Theory of everything: Difference between revisions
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* [[Argument from beauty]] |
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* [[Attractor]] |
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Revision as of 11:34, 6 March 2020
This article needs additional citations for verification. (January 2017) |
Beyond the Standard Model |
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Standard Model |
A theory of everything (TOE
Physicists have experimentally confirmed virtually every prediction made by GR and QFT when in their appropriate domains of applicability. Nevertheless, GR and QFT are mutually incompatible – they cannot both be right. Since the usual domains of applicability of GR and QFT are so different, most situations require that only one of the two theories be used.[4][5]: 842–844 As it turns out, this incompatibility between GR and QFT is only an issue 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 GR and QFT into a seamless whole: the TOE is a single theory that, in principle, is capable of describing all phenomena in the universe.
In pursuit of this goal,
Name
Initially, the term theory of everything was used with an ironic reference to various overgeneralized theories. For example, a grandfather of
Historical antecedents
Antiquity to 19th century
Ancient
The
Following earlier atomistic thought, the
In the late 17th century,
In 1814, building on these results,
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
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 1849–50, Michael Faraday was the first to search for a unification of gravity with electricity and magnetism.[17] 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.[18]
Early 20th century
In the late 1920s, the 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".[19]
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 thirty-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 these last few decades of his life, this quixotic quest isolated Einstein from the mainstream of physics. Understandably, the mainstream was instead far more excited about the newly 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,[20] Theodor Kaluza, Oskar Klein (see Kaluza–Klein theory), and most notably, Albert Einstein and his collaborators. Einstein intensely searched for, but ultimately failed to find, a unifying theory.[21]: ch 17 (But see:Einstein–Maxwell–Dirac equations.) More than a half a century later, Einstein's dream of discovering a unified theory has become the Holy Grail of modern physics.
Late 20th century and the nuclear interactions
In the twentieth century, the search for a unifying theory was interrupted by the discovery of the
Gravity and electromagnetism could always peacefully coexist as entries in a list of classical forces, but for many years it seemed that gravity could not even be incorporated into the quantum framework, let alone unified with the other fundamental forces. For this reason, work on unification, for much of the twentieth century, focused on understanding the three "quantum" forces: electromagnetism and the weak and strong forces. The first two were combined in 1967–68 by Sheldon Glashow, Steven Weinberg, and Abdus Salam into the "electroweak" force.[22] Electroweak unification is a
While the strong and electroweak forces peacefully coexist in the Standard Model of particle physics, they remain distinct. So far, the quest for a theory of everything is thus unsuccessful on two points: neither a unification of the strong and electroweak forces – which Laplace would have called 'contact forces' – nor a unification of these forces with gravitation has been achieved.
Modern physics
Conventional sequence of theories
A Theory of Everything would unify all the
Theory of everything | |||||||||||||||||||||||||||||||||||||||||||
Quantum gravity | |||||||||||||||||||||||||||||||||||||||||||
Space Curvature | Electronuclear force (GUT) | ||||||||||||||||||||||||||||||||||||||||||
Standard model of particle physics | |||||||||||||||||||||||||||||||||||||||||||
Strong interaction SU(3) | Electroweak interaction SU(2) x U(1)Y | ||||||||||||||||||||||||||||||||||||||||||
Weak interaction SU(2) | Electromagnetism U(1)EM | ||||||||||||||||||||||||||||||||||||||||||
Electricity | Magnetism | ||||||||||||||||||||||||||||||||||||||||||
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
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 possible Earth-based particle accelerator. Although the simplest GUTs have been experimentally ruled out, the general idea, especially when linked with supersymmetry, remains a favorite candidate in the theoretical physics community. Supersymmetric GUTs 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 GUT physics (although it does not seem to form an inevitable part of the theory). Yet GUTs 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.[4]
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.
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 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
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 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 11-dimensional supergravity, is the theory of everything. However, there is no widespread consensus on this issue.
A surprising property 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
In the late 1990s, it was noted that one major hurdle in this endeavor is that the number of possible four-dimensional universes is incredibly large. The small, "curled up" extra dimensions can be
One proposed solution is that many or all of these possibilities are realised 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
Loop quantum gravity
Current research on loop quantum gravity may eventually play a fundamental role in a TOE, but that is not its primary aim.[36] Also loop quantum gravity 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.[37] 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. Utilization of quantum computing concepts made it possible to demonstrate that the particles are able to survive quantum fluctuations.[38]
This model leads to an interpretation of electric and colour 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, colour, 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.[39]
Other attempts
Among other attempts to develop a theory of everything is the theory of
Another theory is called
Outside the previously mentioned attempts there is Garrett Lisi's E8 proposal. This theory attempts to construct 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.[41]
Causal dynamical triangulation does not assume any pre-existing arena (dimensional space), but rather attempts to show how the spacetime fabric itself evolves.
