View source for False vacuum

{{Short description|Hypothetical vacuum, less stable than true vacuum}}
{{Cosmology|expansion}}

[[File:Falsevacuum.svg|thumb|upright=0.8|A [[scalar field]] ''φ'' (which represents physical position) in a false vacuum. The energy ''E'' is higher in the false vacuum than that in the true vacuum or [[ground state]], but there is a barrier preventing the field from classically rolling down to the true vacuum. Therefore, the transition to the true vacuum must be stimulated by the creation of [[particle physics|high-energy particles]] or through [[quantum tunnelling|quantum-mechanical tunneling]].]]

In [[quantum field theory]], a '''false vacuum'''<ref name="url[2006.06003] Observing the fate of the false vacuum with a quantum laboratory">{{cite journal |arxiv=2006.06003|last1=Abel|first1=Steven|last2=Spannowsky|first2=Michael|title=Quantum-Field-Theoretic Simulation Platform for Observing the Fate of the False Vacuum|journal=PRX Quantum|year=2021|volume=2|article-number=010349|doi=10.1103/PRXQuantum.2.010349|s2cid=234355374}}</ref> is a hypothetical [[quantum vacuum state|vacuum state]] that is locally stable but does not occupy the most stable possible [[ground state]].<ref>{{Cite web|date=2015-09-13|title=Vacuum decay: the ultimate catastrophe|url=https://cosmosmagazine.com/physics/vacuum-decay-ultimate-catastrophe/|access-date=2020-09-16|website=Cosmos Magazine|language=en-AU}}</ref> In this condition it is called [[metastability|metastable]]. 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")<ref name="fate"/><ref name=Markkanen2018>{{cite journal|doi=10.3389/fspas.2018.00040|title=Cosmological Aspects of Higgs Vacuum Metastability|year=2018|last1=Markkanen|first1=Tommi|last2=Rajantie|first2=Arttu|last3=Stopyra|first3=Stephen|journal=Frontiers in Astronomy and Space Sciences|volume=5|article-number=40|arxiv=1809.06923|bibcode=2018FrASS...5...40R|s2cid=56482474|doi-access=free}}</ref> would spread.

A false vacuum exists at a [[maxima and minima|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.

== Definition of true vs. false vacuum ==
A [[ground state|vacuum]] is defined as a space with as little energy in it as possible. Despite the name, the vacuum still has quantum [[Field (physics)|field]]s. A true vacuum is stable because it is at a [[Maxima and minima|global minimum]] of energy, and is commonly assumed to coincide with the physical [[Quantum vacuum state|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".

== Implications ==

=== Existential threat ===
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.<ref name="urlHow vacuum decay could end the universe - Big Think">{{cite web |date=January 2019 |title=How 'vacuum decay' could end the universe – Big Think |url=https://bigthink.com/surprising-science/vacuum-decay-end-of-the-universe |format=}}</ref><ref name="urlVacuum decay: the ultimate catastrophe - Cosmos Magazine">{{cite web |url=https://cosmosmagazine.com/physics/vacuum-decay-ultimate-catastrophe/ |title=Vacuum decay: the ultimate catastrophe |date=14 September 2015 |format= }}</ref> The effects could range from complete cessation of existing [[Fundamental interaction|fundamental force]]s, [[elementary particle]]s and structures comprising them, to subtle change in some cosmological parameters, mostly depending on the potential difference between true and false vacuum. Some false vacuum decay scenarios are compatible with the survival of structures like galaxies, stars,<ref name=Lorenz2018/><ref name=Landim2016/> and even biological life,<ref name="Crone1991">{{cite journal|url = https://pubs.aip.org/aapt/ajp/article-abstract/59/1/25/1053821/The-environmental-impact-of-vacuum-decay|doi = 10.1119/1.16701|year = 1991|volume = 59|issue = 1|last1 = Crone|first1 = Mary M.|last2 = Sher|first2 = Marc|title = The environmental impact of vacuum decay|journal = American Journal of Physics|page = 25|bibcode = 1991AmJPh..59...25C|url-access = subscription}}</ref> while others involve the full destruction of [[Baryon#Baryonic matter|baryonic matter]]<ref name="turnerwilczek"/> or even immediate [[gravitational collapse]] of the universe.<ref name="colemandeluccia">{{cite journal |first1=Sidney |last1=Coleman |first2=Frank |last2=De Luccia |date=1980-06-15 |title=Gravitational effects on and of vacuum decay |url=https://www.sns.ias.edu/pitp2/2011files/PhysRevD.21.3305.pdf |url-status=live |journal=[[Physical Review D]] |volume=21 |number=12 |pages=3305–3315 |bibcode=1980PhRvD..21.3305C |doi=10.1103/PhysRevD.21.3305 |osti=1445512 |s2cid=1340683 |archive-url=https://web.archive.org/web/20191213005332/https://www.sns.ias.edu/pitp2/2011files/PhysRevD.21.3305.pdf |archive-date=13 December 2019 |access-date=16 January 2020}}</ref> In this more extreme case, the likelihood of a "bubble" forming is very low (i.e. one in 10 to the 868 power<ref>{{Cite journal |last=von Hippel |first=Matthew |date=Spring 2025 |title=The Quantum Bubble that Could Destroy the Universe |journal=[[Scientific American]] |edition=Special |page=100}}</ref> or false vacuum decay may even be impossible).<ref>{{cite arXiv|eprint=hep-th/0211160|last1=Banks|first1=T.|title=Heretics of the False Vacuum: Gravitational Effects on and of Vacuum Decay 2|year=2002 }}</ref>

