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((Short description|Adjustment of parameters to fit data in theoretical physics))
((other uses|Fine-tuning (disambiguation)|Tuning (disambiguation)|Adjustment (disambiguation)))

In [[theoretical physics]], '''fine-tuning''' is the process in which parameters of a model must be adjusted very precisely in order to fit with certain observations. This had led to the discovery that the fundamental constants and quantities fall into such an extraordinarily precise range that if it did not, the origin and evolution of conscious agents in the universe would not be permitted.<ref>((cite book |last= Leslie|first= John A.|author-link=John A. Leslie|date= 1998|title= Modern Cosmology & Philosophy|location= University of Michigan|publisher= Prometheus Books|isbn= 1573922501))</ref>

Theories requiring fine-tuning are regarded as problematic in the absence of a known mechanism to explain why the parameters happen to have precisely the observed values that they return. The heuristic rule that parameters in a fundamental physical theory should not be too fine-tuned is called [[Naturalness (physics)|naturalness]].<ref>((cite journal|last1=Grinbaum|first1=Alexei|title=Which Fine-Tuning Arguments Are Fine?|journal=Foundations of Physics|date=1 February 2012|volume=42|issue=5|pages=615–631|doi=10.1007/s10701-012-9629-9|bibcode = 2012FoPh...42..615G |arxiv=0903.4055|s2cid=15590514))</ref><ref>((cite book|last1=Giudice|first1=Gian|author-link=Gian Giudice|title=LHC Perspectives|chapter=Naturally Speaking: The Naturalness Criterion and Physics at the LHC|arxiv=0801.2562|doi=10.1142/9789812779762_0010|series=Perspectives on LHC Physics|pages=155–178|year=2008|bibcode=2008plnc.book..155G|isbn=978-981-277-975-5|s2cid=15078813))</ref>

== Background == 
((more citations needed section|date=June 2023))
The idea that naturalness will explain fine tuning was brought into question by [[Nima Arkani-Hamed]], a theoretical physicist, in his talk "Why is there a Macroscopic Universe?", a lecture from the mini-series "Multiverse & Fine Tuning" from the "Philosophy of Cosmology" project, a University of Oxford and Cambridge Collaboration 2013. In it he describes how naturalness has usually provided a solution to problems in physics; and that it had usually done so earlier than expected. However, in addressing the problem of the cosmological constant, naturalness has failed to provide an explanation though it would have been expected to have done so a long time ago.

The necessity of fine-tuning leads to various problems that do not show that the theories are incorrect, in the sense of falsifying observations, but nevertheless suggest that a piece of the story is missing. For example, the cosmological constant problem (why is the [[cosmological constant]] so small?); the [[hierarchy problem]]; and the [[strong CP problem]], among others.

Also, Dongshan He's team has suggested a possible solution for the fine tuned Cosmological constant by the universe creation from nothing model.<ref>((cite journal|last1=He|first1=Dongshan|last2=Gao|first2=Dongfeng|last3=Cai|first3=Qing-yu|title=Spontaneous creation of the universe from nothing|journal=Physical Review|date=April 2014|volume=89|issue=8|page=083510|doi=10.1103/PhysRevD.89.083510|arxiv=1404.1207|bibcode=2014PhRvD..89h3510H|s2cid=118371273))</ref>

== Example ==
An example of a fine-tuning problem considered by the scientific community to have a plausible "natural" solution is the cosmological [[flatness problem]], which is solved if [[inflationary theory]] is correct: inflation forces the universe to become very flat, answering the question of why the universe is today observed to be flat to such a high degree.((citation needed|date=September 2017))

== Measurement ==
Although fine-tuning was traditionally measured by ad hoc fine-tuning measures, such as the Barbieri-Giudice-Ellis measure, over the past decade many scientists recognized that fine-tuning arguments were a specific application of [[Bayesian statistics]].<ref>((cite journal|last1=Barbieri|first1=R.|last2=Giudice|first2=G.F.|title=Upper bounds on supersymmetric particle masses|journal=Nuclear Physics B|date=August 1988|volume=306|issue=1|pages=63–76|doi=10.1016/0550-3213(88)90171-X|bibcode=1988NuPhB.306...63B|url=https://cds.cern.ch/record/180560))</ref><ref>((cite journal|last1=Fowlie|first1=Andrew|last2=Balazs|first2=Csaba|last3=White|first3=Graham|last4=Marzola|first4=Luca|last5=Raidal|first5=Martti|title=Naturalness of the relaxion mechanism|journal=Journal of High Energy Physics|date=17 August 2016|volume=2016|issue=8|pages=100|doi=10.1007/JHEP08(2016)100|arxiv=1602.03889|bibcode=2016JHEP...08..100F|s2cid=119102534))</ref><ref>((cite journal|last1=Fowlie|first1=Andrew|title=CMSSM, naturalness and the ?fine-tuning price? of the Very Large Hadron Collider|journal=Physical Review D|date=10 July 2014|volume=90|issue=1|pages=015010|doi=10.1103/PhysRevD.90.015010|arxiv=1403.3407|bibcode=2014PhRvD..90a5010F|s2cid=118362634))</ref><ref>((cite journal|last1=Fowlie|first1=Andrew|title=Is the CNMSSM more credible than the CMSSM?|journal=The European Physical Journal C|date=15 October 2014|volume=74|issue=10|doi=10.1140/epjc/s10052-014-3105-y|arxiv=1407.7534|s2cid=119304794))</ref><ref>((cite journal|doi=10.1088/1126-6708/2009/03/075 | volume=2009 | issue=3 | title=Bayesian approach and naturalness in MSSM analyses for the LHC | journal=Journal of High Energy Physics | page=075| arxiv=0812.0536 | bibcode=2009JHEP...03..075C | year=2009 | last1=Cabrera | first1=Maria Eugenia | last2=Casas | first2=Alberto | last3=Austri | first3=Roberto Ruiz de | s2cid=18276270 ))</ref><ref>((cite journal|last1=Fichet|first1=S.|title=Quantified naturalness from Bayesian statistics|journal=Physical Review D|date=18 December 2012|volume=86|issue=12|pages=125029|doi=10.1103/PhysRevD.86.125029|arxiv=1204.4940|bibcode=2012PhRvD..86l5029F|s2cid=119282331))</ref>((excessive citations inline|date=June 2023))

==See also==
* [[Anthropic principle]]
* [[Fine-tuned universe]]
* [[Hierarchy problem]]
* [[Strong CP problem]]

== References ==
((Reflist))

==External links==
* ((wikiquote-inline))

[[Category:Chaos theory]]
[[Category:Theoretical physics]]

((DEFAULTSORT:Fine-Tuning))

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