Christoph Schiller's Strand Model attempts to account for the
Another attempt may be related to
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
Arguments against
In parallel to the intense search for a TOE, various scholars have seriously debated the possibility of its discovery.
Gödel's incompleteness theorem
A number of scholars claim that
Stanley Jaki, in his 1966 book The Relevance of Physics, pointed out that, because any "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.[45]
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."[46]
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."[47]
Related critique was offered by
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 TOE cannot exist. 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.[52] 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". Einstein himself expressed this view on occasions.[53] 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.
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
Lack 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.
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
Impossibility of being "of everything"
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 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 hadrons), 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,[
The theories generally do not account for the apparent phenomenon of consciousness or free will, which are instead often the subject of philosophy and religion.
Infinite number of onion layers
Frank Close regularly argues that the layers of nature may be like the layers of an onion, and that the number of layers might be infinite.[56] This would imply an infinite sequence of physical theories.
Impossibility of calculation
Weinberg[57] 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
- Absolute (philosophy)
- A New Kind of Science
- Argument from beauty
- Attractor
- Beyond black holes
- Beyond the standard model
- Big Bang
- Bit-string physics
- cGh physics
- Chronology of the universe
- Electroweak interaction
- ER=EPR
- Holographic principle
- Mathematical beauty
- Mathematical universe hypothesis
- Multiverse
- Penrose interpretation
- Scale relativity
- Standard Model (mathematical formulation)
- Superfluid vacuum theory (SVT)
- The Theory of Everything (2014 film)
- Timeline of the Big Bang
- Unified Field Theory
- Zero-energy universe
References
Footnotes
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- ^ Fritzsch, Harald (1977). "THE WORLD OF FLAVOUR AND COLOUR". CERN Report. Ref.TH.2359-CERN. (download at http://cds.cern.ch/record/875256/files/CM-P00061728.pdf )
- ^
Ellis, John (2002). "Physics gets physical (correspondence)". PMID 11875539.
- ^
Ellis, John (1986). "The Superstring: Theory of Everything, or of Nothing?". Nature. 323 (6089): 595–598. doi:10.1038/323595a0.
- ^ ISBN 9781469987361.
- ^ ISBN 978-0-393-08002-5.
- ISBN 978-0-226-57697-8.
- ISBN 978-0-87436-875-8.
- ^
Shapin, Steven (1996). The Scientific Revolution. ISBN 978-0-226-75021-7.
- ^ Newton, Sir Isaac (1729). The Mathematical Principles of Natural Philosophy. Vol. II. p. 255.
- 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. .
- .
- ^ Dirac, P.A.M. (1929). "Quantum mechanics of many-electron systems". .
- ISBN 978-0-8176-4454-3.
- ISBN 978-0-19-152402-8.
- ^ Weinberg (1993), Ch. 5
- PMID 16196251. Retrieved August 13, 2012.
- .
- .
- arXiv:0802.2969v3 [hep-th].
- .
- .
- arXiv:gr-qc/9604051.
- .
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- ISBN 978-0-618-55105-7.
- .
- ^ Chui, Glennda (May 1, 2007). "The Great String Debate". Symmetry Magazine. Retrieved 2018-10-17.
- ^ Potter, Franklin (15 February 2005). "Leptons And Quarks In A Discrete Spacetime" (PDF). Frank Potter's Science Gems. Retrieved 2009-12-01.
- .
- ^ Castelvecchi, Davide; Valerie Jamieson (August 12, 2006). "You are made of space-time". New Scientist (2564).
- ].
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- ].
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- ^ Staff (2016). "This New Equation Could Unite The Two Biggest Theories in Physics". futurism.com. Retrieved May 19, 2017.
- PMID 26581274.
- ^ 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, July 20, 2002
- ^
Schmidhuber, Jürgen (1997). A Computer Scientist's View of Life, the Universe, and Everything. Lecture Notes in Computer Science. Lecture Notes in Computer Science. Vol. 1337. ISBN 978-3-540-63746-2.
- ^ 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. .
- ^ Feferman, Solomon (17 November 2006). "The nature and significance of Gödel's incompleteness theorems" (PDF). Institute for Advanced Study. Retrieved 2009-01-12.
- ^ Robertson, Douglas S. (2007). "Goedel's Theorem, the Theory of Everything, and the Future of Science and Mathematics". .
- ^ Hawking, Stephen (20 July 2002). "Gödel and the end of physics". Retrieved 2009-12-01.
- ^ 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.
- ISBN 978-1584887980.
- ^ Weinberg (1993) p. 5
Bibliography
- ISBN 0-19-853907-X
- ISBN 0-09-177395-4
External links
- The Elegant Universe, Novaepisode 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 George Francis Rayner Ellisand 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, Mar. 25, 2004)