132.170.15.255 (talk) |
OpenScience709 (talk | contribs) |
||
(601 intermediate revisions by more than 100 users not shown) | |||
Line 1: | Line 1: | ||
{{ |
{{Short description|Hypothetical physical concept}} |
||
{{About|the hypothetical physical concept}} |
|||
{{Beyond the Standard Model|expanded=Theories}} |
{{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 only focuses on the three non-gravitational forces for understanding the universe in regions of both very small scale and low mass: [[subatomic particles]], [[atoms]], [[molecules]], etc. 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. |
|||
==Name== |
|||
Initially, the term ''theory of everything'' was used with an ironic reference to various overgeneralized theories. For example, a grandfather of [[Ijon Tichy]] – a character from a cycle of [[Stanisław Lem]]'s [[science fiction]] stories of the 1960s – was known to work on the "[[General Theory of Everything]]". Physicist [[Harald Fritzsch]] used the term in his 1977 lectures in [[Varenna]].<ref>{{Cite journal |
|||
|first=Harald |last=Fritzsch |
|||
|date=1977 |
|||
|journal=CERN Report |
|||
|title=THE WORLD OF FLAVOUR AND COLOUR |
|||
|volume=Ref.TH.2359-CERN}} (download at https://cds.cern.ch/record/875256/files/CM-P00061728.pdf {{Webarchive|url=https://web.archive.org/web/20200212051758/https://cds.cern.ch/record/875256/files/CM-P00061728.pdf |date=2020-02-12 }} )</ref> Physicist [[John Ellis (physicist, born 1946)|John Ellis]] claims<ref> |
|||
{{cite journal |
|||
|first=John |last=Ellis |
|||
|date=2002 |
|||
|journal=[[Nature (journal)|Nature]] |
|||
|title=Physics gets physical (correspondence) |
|||
|volume=415 |page=957 |
|||
|doi=10.1038/415957b |
|||
|bibcode=2002Natur.415..957E |
|||
|issue=6875 |
|||
|pmid=11875539|doi-access=free |
|||
}}</ref> to have introduced the acronym "TOE" into the technical literature in an article in ''[[Nature (magazine)|Nature]]'' in 1986.<ref> |
|||
{{Cite journal |
|||
|first=John |last=Ellis |
|||
|date=1986 |
|||
|journal=Nature |
|||
|title=The Superstring: Theory of Everything, or of Nothing? |
|||
|volume=323 |pages=595–598 |
|||
|doi=10.1038/323595a0 |
|||
|bibcode=1986Natur.323..595E |
|||
|issue=6089|s2cid=4344940 |
|||
}}</ref> Over time, the term stuck in popularizations of [[theoretical physics]] research. |
|||
==Historical antecedents== |
|||
Over the past few decades, a single explanatory framework, called "[[string theory]]", has emerged that intends to be the ultimate theory of the universe. Some physicists{{who|date=August 2015}} believe 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 microscopic level ([[Planck length]]), consists of varying combinations of vibrating strings (or strands) with preferred patterns of vibration. String theory 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). |
|||
===Antiquity to 19th century=== |
|||
Initially, the term ''theory of everything'' was used with an ironic connotation to refer to various overgeneralized theories. For example, a grandfather of [[Ijon Tichy]] — a character from a cycle of [[Stanisław Lem]]'s [[science fiction]] stories of the 1960s — was known to work on the "[[General Theory of Everything]]". Physicist [[John Ellis (physicist)|John Ellis]]<ref>{{cite journal |
|||
Many ancient cultures such as [[Babylonian astronomers]] and [[Indian astronomy]] studied the pattern of the ''Seven Sacred Luminaires''/[[Classical Planets]] against the background of [[stars]], with their interest being to relate celestial movement to human events ([[astrology]]), and the goal being to predict events by recording events against a time measure and then look for recurrent patterns. The debate between the universe having either [[Temporal finitism|a beginning]] or [[Cyclic model|eternal cycles]] can be traced to ancient [[Babylonia]].<ref name="Hodge">{{cite book |last1=Hodge |first1=John C. |title=Theory of Everything: Scalar Potential Model of the Big and the Small |date=2012 |isbn=978-1-4699-8736-1 |pages=1–13, 99 |publisher=CreateSpace Independent Publishing Platform }}</ref> [[Hindu cosmology]] posits that time is infinite with a ''cyclic universe'', where the current universe was preceded and will be followed by an infinite number of universes.<ref>{{cite book |author=Sushil Mittal |author2=Gene Thursby |page=284 |title=Hindu World |publisher=Routledge |year=2012 |isbn=978-1-134-60875-1}}</ref><ref>{{cite book |author=Jones |first=Andrew Zimmerman |title=String Theory For Dummies |publisher=John Wiley & Sons |year=2009 |isbn=978-0-470-59584-8 |page=262}}</ref> Time scales mentioned in [[Hindu cosmology]] correspond to those of modern scientific cosmology. Its cycles run from our ordinary day and night to a day and night of Brahma, 8.64 billion years long.<ref>{{cite book |author=Sagan, Carl |title=Cosmos |year=2006 }}</ref> |
|||
| first = John | last = Ellis |
|||
| date = 2002 |
|||
| journal = [[Nature (journal)|Nature]] |
|||
| title = Physics gets physical (correspondence) |
|||
| volume = 415 | pages =957 |
|||
| doi =10.1038/415957b |
|||
|bibcode = 2002Natur.415..957E |
|||
| issue=6875}}</ref> claims to have introduced the term into the technical literature in an article in ''[[Nature (magazine)|Nature]]'' in 1986.<ref>{{Cite journal |
|||
| first = John | last = Ellis |
|||
| date = 1986 |
|||
| journal = Nature |
|||
| title = The Superstring: Theory of Everything, or of Nothing? |
|||
| volume = 323 | pages = 595–598 |
|||
| doi = 10.1038/323595a0 |
|||
|bibcode = 1986Natur.323..595E |
|||
| issue=6089}}</ref> Over time, the term stuck in popularizations of [[theoretical physics]] research. |
|||
The [[natural philosophy]] of [[atomism]] appeared in several ancient traditions. In ancient [[Greek philosophy]], the [[Pre-Socratic philosophy|pre-Socratic philosophers]] speculated that the apparent diversity of observed phenomena was due to a single type of interaction, namely the motions and collisions of atoms. The concept of 'atom' proposed by [[Democritus]] was an early philosophical attempt to unify phenomena observed in nature. The concept of 'atom' also appeared in the [[Nyaya]]-[[Vaisheshika]] school of ancient [[Indian philosophy]]. |
|||
== Historical antecedents == |
|||
[[Archimedes]] was possibly the first philosopher to have described nature with axioms (or principles) and then deduce new results from them. Any "theory of everything" is similarly expected to be based on axioms and to deduce all observable phenomena from them.<ref name="Impey2012" />{{rp|340}} |
|||
=== From ancient Greece to Einstein === |
|||
[[Archimedes]] was possibly the first scientist known to have described nature with axioms (or principles) and then deduce new results from them.<ref>{{cite web |
|||
|first=Chris |last=Rorres |
|||
|date=2009 |
|||
|title= ARCHIMEDES AND THE QUEST FOR THE THEORY OF EVERYTHING |
|||
|url=http://media.voicesatbeckman.org/dv/102109/index.html |
|||
}}</ref> He thus tried to describe "everything" starting from a few axioms. Any "theory of everything" is similarly expected to be based on axioms and to deduce all observable phenomena from them.<ref name="Impey2012">{{cite book|author=Chris Impey |title=How It Began: A Time-Traveler's Guide to the Universe |url=https://books.google.com/books?id=IjEz8Tq-EdIC |date=26 March 2012 |publisher=W. W. Norton |isbn=978-0-393-08002-5}}</ref>{{rp|340}} |
|||
Following earlier atomistic thought, the [[mechanical philosophy]] of the 17th century posited that all forces could be ultimately reduced to [[contact force]]s between the atoms, then imagined as tiny solid particles.<ref name="Burns2001">{{cite book |author=Burns |first=William E. |title=The Scientific Revolution: An Encyclopedia |date=1 January 2001 |publisher=ABC-CLIO |isbn=978-0-87436-875-8}}</ref>{{rp|184}}<ref> |
|||
{{cite book |
|||
|first=Steven |last=Shapin |
|first=Steven |last=Shapin |
||
|date=1996 |
|date=1996 |
||
|title=The Scientific Revolution |
|title=The Scientific Revolution |
||
|publisher=[[University of Chicago Press]] |
|url=https://archive.org/details/scientificrevolu00shap_0 |url-access=registration |publisher=[[University of Chicago Press]] |
||
|isbn=0-226-75021- |
|isbn=978-0-226-75021-7 |
||
}}</ref> |
}}</ref> |
||
In the late 17th century, [[Isaac Newton]]'s description of the long-distance force of gravity implied that not all forces in nature result from things coming into contact. Newton's work in his ''[[ |
In the late 17th century, [[Isaac Newton]]'s description of the long-distance force of gravity implied that not all forces in nature result from things coming into contact. Newton's work in his ''[[Philosophiæ Naturalis Principia Mathematica|Mathematical Principles of Natural Philosophy]]'' dealt with this in a further example of [[Unification (physics)|unification]], in this case unifying [[Galileo]]'s work on terrestrial gravity, [[Kepler]]'s laws of planetary motion and the phenomenon of [[tide]]s by explaining these apparent actions at a distance under one single law: the law of [[universal gravitation]].<ref>{{cite book |page=255 |url=https://books.google.com/books?id=6EqxPav3vIsC&pg=PA255 |title=The Mathematical Principles of Natural Philosophy |volume=II |last1=Newton |first1=Sir Isaac |date=1729}}</ref> |
||
In 1814, building on these results, [[Laplace]] famously suggested that a [[Laplace's demon|sufficiently powerful intellect]] could, if it knew the position and velocity of every particle at a given time, along with the laws of nature, calculate the position of any particle at any other time:<ref name="Carroll2010">{{cite book|author=Sean |
In 1814, building on these results, [[Laplace]] famously suggested that a [[Laplace's demon|sufficiently powerful intellect]] could, if it knew the position and velocity of every particle at a given time, along with the laws of nature, calculate the position of any particle at any other time:<ref name="Carroll2010">{{cite book <!-- Citation bot deny--> |author=Carroll |first=Sean |title=[[From Eternity to Here: The Quest for the Ultimate Theory of Time]] |publisher=Penguin Group US |year=2010 |isbn=978-1-101-15215-7 |language=en-us}}</ref>{{rp |ch 7}} |
||
{{quote|An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.| |
{{quote|An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.|''Essai philosophique sur les probabilités'', Introduction. 1814}} |
||
Laplace thus envisaged a combination of gravitation and mechanics as a theory of everything. Modern [[quantum mechanics]] implies that [[Heisenberg uncertainty|uncertainty is inescapable]], and thus that Laplace's vision has to be amended: a theory of everything must include gravitation and quantum mechanics. |
Laplace thus envisaged a combination of gravitation and mechanics as a theory of everything. Modern [[quantum mechanics]] implies that [[Heisenberg uncertainty|uncertainty is inescapable]], and thus that Laplace's vision has to be amended: a theory of everything must include gravitation and quantum mechanics. Even ignoring quantum mechanics, [[chaos theory]] is sufficient to guarantee that the future of any sufficiently complex mechanical or astronomical system is unpredictable. |
||
In 1820, [[Hans Christian Ørsted]] discovered a connection between electricity and magnetism, triggering decades of work that culminated in 1865, in [[James Clerk Maxwell]]'s theory of [[electromagnetism]]. During the 19th and early 20th centuries, it gradually became apparent that many common examples of forces – contact forces, [[elasticity (physics)|elasticity]], [[viscosity]], [[friction]], and [[pressure]] – result from electrical interactions between the smallest particles of matter. |
In 1820, [[Hans Christian Ørsted]] discovered a connection between electricity and magnetism, triggering decades of work that culminated in 1865, in [[James Clerk Maxwell]]'s theory of [[electromagnetism]]. During the 19th and early 20th centuries, it gradually became apparent that many common examples of forces – contact forces, [[elasticity (physics)|elasticity]], [[viscosity]], [[friction]], and [[pressure]] – result from electrical interactions between the smallest particles of matter. |
||
In his experiments of |
In his experiments of 1849–1850, [[Michael Faraday]] was the first to search for a unification of [[gravity]] with electricity and magnetism.<ref> |
||
{{Cite journal |
|||
| |
|first=M.|last=Faraday |
||
| |
|date=1850 |
||
| |
|title=Experimental Researches in Electricity. Twenty-Fourth Series. On the Possible Relation of Gravity to Electricity |
||
| |
|journal=Abstracts of the Papers Communicated to the Royal Society of London |
||
| |
|volume=5 |pages=994–995 |
||
| |
|doi=10.1098/rspl.1843.0267 |
||
|doi-access=free |
|||
}}</ref> However, he found no connection. |
|||
}}</ref> However, he found no connection. |
|||
In 1900, [[David Hilbert]] published a famous list of mathematical problems. In [[Hilbert's sixth problem]], he challenged researchers to find an axiomatic basis to all of physics. In this problem he thus asked for what today would be called a theory of everything.<ref>{{Cite journal|doi=10.1090/S0273-0979-2013-01439-3|title=Hilbert's 6th Problem: Exact and approximate hydrodynamic manifolds for kinetic equations|journal=Bulletin of the American Mathematical Society|volume=51|issue=2| |
In 1900, [[David Hilbert]] published a famous list of mathematical problems. In [[Hilbert's sixth problem]], he challenged researchers to find an axiomatic basis to all of physics. In this problem he thus asked for what today would be called a theory of everything.<ref>{{Cite journal |doi=10.1090/S0273-0979-2013-01439-3 |title=Hilbert's 6th Problem: Exact and approximate hydrodynamic manifolds for kinetic equations |journal=Bulletin of the American Mathematical Society |volume=51 |issue=2 |page=187 |year=2013 |last1=Gorban |first1=Alexander N. |last2=Karlin |first2=Ilya|arxiv=1310.0406 |bibcode=2013arXiv1310.0406G |s2cid=7228220 }}</ref> |
||
===Early 20th century=== |
|||
