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In quantum field theory, a false vacuum is a hypothetical vacuum state that is locally stable but does not occupy the most stable possible ground state.

It may last for a very long time in this state, but could eventually decay to the more stable one, an event known as false vacuum decay. The most common suggestion of how such a decay might happen in our universe is called bubble nucleation‌—if a small region of the universe by chance reached a more stable vacuum, this "bubble" (also called "bounce") would spread. A false vacuum exists at a local minimum of energy and is therefore not completely stable, in contrast to a true vacuum, which exists at a global minimum and is stable. A vacuum is defined as a space with as little energy in it as possible. Despite the name, the vacuum still has quantum fields. A true vacuum is stable because it is at a global minimum of energy, and is commonly assumed to coincide with the physical vacuum state in which we live. It is possible that a physical vacuum state is a configuration of quantum fields representing a local minimum but not global minimum of energy. This type of vacuum state is called a "false vacuum".

If our universe is in a false vacuum state rather than a true vacuum state, then the decay from the less stable false vacuum to the more stable true vacuum (called false vacuum decay) could have dramatic consequences. In general, gravitation makes the probability of vacuum decay smaller; in the extreme case of minimal energy-density difference, it can even stabilize the false vacuum, preventing vacuum decay altogether. 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.

A number of theories suggest that cosmic inflation may be an effect of a false vacuum decaying into the true vacuum. The inflation itself may be the consequence of the Higgs field trapped in a false vacuum state with Higgs self-coupling λ and its βλ function very close to zero at the planck scale. Chaotic inflation theory suggests that the universe may be in either a false vacuum or a true vacuum state. In 2014, researchers at the Chinese Academy of Sciences' Wuhan Institute of Physics and Mathematics gave an actual mathematical demonstration of the already existing idea that the universe could have been spontaneously created from nothing (no space, time, nor matter) by quantum fluctuations of a metastable false vacuum causing an expanding bubble of true vacuum.

The corresponding false vacuum hypothesis is called either "electroweak vacuum instability" or "Higgs vacuum instability". If measurements of the Higgs boson and top quark suggest that our universe lies within a false vacuum of this kind, this would imply that the bubble's effects will propagate across the universe at nearly the speed of light from its origin in space-time.

When the false vacuum decays, the lower-energy true vacuum forms through a process known as bubble nucleation. Bubble wall has a finite thickness, depending on ratio between energy barrier and energy gain obtained by creating true vacuum.

However, the authors note that if primordial black holes cause a false vacuum collapse, then it should have happened long before humans evolved on Earth. In 2019, it was found that although small non-spinning black holes may increase true vacuum nucleation rate, rapidly spinning black holes will stabilize false vacuums to decay rates lower than expected for flat space-time.

If all decay paths lead to very massive particles, the energy barrier of such a decay may result in a stable bubble of false vacuum (also known as a Fermi ball) enclosing the false-vacuum particle instead of immediate decay.

Quick Facts

• If our universe is in a false vacuum state rather than a true vacuum state, then the decay from the less stable false vacuum to the more stable true vacuum (called false vacuum decay) could have dramatic consequences.
• This type of vacuum state is called a "false vacuum".
• A false vacuum exists at a local minimum of energy and is therefore not completely stable, in contrast to a true vacuum, which exists at a global minimum and is stable.
• It may last for a very long time in this state, but could eventually decay to the more stable one, an event known as false vacuum decay.
• The corresponding false vacuum hypothesis is called either "electroweak vacuum instability" or "Higgs vacuum instability".

Source material: Wikipedia - "False vacuum". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.