Message 1285 from kiarash niknejad, 05 March 2004 15:51:
In response to message 1284: Re: www.physicsforum.co.uk from kiarash , 05 March 2004:
Theory of everything (TOE) in Physics is a theory that unifies the
four fundamental forces of nature: gravity, the strong nuclear force,
the weak nuclear force, and the electromagnetic force, and is the goal
of researchers in quantum gravity. A TOE is sometimes called a
supergrand unified theory.
A theory of everything is needed to explain phenomena such as the big
bang or gravitational singularities in which the current theories of
general relativity (GR) and quantum mechanics (QM) break down.
Theoretical motivations for finding a theory of everything include the
Platonic belief that the ultimate nature of the universe is simple and
therefore the current models of the universe such as the standard
model cannot be complete because they are too complicated. 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 radicially 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.
Popular candidates for a theory of everything at the moment include
loop quantum gravity, string theory, and M-theory. Most of 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.
In the late 1990's, it was noted that one problem with several of the
candidates for theories of everything was that they did not predict
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 many 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
been seen as less fundamental than the TOE.
Theories of everything must be distinguished from Grand Unified
Theories (GUTs), which attempt to unite all the fundamental forces
except gravity. A unified field theory that unites the electromagnetic
and weak nuclear forces into a single electroweak force has already
been established; GUTs attempt to unify the strong nuclear and
electroweak forces.