False vacuum

In quantum field theory, a false vacuum is a hypothetical vacuum that is somewhat, but not entirely, stable. It may last for a very long time in that state, and might eventually move to a more stable state. The most common suggestion of how such a change might happen is called bubble nucleation – if a small region of the universe by chance reached a more stable vacuum, this 'bubble' would spread.The possibility that we are living in a false vacuum has never been a cheering one to contemplate. Vacuum decay is the ultimate ecological catastrophe; in the new vacuum there are new constants of nature; after vacuum decay, not only is life as we know it impossible, so is chemistry as we know it. However, one could always draw stoic comfort from the possibility that perhaps in the course of time the new vacuum would sustain, if not life as we know it, at least some structures capable of knowing joy. This possibility has now been eliminated.Sidney Coleman and Frank De Luccia In quantum field theory, a false vacuum is a hypothetical vacuum that is somewhat, but not entirely, stable. It may last for a very long time in that state, and might eventually move to a more stable state. The most common suggestion of how such a change might happen is called bubble nucleation – if a small region of the universe by chance reached a more stable vacuum, this 'bubble' would spread. A false vacuum may only exist at a local minimum of energy and is therefore not stable, in contrast to a true vacuum, which exists at a global minimum and is stable. A false vacuum may be very long-lived, or metastable. A vacuum or vacuum state is defined as a space with as little energy in it as possible. Despite the name the vacuum state still has quantum fields. A true vacuum is a global minimum of energy, and coincides with a local vacuum. This configuration is stable. It is possible that the process of removing the largest amount of energy and particles possible from a normal space results in a different configuration of quantum fields with a local minimum of energy. This local minimum is called a 'false vacuum'. In this case, there would be a barrier to entering the true vacuum. Perhaps the barrier is so high that it has never yet been overcome anywhere in the universe. A false vacuum is unstable due to the quantum tunnelling of instantons to lower energy states. Tunnelling 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. If the Standard Model is correct, the particles and forces we observe in our universe exist as they do because of underlying quantum fields. Quantum fields can have states of differing stability, including 'stable', 'unstable', or 'metastable' (meaning very long-lived but not completely stable). If a more stable vacuum state were able to arise, then existing particles and forces would no longer arise as they do in the universe's present state. Different particles or forces would arise from (and be shaped by) whatever new quantum states arose. The world we know depends upon these particles and forces, so if this happened, everything around us, from subatomic particles to galaxies, and all fundamental forces, would be reconstituted into new fundamental particles and forces and structures. The universe would lose all of its present structures and become inhabited by new ones (depending upon the exact states involved) based upon the same quantum fields. Many scientific models of the universe have 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. A universe in a false vacuum state allows for the formation of a bubble of more stable 'true vacuum' at any time or place. This bubble expands 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.