In the late 1920s, the new quantum mechanics showed that the [[chemical bond]]s between [[atom]]s were examples of (quantum) electrical forces, justifying [[Paul Dirac|Dirac]]'s boast that "the underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known".<ref>{{cite journal |
|||
In the late 1920s, the then new quantum mechanics showed that the [[chemical bond]]s between [[atom]]s were examples of (quantum) electrical forces, justifying [[Paul Dirac|Dirac]]'s boast that "the underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known".<ref> |
|||
| last=Dirac | first=P.A.M. |
|||
{{cite journal |
|||
| date=1929 |
|||
|last=Dirac |first=P.A.M. |
|||
| title=Quantum mechanics of many-electron systems |
|||
|date=1929 |
|||
| journal=[[Proceedings of the Royal Society of London A]] |
|||
|title=Quantum mechanics of many-electron systems |
|||
| volume=123 | pages=714 |
|||
|journal=[[Proceedings of the Royal Society of London A]] |
|||
| doi=10.1098/rspa.1929.0094 |
|||
|volume=123 |pages=714–733 |
|||
|bibcode = 1929RSPSA.123..714D |
|||
|doi=10.1098/rspa.1929.0094 |
|||
| issue=792 }}</ref> |
|||
|bibcode=1929RSPSA.123..714D |
|||
|issue=792|doi-access=free |
|||
}}</ref> |
|||
After 1915, when [[Albert Einstein]] published the theory of gravity ([[general relativity]]), the search for a [[unified field theory]] combining gravity with electromagnetism began with a renewed interest. In Einstein's day, the strong and the weak forces had not yet been discovered, yet |
After 1915, when [[Albert Einstein]] published the theory of gravity ([[general relativity]]), the search for a [[unified field theory]] combining gravity with electromagnetism began with a renewed interest. In Einstein's day, the strong and the weak forces had not yet been discovered, yet he found the potential existence of two other distinct forces, gravity and electromagnetism, far more alluring. This launched his 40-year voyage in search of the so-called ''"unified field theory"'' that he hoped would show that these two forces are really manifestations of one grand, underlying principle. During the last few decades of his life, this ambition alienated Einstein from the rest of mainstream of physics, as the mainstream was instead far more excited about the emerging framework of quantum mechanics. Einstein wrote to a friend in the early 1940s, "I have become a lonely old chap who is mainly known because he doesn't wear socks and who is exhibited as a curiosity on special occasions." Prominent contributors were [[Gunnar Nordström]], [[Hermann Weyl]], [[Arthur Eddington]], [[David Hilbert]],<ref>{{cite book |arxiv=physics/0405110 |doi=10.1007/0-8176-4454-7_14 |isbn=978-0-8176-4454-3 | title=Hilbert's "World Equations" and His Vision of a Unified Science |series=Einstein Studies |volume=11 |pages=259–276 |year=2005 |last1=Majer |first1=U. |last2=Sauer |first2=T. |bibcode=2005ugr..book..259M |journal=<!-- Citation bot--> |s2cid=985751 }}</ref> [[Theodor Kaluza]], [[Oskar Klein]] (see [[Kaluza–Klein theory]]), and most notably, Albert Einstein and his collaborators. Einstein searched in earnest for, but ultimately failed to find, a unifying theory<ref name="Pais1982">{{cite book |author=Abraham Pais |title=Subtle is the Lord: The Science and the Life of Albert Einstein: The Science and the Life of Albert Einstein |url=https://archive.org/details/subtleislordscie00pais |url-access=registration |date=23 September 1982 |publisher=Oxford University Press |isbn=978-0-19-152402-8|author-link=Abraham Pais }}</ref>{{rp|ch 17}} (see Einstein–Maxwell–Dirac equations). |
||
=== |
===Late 20th century and the nuclear interactions=== |
||
In the |
In the 20th century, the search for a unifying theory was interrupted by the discovery of the [[strong force|strong]] and [[weak force|weak]] nuclear forces, which differ both from gravity and from electromagnetism. A further hurdle was the acceptance that in a theory of everything, quantum mechanics had to be incorporated from the outset, rather than emerging as a consequence of a deterministic unified theory, as Einstein had hoped. |
||
Gravity and electromagnetism |
Gravity and electromagnetism are able to coexist as entries in a list of classical forces, but for many years it seemed that gravity could not be incorporated into the quantum framework, let alone unified with the other fundamental forces. For this reason, work on unification, for much of the 20th century, focused on understanding the three forces described by quantum mechanics: electromagnetism and the weak and strong forces. The first two were [[electroweak interaction|combined]] in 1967–1968 by [[Sheldon Glashow]], [[Steven Weinberg]], and [[Abdus Salam]] into the electroweak force.<ref>Weinberg (1993), Ch. 5</ref> |
||
Electroweak unification is a [[broken symmetry]]: the electromagnetic and weak forces appear distinct at low energies because the particles carrying the weak force, the [[W and Z bosons]], have non-zero masses |
Electroweak unification is a [[broken symmetry]]: the electromagnetic and weak forces appear distinct at low energies because the particles carrying the weak force, the [[W and Z bosons]], have non-zero masses ({{val|80.4|u=GeV/c2}} and {{val|91.2|u=GeV/c2}}, respectively), whereas the [[photon]], which carries the electromagnetic force, is massless. At higher energies W bosons and Z bosons can be [[matter creation|created]] easily and the unified nature of the force becomes apparent. |
||
While the strong and electroweak forces |
While the strong and electroweak forces coexist under the [[Standard Model]] of particle physics, they remain distinct. Thus, the pursuit of a theory of everything remained unsuccessful: neither a unification of the strong and electroweak forces – which Laplace would have called 'contact forces' – nor a unification of these forces with gravitation had been achieved. |
||
== |
==Modern physics== |
||
[[File:cube_of_theoretical_physics.svg|thumb|A depiction of the [[cGh physics|''cGh'' cube]] ]] |
|||
===Conventional sequence of theories=== |
|||
A theory of everything would unify all the [[fundamental interaction]]s of nature: [[gravitation]], the [[strong interaction]], the [[weak interaction]], and [[electromagnetism]]. Because the weak interaction can transform [[elementary particles]] from one kind into another, the theory of everything should also predict all the different kinds of particles possible. The usual assumed path of theories is given in the following graph, where each unification step leads one level up on the graph. |
|||
{{tree chart/start}} |
|||
=== Conventional sequence of theories === |
|||
{{tree chart| | | | |TOE| | TOE=Theory of everything }} |
|||
A Theory of Everything would unify all the [[fundamental interaction]]s of nature: [[gravitation]], [[strong interaction]], [[weak interaction]], and [[electromagnetism]]. Because the weak interaction can transform [[elementary particles]] from one kind into another, the ToE should also yield a deep understanding of the various different kinds of possible particles. The usual assumed path of theories is given in the following graph, where each unification step leads one level up: |
|||
{{tree chart| | | | | |!| | }} |
|||
{{tree chart| | | | |QG| | QG=[[Quantum gravity]] }} |
|||
{{familytree/start}} |
|||
{{ |
{{tree chart| | | | | |!| | }} |
||
{{tree chart| |REL|-|^|-|GUT| | REL=[[General Relativity|Space Curvature]] | GUT=Electronuclear force ([[Grand Unified Theory]]) }} |
|||
{{familytree| | | | | |!| | }} |
|||
{{ |
{{tree chart| | |!| | | | | |!| | }} |
||
{{tree chart| |SMC| | | |SMP| SMC=[[Lambda-CDM model|Standard model of cosmology]] | SMP=[[Standard model of particle physics]]}} |
|||
{{familytree| | | | | |!| | }} |
|||
{{tree chart| | | | | | | | |!| | }} |
|||
{{familytree| |REL|-|^|-|GUT| | REL=[[General Relativity|Space Curvature]] | GUT=Electronuclear force ([[Grand Unified Theory|GUT]]) }} |
|||
{{tree chart| | | | |QCD|-|^|-|-|EWT| | QCD=[[Strong interaction]]<br />[[Special unitary group|SU(3)]] | EWT=[[Electroweak interaction]]<br />[[Special unitary group|SU(2)]] x [[Unitary group|U(1)]]<sub>[[hypercharge|Y]]</sub> }} |
|||
{{familytree| | |!| | | | | |!| | }} |
|||
{{tree chart| | | | | | | | | | | | |!| | }} |
|||
{{familytree| |SMC| | | |SMP| SMC=[[Lambda-CDM model|Standard model of cosmology]] | SMP=[[Standard model of particle physics]]}} |
|||
{{tree chart| | | | | | | | |WNF|-|^|-|EMF||WNF=[[Weak interaction]]<br />[[Special unitary group|SU(2)]]|EMF=[[Electromagnetism]]<br />[[Unitary group|U(1)]]<sub>EM</sub>}} |
|||
{{familytree| | | | | | | | |!| | }} |
|||
{{tree chart| | | | | | | | | | | | | | | |!| | | | | | }} |
|||
{{familytree| | | | |QCD|-|^|-|-|EWT| | QCD=[[Strong interaction]]<br />[[Special unitary group|SU(3)]] | EWT=[[Electroweak interaction]]<br />[[Special unitary group|SU(2)]] x [[Unitary group|U(1)]]<sub>[[hypercharge|Y]]</sub> }} |
|||
{{ |
{{tree chart| | | | | | | | | | | |EF|-|^|-|MF| |EF=[[Electricity]]|MF=[[Magnetism]] }} |
||
{{tree chart/end}} |
|||
{{familytree| | | | | | | | |WNF|-|^|-|EMF||WNF=[[Weak interaction]]|EMF=[[Electromagnetism]]<br />[[Unitary group|U(1)]]<sub>EM</sub>}} |
|||
{{familytree| | | | | | | | | | | | | | | |!| | | | | | }} |
|||
{{familytree| | | | | | | | | | | |EF|-|^|-|MF| |EF=[[Electricity]]|MF=[[Magnetism]] }} |
|||
{{familytree/end}} |
|||
In this graph, electroweak unification occurs at around 100 GeV, grand unification is predicted to occur at 10<sup>16</sup> GeV, and unification of the GUT force with gravity is expected at the [[Planck energy]], roughly 10<sup>19</sup> GeV. |
In this graph, electroweak unification occurs at around 100 GeV, grand unification is predicted to occur at 10<sup>16</sup> GeV, and unification of the GUT force with gravity is expected at the [[Planck energy]], roughly 10<sup>19</sup> GeV. |
||
Several [[Grand Unified Theory|Grand Unified Theories]] (GUTs) have been proposed to unify electromagnetism and the weak and strong forces. Grand unification would imply the existence of an electronuclear force; it is expected to set in at energies of the order of 10<sup>16</sup> GeV, far greater than could be reached by any |
Several [[Grand Unified Theory|Grand Unified Theories]] (GUTs) have been proposed to unify electromagnetism and the weak and strong forces. Grand unification would imply the existence of an electronuclear force; it is expected to set in at energies of the order of 10<sup>16</sup> GeV, far greater than could be reached by any currently feasible [[particle accelerator]]. Although the simplest grand unified theories have been experimentally ruled out, the idea of a grand unified theory, especially when linked with [[supersymmetry]], remains a favorite candidate in the theoretical physics community. Supersymmetric grand unified theories seem plausible not only for their theoretical "beauty", but because they naturally produce large quantities of dark matter, and because the inflationary force may be related to grand unified theory physics (although it does not seem to form an inevitable part of the theory). Yet grand unified theories are clearly not the final answer; both the current standard model and all proposed GUTs are [[quantum field theory|quantum field theories]] which require the problematic technique of [[renormalization]] to yield sensible answers. This is usually regarded as a sign that these are only [[effective field theory|effective field theories]], omitting crucial phenomena relevant only at very high energies.<ref name="Carlip" /> |
||
The final step in the graph requires resolving the separation between quantum mechanics and gravitation, often equated with [[general relativity]]. Numerous researchers concentrate their efforts on this specific step; nevertheless, no accepted theory of [[quantum gravity]] – and thus no accepted theory of everything – has emerged yet. It is usually assumed that the ToE will also solve the remaining problems of GUTs. |
|||
The final step in the graph requires resolving the separation between quantum mechanics and gravitation, often equated with general relativity. Numerous researchers concentrate their efforts on this specific step; nevertheless, no accepted theory of [[quantum gravity]], and thus no accepted theory of everything, has emerged with observational evidence. It is usually assumed that the theory of everything will also solve the remaining problems of grand unified theories. |
|||
In addition to explaining the forces listed in the graph, a ToE may also explain the status of at least two candidate forces suggested by modern [[cosmology]]: an [[inflation (cosmology)|inflationary force]] and [[dark energy]]. Furthermore, cosmological experiments also suggest the existence of [[dark matter]], supposedly composed of fundamental particles outside the scheme of the standard model. However, the existence of these forces and particles has not been proven yet. |
|||
In addition to explaining the forces listed in the graph, a theory of everything may also explain the status of at least two candidate forces suggested by modern [[physical cosmology|cosmology]]: an [[inflation (cosmology)|inflationary force]] and [[dark energy]]. Furthermore, cosmological experiments also suggest the existence of [[dark matter]], supposedly composed of fundamental particles outside the scheme of the standard model. However, the existence of these forces and particles has not been proven. |
|||
=== String theory and M-theory === |
|||
===String theory and M-theory=== |
|||
{{unsolved|physics|Is [[string theory]], [[superstring theory]], or [[M-theory]], or some other variant on this theme, a step on the road to a "theory of everything", or just a blind alley?}} |
{{unsolved|physics|Is [[string theory]], [[superstring theory]], or [[M-theory]], or some other variant on this theme, a step on the road to a "theory of everything", or just a blind alley?}} |
||
Since the 1990s, some physicists |
