Physicists recently confirmed that the Large Hadron Collider (LHC) at CERN, the particle physics laboratory in Geneva, had indeed found a Higgs boson last July, marking a culmination of one of the longest and most expensive searches in science. The finding also means that our universe could be doomed to fall apart. "If you use all the physics that we know now and you do what you think is a straightforward calculation, it is bad news," says Joseph Lykken, a theorist who works at the Fermilab National Accelerator Laboratory in Illinois. "It may be that the universe we live in is inherently unstable."
The Higgs boson helps explain why particles have the mass they do. The Higgs particle that the LHC has found possesses a mass of approximately 126 giga-electron volts (GeV)—roughly the combined mass of 126 protons (hydrogen nuclei). (One GeV equals a billion electron volts.)
Based on the data analysis so far, the discovered particle is consistent with the Standard Model of particle physics, the highly successful theory that describes the subatomic world, although other models cannot be ruled out. "It is looking very much like the Standard Model Higgs boson—although there may be a very massive Higgs particle that also exists. Our experiment is sensitive enough to detect massive Higgs bosons, but we may simply not yet have enough data," says Joseph Incandela, the spokesman for the CMS (Compact Muon Solenoid) experiment at the LHC, one of the two experiments that detected the current Higgs particle.*
And that very nature of being a Standard Model Higgs may be the reason our universe is ultimately unstable. It has to do with the so-called vacuum stability in the Standard Model.
According to the description currently favored by physicists, a vacuum is not completely devoid of matter but instead teems with particles and antiparticles that pop into existence and then run into one another and annihilate themselves, all in very short times. The inherent uncertainty embodied in quantum mechanics permits these spontaneous fluctuations—as long as the particles don't live for more than a fleeting instant, the process violates no laws of physics.
The Standard Model also says, as Lykken puts it, that "for the vacuum of empty space to be stable, we should be living at a minimum of potential energy." In other words, most things end up resting in a place of lowest energy. A ball rolls downhill and settles in a low point; getting it to move away from this point requires a kick of energy. In the case of the universe it would be like living at the bottom of a valley bordered by hills: the value of the Higgs potential would be lowest point of the valley.
Our universe might end if our valley really isn't the lowest one around. Physicist Benjamin Allanach of the University of Cambridge explains: "The shape of the Higgs potential is determined precisely by the Higgs mass." The observed 126 GeV mass seems to imply the universe does not exist in the lowest possible energy state but is in fact positioned in a slightly unusual place. "It turns out that for a Higgs boson of 126 GeV, we might be in the gray area where the universe is at a local minimum that is not the global minimum," says physicist Matthew Strassler of Rutgers University.
It is sort of like being in a valley whose floor is higher than that of an adjoining valley. If you didn't know that a deep valley was on the other side of the hill, you would think you were at the lowest level you could be. If you somehow managed to get to the other side, however, you could fall much lower.
This situation would normally not pose a problem, as you couldn't travel between valleys—except in quantum mechanics, which allows particles to tunnel through hills unpredictably. As a result, "in the future our universe could spontaneously and randomly tunnel through to the deeper one, with potentially catastrophic consequences," Allanach says.