Editing Gravity (section)

===Gravity and quantum mechanics===
{{Main|Graviton|Quantum gravity}}

Despite its success in predicting the effects of gravity at large scales, general relativity is ultimately incompatible with [[quantum mechanics]]. This is because general relativity describes gravity as a smooth, continuous distortion of spacetime, while quantum mechanics holds that all forces arise from the exchange of discrete particles known as [[quantum|quanta]]. This contradiction is especially vexing to physicists because the other three fundamental forces (strong force, weak force and electromagnetism) were reconciled with a quantum framework decades ago.<ref>{{Cite web |title=Gravity Probe B – Special & General Relativity Questions and Answers |url=https://einstein.stanford.edu/content/relativity/a11758.html#:~:text=Quantum%20mechanics%20is%20incompatible%20with,exchange%20of%20well-defined%20quanta. |access-date=1 August 2022 |website=einstein.stanford.edu |archive-date=6 June 2022 |archive-url=https://web.archive.org/web/20220606161408/https://einstein.stanford.edu/content/relativity/a11758.html#:~:text=Quantum%20mechanics%20is%20incompatible%20with,exchange%20of%20well-defined%20quanta. |url-status=live }}</ref> As a result, modern researchers have begun to search for a theory that could unite both gravity and quantum mechanics under a more general framework.<ref>{{Cite book |last1=Huggett |first1=Nick |title=Beyond Spacetime: The Foundations of Quantum Gravity |last2=Matsubara |first2=Keizo |last3=Wüthrich |first3=Christian |publisher=[[Cambridge University Press]] |year=2020 |isbn=9781108655705 |pages=6 |language=en}}</ref>

One path is to describe gravity in the framework of [[quantum field theory]], which has been successful to accurately describe the other [[fundamental interaction]]s. The electromagnetic force arises from an exchange of virtual [[photon]]s, where the QFT description of gravity is that there is an exchange of [[virtual particle|virtual]] [[graviton]]s.<ref>{{cite book |last= Feynman |first= R.P. |author2=Morinigo, F.B. |author3=Wagner, W.G. |author4=Hatfield, B.  |title= Feynman lectures on gravitation |url= https://archive.org/details/feynmanlectureso0000feyn_g4q1 |url-access= registration |publisher= Addison-Wesley |date= 1995 |isbn=978-0-201-62734-3 }}</ref><ref>{{cite book | author=Zee, A. |title=Quantum Field Theory in a Nutshell | publisher = Princeton University Press | date=2003 | isbn=978-0-691-01019-9}}</ref> This description reproduces general relativity in the [[classical limit]]. However, this approach fails at short distances of the order of the [[Planck length]],<ref name="Randall, Lisa 2005">{{cite book | author=Randall, Lisa | title=Warped Passages: Unraveling the Universe's Hidden Dimensions | publisher=Ecco | date=2005 | isbn=978-0-06-053108-9 | url=https://archive.org/details/warpedpassagesun00rand_1 }}</ref> where a more complete theory of [[quantum gravity]] (or a new approach to quantum mechanics) is required.