Since the 1990s, some physicists such as [[Edward Witten]] believe that 11-dimensional [[M-theory]], which is described in some limits by one of the five [[perturbation theory|perturbative]] [[superstring theory|superstring theories]], and in another by the maximally-[[supersymmetry|supersymmetric]] [[eleven-dimensional supergravity]], is the theory of everything. There is no widespread consensus on this issue. |
||
One remarkable property of [[string theory|string]]/[[M-theory]] is that seven extra dimensions are required for the theory's consistency, on top of the four dimensions in our universe. In this regard, string theory can be seen as building on the insights of the [[Kaluza–Klein theory]], in which it was realized that applying general relativity to a 5-dimensional universe, with one space dimension small and curled up, looks from the 4-dimensional perspective like the usual general relativity together with [[Maxwell's equations|Maxwell's electrodynamics]]. This lent credence to the idea of unifying [[gauge theory|gauge]] and [[gravity]] interactions, and to extra dimensions, but did not address the detailed experimental requirements. Another important property of string theory is its [[supersymmetry]], which together with extra dimensions are the two main proposals for resolving the [[hierarchy problem]] of the [[standard model]], which is (roughly) the question of why gravity is so much weaker than any other force. The extra-dimensional solution involves allowing gravity to propagate into the other dimensions while keeping other forces confined to a 4-dimensional spacetime, an idea that has been realized with explicit stringy mechanisms.<ref>{{cite journal |pmid=16196251 |date=2005 |title=The Beauty of Branes |journal=Scientific American |pages=38–40 |doi=10.1038/scientificamerican1005-38 |url=http://randall.physics.harvard.edu/RandallCV/ScientificAm10-05.pdf |access-date=August 13, 2012 |last1=Holloway |first1=M |volume=293 |issue=4 |bibcode=2005SciAm.293d..38H |archive-date=November 22, 2014 |archive-url=https://web.archive.org/web/20141122023615/http://randall.physics.harvard.edu/RandallCV/ScientificAm10-05.pdf }}</ref> |
|||
Research into string theory has been encouraged by a variety of theoretical and experimental factors. On the experimental side, the particle content of the standard model supplemented with [[Seesaw mechanism|neutrino masses]] fits into a spinor representation of [[ |
Research into string theory has been encouraged by a variety of theoretical and experimental factors. On the experimental side, the particle content of the standard model supplemented with [[Seesaw mechanism|neutrino masses]] fits into a [[spinor]] representation of [[SO(10)]], a subgroup of [[E8 (mathematics)|E8]] that routinely emerges in string theory, such as in [[heterotic string theory]]<ref>{{cite journal |arxiv=0806.3905 |doi=10.1140/epjc/s10052-008-0740-1 |title=From strings to the MSSM |year=2009 |last1=Nilles |first1=Hans Peter |last2=Ramos-Sánchez |first2=Saúl |last3=Ratz |first3=Michael |last4=Vaudrevange |first4=Patrick K. S. |journal=The European Physical Journal C |volume=59 |issue=2 |pages=249–267 |bibcode=2009EPJC...59..249N |s2cid=17452924 }}</ref> or (sometimes equivalently) in [[F-theory]].<ref>{{cite journal |doi=10.1088/1126-6708/2009/01/058 |arxiv=0802.3391 |title=GUTs and exceptional branes in F-theory — I |date=2009 |last1=Beasley |first1=Chris |last2=Heckman |first2=Jonathan J |last3=Vafa |first3=Cumrun |journal=Journal of High Energy Physics |volume=2009 |issue=1 |page=058 |bibcode=2009JHEP...01..058B |s2cid=119309173 }}</ref><ref>{{cite arXiv |eprint=0802.2969v3 |last1=Donagi |first1=Ron |title=Model Building with F-Theory |last2=Wijnholt |first2=Martijn |class=hep-th |year=2008}}</ref> String theory has mechanisms that may explain why fermions come in three hierarchical generations, and explain the [[CKM matrix|mixing rates]] between quark generations.<ref>{{Cite journal |arxiv=0811.2417 |last1=Heckman |first1=Jonathan J. |title=Flavor Hierarchy from F-theory |journal=Nuclear Physics B |volume=837 |issue=1 |pages=137–151 |last2=Vafa |first2=Cumrun |year=2010 |doi=10.1016/j.nuclphysb.2010.05.009 |bibcode=2010NuPhB.837..137H |s2cid=119244083 }}</ref> On the theoretical side, it has begun to address some of the key questions in [[quantum gravity]], such as resolving the [[black hole information paradox]], counting the correct [[black hole thermodynamics|entropy of black holes]]<ref>{{cite journal |doi=10.1016/0370-2693(96)00345-0 |arxiv=hep-th/9601029 |title=Microscopic origin of the Bekenstein-Hawking entropy |date=1996 |last1=Strominger |first1=Andrew |last2=Vafa |first2=Cumrun |journal=Physics Letters B |volume=379 |issue=1–4 |pages=99–104 |bibcode=1996PhLB..379...99S |s2cid=1041890 }}</ref><ref>{{cite arXiv<!--Citation bot deny, the arxiv metadata is wrong-->|arxiv=gr-qc/9604051 |last1=Horowitz |first1=Gary |title=The Origin of Black Hole Entropy in String Theory}}</ref> and allowing for [[topology]]-changing processes.<ref>{{cite journal |doi=10.1016/0550-3213(95)00371-X |arxiv=hep-th/9504145 |title=Black hole condensation and the unification of string vacua |date=1995 |last1=Greene |first1=Brian R. |last2=Morrison |first2=David R. |last3=Strominger |first3=Andrew |journal=Nuclear Physics B |volume=451 |issue=1–2 |pages=109–120 |bibcode=1995NuPhB.451..109G |s2cid=11145691 }}</ref><ref>{{cite journal |doi=10.1016/0550-3213(94)90321-2 |arxiv=hep-th/9309097 |title=Calabi-Yau moduli space, mirror manifolds and spacetime topology change in string theory |date=1994 |last1=Aspinwall |first1=Paul S. |last2=Greene |first2=Brian R. |last3=Morrison |first3=David R. |journal=Nuclear Physics B |volume=416 |issue=2 |page=414 |bibcode=1994NuPhB.416..414A |s2cid=10927539 }}</ref><ref>{{cite journal |doi=10.1088/1126-6708/2005/10/033 |arxiv=hep-th/0502021 |title=Things fall apart: Topology change from winding tachyons |date=2005|author-link1=Allan Adams |last1=Adams |first1=Allan |last2=Liu |first2=Xiao |last3=McGreevy |first3=John |last4=Saltman |first4=Alex |last5=Silverstein |first5=Eva |journal=Journal of High Energy Physics |volume=2005 |issue=10 |page=033 |bibcode=2005JHEP...10..033A |s2cid=14320855 }}</ref> It has also led to many insights in [[pure mathematics]] and in ordinary, strongly-coupled [[gauge theory]] due to the [[AdS/CFT|Gauge/String duality]]. |
||
In the late 1990s, it was noted that one major hurdle in this endeavor is that the number of possible |
In the late 1990s, it was noted that one major hurdle in this endeavor is that the number of possible 4-dimensional universes is incredibly large. The small, "curled up" extra dimensions can be [[compact dimension|compactified]] in an enormous number of different ways (one estimate is 10<sup>500</sup> ) each of which leads to different properties for the low-energy particles and forces. This array of models is known as the [[string theory landscape]].<ref name="Impey2012" />{{rp|347}} |
||
One proposed solution is that many or all of these possibilities are |
One proposed solution is that many or all of these possibilities are realized in one or another of a huge number of universes, but that only a small number of them are habitable. Hence what we normally conceive as the [[fundamental constants]] of the universe are ultimately the result of the [[anthropic principle]] rather than dictated by theory. This has led to criticism of string theory,<ref>{{cite book |last=Smolin |first=Lee |title=The Trouble With Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next |date=2006 |publisher=Houghton Mifflin |isbn=978-0-618-55105-7|title-link=The Trouble With Physics }}</ref> arguing that it cannot make useful (i.e., original, [[falsifiable]], and verifiable) predictions and regarding it as a [[pseudoscience]]/[[philosophy]]. Others disagree,<ref>{{cite journal |author=Duff, M. J. |arxiv=1112.0788 |doi=10.1007/s10701-011-9618-4 |title=String and M-Theory: Answering the Critics |date=2011 |journal=Foundations of Physics |volume=43 |issue=1 |pages=182–200 |bibcode=2013FoPh...43..182D |s2cid=55066230 }}</ref> and string theory remains an active topic of investigation in [[theoretical physics]].<ref>{{Cite news|url=https://www.symmetrymagazine.org/article/may-2007/the-great-string-debate|title=The Great String Debate|last=Chui|first=Glennda|date=May 1, 2007|work=Symmetry Magazine|access-date=2018-10-17|language=en|archive-date=2018-10-17|archive-url=https://web.archive.org/web/20181017123651/https://www.symmetrymagazine.org/article/may-2007/the-great-string-debate|url-status=live}}</ref> |
||
=== |
===Loop quantum gravity=== |
||
Current research on [[loop quantum gravity]] may eventually play a fundamental role in a theory of everything, but that is not its primary aim.<ref>{{cite web |
|||
|last=Potter |
|||
Current research on [[loop quantum gravity]] may eventually play a fundamental role in a ToE, but that is not its primary aim.<ref>{{cite web |
|||
|first=Franklin |
|||
|date=15 February 2005 |
|date=15 February 2005 |
||
|url=http://www.sciencegems.com/discretespace.pdf |
|url=http://www.sciencegems.com/discretespace.pdf |
||
|title=Leptons And Quarks In A Discrete Spacetime |
|title=Leptons And Quarks In A Discrete Spacetime |
||
|work=Frank Potter's Science Gems |
|work=Frank Potter's Science Gems |
||
| |
|access-date=2009-12-01 |
||
|archive-date=2021-03-09 |
|||
}}</ref> Also loop quantum gravity introduces a lower bound on the possible length scales. |
|||
|archive-url=https://web.archive.org/web/20210309121814/http://www.sciencegems.com/discretespace.pdf |
|||
|url-status=live |
|||
}}</ref> Loop quantum gravity also introduces a lower bound on the possible length scales. |
|||
There have been recent claims that loop quantum gravity may be able to reproduce features resembling the [[Standard Model]]. So far only the first generation of [[fermion]]s ([[lepton]]s and [[quark]]s) with correct parity properties have been modelled by [[Sundance Bilson-Thompson]] using [[preon]]s constituted of braids of spacetime as the building blocks.<ref>{{cite journal | |
There have been recent claims that loop quantum gravity may be able to reproduce features resembling the [[Standard Model]]. So far only the first generation of [[fermion]]s ([[lepton]]s and [[quark]]s) with correct parity properties have been modelled by [[Sundance Bilson-Thompson]] using [[preon]]s constituted of braids of spacetime as the building blocks.<ref>{{cite journal |title=Quantum gravity and the standard model |last=Bilson-Thompson |first=Sundance O. |author2=Markopoulou, Fotini |author3=Smolin, Lee |doi=10.1088/0264-9381/24/16/002 |date=2007 |journal=Classical and Quantum Gravity |volume=24 |issue=16 |pages=3975–3994 |arxiv=hep-th/0603022 |bibcode=2007CQGra..24.3975B|s2cid=37406474 }}</ref> However, there is no derivation of the [[Lagrangian (field theory)|Lagrangian]] that would describe the interactions of such particles, nor is it possible to show that such particles are fermions, nor that the gauge groups or interactions of the Standard Model are realised. Use of [[quantum computing]] concepts made it possible to demonstrate that the particles are able to survive [[quantum fluctuation]]s.<ref>{{cite journal |url=https://www.newscientist.com/channel/fundamentals/mg19125645.800 |journal=New Scientist |title=You are made of space-time |first=Davide |last=Castelvecchi |author2=Valerie Jamieson |issue=2564 |date=August 12, 2006 |access-date=September 16, 2017 |archive-date=February 9, 2008 |archive-url=https://web.archive.org/web/20080209025208/http://www.newscientist.com/channel/fundamentals/mg19125645.800 |url-status=live }}</ref> |
||
This model leads to an interpretation of electric and |
This model leads to an interpretation of electric and color charge as topological quantities (electric as number and chirality of twists carried on the individual ribbons and colour as variants of such twisting for fixed electric charge). |
||
Bilson-Thompson's original paper suggested that the higher-generation fermions could be represented by more complicated braidings, although explicit constructions of these structures were not given. The electric charge, |
Bilson-Thompson's original paper suggested that the higher-generation fermions could be represented by more complicated braidings, although explicit constructions of these structures were not given. The electric charge, color, and parity properties of such fermions would arise in the same way as for the first generation. The model was expressly generalized for an infinite number of generations and for the weak force bosons (but not for photons or gluons) in a 2008 paper by Bilson-Thompson, Hackett, Kauffman and Smolin.<ref>{{cite arXiv |eprint=0804.0037 |class=hep-th |first1=Sundance |last1=Bilson-Thompson |first2=Jonathan |last2=Hackett |title=Particle Identifications from Symmetries of Braided Ribbon Network Invariants |date=2008 |author3=Kauffman, Lou |author4=Smolin, Lee}}</ref> |
||
=== |
===Other attempts=== |
||
Among other attempts to develop a theory of everything is the theory of [[causal fermion system]]s,<ref name="CFSIntro">{{Cite journal |author=Finster |first1=F. |last2=Kleiner |first2=J. |date=2015 |title=Causal fermion systems as a candidate for a unified physical theory |journal=Journal of Physics: Conference Series |volume=626 |issue=2015 |page=012020 |arxiv=1502.03587 |bibcode=2015JPhCS.626a2020F |doi=10.1088/1742-6596/626/1/012020 |s2cid=33471826}}</ref> giving the two current physical theories ([[general relativity]] and [[quantum field theory]]) as limiting cases. |
|||
Another theory is called [[Causal Sets]]. As some of the approaches mentioned above, its direct goal isn't necessarily to achieve a theory of everything but primarily a working theory of quantum gravity, which might eventually include the standard model and become a candidate for a theory of everything. Its founding principle is that spacetime is fundamentally discrete and that the spacetime events are related by a [[partial order]]. This partial order has the physical meaning of the [[causality relation]]s between relative [[past and future distinguishing]] spacetime events.<!--Please do _not_ insert "Time Cube" and "Heim Theory" here without first gaining a consensus on the talk page for including these theories. Changes without such a consensus will be promptly reverted. Thanks!--> |
