Finally there are hints that physics theory and experiment are meeting up again, in a way that may elucidate what British cosmologist Stephen Hawking calls “the mind of God.” He means not merely a description of nature but an explanation of why it is this way and not some other. That is, did God have any choice when she made the cosmos? The newest theory may explain why the standard model is what it is.
For 25 years that “why” has been maddeningly elusive. The standard model has 18 crucial numbers, including the masses of 13 fundamental particles; the theory gives no reason why creation opted for those numbers and not some others. For a science that’s supposed to explain why nature is what it is, that’s a fairly serious lapse. “We just never understood why particles have the masses they do,” says Hall. “We had to measure them. We couldn’t derive them from something more fundamental.” But now Hall, Savas Dimopoulos of Stanford University and Stuart Raby of Ohio State University may have an explanation for some of those out-of-thin-air values.
Imagine that space is filled with goopy honey. If you push a large Frisbee through, the Frisbee picks up lots of sticky stuff and becomes even heavier, Dimopoulos explains. If you push a coin through, it picks up some middling amount of honey, gaining just a little weight. A pinhead picks up only the tiniest bit of extra weight. It turns out that space is pervaded by something–not honey, of course, but an exotic sea of energy called the Higgs field. At the beginning of time, space was abuzz with speeding quarks, the whimsically named particle believed to be the indivisible building blocks of matter. As the quarks through the Higgs sea, says the new theory, they gained weight, and pieces broke o them. Medium and tiny pieces picked up mass from the Higgs field, too, eventually reaching the mass of today’s mediumweight quarks and bantamweight quarks. How much mass did they acquire? An amount calculated from the relationships, or symmetries, between the quarks. (The mathematics of this calculation are not fit for publication in a family magazine.) Using these symmetries, Raby, Hall and Dimopoulos derived seven of the old measures of mass.
No one claims the work has practical benefit. After all, it involves particles that last made an appearance in the big bang. Of the six quarks, today only “up” and “down” (quark names have nothing to do with the usual meanings of the words) exist outside atom smashers. They constitute the protons and neutrons of ordinary atoms. “Top” and “bottom” belong to the heaviest particle family; top has never been found, and bottom pops into existence only fleetingly in particle accelerators. The quarks in the middle family, “charm” and “strange,” also exist only in the rare particles made by accelerators. It’s always possible that by explaining something as basic as why these smallest units of matter have the weights they do, the new theory will explain some puzzle in chemistry, which will in turn explain some mystery in biology. But that’s a long way off. If the mass theory holds up, its relevance will lie, first, in fundamental physics. But it will also address the philosophical puzzle of whether creation had to be this way.
Is the mass theory right? It makes several testable predictions. One is the mass of the “top” quark. Top is estimated to be some 20,000 times heavier than up. For months there have been rumors that a team at Fermilab, outside Chicago, has finally snared top. The lab’s Melvyn Shochet told NEWSWEEK that the data aren’t solid enough to claim the quarry, but they do rule out a top quark lighter than 108 of the units physicists use (called GeV). Hall and colleagues predict a top quark weighing 170 to 190-so their mass theory is alive. Other tests require the SSC, which, if it survives Washington’s budget cutters, could come on line by 1999.
Other physicists, though impressed with the model, are withholding judgment until more of its predictions are borne out. But many are elated that particle physics finally has a new, testable theory, one firmly grounded in reality. If the model passes the tests that experimentalists are cooking up, physicists will have real reasons for self-esteem.
