A theory of everything (TOE) is a theory of theoretical physics and mathematics that fully explains and links together all known physical phenomena (i.e. "everything"). Initially the term was used with an ironical connotation, to refer to various overgeneralized theories. For example, an uncle of Ijon Tichy— a character from a cycle of Stanislaw Lem's science fiction stories of early 1970s — was known to work on "General Theory of Everything" (Polish: "Ogólna Teoria Wszystkiego"). Over time, the term stuck in popularizations of quantum physics to describe a theory that would unify the theories of the four fundamental interactions of nature, possibly due to the influence of The Theory of Everything, a book with material written by Stephen Hawking but disowned by him.
There have been numerous theories of everything proposed by theoretical physicists over the last century, but as yet none has been able to stand up to experimental scrutiny or there is tremendous difficulty in getting the theories to produce even experimentally testable results. The primary problem in producing a theory of everything is that quantum mechanics and general relativity have radically different descriptions of the universe, and the obvious ways of combining the two lead quickly to the renormalization problem in which the theory does not give finite results for experimentally testable quantities.
Mainstream physics
Albert Einstein was the first serious scientist who spent most of his life trying to find a TOE; he believed that the only task was to unify general relativity and electromagnetism.
Current mainstream physics concepts require that a TOE unify the four fundamental interactions of nature: gravity, the strong nuclear force, the weak nuclear force, and the electromagnetic force; it should also explain the spectrum of elementary particles. There has been progress toward a TOE in unifying electromagnetism and the weak nuclear force in an electroweak unified field theory and in unifying all of the forces except for gravity (which in the present theory of general relativity is not a force) in the grand unified theory. One missing piece in a theory of everything involves combining quantum mechanics and general relativity into a theory of quantum gravity.
The only serious candidate for a theory of everything at the moment is superstring theory / M-theory; current research on loop quantum gravity may eventually play a fundamental role in a TOE, but that is not its primary aim. These theories attempt to deal with the renormalization problem by setting up some lower bound on the length scales possible. Also, early 21st century theories of everything tend to suppose that the universe actually has more dimensions than the easily observed three of space and one of time. The motivation behind this approach began with the Kaluza-Klein theory in which it was noted that adding one dimension to general relativity would produce the electromagnetic Maxwell's equations. This has led to efforts to work with theories with large number of dimensions in the hopes that this would produce equations which are similar to known laws of physics. The notion of extra dimensions also helps to resolve the hierarchy problem which is the question of why gravity is so much weaker than any other force. The common answer involves gravity leaking into the extra dimensions in ways that the other forces do not.
In the late 1990s, it was noted that one problem with several of the candidates for theories of everything was that they did not constrain the characteristics of the predicted universe. For example, many theories of quantum gravity can create universes with arbitrary numbers of dimensions or with arbitrary cosmological constants. One bit of speculation is that there may indeed be a huge number of universes, but that only a small number of them are habitable, and hence the fundamental constants of the universe are ultimately the result of the anthropic principle rather than a consequence of the theory of everything.
There is also a philosophical debate within the physics community as to whether or not a "theory of everything" should be seen as the fundamental law of the universe. One view is the hard reductionist view that the TOE is the fundamental law of the universe and that all other theories of the universe are a consequence of the TOE. Another view is that there are laws which Steven Weinberg calls free floating laws which govern the behavior of complex systems, and while these laws are related to the theory of everything, they cannot be seen as less fundamental than the TOE. Some argue that this explanation would violate Occam's Razor if a completely valid TOE were formulated.
Other possibilities which may frustrate the explanatory capacity of a TOE may include sensitivity to the boundary conditions of the universe, or the existence of mathematical chaos in its solutions, making its predictions precise, but useless.