|||
A recent development is the theory of [[causal fermion system]]s,<ref name="CFSIntro">{{Cite journal|author=F. Finster |author2=J. Kleiner |arxiv=1502.03587 |title=Causal fermion systems as a candidate for a unified physical theory |journal=Journal of Physics: Conference Series |volume=626 |issue=2015 |pages=012020 |date=2015 |doi=10.1088/1742-6596/626/1/012020 |bibcode = 2015JPhCS.626a2020F }}</ref> giving all two current physical theories ([[general relativity]] and [[quantum field theory]]) as limiting cases. |
|||
A recent attempt is called [[Causal Sets]]. As some of the approaches mentioned above, its direct goal isn't necessarily to achieve a ToE but primarily a working theory of quantum gravity, which might eventually include the standard model and become a candidate for a ToE. Its founding principle is that spacetime is fundamentally discrete and that the spacetime events are related by a [[partial order]]. This partial order has the physical meaning of the [[causality relation]]s between relative [[past and future distinguishing]] spacetime events.<!--Please do _not_ insert "Time Cube" and "Heim Theory" here without first gaining a consensus on the talk page for including these theories. Changes without such a consensus will be promptly reverted. Thanks!--> |
|||
Outside the previously mentioned attempts there is [[An Exceptionally Simple Theory of Everything|Garrett Lisi's E8 proposal]]. This theory provides an attempt of identifying general relativity and the standard model within the Lie group E8. The theory doesn't provide a novel quantization procedure and the author suggests its quantization might follow the Loop Quantum Gravity approach above mentioned.<ref name="Lisi-E8">{{cite arXiv |author=A. G. Lisi |eprint=0711.0770 |title=An Exceptionally Simple Theory of Everything |date=2007 |class=hep-th }}</ref> |
|||
[[Causal dynamical triangulation]] does not assume any pre-existing arena (dimensional space), but rather attempts to show how the spacetime fabric itself evolves. |
[[Causal dynamical triangulation]] does not assume any pre-existing arena (dimensional space), but rather attempts to show how the spacetime fabric itself evolves. |
||
Another attempt may be related to [[ER=EPR]], a conjecture in physics stating that [[Quantum entanglement|entangled]] particles are connected by a [[wormhole]] (or Einstein–Rosen bridge).<ref name=Cowen>{{cite journal|last1=Cowen|first1=Ron|title=The quantum source of space-time|journal=Nature|date=16 November 2015|volume=527|issue=7578|pages=290–293|bibcode=2015Natur.527..290C|doi=10.1038/527290a|pmid=26581274|s2cid=4447880}}</ref> |
|||
Christoph Schiller's Strand Model attempts to account for the [[Gauge theory|gauge symmetry]] of the [[Standard model#Construction of the Standard Model Lagrangian|Standard Model]] of particle physics, [[Unitary group|U(1)]]×[[Special unitary group|SU(2)]]×[[Special unitary group#n = 3|SU(3)]], with the three [[Reidemeister move]]s of knot theory by equating each [[elementary particle]] to a different tangle of one, two, or three strands (selectively a long prime knot or unknotted curve, a [[Tangle theory|rational tangle]], or a [[braid]]ed tangle respectively). |
|||
=== Present status === |
|||
At present, there is no candidate theory of everything that includes the standard model of particle physics and general relativity. For example, no candidate theory is able to calculate the fine structure constant or the mass of the electron. Most particle physicists expect that the outcome of the ongoing experiments – the search for new particles at the large [[particle accelerator]]s and for [[dark matter]] – are needed in order to provide further input for a ToE. |
|||
== Theory of everything and philosophy == |
|||
{{Main article|Theory of everything (philosophy)}} |
|||
The philosophical implications of a physical ToE are frequently debated. For example, if philosophical [[physicalism]] is true, a physical ToE will coincide with a philosophical theory of everything. |
|||
The [[Metaphysics#Styles and methods of metaphysics|"system building"]] style of [[metaphysics]] attempts to answer ''all'' the important questions in a coherent way, providing a complete picture of the world. [[Plato]] and [[Aristotle]] could be said to have created early examples of comprehensive systems. In the early modern period (17th and 18th centuries), the system-building ''scope'' of philosophy is often linked to the rationalist ''method'' of philosophy, which is the technique of deducing the nature of the world by pure ''[[a priori and a posteriori|a priori]]'' reason. Examples from the early modern period include the [[Gottfried Leibniz|Leibniz]]'s [[Monadology]], [[René Descartes|Descarte]]'s [[Dualism]], and [[Baruch Spinoza|Spinoza]]'s [[Monism]]. [[Georg Wilhelm Friedrich Hegel|Hegel]]'s [[Absolute idealism]] and [[Alfred North Whitehead|Whitehead]]'s [[Process philosophy]] were later systems. |
|||
===Present status=== |
|||
== Arguments against a theory of everything == |
|||
At present, there is no candidate theory of everything that includes the standard model of particle physics and general relativity and that, at the same time, is able to calculate the [[fine-structure constant]] or the [[mass of the electron]].<ref name="NYT-20201123" /> Most particle physicists expect that the outcome of ongoing experiments – the search for new particles at the large [[particle accelerator]]s and for [[dark matter]] – are needed in order to provide further input for a theory of everything. |
|||
==Arguments against== |
|||
In parallel to the intense search for a ToE, various scholars have seriously debated the possibility of its discovery. |
|||
In parallel to the intense search for a theory of everything, various scholars have debated the possibility of its discovery. |
|||
=== |
===Gödel's incompleteness theorem=== |
||
A number of scholars claim that [[Gödel's incompleteness theorem]] suggests that |
A number of scholars claim that [[Gödel's incompleteness theorem]] suggests that attempts to construct a theory of everything are bound to fail. Gödel's theorem, informally stated, asserts that any formal theory sufficient to express elementary arithmetical facts and strong enough for them to be proved is either inconsistent (both a statement and its denial can be derived from its axioms) or incomplete, in the sense that there is a true statement that can't be derived in the formal theory. |
||
[[Stanley Jaki]], in his 1966 book ''The Relevance of Physics'', pointed out that, because |
[[Stanley Jaki]], in his 1966 book ''The Relevance of Physics'', pointed out that, because a "theory of everything" will certainly be a consistent non-trivial mathematical theory, it must be incomplete. He claims that this dooms searches for a deterministic theory of everything.<ref> |
||
{{cite book |
|||
|last=Jaki |first=S.L. |
|last=Jaki |first=S.L. |
||
|date=1966 |
|date=1966 |
||
Line 182: | Line 190: | ||
|title=The Relevance of Physics |
|title=The Relevance of Physics |
||
|publisher=Chicago Press |
|publisher=Chicago Press |
||
}}</ref> |
|||
}}</ref> In a later reflection, Jaki states that it is wrong to say that a final theory is impossible, but rather that "when it is on hand one cannot know rigorously that it is a final theory."<ref>Stanley L. Jaki (2004) "[http://www.sljaki.com/JakiGodel.pdf A Late Awakening to Gödel in Physics]", pp. 8–9.</ref> |
|||
[[Freeman Dyson]] has stated that "Gödel's theorem implies that pure mathematics is inexhaustible. No matter how many problems we solve, there will always be other problems that cannot be solved within the existing rules. […] Because of Gödel's theorem, physics is inexhaustible too. The laws of physics are a finite set of rules, and include the rules for doing mathematics, so that Gödel's theorem applies to them."<ref>Freeman Dyson, NYRB, May 13, 2004</ref> |
[[Freeman Dyson]] has stated that "Gödel's theorem implies that pure mathematics is inexhaustible. No matter how many problems we solve, there will always be other problems that cannot be solved within the existing rules. […] Because of Gödel's theorem, physics is inexhaustible too. The laws of physics are a finite set of rules, and include the rules for doing mathematics, so that Gödel's theorem applies to them."<ref>Freeman Dyson, NYRB, May 13, 2004</ref> |
||
[[Stephen Hawking]] was originally a believer in the Theory of Everything but |
[[Stephen Hawking]] was originally a believer in the Theory of Everything, but after considering Gödel's Theorem, he concluded that one was not obtainable. "Some people will be very disappointed if there is not an ultimate theory that can be formulated as a finite number of principles. I used to belong to that camp, but I have changed my mind."<ref>Stephen Hawking, [http://www.hawking.org.uk/godel-and-the-end-of-physics.html Gödel and the end of physics] {{Webarchive|url=https://web.archive.org/web/20200529232552/http://www.hawking.org.uk/godel-and-the-end-of-physics.html |date=2020-05-29 }}, July 20, 2002</ref> |
||
[[Jürgen Schmidhuber]] (1997) has argued against this view; he |
[[Jürgen Schmidhuber]] (1997) has argued against this view; he asserts that Gödel's theorems are irrelevant for [[computable]] physics.<ref>{{cite book |
||
|last=Schmidhuber |
|last=Schmidhuber |
||
|first=Jürgen |
|||
|date=1997 |
|date=1997 |
||
|title=A Computer Scientist's View of Life, the Universe, and Everything. Lecture Notes in Computer Science |
|title=A Computer Scientist's View of Life, the Universe, and Everything. Lecture Notes in Computer Science |
||
|volume=1337 |
|||
|url=http://www.idsia.ch/~juergen/everything/ |
|url=http://www.idsia.ch/~juergen/everything/ |
||
|pages=201–208 |
|pages=201–208 |
||
Line 197: | Line 207: | ||
|isbn=978-3-540-63746-2 |
|isbn=978-3-540-63746-2 |
||
|doi=10.1007/BFb0052071 |
|doi=10.1007/BFb0052071 |
||
|citeseerx=10.1.1.580.1970 |
|||
}}</ref> In 2000, Schmidhuber explicitly constructed limit-computable, deterministic universes whose [[pseudo-randomness]] based on [[undecidable problem|undecidable]], Gödel-like [[halting problem]]s is extremely hard to detect but does not at all prevent formal ToEs describable by very few bits of information.<ref>{{Cite journal|author=Schmidhuber, Jürgen |
|||
|s2cid=21317070 |
|||
|access-date=2008-03-26 |
|||
|archive-date=2014-02-27 |
|||
|archive-url=https://web.archive.org/web/20140227162350/http://www.idsia.ch/~juergen/everything/ |
|||
|url-status=live |
|||
}}</ref> In 2000, Schmidhuber explicitly constructed limit-computable, deterministic universes whose [[pseudo-randomness]] based on [[undecidable problem|undecidable]], Gödel-like [[halting problem]]s is extremely hard to detect but does not prevent formal theories of everything describable by very few bits of information.<ref> |
|||
{{Cite journal |
|||
|author=Schmidhuber, Jürgen |
|||
|date=2002 |
|date=2002 |
||
|title=Hierarchies of generalized Kolmogorov complexities and nonenumerable universal measures computable in the limit |
|title=Hierarchies of generalized Kolmogorov complexities and nonenumerable universal measures computable in the limit |
||
|journal=International Journal of Foundations of Computer Science |
|||
|journal=Sections in: Hierarchies of generalized Kolmogorov complexities and nonenumerable universal measures computable in the limit. International Journal of Foundations of Computer Science ():587-612 (2002). Section 6 in: the Speed Prior: A New Simplicity Measure Yielding Near-Optimal Computable Predictions. in J. Kivinen and R. H. Sloan, editors, Proceedings of the 15th Annual Conference on Computational Learning Theory (COLT 2002), Sydney, Australia, Lecture Notes in Artificial Intelligence, pages 216--228. Springer, 2002 |
|||
|volume=13 |
|volume=13 |
||
|issue=4 |
|issue=4 |
||
|pages= |
|pages=587–612 |
||
|arxiv=quant-ph/0011122 |
|arxiv=quant-ph/0011122 |
||
|bibcode |
|bibcode=2000quant.ph.11122S |
||
|doi=10.1142/s0129054102001291 |
|||
}}</ref> |
|||
Related critique was offered by [[Solomon Feferman]] |
Related critique was offered by [[Solomon Feferman]]<ref>{{cite web |
||
|last=Feferman |
|last=Feferman |
||
|first=Solomon |
|||
|url=http://math.stanford.edu/~feferman/papers/Godel-IAS.pdf |
|url=http://math.stanford.edu/~feferman/papers/Godel-IAS.pdf |
||
|title=The nature and significance of |
|title=The nature and significance of Gödel's incompleteness theorems |
||
|publisher=[[Institute for Advanced Study]] |
|publisher=[[Institute for Advanced Study]] |
||
|date=17 November 2006 |
|date=17 November 2006 |
||
| |
|access-date=2009-01-12 |
||
|archive-date=2008-12-17 |
|||
}}</ref> among others. Douglas S. Robertson offers [[Conway's game of life]] as an example:<ref>{{cite journal |
|||
|archive-url=https://web.archive.org/web/20081217035530/http://math.stanford.edu/~feferman/papers/Godel-IAS.pdf |
|||
| last=Robertson |first=Douglas S. |
|||
|url-status=live |
|||
| date=2007 |
|||
}}</ref> and others. Douglas S. Robertson offers [[Conway's game of life]] as an example:<ref> |
|||
| title=Goedel's Theorem, the Theory of Everything, and the Future of Science and Mathematics |
|||
{{cite journal |
|||
| journal=[[Complexity (journal)|Complexity]] |
|||
|last=Robertson |first=Douglas S. |
|||
| volume=5 | pages=22–27 |
|||
|date=2007 |
|||
| doi=10.1002/1099-0526(200005/06)5:5<22::AID-CPLX4>3.0.CO;2-0 |
|||
|title=Goedel's Theorem, the Theory of Everything, and the Future of Science and Mathematics |
|||
| issue=5 |
|||
|journal=[[Complexity (journal)|Complexity]] |
|||
}}</ref> The underlying rules are simple and complete, but there are formally undecidable questions about the game's behaviors. Analogously, it may (or may not) be possible to completely state the underlying rules of physics with a finite number of well-defined laws, but there is little doubt that there are questions about the behavior of physical systems which are formally undecidable on the basis of those underlying laws. |
