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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" (also called "bounce") would spread. A false vacuum exists 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. It may be very longlived, or metastable.
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 a global minimum of energy, and is commonly assumed to coincide with a physical vacuum state we live in.
Synonyms for physical vacuum state are the following: Standard Model vacuum, normal vacuum, normal space, physical space, our spacetime, fabric of spacetime, universe.
The configuration with quantum fields at global energy minimum is stable. The false vacuum is a local minimum, but not the lowest energy state of quantum fields.
It is possible that a physical vacuum state is a configuration of quantum fields representing a local minimum but not global minimum of energy. In this case vacuum state is called a "false vacuum".
If a more stable vacuum state were able to arise, the effects may vary from complete cessation of existing fundamental forces, elementary particles and structures comprising them, to subtle change in some cosmological parameters, mostly depending on potential difference between true and false vacuum. Some false vacuum decay scenarios are compatible with survival of structures like galaxies and stars^{[1]}^{[2]} or even life^{[3]} while others involve the full destruction of baryonic matter^{[4]} or even immediate gravitational collapse of the universe,^{[5]}^^{Note 1} although in this last case the possibility to causally connect (i.e nucleate) the true vacuum from inside of the false vacuum area is dubious.^{[6]}
In a 2005 paper published in Nature, as part of their investigation into global catastrophic risks, MIT physicist Max Tegmark and Oxford philosopher Nick Bostrom calculate the natural risks of the destruction of the Earth at less than 1 per gigayear from all events, including a transition to a lower vacuum state. They argue that due to observer selection effects, we might underestimate the chances of being destroyed by vacuum decay because any information about this event would reach us only at the instant when we too were destroyed. This is in contrast to events like risks from impacts, gammaray bursts, supernovae and hypernovae, the frequencies of which we have adequate direct measures.^{[7]}
The stability criteria for Electroweak interaction was first formulated in 1979,^{[14]} that time as function of masses of theoretical Higgs boson and heaviest fermion. Discovery of Top quark in 1995 and Higgs boson in 2012 have allowed to validate the criteria against experiment, therefore since 2012 Electroweak interaction is considered as most promising candidate for metastable fundamental force.^{[9]}. The corresponding false vacuum hypothesis is called either 'Electroweak vacuum instability' or 'Higgs vacuum instability'.^{[15]}. The present false vacuum state is called [math]\displaystyle{ dS }[/math] (De Sitter space), while tentative true vacuum is called [math]\displaystyle{ AdS }[/math] (Antide Sitter space).^{[16]}^{[17]}
Diagrams on right are showing the uncertainty ranges of Higgs boson and top quark masses as ovalshaped lines. Underlying colors are indicating if the electroweak vacuum state is likely to be stable, merely longlived or completely unstable for given combination of masses.^{[18]} ^{[19]} The "electroweak vacuum decay" hypothesis was sometimes misreported as the Higgs boson "ending" the universe.^{[20]} ^{[21]}^{[22]} A 125.18±0.16 GeV/c^{2}^{[23]} Higgs boson mass is likely to be on the metastable side of stablemetastable boundary (estimated in 2012 as 123.8–135.0 GeV. ^{[9]} ) However, a definitive answer requires much more precise measurements of the top quark's pole mass,^{[9]}, although improved measurement precision of Higgs boson and top quark masses further reinforced the claim of physical electroweak vacuum being in the metastable state as in 2018.^{[13]} Nonetheless, new physics beyond the Standard Model of Particle Physics could drastically change the stability landscape division lines, rendering previous stability and metastability criteria incorrect. ^{[24]}^{[25]}
If measurements of Higgs boson and top quark suggests that our universe lies within a false vacuum of this kind, then it would imply—more than likely in many billions of years^{[26]} the bubble's effects would be expected to propagate across the universe at nearly the speed of light from wherever it occurred. However space is vast—with even the nearest galaxy being over 2 million lightyears from us, and others being many billions of lightyears distant, so the effect of such an event would be unlikely to arise here for billions of years after first occurring.^{[26]}^{[27]}
In the theoretical physics of the false vacuum, the system moves to a lower energy state – either the true vacuum, or another, lower energy vacuum – through a process known as bubble nucleation.^{[28]}^{[29]}^{[30]}^{[31]}^{[32]}^{[33]} In this, instanton effects cause a bubble to appear in which fields have their true vacuum values inside. Therefore, the interior of the bubble has a lower energy. The walls of the bubble (or domain walls) have a surface tension, as energy is expended as the fields roll over the potential barrier to the lower energy vacuum. The critical size of the bubble is determined in the semiclassical approximation to be such that the bubble has zero total change in the energy: the decrease in energy by the true vacuum in the interior is compensated by the tension of the walls.
To convert initially small true vacuum bubble (bounce) into bubble with zero total energy, an energy barrier must be overcome, and barrier height [math]\displaystyle{ \Phi_c }[/math] is follows equation^{[33]}
[math]\displaystyle{ \Phi_c=3A/4R^2\Delta\Phi; }[/math] 

( ) 
, where [math]\displaystyle{ \Delta\Phi }[/math]  potential difference between true and false vacuums, [math]\displaystyle{ A }[/math] is unknown constant (surface tension of interface between different vacua), and [math]\displaystyle{ R }[/math]  radius of bubble. Perhaps the unknown constant [math]\displaystyle{ A }[/math] is so high that bubble large enough to have barrier vanished has never yet been formed anywhere in the universe. Rewriting the Eq. 1, one can get true vacuum bubble critical radius as
[math]\displaystyle{ R=\sqrt{3A/(4\Delta\Phi)}; }[/math] 

( ) 
Bubble of true vacuum smaller than critical size can overcome the potential barrier due to the quantum tunnelling of instantons to lower energy states. Tunneling can be caused by quantum fluctuations, and tunneling rate to expanding state for bubble smaller than critical size can be expressed as^{[34]}
[math]\displaystyle{ \omega=\tfrac{1}{A}\sqrt{\tfrac{2\Phi_c}{h}} e^{\Phi_c/h}; }[/math] 

( ) 
where [math]\displaystyle{ h }[/math] is Planck constant.
Also, small bubble of true vacuum can be inflated to critical size by externally supplied energy,^{[35]} although required energy densities are several orders of magnitude beyond capability of any natural or artificial process.^{[4]} Energydriven bubble inflation mechanism should not be confused with the speculative nucleation barrier lowering by gravity field of miniature black holes.
As soon as a bubble of lowerenergy vacuum grows beyond the critical radius defined by Eq. 2, the bubble's wall will begin to accelerate outward. The expansion will then decrease the bubble`s potential energy, as the energy of the wall increases as the surface area of a sphere [math]\displaystyle{ 4 \pi r^2 }[/math] but the negative contribution of the interior increases more quickly, as the volume of a sphere [math]\displaystyle{ \textstyle\frac{4}{3} \pi r^3 }[/math]. With the expected large potential differences between false and true vacuum states in most vacuum decay scenarios, the velocity of the bubble surface becomes practically indistinguishable from the speed of light in a fraction of second. The single bubble does not produce any gravitational effects on surrounding objects during expansion, because the negative energy density of the bubble interior is cancelled by the positive kinetic energy of the wall.^{[5]} If two bubbles are nucleated and they eventually collide, it is thought that particle production would occur where the walls collide.
False vacuum decay event is occasionally used as a plot device in works picturing a doomsday event.