Editing Theory of everything (section)

{{Short description|Hypothetical physical concept}}
{{About|the hypothetical physical concept}}
{{Beyond the Standard Model|expanded=Theories}}

A '''theory of everything''' ('''TOE'''), '''final theory''', '''ultimate theory''', '''unified field theory''', or '''master theory''' is a hypothetical singular, all-encompassing, coherent [[theoretical physics|theoretical framework of physics]] that fully explains and links together all aspects of the [[universe]].<ref name="Weinberg2011">{{cite book |author=Weinberg |first=Steven |title=Dreams of a Final Theory: The Scientist's Search for the Ultimate Laws of Nature |date=2011-04-20 |publisher=Knopf Doubleday Publishing Group |isbn=978-0-307-78786-6 |language=en-us}}</ref>{{rp|6}} Finding a theory of everything is one of the major [[unsolved problems in physics]].<ref name="NYT-20201123" /><ref name="NYT-20230911">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=11 September 2023 |title=Don't Expect a 'Theory of Everything' to Explain It All – Not even the most advanced physics can reveal everything we want to know about the history and future of the cosmos, or about ourselves. |work=[[The New York Times]] |url=https://www.nytimes.com/2023/09/11/science/space/astronomy-universe-simulations.html |url-status=live |access-date=11 September 2023 |archive-url=https://archive.today/20230911043212/https://www.nytimes.com/2023/09/11/science/space/astronomy-universe-simulations.html |archive-date=11 September 2023}}</ref>

Over the past few centuries, two theoretical frameworks have been developed that, together, most closely resemble a theory of everything. These two theories upon which all modern physics rests are [[general relativity]] and [[quantum mechanics]]. General relativity is a theoretical framework that only focuses on [[gravity]] for understanding the universe in regions of both large scale and high mass: [[planets]], [[stars]], [[galaxies]], [[Galaxy cluster|clusters of galaxies]], etc. On the other hand, quantum mechanics is a theoretical framework that focuses primarily on three non-gravitational forces for understanding the universe in regions of both very small scale and low mass: [[subatomic particles]], [[atoms]], and [[molecules]]. Quantum mechanics successfully implemented the [[Standard Model]] that describes the three non-gravitational forces: [[strong force|strong nuclear]], [[weak force|weak nuclear]], and [[electromagnetism|electromagnetic]] force – as well as all observed elementary particles.<ref name="Hawking2006">{{cite book |author=Hawking |first=Stephen W. |title=The Theory of Everything: The Origin and Fate of the Universe |date=28 February 2006 |publisher=Phoenix Books; Special Anniversary |isbn=978-1-59777-508-3}}</ref>{{rp|122}}

General relativity and quantum mechanics have been repeatedly validated in their separate fields of relevance. Since the usual domains of applicability of general relativity and quantum mechanics are so different, most situations require that only one of the two theories be used.<ref>{{cite journal |last1=SMOLIN |first1=L. |title=An Invitation to Loop Quantum Gravity |date=2004 |journal=Quantum Theory and Symmetries |volume=[] |pages=655–682 | doi=10.1142/9789812702340_0078|arxiv=hep-th/0408048 |bibcode=2004qts..conf..655S |isbn=978-981-256-068-1 |s2cid=16195175}}</ref><ref name="Carlip">{{cite journal |last=Carlip |first=Steven |title=Quantum Gravity: a Progress Report |journal=Reports on Progress in Physics |volume=64 |issue=8 |pages=885–942 |date=2001 |doi=10.1088/0034-4885/64/8/301 |arxiv=gr-qc/0108040 |bibcode=2001RPPh...64..885C |s2cid=118923209 }}</ref><ref name="Priest2010">{{cite book |author=Priest |first=Susanna Hornig |title=Encyclopedia of Science and Technology Communication |date=14 July 2010 |publisher=SAGE Publications |isbn=978-1-4522-6578-0}}</ref>{{rp|842–844}} The two theories are considered incompatible in regions of extremely small scale – the [[Planck scale]] – such as those that exist within a black hole or during the beginning stages of the universe (i.e., the moment immediately following the [[Big Bang]]). To resolve the incompatibility, a theoretical framework revealing a deeper underlying reality, unifying gravity with the other three interactions, must be discovered to harmoniously integrate the realms of general relativity and quantum mechanics into a seamless whole: a theory of everything may be defined as a comprehensive theory that, in principle, would be capable of describing all physical phenomena in the universe. 

In pursuit of this goal, [[quantum gravity]] has become one area of active research.<ref name="NYT-20221010">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=10 October 2022 |title=Black Holes May Hide a Mind-Bending Secret About Our Universe – Take gravity, add quantum mechanics, stir. What do you get? Just maybe, a holographic cosmos. |work=[[The New York Times]] |url=https://www.nytimes.com/2022/10/10/science/black-holes-cosmology-hologram.html |url-status=live |access-date=22 October 2022 |archive-url=https://web.archive.org/web/20221116151210/https://www.nytimes.com/2022/10/10/science/black-holes-cosmology-hologram.html |archive-date=16 November 2022}}</ref><ref name="SA-20221116">{{cite news |last=Starr |first=Michelle |title=Scientists Created a Black Hole in The Lab, And Then It Started to Glow |url=https://www.sciencealert.com/scientists-created-a-black-hole-in-the-lab-and-then-it-started-to-glow |date=16 November 2022 |work=[[ScienceAlert]] |access-date=16 November 2022 |archive-date=15 November 2022 |archive-url=https://web.archive.org/web/20221115234327/https://www.sciencealert.com/scientists-created-a-black-hole-in-the-lab-and-then-it-started-to-glow |url-status=live }}</ref> One example is [[string theory]], which evolved into a candidate for the theory of everything, but not without drawbacks (most notably, its apparent lack of currently [[testable]] [[prediction]]s) and controversy. String theory posits that at the [[Planck epoch|beginning of the universe]] (up to 10<sup>−43</sup> seconds after the Big Bang), the [[four fundamental forces]] were once a single fundamental force. According to string theory, every particle in the universe, at its most ultramicroscopic level ([[Planck length]]), consists of varying combinations of vibrating strings (or strands) with preferred patterns of vibration. String theory further claims that it is through these specific oscillatory patterns of strings that a particle of unique mass and force charge is created (that is to say, the [[electron]] is a type of string that vibrates one way, while the [[up quark]] is a type of string vibrating another way, and so forth). String theory/[[M-theory]] proposes six or seven [[dimensions]] of [[spacetime]] in addition to the four common dimensions for a ten- or eleven-dimensional spacetime.