|||
|volume=5 |pages=22–27 |
|||
|doi=10.1002/1099-0526(200005/06)5:5<22::AID-CPLX4>3.0.CO;2-0 |
|||
|issue=5 |
|||
|bibcode=2000Cmplx...5e..22R}}</ref> The underlying rules are simple and complete, but there are formally undecidable questions about the game's behaviors. Analogously, it may (or may not) be possible to completely state the underlying rules of physics with a finite number of well-defined laws, but there is little doubt that there are questions about the behavior of physical systems which are formally undecidable on the basis of those underlying laws. |
|||
Since most physicists would consider the statement of the underlying rules to suffice as the definition of a "theory of everything", most physicists argue that Gödel's Theorem does ''not'' mean that a |
Since most physicists would consider the statement of the underlying rules to suffice as the definition of a "theory of everything", most physicists argue that Gödel's Theorem does ''not'' mean that a theory of everything cannot exist.{{Citation needed|reason=Precarious wording, unclear significance, and any relevance of the purported affidavits necessitate scrutiny|date=August 2021}} On the other hand, the scholars invoking Gödel's Theorem appear, at least in some cases, to be referring not to the underlying rules, but to the understandability of the behavior of all physical systems, as when Hawking mentions arranging blocks into rectangles, turning the computation of [[prime number]]s into a physical question.<ref>{{cite web |
||
|last=Hawking |
|last=Hawking |
||
|first=Stephen |
|||
|date=20 July 2002 |
|date=20 July 2002 |
||
|title=Gödel and the end of physics |
|title=Gödel and the end of physics |
||
|url=http://www.damtp.cam.ac.uk/strings02/dirac/hawking/ |
|url=http://www.damtp.cam.ac.uk/strings02/dirac/hawking/ |
||
| |
|access-date=2009-12-01 |
||
|archive-date=2011-05-21 |
|||
}}</ref> This definitional discrepancy may explain some of the disagreement among researchers. |
|||
|archive-url=https://web.archive.org/web/20110521123113/http://www.damtp.cam.ac.uk/strings02/dirac/hawking/ |
|||
}}</ref> This definitional discrepancy may explain some of the disagreement among researchers. |
|||
=== |
===Fundamental limits in accuracy=== |
||
No physical theory to date is believed to be precisely accurate. Instead, physics has proceeded by a series of "successive approximations" allowing more and more accurate predictions over a wider and wider range of phenomena. Some physicists believe that it is therefore a mistake to confuse theoretical models with the true nature of reality, and hold that the series of approximations will never terminate in the "truth".<ref>{{cite book|title=The New Cosmic Onion: Quarks and the Nature of the Universe|first=search|last=results|date=17 December 2006|publisher=CRC Press|isbn = 978-1-58488-798-0}}</ref> Einstein himself expressed this view on occasions.<ref>Einstein, letter to Felix Klein, 1917. (On determinism and approximations.) Quoted in Pais (1982), Ch. 17.</ref> |
|||
===Definition of fundamental laws=== |
|||
No physical theory to date is believed to be precisely accurate. Instead, physics has proceeded by a series of "successive approximations" allowing more and more accurate predictions over a wider and wider range of phenomena. Some physicists believe that it |
|||
There is a philosophical debate within the physics community as to whether a theory of everything deserves to be called ''the'' fundamental law of the universe.<ref>Weinberg (1993), Ch 2.</ref> One view is the hard [[reductionist]] position that the theory of everything is the fundamental law and that all other theories that apply within the universe are a consequence of the theory of everything. Another view is that [[emergence|emergent]] laws, which govern the behavior of [[complex system]]s, should be seen as equally fundamental. Examples of emergent laws are the [[second law of thermodynamics]] and the theory of [[natural selection]]. The advocates of emergence argue that emergent laws, especially those describing complex or living systems are independent of the low-level, microscopic laws. In this view, emergent laws are as fundamental as a theory of everything. |
|||
is therefore a mistake to confuse theoretical models with the true nature of reality, and |
|||
hold that the series of approximations will never terminate in the "truth". Einstein himself |
|||
expressed this view on occasions.<ref>Einstein, letter to Felix Klein, 1917. (On determinism and approximations.) Quoted in Pais (1982), Ch. 17.</ref> Following this view, we may reasonably hope for ''a'' theory of everything which self-consistently incorporates all currently known forces, but we should not expect it to be the final answer. |
|||
The debates do not make the point at issue clear. Possibly the only issue at stake is the right to apply the high-status term "fundamental" to the respective subjects of research. A well-known debate over this took place between Steven Weinberg and [[Philip Warren Anderson|Philip Anderson]].<ref>{{Cite book|title=Superstrings, P-branes and M-theory|page=7}}</ref> |
|||
On the other hand, it is often claimed that, despite the apparently ever-increasing complexity of the mathematics of each new theory, in a deep sense associated with their underlying [[gauge symmetry]] and the number of [[fundamental physical constant]]s, the theories are becoming simpler. If this is the case, the process of simplification cannot continue indefinitely. |
|||
=== |
====Impossibility of calculation==== |
||
Weinberg<ref>Weinberg (1993) p. 5</ref> points out that calculating the precise motion of an actual projectile in the Earth's atmosphere is impossible. So how can we know we have an adequate theory for describing the motion of projectiles? Weinberg suggests that we know ''principles'' (Newton's laws of motion and gravitation) that work "well enough" for simple examples, like the motion of planets in empty space. These principles have worked so well on simple examples that we can be reasonably confident they will work for more complex examples. For example, although [[general relativity]] includes equations that do not have exact solutions, it is widely accepted as a valid theory because all of its equations with exact solutions have been experimentally verified. Likewise, a theory of everything must work for a wide range of simple examples in such a way that we can be reasonably confident it will work for every situation in physics. Difficulties in creating a theory of everything often begin to appear when combining [[quantum mechanics]] with the theory of [[general relativity]], as the equations of quantum mechanics begin to falter when the force of gravity is applied to them. |
|||
There is a philosophical debate within the physics community as to whether a theory of everything deserves to be called ''the'' fundamental law of the universe.<ref>Weinberg (1993), Ch 2.</ref> One view is the hard [[reductionist]] position that the ToE is the fundamental law and that all other theories that apply within the universe are a consequence of the ToE. Another view is that [[emergence|emergent]] laws, which govern the behavior of [[complex system]]s, should be seen as equally fundamental. Examples of emergent laws are the [[second law of thermodynamics]] and the theory of [[natural selection]]. The advocates of emergence argue that emergent laws, especially those describing complex or living systems are independent of the low-level, microscopic laws. In this view, emergent laws are as fundamental as a ToE. |
|||
==See also== |
|||
The debates do not make the point at issue clear. Possibly the only issue at stake is the right to apply the high-status term "fundamental" to the respective subjects of research. A well-known one took place between Steven Weinberg and [[Philip Warren Anderson|Philip Anderson]]{{Citation needed|date=May 2010}} |
|||
{{Portal|Physics}} |
|||
{{div col|colwidth=30}} |
|||
* {{Annotated link|Absolute (philosophy)}} |
|||
* {{Annotated link|Argument from beauty}} |
|||
* {{Annotated link|Attractor}} |
|||
* {{Annotated link|Black hole thermodynamics#Beyond black holes|Beyond black holes}} |
|||
* {{Annotated link|Beyond the standard model}} |
|||
* {{Annotated link|cGh physics}} |
|||
* {{Annotated link|Chronology of the universe}} |
|||
* {{Annotated link|ER{{=}}EPR}} |
|||
* {{Annotated link|Grand Unified Theory}} |
|||
* {{Annotated link|Holographic principle}} |
|||
* {{Annotated link|List of unsolved problems in mathematics}} |
|||
* {{Annotated link|List of unsolved problems in neuroscience}} |
|||
* {{Annotated link|List of unsolved problems in physics}} |
|||
* {{Annotated link|Mathematical beauty}} |
|||
* {{Annotated link|Mathematical universe hypothesis}} |
|||
* {{Annotated link|Multiverse}} |
|||
* {{Annotated link|Penrose interpretation}} |
|||
* {{Annotated link|Standard Model (mathematical formulation)}} |
|||
* {{Annotated link|Superfluid vacuum theory}} (SVT) |
|||
* {{Annotated link|The Theory of Everything (2014 film)|''The Theory of Everything''}} |
|||
* {{Annotated link|Timeline of the Big Bang}} |
|||
* {{Annotated link|Unification (physics)|Unification}} |
|||
* {{Annotated link|Unity of science}} |
|||
* {{Annotated link|Zero-energy universe}} |
|||
{{div col end}} |
|||
==References== |
|||
=== Impossibility of being "of everything" === |
|||
{{reflist|35em|refs= |
|||
<ref name="Impey2012">{{cite book |author=Impey |first=Chris |url=https://archive.org/details/howitbegantimetr0000impe |title=How It Began: A Time-Traveler's Guide to the Universe |date=26 March 2012 |publisher=W. W. Norton |isbn=978-0-393-08002-5 |url-access=registration}}</ref> |
|||
Although the name "theory of everything" suggests the determinism of Laplace's quotation, this gives a very misleading impression. Determinism is frustrated by the probabilistic nature of quantum mechanical predictions, by the extreme sensitivity to initial conditions that leads to [[Chaos theory|mathematical chaos]], by the limitations due to event horizons, and by the extreme mathematical difficulty of applying the theory. Thus, although the current standard model of particle physics "in principle" predicts almost all known non-gravitational phenomena, in practice only a few quantitative results have been derived from the full theory (e.g., the masses of some of the simplest [[hadron]]s), and these results (especially the particle masses which are most relevant for low-energy physics) are less accurate than existing experimental measurements. The ToE would almost certainly be even harder to apply for the prediction of experimental results, and thus might be of limited use. |
|||
A motive for seeking a ToE,{{citation needed|date=November 2010}} apart from the pure intellectual satisfaction of completing a centuries-long quest, is that prior examples of unification have predicted new phenomena, some of which (e.g., [[electrical generator]]s) have proved of great practical importance. And like in these prior examples of unification, the ToE would probably allow us to confidently define the domain of validity and residual error of low-energy approximations to the full theory. |
|||
=== Infinite number of onion layers === |
|||
[[Lee Smolin]] regularly argues that the layers of nature may be like the layers of an onion, and that the number of layers might be infinite.{{Citation needed|date=October 2011}} This would imply an infinite sequence of physical theories. |
|||
The argument is not universally accepted, because it is not obvious that infinity is a concept that applies to the foundations of nature. |
|||
=== Impossibility of calculation === |
|||
Weinberg<ref>Weinberg (1993) p. 5</ref> points out that calculating the precise motion of an actual projectile in the Earth's atmosphere is impossible. So how can we know we have an adequate theory for describing the motion of projectiles? Weinberg suggests that we know ''principles'' (Newton's laws of motion and gravitation) that work "well enough" for simple examples, like the motion of planets in empty space. These principles have worked so well on simple examples that we can be reasonably confident they will work for more complex examples. For example, although [[general relativity]] includes equations that do not have exact solutions, it is widely accepted as a valid theory because all of its equations with exact solutions have been experimentally verified. Likewise, a ToE must work for a wide range of simple examples in such a way that we can be reasonably confident it will work for every situation in physics. |
|||
== See also == |
|||
{{Portal|Physics}} |
|||
{{Colbegin|colwidth=30em}} |
|||
* [[Absolute (philosophy)]] |
|||
* [[Argument from beauty]] |
|||
* [[Attractor]] |
|||
* [[Biocentric universe]] |
|||
* [[Black hole thermodynamics#Beyond black holes|Beyond black holes]] |
|||
* [[Beyond the standard model]] |
|||
* [[Big Bang]] |
|||
* [[cGh physics]] |
|||
* [[Chronology of the universe]] |
|||
* [[Electroweak interaction]] |
|||
* [[Holographic principle]] |
|||
* [[Mathematical beauty]] |
|||
* [[Mathematical universe hypothesis]] |
|||
* [[Multiverse]] |
|||
* [[Penrose interpretation]] |
|||
* [[Standard Model (mathematical formulation)]] |
|||
* [[Superfluid vacuum theory]] (SVT) |
|||
* ''[[The Theory of Everything (2014 film)]]'' – a feature film about Prof. Stephen Hawking and his first wife [[Jane Hawking]] |
|||
* [[Timeline of the Big Bang]] |
|||
* [[Zero-energy universe]] |
|||
{{colend}} |
|||