A paper by Coleman and De Luccia that attempted to include simple gravitational assumptions into these theories noted that if this was an accurate representation of nature, then the resulting universe "inside the bubble" in such a case would appear to be extremely unstable and would almost immediately collapse:
{{Blockquote|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. We believe we understand this. For the vacuum to decay, building a bubble of total energy zero must be possible. In the absence of gravitation, this is no problem, no matter how small the energy-density difference; all one has to do is make the bubble big enough, and the volume/surface ratio will do the job. In the presence of gravitation, though, the negative energy density of the true vacuum distorts geometry within the bubble with the result that, for a small enough energy density, there is no bubble with a big enough volume/surface ratio. Within the bubble, the effects of gravitation are more dramatic. The geometry of space-time within the bubble is that of [[anti-de Sitter space]], a space much like conventional [[de Sitter space]] except that its group of symmetries is O(3, 2) rather than O(4, 1). Although this space-time is free of singularities, it is unstable under small perturbations, and inevitably suffers gravitational collapse of the same sort as the end state of a contracting [[Friedmann equations|Friedmann universe]]. The time required for the collapse of the interior universe is on the order of ... microseconds or less.

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. Nonetheless, one could always draw [[stoicism|stoic]] comfort from the possibility that perhaps over 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.

The second special case is decay into a space of vanishing cosmological constant, the case that applies if we are now living in the debris of a false vacuum that decayed at some early cosmic epoch. This case presents us with less interesting physics and with fewer occasions for rhetorical excess than the preceding one. It is now the interior of the bubble that is ordinary [[Minkowski space]]&nbsp;...|source = [[Sidney Coleman]] and Frank De Luccia<ref name="colemandeluccia" />
}}

In a 2005 paper published in ''[[Nature (journal)|Nature]]'', as part of their investigation into [[global catastrophic risk]]s, MIT physicist [[Max Tegmark]] and Oxford philosopher [[Nick Bostrom]] calculate the natural risks of the destruction of the Earth at less than 1/10<sup>9</sup> per year from all natural (i.e. non-anthropogenic) events, including a transition to a lower vacuum state. They argue that due to [[Anthropic principle|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, [[gamma-ray burst]]s, [[supernova]]e and [[hypernova]]e, the frequencies of which we have adequate direct measures.<ref name="tegmarkbostrom">{{cite journal |author=Tegmark |first1=M. |last2=Bostrom |first2=N. |date=2005 |title=Is a doomsday catastrophe likely? |url=http://www.fhi.ox.ac.uk/wp-content/uploads/is-doomsday-likely.pdf |journal=Nature |volume=438 |issue=5875 |page=754 |bibcode=2005Natur.438..754T |doi=10.1038/438754a |pmid=16341005 |s2cid=4390013 |archive-url=https://web.archive.org/web/20140409031127/http://www.fhi.ox.ac.uk/is-doomsday-likely.pdf |archive-date=2014-04-09 |access-date=2016-03-16}}</ref>

=== Inflation ===
A number of theories suggest that [[inflation (cosmology)|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 boson|Higgs field]] trapped in a false vacuum state<ref>{{Cite web |author=Smeenk |first=Chris |title=False Vacuum: Early Universe Cosmology and the Development of Inflation |url=http://publish.uwo.ca/~csmeenk2/files/FalseVacuum.pdf}}</ref> with Higgs [[coupling (physics)|self-coupling]] λ and its β<sub>λ</sub> function very close to zero at the [[Planck units#Planck scale|planck scale]].<ref name="Alekhin 2012" />{{rp|218}} A future electron-positron collider would be able to provide the precise measurements of the top quark needed for such calculations.<ref name="Alekhin 2012" />

[[Eternal inflation|Chaotic inflation theory]] suggests that the universe may be in either a false vacuum or a true vacuum state. [[Alan Guth]], in his original proposal for cosmic inflation,<ref name="guth">{{cite journal |author=Guth |first=Allan H. |author-link=Alan Guth |date=1981-01-15 |title=The Inflationary Universe: A Possible Solution to the Horizon and Flatness Problems |journal=Physical Review D |volume=23 |issue=2 |pages=347–356 |bibcode=1981PhRvD..23..347G |doi=10.1103/physrevd.23.347 |oclc=4433735058 |doi-access=free}}</ref> proposed that inflation could end through quantum mechanical bubble nucleation of the sort described above. See [[Eternal inflation#Development of the theory|history of Chaotic inflation theory]]. It was soon understood that a homogeneous and isotropic universe could not be preserved through the violent tunneling process. This led [[Andrei Linde]]<ref name="linde">{{cite journal |author=Linde |first=Andrei |date=1982 |title=A New Inflationary Universe Scenario: A Possible Solution Of The Horizon, Flatness, Homogeneity, Isotropy And Primordial Monopole Problems |journal=Phys. Lett. B |volume=108 |issue=6 |page=389 |bibcode=1982PhLB..108..389L |doi=10.1016/0370-2693(82)91219-9}}</ref> and, independently, [[Andreas Albrecht (cosmologist)|Andreas Albrecht]] and [[Paul Steinhardt]],<ref name="albrechtsteinhardt">{{cite journal |last1=Albrecht |first1=A. |last2=Steinhardt |first2=P. J. |date=1982 |title=Cosmology For Grand Unified Theories With Radiatively Induced Symmetry Breaking |journal=Physical Review Letters |volume=48 |issue=17 |pages=1220–1223 |bibcode=1982PhRvL..48.1220A |doi=10.1103/PhysRevLett.48.1220}}</ref> to propose "new inflation" or "slow roll inflation" in which no tunnelling occurs, and the inflationary scalar field instead graphs as a gentle slope.