Where the Standard Model comes up short
The Standard Model of physics is among the most successful theories in history, but it fails to explain everything. It doesn't explain the origins of the universe before the big bang. There are 18 arbitrary constants and several dozen elementary particles in the Standard Model. Why are there so many? The Standard Model also fails to explain over 90% of the apparent mass-energy of the universe. The existence of dark matter and dark energy, although never observed directly, is all but guaranteed if current theory is correct.
Why is so much of the universe invisible? What is the state of matter within a black hole? Is space-time curved, or is it flat? How many dimensions of space and time are there? What is the origin of matter and energy? What is the reason for them at all? Is there a most fundamental particle? What happens beyond Planck scales? Why is momentum quantized? Is the speed of light the fastest speed in the universe? These are among the many questions left unanswered by the most modern theories in physics. A successful Theory of Everything would explain each of these questions and provide solutions to every situation which could exist in the universe.
Speculative ideas
Attempts to create theories of everything are common among people outside the professional physics community. Some are created by amateurs, and their theories are often criticised on the basis of inability to make quantifiable and/or falsifiable predictions (for instance, Expansion theory). For example, a theory of everything would provide some insight into the relative strength of forces, and predictions of particle lifetimes and cross sections. It would need to be shown to explain all known universal phenomena. Unlike professional physicists, who are generally aware that their proposed theory is incomplete, untested, and likely to be wrong and who are aware of the huge difficulties and challenges involved in creating a TOE, amateurs who create TOE's tend to be unaware of what work has already been done, the mechanisms for testing scientific theories and the fact that most proposed theories are wrong.
Evans Unified Theory
Dr. Mayron Evans has published the Evans Unified Theory which with mathematical rigour relates all forces in the known Universe ( see www.aias.us ). Electromagnetism is described as spinning spacetime while gravity is described as curved spacetime. A rigorous relationship between electromagnetism and gravity is presented allowing OU machines (over unity) and anti-gravity devices.
Time Cube
Gene Ray's Time Cube concept is an example of an amateur TOE that is quite well-known, although some argue that this is primarily due to its entertainment value rather than its scientific merit. Mr. Ray claims to explain all known universal phenomena through the postulate that "Time is cubic, not linear". See list of alternative, speculative and disputed theories. Like many similar theories, it is regarded by some as pseudoscience. Academians tend to oppose Mr. Ray's ideas and consider them lunacy, but some acknowledge that there may be a kernel of truth in the mathematical idea of cubic, or three dimensional, time. More research into the nature of time's passage will be necessary to rule out the possibility.
Burkhard Heim and quantised general relativity
Burkhard Heim's theory of quantised general relativity purports to be a TOE but this theory, begun in the 1950s and still under development, had until recently sunk into obscurity. A sign that it is undergoing a renewal of interest is that a paper by Droescher and Haeuser on aerospace applications of Heim Theory was published by the AIAA in 2005 and will be awarded the prize for best paper of the year by the Nuclear and Future Flight Propulsion Technical Committee. Supporters claim that Heim's six dimensional theory can predict the masses of some fundamental particles with considerable accuracy, which no established theory has yet been able to do.
Eino Kaila
The prolific Finnish philosopher Eino Kaila attempted to construct a theory of everything based on the philosophical implications of quantum mechanics in the 1950s. His attempt did not get much attention outside Finland, and he only managed to write the first part of what he planned on making an extensive study on the subject. "TERMINALKAUSALITÄT ALS DIE GRUNDLAGE EINES UNITARISCHEN NATURBEGRIFFS" ("terminal causality as the foundation of a unitarian notion of nature"), published in 1956, formulated a new type of causality and was meant to be followed by similar works on psychology and biology.
TOE and Religion
Some people believe that the finding of the TOE could disprove the existence of a God. Many theistic people hold the nihilist belief that we will never find the TOE. Other theists believe that a Theory of Everything would ultimately prove the power of God's intellect to design such an elegant universe.
External links
- The Elegant Universe-Nova online- a 3 hour PBS show about the search for the Theory of everything and string theory.