<ref name="NYT-20201123">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=23 November 2020 |title=Can a Computer Devise a Theory of Everything? - It might be possible, physicists say, but not anytime soon. And there's no guarantee that we humans will understand the result. |work=[[The New York Times]] |url=https://www.nytimes.com/2020/11/23/science/artificial-intelligence-ai-physics-theory.html |archive-url=https://web.archive.org/web/20201123100612/https://www.nytimes.com/2020/11/23/science/artificial-intelligence-ai-physics-theory.html |archive-date=23 November 2020 |url-status=live |access-date=23 November 2020}}</ref> |
|||
== References == |
|||
}} |
|||
=== Footnotes === |
|||
{{Reflist|35em}} |
|||
=== |
===Bibliography=== |
||
* [[Abraham Pais|Pais, Abraham]] (1982) ''Subtle is the Lord |
* [[Abraham Pais|Pais, Abraham]] (1982) ''[[Subtle is the Lord: The Science and the Life of Albert Einstein]]'' (Oxford University Press, Oxford. Ch. 17, {{ISBN|0-19-853907-X}} |
||
* [[Steven Weinberg|Weinberg, Steven]] (1993) ''Dreams of a Final Theory: The Search for the Fundamental Laws of Nature'', Hutchinson Radius, London, ISBN |
* [[Steven Weinberg|Weinberg, Steven]] (1993) ''Dreams of a Final Theory: The Search for the Fundamental Laws of Nature'', Hutchinson Radius, London, {{ISBN|0-09-177395-4}} |
||
* [[Corey S. Powell]] ''Relativity versus quantum mechanics: the battle for the universe'', The Guardian (2015) [https://www.theguardian.com/news/2015/nov/04/relativity-quantum-mechanics-universe-physicists Relativity versus quantum mechanics: the battle for the universe] |
|||
== |
==External links== |
||
{{commons category}} |
|||
* [http://www.pbs.org/wgbh/nova/elegant/program.html The Elegant Universe], ''[[Nova (TV series)|Nova]]'' episode about the search for the theory of everything and string theory. |
|||
{{wikiquote}} |
|||
* [https://www.pbs.org/wgbh/nova/elegant/program.html The Elegant Universe], ''[[Nova (American TV series)|Nova]]'' episode about the search for the theory of everything and string theory. |
|||
* [http://www.vega.org.uk/video/programme/7 Theory of Everything], freeview video by the [[Vega Science Trust]], BBC and [[Open University]]. |
* [http://www.vega.org.uk/video/programme/7 Theory of Everything], freeview video by the [[Vega Science Trust]], BBC and [[Open University]]. |
||
* [http://iai.tv/video/the-theory-of-everything The Theory of Everything]: Are we getting closer, or is a final theory of matter and the universe impossible? Debate between [[John Ellis (physicist)]], [[Frank Close]] and [[Nicholas Maxwell]]. |
* [http://iai.tv/video/the-theory-of-everything The Theory of Everything]: Are we getting closer, or is a final theory of matter and the universe impossible? Debate between [[John Ellis (physicist, born 1946)|John Ellis (physicist)]], [[Frank Close]] and [[Nicholas Maxwell]]. |
||
* [http://iai.tv/video/why-the-world-exists Why The World Exists], a discussion between physicist [[Laura Mersini-Houghton]], cosmologist [[George Francis Rayner Ellis]] and philosopher David Wallace about dark matter, parallel universes and explaining why these and the present Universe exist. |
* [http://iai.tv/video/why-the-world-exists Why The World Exists], a discussion between physicist [[Laura Mersini-Houghton]], cosmologist [[George Francis Rayner Ellis]] and philosopher David Wallace about dark matter, parallel universes and explaining why these and the present Universe exist. |
||
* [https://www.bbc.co.uk/programmes/p004y24b Theories of Everything], BBC Radio 4 discussion with Brian Greene, John Barrow & Val Gibson (''In Our Time'', March 25, 2004). |
|||
* [https://scholar.google.com/citations?view_op=view_citation&hl=en&user=m7lSuQUAAAAJ&citation_for_view=m7lSuQUAAAAJ:d1gkVwhDpl0C Modern Research Results] |
|||
{{Theories of gravitation|selected=GR alternatives}} |
{{Theories of gravitation|selected=GR alternatives}} |
||
{{World view}} |
{{World view}} |
||
{{Standard model of physics}} |
|||
{{Authority control}} |
{{Authority control}} |
||
[[Category:Physics beyond the Standard Model]] |
[[Category:Physics beyond the Standard Model]] |
||
[[Category: |
[[Category:Theories of gravity]] |
||
[[Category:Theories of gravitation]] |
Revision as of 21:52, 12 June 2024
Beyond the Standard Model |
---|
![]() |
Standard Model |
A theory of everything (TOE), final theory, ultimate theory, unified field theory or master theory is a hypothetical, singular, all-encompassing, coherent theoretical framework of physics that fully explains and links together all aspects of the universe.[1]: 6 Finding a theory of everything is one of the major unsolved problems in physics.[2][3]
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, clusters of galaxies, etc. On the other hand, quantum mechanics is a theoretical framework that only focuses on the three non-gravitational forces for understanding the universe in regions of both very small scale and low mass: subatomic particles, atoms, molecules, etc. Quantum mechanics successfully implemented the Standard Model that describes the three non-gravitational forces: strong nuclear, weak nuclear, and electromagnetic force – as well as all observed elementary particles.[4]: 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.[5][6][7]: 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.[8][9] 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 predictions) and controversy. String theory posits that at the beginning of the universe (up to 10−43 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.
Name
Initially, the term theory of everything was used with an ironic reference to various overgeneralized theories. For example, a grandfather of Ijon Tichy – a character from a cycle of Stanisław Lem's science fiction stories of the 1960s – was known to work on the "General Theory of Everything". Physicist Harald Fritzsch used the term in his 1977 lectures in Varenna.[10] Physicist John Ellis claims[11] to have introduced the acronym "TOE" into the technical literature in an article in Nature in 1986.[12] Over time, the term stuck in popularizations of theoretical physics research.
Historical antecedents
Antiquity to 19th century
Many ancient cultures such as Babylonian astronomers and Indian astronomy studied the pattern of the Seven Sacred Luminaires/Classical Planets against the background of stars, with their interest being to relate celestial movement to human events (astrology), and the goal being to predict events by recording events against a time measure and then look for recurrent patterns. The debate between the universe having either a beginning or eternal cycles can be traced to ancient Babylonia.[13] Hindu cosmology posits that time is infinite with a cyclic universe, where the current universe was preceded and will be followed by an infinite number of universes.[14][15] Time scales mentioned in Hindu cosmology correspond to those of modern scientific cosmology. Its cycles run from our ordinary day and night to a day and night of Brahma, 8.64 billion years long.[16]
The natural philosophy of atomism appeared in several ancient traditions. In ancient Greek philosophy, the pre-Socratic philosophers speculated that the apparent diversity of observed phenomena was due to a single type of interaction, namely the motions and collisions of atoms. The concept of 'atom' proposed by Democritus was an early philosophical attempt to unify phenomena observed in nature. The concept of 'atom' also appeared in the Nyaya-Vaisheshika school of ancient Indian philosophy.
Archimedes was possibly the first philosopher to have described nature with axioms (or principles) and then deduce new results from them. Any "theory of everything" is similarly expected to be based on axioms and to deduce all observable phenomena from them.[17]: 340
Following earlier atomistic thought, the mechanical philosophy of the 17th century posited that all forces could be ultimately reduced to contact forces between the atoms, then imagined as tiny solid particles.[18]: 184 [19]
In the late 17th century, Isaac Newton's description of the long-distance force of gravity implied that not all forces in nature result from things coming into contact. Newton's work in his Mathematical Principles of Natural Philosophy dealt with this in a further example of unification, in this case unifying Galileo's work on terrestrial gravity, Kepler's laws of planetary motion and the phenomenon of tides by explaining these apparent actions at a distance under one single law: the law of universal gravitation.[20]
In 1814, building on these results, Laplace famously suggested that a sufficiently powerful intellect could, if it knew the position and velocity of every particle at a given time, along with the laws of nature, calculate the position of any particle at any other time:[21]: ch 7
An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.
— Essai philosophique sur les probabilités, Introduction. 1814
Laplace thus envisaged a combination of gravitation and mechanics as a theory of everything. Modern quantum mechanics implies that uncertainty is inescapable, and thus that Laplace's vision has to be amended: a theory of everything must include gravitation and quantum mechanics. Even ignoring quantum mechanics, chaos theory is sufficient to guarantee that the future of any sufficiently complex mechanical or astronomical system is unpredictable.
In 1820, Hans Christian Ørsted discovered a connection between electricity and magnetism, triggering decades of work that culminated in 1865, in James Clerk Maxwell's theory of electromagnetism. During the 19th and early 20th centuries, it gradually became apparent that many common examples of forces – contact forces, elasticity, viscosity, friction, and pressure – result from electrical interactions between the smallest particles of matter.
In his experiments of 1849–1850, Michael Faraday was the first to search for a unification of gravity with electricity and magnetism.[22] However, he found no connection.
In 1900, David Hilbert published a famous list of mathematical problems. In Hilbert's sixth problem, he challenged researchers to find an axiomatic basis to all of physics. In this problem he thus asked for what today would be called a theory of everything.[23]
Early 20th century
In the late 1920s, the then new quantum mechanics showed that the chemical bonds between atoms were examples of (quantum) electrical forces, justifying Dirac's boast that "the underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known".[24]
After 1915, when Albert Einstein published the theory of gravity (general relativity), the search for a unified field theory combining gravity with electromagnetism began with a renewed interest. In Einstein's day, the strong and the weak forces had not yet been discovered, yet he found the potential existence of two other distinct forces, gravity and electromagnetism, far more alluring. This launched his 40-year voyage in search of the so-called "unified field theory" that he hoped would show that these two forces are really manifestations of one grand, underlying principle. During the last few decades of his life, this ambition alienated Einstein from the rest of mainstream of physics, as the mainstream was instead far more excited about the emerging framework of quantum mechanics. Einstein wrote to a friend in the early 1940s, "I have become a lonely old chap who is mainly known because he doesn't wear socks and who is exhibited as a curiosity on special occasions." Prominent contributors were Gunnar Nordström, Hermann Weyl, Arthur Eddington, David Hilbert,[25] Theodor Kaluza, Oskar Klein (see Kaluza–Klein theory), and most notably, Albert Einstein and his collaborators. Einstein searched in earnest for, but ultimately failed to find, a unifying theory[26]: ch 17 (see Einstein–Maxwell–Dirac equations).
Late 20th century and the nuclear interactions
In the 20th century, the search for a unifying theory was interrupted by the discovery of the strong and weak nuclear forces, which differ both from gravity and from electromagnetism. A further hurdle was the acceptance that in a theory of everything, quantum mechanics had to be incorporated from the outset, rather than emerging as a consequence of a deterministic unified theory, as Einstein had hoped.
Gravity and electromagnetism are able to coexist as entries in a list of classical forces, but for many years it seemed that gravity could not be incorporated into the quantum framework, let alone unified with the other fundamental forces. For this reason, work on unification, for much of the 20th century, focused on understanding the three forces described by quantum mechanics: electromagnetism and the weak and strong forces. The first two were combined in 1967–1968 by Sheldon Glashow, Steven Weinberg, and Abdus Salam into the electroweak force.[27] Electroweak unification is a broken symmetry: the electromagnetic and weak forces appear distinct at low energies because the particles carrying the weak force, the W and Z bosons, have non-zero masses (80.4 GeV/c2 and 91.2 GeV/c2, respectively), whereas the photon, which carries the electromagnetic force, is massless. At higher energies W bosons and Z bosons can be created easily and the unified nature of the force becomes apparent.
While the strong and electroweak forces coexist under the Standard Model of particle physics, they remain distinct. Thus, the pursuit of a theory of everything remained unsuccessful: neither a unification of the strong and electroweak forces – which Laplace would have called 'contact forces' – nor a unification of these forces with gravitation had been achieved.
Modern physics
![](https://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Cube_of_theoretical_physics.svg/220px-Cube_of_theoretical_physics.svg.png)
Conventional sequence of theories
A theory of everything would unify all the fundamental interactions of nature: gravitation, the strong interaction, the weak interaction, and electromagnetism. Because the weak interaction can transform elementary particles from one kind into another, the theory of everything should also predict all the different kinds of particles possible. The usual assumed path of theories is given in the following graph, where each unification step leads one level up on the graph.