In 2014, researchers at the [[Chinese Academy of Sciences|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 [[Why is there anything at all?|spontaneously created from nothing]] (no [[space]], [[time]], nor [[matter]]) by [[quantum fluctuation]]s of a metastable false vacuum causing an expanding bubble of true vacuum.<ref name="url[1404.1207] Spontaneous creation of the universe from nothing">{{cite journal |title=Spontaneous creation of the universe from nothing |year=2014 |doi=10.1103/PhysRevD.89.083510 |arxiv=1404.1207 |last1=He |first1=Dongshan |last2=Gao |first2=Dongfeng |last3=Cai |first3=Qing-yu |journal=Physical Review D |volume=89 |issue=8 |article-number=083510 |bibcode=2014PhRvD..89h3510H |s2cid=118371273 }}</ref>

==Vacuum decay varieties==
===Electroweak vacuum decay===
[[File:Higgs-Mass-MetaStability.svg|thumb|upright=1.5|Electroweak vacuum stability landscape as estimated in 2012<ref name="Alekhin 2012" />]]
[[File:Higgs_FalseVacuum2018.jpg|thumb|upright=1.5|Electroweak vacuum stability landscape as estimated in 2018.<ref name=Markkanen2018/> T<sub>RH</sub> is grand unification energy. ξ is the degree of non-minimal coupling between fundamental forces.]]
The stability criteria for the [[electroweak interaction]] was first formulated in 1979<ref>{{Cite web |last1=Cabibbo |first1=N. |last2=Maiani |first2=L. |last3=Parisi |first3=G. |last4=Petronzio |first4=R. |year=1979 |title=Bounds on the Fermions and Higgs Boson Masses in Grand Unified Theories |url=https://cds.cern.ch/record/133331/files/197907145.pdf}}</ref> as a function of the masses of the theoretical [[Higgs boson]] and the heaviest [[fermion]]. Discovery of the [[top quark]] in 1995 and the Higgs boson in 2012 have allowed physicists to validate the criteria against experiment, therefore since 2012 the [[electroweak interaction]] is considered as the most promising candidate for a [[Metastability|metastable]] [[Fundamental interaction|fundamental force]], also known as "pseudostable fundamental force".<ref name="Alekhin 2012" /> The corresponding false vacuum hypothesis is called either "electroweak vacuum instability" or "Higgs vacuum instability".<ref>{{cite journal|arxiv=1704.06884|doi=10.1103/PhysRevD.98.103521|bibcode=2018PhRvD..98j3521K|title=Electroweak vacuum instability and renormalized vacuum field fluctuations in Friedmann-Lemaitre-Robertson-Walker background|year=2018|last1=Kohri|first1=Kazunori|last2=Matsui|first2=Hiroki|s2cid=39999058|journal=Physical Review D|volume=98|issue=10|article-number=103521}}</ref> The present false vacuum state is called <math>dS</math> ([[de Sitter space]]), while tentative true vacuum is called <math>AdS</math> ([[Anti-de Sitter space]]).<ref>{{cite journal|arxiv=1404.5953|doi=10.1007/JHEP01(2015)061|bibcode=2015JHEP...01..061H|title=Probable or improbable universe? Correlating electroweak vacuum instability with the scale of inflation|year=2015|last1=Hook|first1=Anson|last2=Kearney|first2=John|last3=Shakya|first3=Bibhushan|last4=Zurek|first4=Kathryn M.|s2cid=118737905|journal=Journal of High Energy Physics|volume=2015|issue=1|page=61}}</ref><ref>{{cite journal|arxiv=1607.08133|doi=10.1088/1475-7516/2017/08/011|bibcode=2017JCAP...08..011K|title=Electroweak vacuum instability and renormalized Higgs field vacuum fluctuations in the inflationary universe|year=2017|last1=Kohri|first1=Kazunori|last2=Matsui|first2=Hiroki|s2cid=119216421|journal=Journal of Cosmology and Astroparticle Physics|volume=2017|issue=8|page=011}}</ref>

