mass to most particles -- first appeared in the early 1960s. This was just after physicists had come up with the first successful theory of superconductivity, as they worked to explain why certain other particles -- the W and Z bosons involved in the so-called weak interactions responsible for radioactivity --have large masses.
Lessons learned from the magnet and from metals were put together to outline possibilities for physics on a larger scale. Perhaps, British physicist Peter Higgs and others proposed, the entire universe might be closely akin to a superconductor we cannot get out of, which is filled with a mysterious field akin to that supersensitive electron liquid. Particles have mass by virtue of their interactions as they move through it. Without knowing its historical setting, this sounds like a preposterous, crazy idea.
But it’s an idea fully inspired by concrete examples of how nature works. It is the result not only of mathematics, but also of metaphor and analogy. The world -- if the claims for the Higgs boson turn out to be right -- may indeed be rather like a cosmic superconductor.
(Mark Buchanan, a theoretical physicist and the author of “The Social Atom: Why the Rich Get Richer, Cheaters Get Caught and Your Neighbor Usually Looks Like You,” is a Bloomberg View columnist. The opinions expressed are his own.)
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