In this graph, electroweak unification occurs at around 100 GeV, grand unification is predicted to occur at 1016 GeV, and unification of the GUT force with gravity is expected at the Planck energy, roughly 1019 GeV.
Several Grand Unified Theories (GUTs) have been proposed to unify electromagnetism and the weak and strong forces. Grand unification would imply the existence of an electronuclear force; it is expected to set in at energies of the order of 1016 GeV, far greater than could be reached by any currently feasible particle accelerator. Although the simplest grand unified theories have been experimentally ruled out, the idea of a grand unified theory, especially when linked with supersymmetry, remains a favorite candidate in the theoretical physics community. Supersymmetric grand unified theories seem plausible not only for their theoretical "beauty", but because they naturally produce large quantities of dark matter, and because the inflationary force may be related to grand unified theory physics (although it does not seem to form an inevitable part of the theory). Yet grand unified theories are clearly not the final answer; both the current standard model and all proposed GUTs are quantum field theories which require the problematic technique of renormalization to yield sensible answers. This is usually regarded as a sign that these are only effective field theories, omitting crucial phenomena relevant only at very high energies.[6]
The final step in the graph requires resolving the separation between quantum mechanics and gravitation, often equated with general relativity. Numerous researchers concentrate their efforts on this specific step; nevertheless, no accepted theory of quantum gravity, and thus no accepted theory of everything, has emerged with observational evidence. It is usually assumed that the theory of everything will also solve the remaining problems of grand unified theories.
In addition to explaining the forces listed in the graph, a theory of everything may also explain the status of at least two candidate forces suggested by modern cosmology: an inflationary force and dark energy. Furthermore, cosmological experiments also suggest the existence of dark matter, supposedly composed of fundamental particles outside the scheme of the standard model. However, the existence of these forces and particles has not been proven.
String theory and M-theory
Since the 1990s, some physicists such as Edward Witten believe that 11-dimensional M-theory, which is described in some limits by one of the five perturbative superstring theories, and in another by the maximally-supersymmetric eleven-dimensional supergravity, is the theory of everything. There is no widespread consensus on this issue.
One remarkable property of string/M-theory is that seven extra dimensions are required for the theory's consistency, on top of the four dimensions in our universe. In this regard, string theory can be seen as building on the insights of the Kaluza–Klein theory, in which it was realized that applying general relativity to a 5-dimensional universe, with one space dimension small and curled up, looks from the 4-dimensional perspective like the usual general relativity together with Maxwell's electrodynamics. This lent credence to the idea of unifying gauge and gravity interactions, and to extra dimensions, but did not address the detailed experimental requirements. Another important property of string theory is its supersymmetry, which together with extra dimensions are the two main proposals for resolving the hierarchy problem of the standard model, which is (roughly) the question of why gravity is so much weaker than any other force. The extra-dimensional solution involves allowing gravity to propagate into the other dimensions while keeping other forces confined to a 4-dimensional spacetime, an idea that has been realized with explicit stringy mechanisms.[28]
Research into string theory has been encouraged by a variety of theoretical and experimental factors. On the experimental side, the particle content of the standard model supplemented with neutrino masses fits into a spinor representation of SO(10), a subgroup of E8 that routinely emerges in string theory, such as in heterotic string theory[29] or (sometimes equivalently) in F-theory.[30][31] String theory has mechanisms that may explain why fermions come in three hierarchical generations, and explain the mixing rates between quark generations.[32] On the theoretical side, it has begun to address some of the key questions in quantum gravity, such as resolving the black hole information paradox, counting the correct entropy of black holes[33][34] and allowing for topology-changing processes.[35][36][37] It has also led to many insights in pure mathematics and in ordinary, strongly-coupled gauge theory due to the Gauge/String duality.
In the late 1990s, it was noted that one major hurdle in this endeavor is that the number of possible 4-dimensional universes is incredibly large. The small, "curled up" extra dimensions can be compactified in an enormous number of different ways (one estimate is 10500 ) each of which leads to different properties for the low-energy particles and forces. This array of models is known as the string theory landscape.[17]: 347
One proposed solution is that many or all of these possibilities are realized in one or another of a huge number of universes, but that only a small number of them are habitable. Hence what we normally conceive as the fundamental constants of the universe are ultimately the result of the anthropic principle rather than dictated by theory. This has led to criticism of string theory,[38] arguing that it cannot make useful (i.e., original, falsifiable, and verifiable) predictions and regarding it as a pseudoscience/philosophy. Others disagree,[39] and string theory remains an active topic of investigation in theoretical physics.[40]
Loop quantum gravity
Current research on loop quantum gravity may eventually play a fundamental role in a theory of everything, but that is not its primary aim.[41] Loop quantum gravity also introduces a lower bound on the possible length scales.
There have been recent claims that loop quantum gravity may be able to reproduce features resembling the Standard Model. So far only the first generation of fermions (leptons and quarks) with correct parity properties have been modelled by Sundance Bilson-Thompson using preons constituted of braids of spacetime as the building blocks.[42] However, there is no derivation of the Lagrangian that would describe the interactions of such particles, nor is it possible to show that such particles are fermions, nor that the gauge groups or interactions of the Standard Model are realised. Use of quantum computing concepts made it possible to demonstrate that the particles are able to survive quantum fluctuations.[43]
This model leads to an interpretation of electric and color charge as topological quantities (electric as number and chirality of twists carried on the individual ribbons and colour as variants of such twisting for fixed electric charge).
Bilson-Thompson's original paper suggested that the higher-generation fermions could be represented by more complicated braidings, although explicit constructions of these structures were not given. The electric charge, color, and parity properties of such fermions would arise in the same way as for the first generation. The model was expressly generalized for an infinite number of generations and for the weak force bosons (but not for photons or gluons) in a 2008 paper by Bilson-Thompson, Hackett, Kauffman and Smolin.[44]
Other attempts
Among other attempts to develop a theory of everything is the theory of causal fermion systems,[45] giving the two current physical theories (general relativity and quantum field theory) as limiting cases.
Another theory is called Causal Sets. As some of the approaches mentioned above, its direct goal isn't necessarily to achieve a theory of everything but primarily a working theory of quantum gravity, which might eventually include the standard model and become a candidate for a theory of everything. Its founding principle is that spacetime is fundamentally discrete and that the spacetime events are related by a partial order. This partial order has the physical meaning of the causality relations between relative past and future distinguishing spacetime events.
Causal dynamical triangulation does not assume any pre-existing arena (dimensional space), but rather attempts to show how the spacetime fabric itself evolves.
Another attempt may be related to ER=EPR, a conjecture in physics stating that entangled particles are connected by a wormhole (or Einstein–Rosen bridge).[46]
Present status
At present, there is no candidate theory of everything that includes the standard model of particle physics and general relativity and that, at the same time, is able to calculate the fine-structure constant or the mass of the electron.[2] Most particle physicists expect that the outcome of ongoing experiments – the search for new particles at the large particle accelerators and for dark matter – are needed in order to provide further input for a theory of everything.
Arguments against
In parallel to the intense search for a theory of everything, various scholars have debated the possibility of its discovery.
Gödel's incompleteness theorem
A number of scholars claim that Gödel's incompleteness theorem suggests that attempts to construct a theory of everything are bound to fail. Gödel's theorem, informally stated, asserts that any formal theory sufficient to express elementary arithmetical facts and strong enough for them to be proved is either inconsistent (both a statement and its denial can be derived from its axioms) or incomplete, in the sense that there is a true statement that can't be derived in the formal theory.
Stanley Jaki, in his 1966 book The Relevance of Physics, pointed out that, because a "theory of everything" will certainly be a consistent non-trivial mathematical theory, it must be incomplete. He claims that this dooms searches for a deterministic theory of everything.[47]
Freeman Dyson has stated that "Gödel's theorem implies that pure mathematics is inexhaustible. No matter how many problems we solve, there will always be other problems that cannot be solved within the existing rules. […] Because of Gödel's theorem, physics is inexhaustible too. The laws of physics are a finite set of rules, and include the rules for doing mathematics, so that Gödel's theorem applies to them."[48]
Stephen Hawking was originally a believer in the Theory of Everything, but after considering Gödel's Theorem, he concluded that one was not obtainable. "Some people will be very disappointed if there is not an ultimate theory that can be formulated as a finite number of principles. I used to belong to that camp, but I have changed my mind."[49]
Jürgen Schmidhuber (1997) has argued against this view; he asserts that Gödel's theorems are irrelevant for computable physics.[50] In 2000, Schmidhuber explicitly constructed limit-computable, deterministic universes whose pseudo-randomness based on undecidable, Gödel-like halting problems is extremely hard to detect but does not prevent formal theories of everything describable by very few bits of information.[51]
Related critique was offered by Solomon Feferman[52] and others. Douglas S. Robertson offers Conway's game of life as an example:[53] The underlying rules are simple and complete, but there are formally undecidable questions about the game's behaviors. Analogously, it may (or may not) be possible to completely state the underlying rules of physics with a finite number of well-defined laws, but there is little doubt that there are questions about the behavior of physical systems which are formally undecidable on the basis of those underlying laws.
Since most physicists would consider the statement of the underlying rules to suffice as the definition of a "theory of everything", most physicists argue that Gödel's Theorem does not mean that a theory of everything cannot exist.[citation needed] On the other hand, the scholars invoking Gödel's Theorem appear, at least in some cases, to be referring not to the underlying rules, but to the understandability of the behavior of all physical systems, as when Hawking mentions arranging blocks into rectangles, turning the computation of prime numbers into a physical question.[54] This definitional discrepancy may explain some of the disagreement among researchers.
Fundamental limits in accuracy
No physical theory to date is believed to be precisely accurate. Instead, physics has proceeded by a series of "successive approximations" allowing more and more accurate predictions over a wider and wider range of phenomena. Some physicists believe that it is therefore a mistake to confuse theoretical models with the true nature of reality, and hold that the series of approximations will never terminate in the "truth".[55] Einstein himself expressed this view on occasions.[56]
Definition of fundamental laws
There is a philosophical debate within the physics community as to whether a theory of everything deserves to be called the fundamental law of the universe.[57] One view is the hard reductionist position that the theory of everything is the fundamental law and that all other theories that apply within the universe are a consequence of the theory of everything. Another view is that emergent laws, which govern the behavior of complex systems, should be seen as equally fundamental. Examples of emergent laws are the second law of thermodynamics and the theory of natural selection. The advocates of emergence argue that emergent laws, especially those describing complex or living systems are independent of the low-level, microscopic laws. In this view, emergent laws are as fundamental as a theory of everything.
The debates do not make the point at issue clear. Possibly the only issue at stake is the right to apply the high-status term "fundamental" to the respective subjects of research. A well-known debate over this took place between Steven Weinberg and Philip Anderson.[58]
Impossibility of calculation
Weinberg[59] points out that calculating the precise motion of an actual projectile in the Earth's atmosphere is impossible. So how can we know we have an adequate theory for describing the motion of projectiles? Weinberg suggests that we know principles (Newton's laws of motion and gravitation) that work "well enough" for simple examples, like the motion of planets in empty space. These principles have worked so well on simple examples that we can be reasonably confident they will work for more complex examples. For example, although general relativity includes equations that do not have exact solutions, it is widely accepted as a valid theory because all of its equations with exact solutions have been experimentally verified. Likewise, a theory of everything must work for a wide range of simple examples in such a way that we can be reasonably confident it will work for every situation in physics. Difficulties in creating a theory of everything often begin to appear when combining quantum mechanics with the theory of general relativity, as the equations of quantum mechanics begin to falter when the force of gravity is applied to them.
See also
- Absolute (philosophy) – Philosophical or theological concept
- Argument from beauty – Argument for the existence of God based on the observable beauty of the world
- Attractor – Concept in dynamical systems
- Beyond black holes – Area of study
- Beyond the standard model – Theories trying to extend known physics
- cGh physics – Attempts to unify relativity, gravitation, and quantum mechanics
- Chronology of the universe – History and future of the universe
- ER=EPR – Conjecture unifying entanglement and wormholes
- Grand Unified Theory – Comprehensive physical model
- Holographic principle – Physics inside a bounded region is fully captured by physics at the boundary of the region
- List of unsolved problems in mathematics
- List of unsolved problems in neuroscience
- List of unsolved problems in physics
- Mathematical beauty – Aesthetic value of mathematics
- Mathematical universe hypothesis – Cosmological theory
- Multiverse – Hypothetical group of multiple universes
- Penrose interpretation – Interpretation of quantum mechanics
- Standard Model (mathematical formulation) – Mathematics of a particle physics model
- Superfluid vacuum theory – Theory of fundamental physics (SVT)
- The Theory of Everything – 2014 biographical film of the life of Stephen Hawking
- Timeline of the Big Bang – History and future of the universe
- Unification – Idea of connecting all of physics into one set of equations
- Unity of science – Theory in the philosophy of science
- Zero-energy universe – Hypothesis that the total amount of energy in the universe is exactly zero
References
- ^ Weinberg, Steven (2011-04-20). Dreams of a Final Theory: The Scientist's Search for the Ultimate Laws of Nature. Knopf Doubleday Publishing Group. ISBN 978-0-307-78786-6.
- ^ a b Overbye, Dennis (23 November 2020). "Can a Computer Devise a Theory of Everything? - It might be possible, physicists say, but not anytime soon. And there's no guarantee that we humans will understand the result". The New York Times. Archived from the original on 23 November 2020. Retrieved 23 November 2020.
- ^ Overbye, Dennis (11 September 2023). "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". The New York Times. Archived from the original on 11 September 2023. Retrieved 11 September 2023.