The diagrams show the uncertainty ranges of Higgs boson and top quark masses as oval-shaped lines. Underlying colors indicate if the electroweak vacuum state is likely to be stable, merely long-lived or completely unstable for given combination of masses.<ref>
{{cite journal |last1=Ellis |first1=J. |last2=Espinosa |first2=J. R. |last3=Giudice |first3=G. F. |last4=Hoecker |first4=A. |last5=Riotto |first5=A. |date=2009 |title=The Probable Fate of the Standard Model |journal=Phys. Lett. B |volume=679 |issue=4 |pages=369–375 |arxiv=0906.0954 |bibcode=2009PhLB..679..369E |doi=10.1016/j.physletb.2009.07.054 |s2cid=17422678}}
</ref><ref>
{{cite journal |last=Masina |first=Isabella |title=Higgs boson and top quark masses as tests of electroweak vacuum stability |journal=Physical Review D |date=2013-02-12 |doi=10.1103/physrevd.87.053001 |arxiv = 1209.0393 |bibcode = 2013PhRvD..87e3001M |volume=87|issue=5 |article-number=053001 |s2cid=118451972 }}</ref> The "electroweak vacuum decay" hypothesis was sometimes misreported as the Higgs boson "ending" the universe.<ref>{{cite news |author=Klotz, Irene |editor1=Adams, David |editor2=Eastham, Todd |title=Universe has finite lifespan, Higgs boson calculations suggest |url=https://huffingtonpost.com/2013/02/19/universe-lifespan-finite-unstable-higgs-boson_n_2713053.html |access-date=21 February 2013 |newspaper=Huffington Post |date=18 February 2013 |agency=Reuters |quote=Earth will likely be long gone before any Higgs boson particles set off an apocalyptic assault on the universe |archive-date=20 February 2013 |archive-url=https://web.archive.org/web/20130220141633/http://www.huffingtonpost.com/2013/02/19/universe-lifespan-finite-unstable-higgs-boson_n_2713053.html |url-status=live }}</ref><ref>{{cite web |last=Hoffman |first=Mark |title=Higgs boson will destroy the universe, eventually |url=http://www.scienceworldreport.com/articles/5038/20130219/higgs-boson-instability-will-destroy-universe-eventually.htm |access-date=21 February 2013 |website=Science World Report |date=19 February 2013 |archive-date=11 June 2019 |archive-url=https://web.archive.org/web/20190611181953/https://www.scienceworldreport.com/articles/5038/20130219/higgs-boson-instability-will-destroy-universe-eventually.htm |url-status=live }}</ref><ref>{{cite news |title=Higgs boson will aid in creation of the universe—and how it will end |url=http://www.catholic.org/technology/story.php?id=49808 |access-date=21 February 2013 |newspaper=Catholic Online/NEWS CONSORTIUM |date=2013-02-20 |archive-url=https://web.archive.org/web/20130926215031/http://www.catholic.org/technology/story.php?id=49808 |archive-date=26 September 2013 }}
</ref>
A 125.18±0.16 {{val|ul=GeV/c2}}&nbsp;<ref>{{cite journal |author=Tanabashi |first=M. |display-authors=et al. |year=2018 |title=Review of Particle Physics |url=http://pdglive.lbl.gov/Particle.action?node=S126&init=0 |journal=Physical Review D |volume=98 |issue=3 |pages=1–708 |article-number=030001 |bibcode=2018PhRvD..98c0001T |doi=10.1103/PhysRevD.98.030001 |pmid=10020536 |doi-access=free |hdl-access=free |hdl=10044/1/68623}}</ref> Higgs boson mass is likely to be on the metastable side of stable-metastable boundary (estimated in 2012 as {{nowrap|123.8–135.0 GeV}}.<ref name="Alekhin 2012">{{cite journal |title=The top quark and Higgs boson masses and the stability of the electroweak vacuum |journal=Physics Letters B |date=2012-08-13 |doi=10.1016/j.physletb.2012.08.024|arxiv = 1207.0980 |bibcode = 2012PhLB..716..214A |volume=716 |issue=1 |pages=214–219|last1=Alekhin |first1=S. |last2=Djouadi |first2=A. |last3=Moch |first3=S. |last4=Hoecker |first4=A. |last5=Riotto |first5=A. |s2cid=28216028 }}</ref>) A definitive answer requires much more precise measurements of the top quark's [[pole mass]],<ref name="Alekhin 2012" /> however, 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 of 2018.<ref name=Markkanen2018/> Nonetheless, new physics [[Physics beyond the Standard Model|beyond the Standard Model of Particle Physics]] could drastically change the stability landscape division lines, rendering previous stability and metastability criteria incorrect.<ref name="Salvio 2015">{{cite journal|last=Salvio|first=Alberto|s2cid=119279576|title=A Simple Motivated Completion of the Standard Model below the Planck Scale: Axions and Right-Handed Neutrinos |journal=Physics Letters B|date=2015-04-09| volume=743|pages=428–434|doi=10.1016/j.physletb.2015.03.015|arxiv = 1501.03781 |bibcode = 2015PhLB..743..428S }}</ref><ref>{{cite journal|arxiv=1407.4112|doi=10.1007/JHEP09(2014)182|bibcode=2014JHEP...09..182B|title=Top mass determination, Higgs inflation, and vacuum stability|year=2014|last1=Branchina|first1=Vincenzo|last2=Messina|first2=Emanuele|last3=Platania|first3=Alessia|s2cid=102338312|journal=Journal of High Energy Physics|volume=2014|issue=9|page=182}}</ref> Reanalysis of 2016 LHC run data in 2022 has yielded a slightly lower top quark mass of 171.77{{±|0.38}} GeV, close to vacuum stability line but still in the metastable zone.<ref>{{citation|arxiv=2211.11398|year=2022|title=Direct top quark mass measurements with the ATLAS and CMS detectors |last1=Vanadia |first1=Marco }}</ref><ref>{{cite journal |last1=CMS Collaboration |year=2023 |title=Measurement of the top quark mass using a profile likelihood approach with the lepton + jets final states in proton–proton collisions at <math>\sqrt{s}=13~\text{TeV}</math> |journal=The European Physical Journal C |volume=83 |issue=10 |page=963 |arxiv=2302.01967 |doi=10.1140/epjc/s10052-023-12050-4 |pmc=10600315 |pmid=37906635 |s2cid=264442852}}</ref>

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.<ref name="Boyle">{{cite news |last=Boyle |first=Alan |date=19 February 2013 |title=Will our universe end in a 'big slurp'? Higgs-like particle suggests it might |url=https://www.nbcnews.com/sciencemain/will-our-universe-end-big-slurp-higgs-particle-suggests-it-1c8415998 |url-status=live |archive-url=https://web.archive.org/web/20250208175221/https://www.nbcnews.com/sciencemain/will-our-universe-end-big-slurp-higgs-particle-suggests-it-1c8415998 |archive-date=8 February 2025 |access-date=8 February 2025 |website=NBC News' Cosmic blog}}</ref> A direct calculation within the [[Standard Model]] of the lifetime of our vacuum state finds that it is greater than <math>10^{65}</math>years with 95% confidence.<ref name="Andreassen">{{cite journal |last1=Andreassen |first1=Anders |last2=Frost |first2=William |last3=Schwartz |first3=Matthew D. |title=Scale Invariant Instantons and the Complete Lifetime of the Standard Model |journal=Physical Review D  |date=2018 |volume=97 |issue=5 |article-number=056006 |doi=10.1103/PhysRevD.97.056006|arxiv=1707.08124|bibcode=2018PhRvD..97e6006A |s2cid=118843387 }}</ref>

