The original version of this story appeared in Quanta Magazine.
Vacuum decay, a process that could end the universe as we know it, may happen 10,000 times sooner than expected. Fortunately, it still won’t happen for a very, very long time.
When physicists speak of “the vacuum,” the term sounds as though it refers to empty space, and in a sense it does. More specifically, it refers to a set of defaults, like settings on a control board. When the quantum fields that permeate space sit at these default values, you consider space to be empty. Small tweaks to the settings create particles—turn the electromagnetic field up a bit, and you get a photon. Big tweaks, on the other hand, are best thought of as new defaults altogether. They create a different definition of empty space, with different traits.
One quantum field is special because its default value can change. Called the Higgs field, it controls the mass of many fundamental particles, like electrons and quarks. Unlike every other quantum field physicists have discovered, the Higgs field has a default value above zero. Dialing the Higgs field value up or down would increase or decrease the mass of electrons and other particles. If the setting of the Higgs field were zero, those particles would be massless.
We could stay at the nonzero default for eternity, were it not for quantum mechanics. A quantum field can “tunnel,” jumping to a new, lower-energy value even if it doesn’t have enough energy to pass through the higher-energy intermediate settings, an effect akin to tunneling through a solid wall.
For this to happen, you need to have a lower-energy state to tunnel to. And before building the Large Hadron Collider, physicists thought that the current state of the Higgs field could be the lowest. That belief has now changed.
The curve that represents the energy required for different settings of the Higgs field was always known to resemble a sombrero with an upturned brim. The current setting of the Higgs field can be pictured as a ball resting at the bottom of the brim.
Ilustration: Credit: Mark Belan for Quanta Magazine
However, subtle quantum corrections can change the shape of the curve. Quantum fields feed energy back and forth between one another. The quantum interactions between electrons and the electromagnetic field shift the energy levels of atoms, for instance—an effect discovered in the 1940s.
For the Higgs field, the curvature of the sombrero’s brim is determined by the mass of the Higgs boson, the elementary particle that conveys the Higgs field’s effects, which was discovered at the Large Hadron Collider in 2012. Further corrections to the shape of the curve come from particles that interact strongly with the Higgs: those with high mass like the top quark, the heaviest known elementary particle. By comparing the mass of the Higgs boson to that of the top quark, physicists now think that the sombrero most likely dips down again. At a much higher setting of the Higgs field, there’s a lower-energy state.
In that case, the Higgs field should eventually tunnel to that state, or “decay.” This decay would start in one place and then spread, a spherical bubble growing at the speed of light, transforming the universe. Fundamental particles would become much heavier, so that they would be drawn together by gravity more strongly than the other forces held them apart. Atoms would collapse.
We won’t tunnel to that higher Higgs setting any time soon, though. Physicists estimate the chances of vacuum decay in different ways. In the most direct method, they keep an account of the different transformations that would be necessary to get the field from one value to the other—transformations that violate the conservation of energy, which quantum mechanics allows to briefly happen—weighting each scenario according to how greatly it violates rules like energy conservation. According to these estimates, a cubic gigaparsec of space will see vacuum decay once every 10794 years, or the digit 1 followed by 794 zeros—an absurd span of time. Only 1010 years have passed so far since the Big Bang.
Recently, a group of physicists in Slovenia claimed to have found a small error in the calculation, one that quickens the end of the universe as we know it to 10790 years, instead of 10794. While a change by a factor of 10,000 may seem huge, it is much smaller than the uncertainty from other parts of the calculation. Most important: None of these uncertainties are big enough to cut through the eons that lie between us and the horrors of vacuum decay.
Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.