- ^ Hawking, Stephen W. (28 February 2006). The Theory of Everything: The Origin and Fate of the Universe. Phoenix Books; Special Anniversary. ISBN 978-1-59777-508-3.
- ^ SMOLIN, L. (2004). "An Invitation to Loop Quantum Gravity". Quantum Theory and Symmetries. []: 655–682. arXiv:hep-th/0408048. Bibcode:2004qts..conf..655S. doi:10.1142/9789812702340_0078. ISBN 978-981-256-068-1. S2CID 16195175.
- ^ a b Carlip, Steven (2001). "Quantum Gravity: a Progress Report". Reports on Progress in Physics. 64 (8): 885–942. arXiv:gr-qc/0108040. Bibcode:2001RPPh...64..885C. doi:10.1088/0034-4885/64/8/301. S2CID 118923209.
- ^ Priest, Susanna Hornig (14 July 2010). Encyclopedia of Science and Technology Communication. SAGE Publications. ISBN 978-1-4522-6578-0.
- ^ Overbye, Dennis (10 October 2022). "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". The New York Times. Archived from the original on 16 November 2022. Retrieved 22 October 2022.
- ^ Starr, Michelle (16 November 2022). "Scientists Created a Black Hole in The Lab, And Then It Started to Glow". ScienceAlert. Archived from the original on 15 November 2022. Retrieved 16 November 2022.
- ^ Fritzsch, Harald (1977). "THE WORLD OF FLAVOUR AND COLOUR". CERN Report. Ref.TH.2359-CERN. (download at https://cds.cern.ch/record/875256/files/CM-P00061728.pdf Archived 2020-02-12 at the Wayback Machine )
- ^ Ellis, John (2002). "Physics gets physical (correspondence)". Nature. 415 (6875): 957. Bibcode:2002Natur.415..957E. doi:10.1038/415957b. PMID 11875539.
- ^ Ellis, John (1986). "The Superstring: Theory of Everything, or of Nothing?". Nature. 323 (6089): 595–598. Bibcode:1986Natur.323..595E. doi:10.1038/323595a0. S2CID 4344940.
- ^ Hodge, John C. (2012). Theory of Everything: Scalar Potential Model of the Big and the Small. CreateSpace Independent Publishing Platform. pp. 1–13, 99. ISBN 978-1-4699-8736-1.
- ^ Sushil Mittal; Gene Thursby (2012). Hindu World. Routledge. p. 284. ISBN 978-1-134-60875-1.
- ^ Jones, Andrew Zimmerman (2009). String Theory For Dummies. John Wiley & Sons. p. 262. ISBN 978-0-470-59584-8.
- ^ Sagan, Carl (2006). Cosmos.
- ^ a b Impey, Chris (26 March 2012). How It Began: A Time-Traveler's Guide to the Universe. W. W. Norton. ISBN 978-0-393-08002-5.
- ^ Burns, William E. (1 January 2001). The Scientific Revolution: An Encyclopedia. ABC-CLIO. ISBN 978-0-87436-875-8.
- ^ Shapin, Steven (1996). The Scientific Revolution. University of Chicago Press. ISBN 978-0-226-75021-7.
- ^ Newton, Sir Isaac (1729). The Mathematical Principles of Natural Philosophy. Vol. II. p. 255.
- ^ Carroll, Sean (2010). From Eternity to Here: The Quest for the Ultimate Theory of Time. Penguin Group US. ISBN 978-1-101-15215-7.
- ^ Faraday, M. (1850). "Experimental Researches in Electricity. Twenty-Fourth Series. On the Possible Relation of Gravity to Electricity". Abstracts of the Papers Communicated to the Royal Society of London. 5: 994–995. doi:10.1098/rspl.1843.0267.
- ^ Gorban, Alexander N.; Karlin, Ilya (2013). "Hilbert's 6th Problem: Exact and approximate hydrodynamic manifolds for kinetic equations". Bulletin of the American Mathematical Society. 51 (2): 187. arXiv:1310.0406. Bibcode:2013arXiv1310.0406G. doi:10.1090/S0273-0979-2013-01439-3. S2CID 7228220.
- ^ Dirac, P.A.M. (1929). "Quantum mechanics of many-electron systems". Proceedings of the Royal Society of London A. 123 (792): 714–733. Bibcode:1929RSPSA.123..714D. doi:10.1098/rspa.1929.0094.
- ^ Majer, U.; Sauer, T. (2005). Hilbert's "World Equations" and His Vision of a Unified Science. Einstein Studies. Vol. 11. pp. 259–276. arXiv:physics/0405110. Bibcode:2005ugr..book..259M. doi:10.1007/0-8176-4454-7_14. ISBN 978-0-8176-4454-3. S2CID 985751.
- ^ Abraham Pais (23 September 1982). Subtle is the Lord: The Science and the Life of Albert Einstein: The Science and the Life of Albert Einstein. Oxford University Press. ISBN 978-0-19-152402-8.
- ^ Weinberg (1993), Ch. 5
- ^ Holloway, M (2005). "The Beauty of Branes" (PDF). Scientific American. 293 (4): 38–40. Bibcode:2005SciAm.293d..38H. doi:10.1038/scientificamerican1005-38. PMID 16196251. Archived from the original (PDF) on November 22, 2014. Retrieved August 13, 2012.
- ^ Nilles, Hans Peter; Ramos-Sánchez, Saúl; Ratz, Michael; Vaudrevange, Patrick K. S. (2009). "From strings to the MSSM". The European Physical Journal C. 59 (2): 249–267. arXiv:0806.3905. Bibcode:2009EPJC...59..249N. doi:10.1140/epjc/s10052-008-0740-1. S2CID 17452924.
- ^ Beasley, Chris; Heckman, Jonathan J; Vafa, Cumrun (2009). "GUTs and exceptional branes in F-theory — I". Journal of High Energy Physics. 2009 (1): 058. arXiv:0802.3391. Bibcode:2009JHEP...01..058B. doi:10.1088/1126-6708/2009/01/058. S2CID 119309173.
- ^ Donagi, Ron; Wijnholt, Martijn (2008). "Model Building with F-Theory". arXiv:0802.2969v3 [hep-th].
- ^ Heckman, Jonathan J.; Vafa, Cumrun (2010). "Flavor Hierarchy from F-theory". Nuclear Physics B. 837 (1): 137–151. arXiv:0811.2417. Bibcode:2010NuPhB.837..137H. doi:10.1016/j.nuclphysb.2010.05.009. S2CID 119244083.
- ^ Strominger, Andrew; Vafa, Cumrun (1996). "Microscopic origin of the Bekenstein-Hawking entropy". Physics Letters B. 379 (1–4): 99–104. arXiv:hep-th/9601029. Bibcode:1996PhLB..379...99S. doi:10.1016/0370-2693(96)00345-0. S2CID 1041890.
- ^ Horowitz, Gary. "The Origin of Black Hole Entropy in String Theory". arXiv:gr-qc/9604051.
- ^ Greene, Brian R.; Morrison, David R.; Strominger, Andrew (1995). "Black hole condensation and the unification of string vacua". Nuclear Physics B. 451 (1–2): 109–120. arXiv:hep-th/9504145. Bibcode:1995NuPhB.451..109G. doi:10.1016/0550-3213(95)00371-X. S2CID 11145691.
- ^ Aspinwall, Paul S.; Greene, Brian R.; Morrison, David R. (1994). "Calabi-Yau moduli space, mirror manifolds and spacetime topology change in string theory". Nuclear Physics B. 416 (2): 414. arXiv:hep-th/9309097. Bibcode:1994NuPhB.416..414A. doi:10.1016/0550-3213(94)90321-2. S2CID 10927539.
- ^ Adams, Allan; Liu, Xiao; McGreevy, John; Saltman, Alex; Silverstein, Eva (2005). "Things fall apart: Topology change from winding tachyons". Journal of High Energy Physics. 2005 (10): 033. arXiv:hep-th/0502021. Bibcode:2005JHEP...10..033A. doi:10.1088/1126-6708/2005/10/033. S2CID 14320855.
- ^ Smolin, Lee (2006). The Trouble With Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next. Houghton Mifflin. ISBN 978-0-618-55105-7.
- ^ Duff, M. J. (2011). "String and M-Theory: Answering the Critics". Foundations of Physics. 43 (1): 182–200. arXiv:1112.0788. Bibcode:2013FoPh...43..182D. doi:10.1007/s10701-011-9618-4. S2CID 55066230.
- ^ Chui, Glennda (May 1, 2007). "The Great String Debate". Symmetry Magazine. Archived from the original on 2018-10-17. Retrieved 2018-10-17.
- ^ Potter, Franklin (15 February 2005). "Leptons And Quarks In A Discrete Spacetime" (PDF). Frank Potter's Science Gems. Archived (PDF) from the original on 2021-03-09. Retrieved 2009-12-01.
- ^ Bilson-Thompson, Sundance O.; Markopoulou, Fotini; Smolin, Lee (2007). "Quantum gravity and the standard model". Classical and Quantum Gravity. 24 (16): 3975–3994. arXiv:hep-th/0603022. Bibcode:2007CQGra..24.3975B. doi:10.1088/0264-9381/24/16/002. S2CID 37406474.
- ^ Castelvecchi, Davide; Valerie Jamieson (August 12, 2006). "You are made of space-time". New Scientist (2564). Archived from the original on February 9, 2008. Retrieved September 16, 2017.
- ^ Bilson-Thompson, Sundance; Hackett, Jonathan; Kauffman, Lou; Smolin, Lee (2008). "Particle Identifications from Symmetries of Braided Ribbon Network Invariants". arXiv:0804.0037 [hep-th].
- ^ Finster, F.; Kleiner, J. (2015). "Causal fermion systems as a candidate for a unified physical theory". Journal of Physics: Conference Series. 626 (2015): 012020. arXiv:1502.03587. Bibcode:2015JPhCS.626a2020F. doi:10.1088/1742-6596/626/1/012020. S2CID 33471826.
- ^ Cowen, Ron (16 November 2015). "The quantum source of space-time". Nature. 527 (7578): 290–293. Bibcode:2015Natur.527..290C. doi:10.1038/527290a. PMID 26581274. S2CID 4447880.
- ^ Jaki, S.L. (1966). The Relevance of Physics. Chicago Press. pp. 127–130.
- ^ Freeman Dyson, NYRB, May 13, 2004
- ^ Stephen Hawking, Gödel and the end of physics Archived 2020-05-29 at the Wayback Machine, July 20, 2002
- ^ Schmidhuber, Jürgen (1997). A Computer Scientist's View of Life, the Universe, and Everything. Lecture Notes in Computer Science. Vol. 1337. Springer. pp. 201–208. CiteSeerX 10.1.1.580.1970. doi:10.1007/BFb0052071. ISBN 978-3-540-63746-2. S2CID 21317070. Archived from the original on 2014-02-27. Retrieved 2008-03-26.
- ^ Schmidhuber, Jürgen (2002). "Hierarchies of generalized Kolmogorov complexities and nonenumerable universal measures computable in the limit". International Journal of Foundations of Computer Science. 13 (4): 587–612. arXiv:quant-ph/0011122. Bibcode:2000quant.ph.11122S. doi:10.1142/s0129054102001291.
- ^ Feferman, Solomon (17 November 2006). "The nature and significance of Gödel's incompleteness theorems" (PDF). Institute for Advanced Study. Archived (PDF) from the original on 2008-12-17. Retrieved 2009-01-12.
- ^ Robertson, Douglas S. (2007). "Goedel's Theorem, the Theory of Everything, and the Future of Science and Mathematics". Complexity. 5 (5): 22–27. Bibcode:2000Cmplx...5e..22R. doi:10.1002/1099-0526(200005/06)5:5<22::AID-CPLX4>3.0.CO;2-0.
- ^ Hawking, Stephen (20 July 2002). "Gödel and the end of physics". Archived from the original on 2011-05-21. Retrieved 2009-12-01.
- ^ results, search (17 December 2006). The New Cosmic Onion: Quarks and the Nature of the Universe. CRC Press. ISBN 978-1-58488-798-0.
- ^ Einstein, letter to Felix Klein, 1917. (On determinism and approximations.) Quoted in Pais (1982), Ch. 17.
- ^ Weinberg (1993), Ch 2.
- ^ Superstrings, P-branes and M-theory. p. 7.
- ^ Weinberg (1993) p. 5
Bibliography
- Pais, Abraham (1982) Subtle is the Lord: The Science and the Life of Albert Einstein (Oxford University Press, Oxford. Ch. 17, ISBN 0-19-853907-X
- Weinberg, Steven (1993) Dreams of a Final Theory: The Search for the Fundamental Laws of Nature, Hutchinson Radius, London, ISBN 0-09-177395-4
- Corey S. Powell Relativity versus quantum mechanics: the battle for the universe, The Guardian (2015) Relativity versus quantum mechanics: the battle for the universe
External links
- The Elegant Universe, Nova episode about the search for the theory of everything and string theory.
- Theory of Everything, freeview video by the Vega Science Trust, BBC and Open University.
- The Theory of Everything: Are we getting closer, or is a final theory of matter and the universe impossible? Debate between John Ellis (physicist), Frank Close and Nicholas Maxwell.
- Why The World Exists, a discussion between physicist Laura Mersini-Houghton, cosmologist George Francis Rayner Ellis and philosopher David Wallace about dark matter, parallel universes and explaining why these and the present Universe exist.
- Theories of Everything, BBC Radio 4 discussion with Brian Greene, John Barrow & Val Gibson (In Our Time, March 25, 2004).