False vacuum

In quantum field theory, a false vacuum is a metastable sector of space that appears to be a perturbative vacuum, but is unstable due to instanton effects that may tunnel to a lower energy state. This tunneling can be caused by quantum fluctuations or the creation of high-energy particles. The false vacuum is a local minimum, but not the lowest energy state, even though it may remain stable for some time.

In quantum field theory, vacuum refers to the ground state of space, i.e. space with as little energy in it as possible. However, the vacuum state is not empty; quantum fields are still present in it. It is possible that when we start with normal space and remove as much energy and particles as possible, we wind up in a local minimum of energy, called a "false vacuum", rather than the global minimum of energy ("true vacuum") which has a different configuration of quantum fields. In this case, there would be a barrier to entering the true vacuum (analogous to activation energy in chemistry), and perhaps the barrier is so high that it has never yet been overcome anywhere in the universe.

Along these lines, scientific models of our universe have long included the possibility that it exists as a long-lived, but not completely stable, sector of space, which could potentially at some time be destroyed upon 'toppling' into a more stable vacuum state. If the universe were indeed in such a false vacuum state, a catastrophic bubble of more stable "true vacuum" could theoretically occur at any time or place expanding outward at the speed of light. The Standard Model of particle physics opens the possibility of calculating, from the masses of the Higgs boson and the top quark, whether the universe's present electroweak vacuum state is likely to be stable or merely long-lived. (This was sometimes misreported as the Higgs boson "ending" the universe). A 125–127 GeV Higgs mass seems to be extremely close to the boundary for stability (estimated in 2012 as 123.8–135.0 GeV). However, a definitive answer requires much more precise measurements of the top quark's pole mass, and new physics beyond the Standard Model of Particle Physics could drastically change this picture.

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