===Other decay modes===
* Decay to smaller [[vacuum expectation value]], resulting in decrease of [[Casimir effect]] and destabilization of [[proton|protons]].<ref name="turnerwilczek">{{cite journal |author=Turner |first1=M. S. |last2=Wilczek |first2=F. |date=1982-08-12 |title=Is our vacuum metastable? |url=http://ctp.lns.mit.edu/Wilczek_Nature/%2872%29vacuum_metastable.pdf |url-status=live |journal=[[Nature (journal)|Nature]] |volume=298 |issue=5875 |pages=633–634 |bibcode=1982Natur.298..633T |doi=10.1038/298633a0 |s2cid=4274444 |archive-url=https://web.archive.org/web/20191213005331/http://ctp.lns.mit.edu/Wilczek_Nature/(72)vacuum_metastable.pdf |archive-date=13 December 2019 |access-date=31 October 2015}}</ref>
* Decay to vacuum with larger neutrino mass (may have happened as late as few billion years ago).<ref name=Lorenz2018>{{cite journal|arxiv=1811.01991|doi=10.1103/PhysRevD.99.023501|title=Time-varying neutrino mass from a supercooled phase transition: Current cosmological constraints and impact on the Ω<sub>m</sub>−σ<sub>8</sub> plane|year=2019|last1=Lorenz|first1=Christiane S.|last2=Funcke|first2=Lena|last3=Calabrese|first3=Erminia|last4=Hannestad|first4=Steen|s2cid=119344201|journal=Physical Review D|volume=99|issue=2|article-number=023501}}</ref>
* Decay to vacuum with no [[dark energy]].<ref name=Landim2016>{{cite journal|arxiv=1611.00428|doi=10.1016/j.physletb.2016.11.044|bibcode=2017PhLB..764..271L|title=Metastable dark energy|year=2017|last1=Landim|first1=Ricardo G.|last2=Abdalla|first2=Elcio|s2cid=119279028|journal=Physics Letters B|volume=764|pages=271–276}}</ref>
* Decay of the false vacuum at finite temperature<ref name="Linde83">{{cite journal |last1=Linde |first1=Andrei D. |year=1983 |title=Decay of the false vacuum at finite temperature |journal=Nucl. Phys. B |volume=216 |issue=2 |pages=421–445 |bibcode=1983NuPhB.216..421L |doi=10.1016/0550-3213(83)90293-6}}</ref> was first observed in ferromagnetic superfluids of ultracold atoms.<ref name=Zenesini24>{{cite journal|doi=10.1038/s41567-023-02345-4|title=False vacuum decay via bubble formation in ferromagnetic superfluids|year=2024|last1=Zenesini|first1=Alessandro|last2=Berti|first2=Anna|last3=Cominotti|first3=Riccardo|last4=Rogora|first4=Chiara|last5=Moss|first5=Ian G.|last6=Billam|first6=Tom P.|last7=Carusotto|first7=Iacopo|last8=Lamporesi|first8=Giacomo|last9=Recati|first9=Alessio|last10=Ferrari|first10=Gabriele|journal= Nat. Phys.|volume=10|issue=4 |pages=558–563 |arxiv=2305.05225|bibcode=2024NatPh..20..558Z }}</ref>

==Bubble nucleation==
<!-- [[Bubble nucleation]] redirects here -->
When the false vacuum decays, the lower-energy true vacuum forms through a process known as '''bubble [[nucleation]]'''<!--boldface per WP:R#PLA-->.<ref name="M. Stone 1976 3568–3573">{{cite journal |author=Stone |first=M. |date=1976 |title=Lifetime and decay of excited vacuum states |journal=Physical Review D |volume=14 |issue=12 |pages=3568–3573 |bibcode=1976PhRvD..14.3568S |doi=10.1103/PhysRevD.14.3568}}</ref><ref name="P.H. Frampton 1976 1378–1380">{{cite journal |author=Frampton |first=P. H. |date=1976 |title=Vacuum Instability and Higgs Scalar Mass |journal=Physical Review Letters |volume=37 |issue=21 |pages=1378–1380 |bibcode=1976PhRvL..37.1378F |doi=10.1103/PhysRevLett.37.1378}}</ref><ref>{{cite journal |author=Stone |first=M. |date=1977 |title=Semiclassical methods for unstable states |journal=Phys. Lett. B |volume=67 |issue=2 |pages=186–188 |bibcode=1977PhLB...67..186S |doi=10.1016/0370-2693(77)90099-5}}</ref><ref>{{cite journal |author=Frampton |first=P. H. |date=1977 |title=Consequences of Vacuum Instability in Quantum Field Theory |journal=Physical Review D |volume=15 |issue=10 |pages=2922–28 |bibcode=1977PhRvD..15.2922F |doi=10.1103/PhysRevD.15.2922}}</ref><ref>{{cite journal |author=Coleman |first=S. |date=1977 |title=Fate of the false vacuum: Semiclassical theory |journal=Physical Review D |volume=15 |issue=10 |pages=2929–36 |bibcode=1977PhRvD..15.2929C |doi=10.1103/physrevd.15.2929}}</ref><ref name="fate">{{cite journal |last1=Callan |first1=C. |last2=Coleman |first2=S. |date=1977 |title=Fate of the false vacuum. II. First quantum corrections |journal=Physical Review D |volume=D16 |issue=6 |pages=1762–1768 |bibcode=1977PhRvD..16.1762C |doi=10.1103/physrevd.16.1762}}</ref> In this process, [[instanton]] effects cause a bubble containing the true vacuum to appear. The walls of the bubble (or [[Domain wall (string theory)|domain walls]]) have a positive [[surface tension]], as energy is expended as the fields roll over the potential barrier to the true vacuum. The former tends as the cube of the bubble's radius while the latter is proportional to the square of its radius, so there is a critical size <math>R_c</math> at which the total energy of the bubble is zero; smaller bubbles tend to shrink, while larger bubbles tend to grow. To be able to nucleate, the bubble must overcome an energy barrier of height<ref name="fate"/>
{{NumBlk|:|<math>\Phi_c = \frac{3\gamma}{4R^2} - \Delta\Phi,</math>|{{EquationRef|Eq. 1}}}}
where <math>\Delta\Phi</math> is the difference in energy between the true and false vacuums, <math>\gamma</math> is the unknown (possibly extremely large) [[surface tension]] of the domain wall, and <math>R</math> is the radius of the bubble. Rewriting {{EquationNote|Eq. 1}} gives the critical radius as
{{NumBlk|:|<math>R_c = \sqrt{\frac{3\gamma}{4\Delta\Phi}}.</math>|{{EquationRef|Eq. 2}}}}

