Vacuum decay
In quantum field theory, a false vacuum is a metastable sector of space that appears to be a perturbative vacuum.
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 as much energy and particles as 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. 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.
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, long-lived but capable of being "toppled" in the right circumstances). 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.
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