Unification Theory
In particle physics, an attempt to explain all
of the fundamental forces and
their relationships between elementary
particles in single framework was
accomplished in theory by the g.u.t. by the
grand unification theory. In
relation to physics these forces can be
described as fields that mediate
interactions between separate or distant
objects. These theories such as
eltromagnetism and general relativity started
to attempt the unification of
theories, however they would emerge as the
fundamental basics of the g.u.t. Or
the grand unification theory. At sub
atomic levels, these fields are described
as quantum field theories, which
started the ideas of quantum mechanics. In the
1940’s the ideas quantum
electrodynamics (QED), the quantum field theory of
electromagnetism, became
fully developed. In QED, charged particles interact as
they emit and absorb
photons (minute packets of electromagnetic radiation), in
effect exchanging
the photons in a game of subatomic "catch." This
theory has become the
prototype for theories of the other forces. During the
1960s and '70s
particle physicists discovered that matter is composed of two
types of basic
building block--the fundamental particles known as quarks and
leptons. The
quarks are always bound together within larger observable
particles, such as
protons and neutrons. They are bound by the short-range
strong force, which
overwhelms electromagnetism at sub nuclear distances. The
leptons, which
include the electron, do not "feel" the strong force.
However, quarks and
leptons both experience a second nuclear force, the weak
force. This force,
which is responsible for certain types of radioactivity
classed together as
beta decay, is feeble in comparison with electromagnetism.
At the same
time that the picture of quarks and leptons began to crystallize,
major
advances led to the possibility of developing a unified theory.
Theorists
began to invoke the concept of local gauge invariance, which
postulates
symmetries of the basic field equations at each point in space and
time. Both
electromagnetism and general relativity already involved such
symmetries, but
the important step was the discovery that a gauge-invariant
quantum field theory
of the weak force had to include an additional
interaction--namely, the
electromagnetic interaction. Sheldon Glashow and
peers independently proposed a
unified "electro weak" theory these forces
based on the exchange of four
particles: the photon for electromagnetic
interactions, and two charged W
particles and a neutral Z particle for weak
interactions. During the 1970s a
similar quantum field theory for the strong
force, called quantum thermodynamics
(QCD), was developed. In QCD, quarks
interact through the exchange of particles
called gluons. The aim of
researchers now is to discover whether the strong
force can be unified with
the electro weak force in a grand unified theory
(GUT). There is evidence
that the strengths of the different forces vary with
energy in such a way
that they converge at high energies. However, the energies
involved are
extremely high, more than a million times as great as the energy
scale of
electro weak unification, which has already been verified by
many
experiments. Grand unified theories describe the interactions of quarks
and
leptons within the same theoretical structure. This gives rise to
the
possibility that quarks can decay to leptons and specifically that the
proton
can decay. Early attempts at a GUT predicted that the proton's
lifetime must be
in the region of 1032 years. This prediction has been tested
in experiments that
monitor large amounts of matter containing on the order
of 1032 protons, but
there is no evidence that protons decay. If they do in
fact decay, they must do
so with a lifetime greater than that predicted by
the simplest GUTs. There is
also evidence to suggest that the strengths of
the forces do not converge
exactly unless new effects come into play at
higher energies. One such effect
could be a new symmetry called supersymetry,
which is part of the g.u.t.