A bubble smaller than the critical size can overcome the potential barrier via [[quantum tunnelling]] of [[instanton]]s to lower energy states. For a large potential barrier, the tunneling rate per unit volume of space is given by<ref>{{Cite web |author=Ai |first=Wenyuan |year=2019 |title=Aspects of False Vacuum Decay |url=http://mediatum.ub.tum.de/doc/1480995/1480995.pdf}}</ref>
{{NumBlk|:|<math>\omega \approx \frac{1}{\gamma}\sqrt{\frac{2\Phi_c}{\hbar}} e^{-\Phi_c/\hbar},</math>|{{EquationRef|Eq. 3}}}}
where <math>\hbar</math> is the [[Planck constant#Reduced Planck constant|reduced Planck constant]]. As soon as a bubble of lower-energy vacuum grows beyond the critical radius defined by {{EquationNote|Eq. 2}}, the bubble's wall will begin to accelerate outward. Due to the typically large difference in energy between the false and true vacuums, the speed of the wall approaches the speed of light extremely quickly. The bubble does not produce any gravitational effects because the negative energy density of the bubble interior is cancelled out by the positive kinetic energy of the wall.<ref name="colemandeluccia" />

Small bubbles of true vacuum can be inflated to critical size by providing energy,<ref>{{cite arXiv|eprint=hep-ph/9212303|last1=Arnold|first1=Peter|title=A Review of the Instability of Hot Electroweak Theory and its Bounds on ''m''<sub>h</sub> and ''m''<sub>t</sub>|year=1992}}</ref> although required energy densities are several orders of magnitude larger than what is attained in any natural or artificial process.<ref name="turnerwilczek" /> It is also thought that certain environments can catalyze bubble formation by lowering the potential barrier.<ref name="BurdaGregory2015">{{cite journal|last1=Burda|first1=Philipp|last2=Gregory|first2=Ruth|last3=Moss|first3=Ian G.|s2cid=53978709|title=Vacuum metastability with black holes|journal=Journal of High Energy Physics|volume=2015|issue=8|page=114|year=2015|issn=1029-8479|doi=10.1007/JHEP08(2015)114|arxiv=1503.07331|bibcode=2015JHEP...08..114B}}</ref>

Bubble wall has a finite thickness, depending on ratio between energy barrier and energy gain obtained by creating true vacuum. In the case when potential barrier height between true and false vacua is much smaller than energy difference between vacua, shell thickness become comparable with critical radius.<ref name="vfmukhanov">{{citation|arxiv=2206.13994|year=2022|title=Instantons: Thick-wall approximation|doi=10.1007/JHEP07(2022)147 |last1=Mukhanov |first1=V. F. |last2=Sorin |first2=A. S. |journal=Journal of High Energy Physics |volume=2022 |issue=7 |page=147 |bibcode=2022JHEP...07..147M |s2cid=250088782 }}</ref>

===Nucleation seeds===
{{Further|Relativistic Heavy Ion Collider#Critics of high-energy experiments|Safety of high-energy particle collision experiments#Large Hadron Collider}}
In general, gravity is believed to stabilize a false vacuum state,<ref>{{citation|arxiv=2205.03140|year=2022|page=83|title=False vacuum decay: An introductory review|doi=10.1088/1361-6471/ac7f24 |last1=Devoto |first1=Federica |last2=Devoto |first2=Simone |last3=Di Luzio |first3=Luca |last4=Ridolfi |first4=Giovanni |journal=Journal of Physics G: Nuclear and Particle Physics |volume=49 |issue=10 |bibcode=2022JPhG...49j3001D |s2cid=248563024 }}</ref> at least for transition from <math>dS</math> (de Sitter space) to <math>AdS</math> (Anti-de Sitter space),<ref>{{citation|arxiv=2106.15505|year=2021|title=Exactly solvable vacuum decays with gravity|page=20|doi=10.1103/PhysRevD.104.065007 |last1=Espinosa |first1=J. R. |last2=Fortin |first2=J.-F. |last3=Huertas |first3=J. |journal=Physical Review D |volume=104 |issue=6 |bibcode=2021PhRvD.104f5007E |s2cid=235669653 }}</ref> while topological defects including [[cosmic string]]s<ref>{{cite journal|arxiv=2002.04856|last1=Firouzjahi|first1=Hassan|last2=Karami|first2=Asieh|last3=Rostami|first3=Tahereh|s2cid=211082988|title=Vacuum decay in the presence of a cosmic string|journal=Physical Review D|year=2020|volume=101|issue=10|article-number=104036|doi=10.1103/PhysRevD.101.104036|bibcode=2020PhRvD.101j4036F}}</ref> and [[magnetic monopole]]s may enhance decay probability.<ref name="turnerwilczek" />

====Black holes as nucleation seeds====
In a study in 2015,<ref name="BurdaGregory2015"/> it was pointed out that the vacuum decay rate could be vastly increased in the vicinity of black holes, which would serve as a '''nucleation seed'''.<ref>{{Cite web | url=https://medium.com/starts-with-a-bang/could-black-holes-destroy-the-universe-de8a3135856f | title=Could Black Holes Destroy the Universe?| date=2015-04-02}}</ref> According to this study, a potentially catastrophic vacuum decay could be triggered at any time by [[primordial black hole]]s, should they exist. 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. A subsequent study in 2017 indicated that the bubble would collapse into a primordial black hole rather than originate from it, either by ordinary collapse or by bending space in such a way that it breaks off into a new universe.<ref>{{cite journal|arxiv=1710.02865|doi=10.1088/1475-7516/2017/12/044|bibcode=2017JCAP...12..044D|title=Primordial black hole formation by vacuum bubbles|year=2017|last1=Deng|first1=Heling|last2=Vilenkin|first2=Alexander|s2cid=119442566|journal=Journal of Cosmology and Astroparticle Physics|volume=2017|issue=12|page=044}}</ref> 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.<ref>{{cite journal|arxiv=1909.01378|doi=10.1007/JHEP01(2020)015|bibcode=2020JHEP...01..015O|title=Vacuum decays around spinning black holes|year=2020|last1=Oshita|first1=Naritaka|last2=Ueda|first2=Kazushige|last3=Yamaguchi|first3=Masahide|s2cid=202541418|journal=Journal of High Energy Physics|volume=2020|issue=1|page=015}}</ref><ref>{{citation|arxiv=2208.07504|year=2023|title=Stationary vacuum bubble in a Kerr–de Sitter spacetime|last1=Saito |first1=Daiki |last2=Yoo |first2=Chul-Moon |journal=Physical Review D |volume=107 |issue=6 |article-number=064043 |doi=10.1103/PhysRevD.107.064043 |bibcode=2023PhRvD.107f4043S |s2cid=251589418 }}</ref>

If particle collisions produce mini black holes, then energetic collisions such as the ones produced in the [[Large Hadron Collider]] (LHC) could trigger such a vacuum decay event, a scenario that has attracted the attention of the news media. It is likely to be unrealistic, because if such mini black holes can be created in collisions, they would also be created in the much more energetic collisions of cosmic radiation particles with planetary surfaces or during the early life of the universe as tentative [[primordial black hole]]s.<ref>{{cite web|last1=Cho|first1=Adrian|title=Tiny black holes could trigger collapse of universe—except that they don't|url=https://www.science.org/content/article/tiny-black-holes-could-trigger-collapse-universe-except-they-dont|website=Sciencemag.org|date=2015-08-03}}</ref> Hut and Rees<ref name="hutrees">{{cite journal |last1=Hut |first1=P. |last2=Rees |first2=M. J. |date=1983 |title=How stable is our vacuum? |journal=Nature |volume=302 |issue=5908 |pages=508–509 |bibcode=1983Natur.302..508H |doi=10.1038/302508a0 |s2cid=4347886}}</ref> note that, because [[cosmic ray]] collisions have been observed at much higher energies than those produced in terrestrial particle accelerators, these experiments should not, at least for the foreseeable future, pose a threat to our current vacuum. Particle accelerators have reached energies of only approximately eight [[Tera-|tera]] [[Electronvolt|electron volts]] (8×10<sup>12</sup> eV). Cosmic ray collisions have been observed at and beyond energies of 5×10<sup>19</sup> [[Electronvolt|eV]], six million times more powerful&nbsp;– the so-called [[Greisen–Zatsepin–Kuzmin limit]] – and cosmic rays in vicinity of origin may be more powerful yet. John Leslie has argued<ref name="leslie">{{cite book |author=Leslie |first=John |title=The End of the World:The Science and Ethics of Human Extinction |date=1998 |publisher=Routledge |isbn=978-0-415-14043-0}}</ref> that if present trends continue, particle accelerators will exceed the energy given off in naturally occurring cosmic ray collisions by the year 2150. Fears of this kind were raised by critics of both the [[Relativistic Heavy Ion Collider]] and the [[Large Hadron Collider]] at the time of their respective proposal, and determined to be unfounded by scientific inquiry.

In a 2021 paper by Rostislav Konoplich and others, it was postulated that the area between a pair of large black holes on the verge of colliding could provide the conditions to create bubbles of "true vacuum". Intersecting surfaces between these bubbles could then become infinitely dense and form micro-black holes. These would in turn evaporate by emitting Hawking radiation in the 10 milliseconds or so before the larger black holes collided and devoured any bubbles or micro-black holes in their way. The theory could be tested by looking for the [[Hawking radiation]] emitted just before the black holes merge.<ref>{{Cite web|last=Crane|first=Leah|date=26 November 2021|title=Merging black holes may create bubbles that could swallow the universe|url=https://www.newscientist.com/article/2298989-merging-black-holes-may-create-bubbles-that-could-swallow-the-universe/|access-date=2021-11-27|website=New Scientist|language=en-US}}</ref><ref>{{cite journal|last1=Chitishvili|first1=Mariam|last2=Gogberashvili|first2=Merab|last3=Konoplich|first3=Rostislav|last4=Sakharov|first4=Alexander S.|title=Higgs Field-Induced Triboluminescence in Binary Black Hole Mergers|journal=Universe |year=2023 |volume=9 |issue=7 |page=301 |doi=10.3390/universe9070301 |arxiv=2111.07178 |bibcode=2023Univ....9..301C |doi-access=free }}</ref>

== Bubble propagation==
A bubble wall, propagating outward at nearly the speed of light, has a finite thickness, depending on the ratio between the energy barrier and the energy gain obtained by creating true vacuum. In the case when the potential barrier height between true and false vacua is much smaller than the energy difference between vacua, the bubble wall thickness becomes comparable to the critical radius.<ref name="vfmukhanov"/>

Elementary particles entering the wall will likely decay to other particles or black holes. 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. Multi-particle objects can be stabilized as [[Q-ball]]s, although these objects will eventually collide and decay either into black holes or true-vacuum particles.<ref>{{citation|arxiv=2206.09923|year=2022|title=First-order phase transition and fate of false vacuum remnants|last1=Kawana |first1=Kiyoharu |last2=Lu |first2=Philip |last3=Xie |first3=Ke-Pan |journal=Journal of Cosmology and Astroparticle Physics |volume=2022 |issue=10 |page=030 |doi=10.1088/1475-7516/2022/10/030 |bibcode=2022JCAP...10..030K |s2cid=249889432 }}</ref>

== False vacuum decay in fiction ==
False vacuum decay event is occasionally used as a [[plot device]] in works picturing a [[global catastrophic risk|doomsday event]].

*1980 by [[Jack L. Chalker]] in his science-fiction novel [[The Return of Nathan Brazil]], the fourth book in the [[Well of Souls series]] (although not named as such in the novel).
*1988 by [[Geoffrey A. Landis]] in his science-fiction short story ''Vacuum States''<ref name="landis">{{cite journal |author=Landis |first=Geoffrey A. |date=1988 |title=Vacuum States |journal=Isaac Asimov's Science Fiction |pages=July}}</ref>
*2000 by [[Stephen Baxter (author)|Stephen Baxter]] in his science fiction novel ''[[Time (Baxter novel)|Time]]''<ref name="Baxter">{{cite book |author=Baxter |first=Stephen |url=https://archive.org/details/agesinchaosjames0000unse |title=Time |date=2000 |publisher=Macmillan |isbn=978-0-7653-1238-9 |url-access=registration}}</ref>
*2002 by [[Greg Egan]] in his science fiction novel ''[[Schild's Ladder]]''
*2002 by [[Liu Cixin]] in his science fiction short story ''[[Heard It in the Morning]]''
*2008 by [[Koji Suzuki]] in his science fiction novel ''Edge''
*2015 by [[Alastair Reynolds]] in his science fiction novel ''[[Poseidon's Wake]]''
*2018 by System Erasure in their video game ''[[ZeroRanger]]''
*2020 by [[Phillip P. Peterson]] in his science fiction novel ''[[:de:Vakuum_(Roman)|Vakuum]]''

== See also ==
* {{annotated link|Eternal inflation}}
* {{annotated link|Supercooling}}
* {{annotated link|Superheating}}
* {{annotated link|Void (astronomy)|Void}}
* {{annotated link|Quantum cosmology}}
* {{annotated link|{{slink|Why is there anything at all?|Something may exist necessarily}}}}
* {{annotated link|Bubble of nothing}}

== References ==
{{Reflist}}

== Further reading ==
* {{Cite book |last1=Rafelski |first1=Johann |author-link1=Johann Rafelski |title=The Structured Vacuum: Thinking about Nothing |last2=Müller |first2=Berndt |author-link2=Berndt Müller |date=1985 |publisher=[[H. Deutsch]] |isbn=978-3-87144-889-8 |location=Thun}}
* {{Cite book |last=Coleman |first=Sidney |author-link=Sidney Coleman |url=https://books.google.com/books?id=PX2Al8LE9FkC |title=Aspects of Symmetry: Selected Erice Lectures |date=1988 |publisher=[[Cambridge University Press]] |isbn=978-0-521-31827-3 |location=Cambridge}}

== External links ==
* {{GitHub|rsato64/SimpleBounce}} calculates the Euclidean action for the bounce solution that contributes to the false vacuum decay.
* {{Cite book
| url=http://www.physics.arizona.edu/~rafelski/Books/StructVacuumE.pdf
| title=The Structured Vacuum – thinking about nothing
| first1=Johann
| last1=Rafelski
| author-link1=Johann Rafelski
| first2=Berndt
| last2=Müller
| date=1985
| publisher=H. Deutsch
| isbn=3-87144-889-3}}
* {{cite web
| url=http://www.pbs.org/wnet/hawking/mysteries/html/uns_guth_1.html
| title=An eternity of bubbles?
| first=Alan
| last=Guth
| website=[[PBS]]
| author-link=Alan Guth
| archive-url=https://web.archive.org/web/20120825013818/http://www.pbs.org/wnet/hawking/mysteries/html/uns_guth_1.html
| archive-date=2012-08-25
}}

* {{cite web
| url=https://sten.astronomycafe.net/falsevacuum/
| title=The Decay of the False Vacuum
| first=Sten
| last=Odenwald
| author-link=Sten Odenwald
| date=1983}}

* {{YouTube|HBUPknArdYE|Simulation of False Vacuum Decay by Bubble Nucleation}} – Joel Thorarinson.

{{Global catastrophic risks}}

[[Category:Physical cosmological concepts]]
[[Category:Quantum field theory]]
[[Category:Cosmic inflation]]
[[Category:Space hazards]]
[[Category:Ultimate fate of the universe]]
[[Category:Vacuum]]