The Standard Model is a theory which describes all of the phenomena we
have observed so far in high-energy collisions of particles at
accelerator laboratories. Starting in the 1940's, an "zoo" of
ever-increasing size of seemingly elementary particles was being
uncovered. In the 1960's, the rules of structure describing how these
particles arrange themselves according to their constituents and their
interactions became more clear. For example, we now know that a proton
is made up of three quarks -- two up-quarks and one down-quark, while
the neutron is made up of two down-quarks and one up-quark. Both are
held together by the exchange of gluons. Other particles are made up of
combinations of quarks and antiquarks, such as a charged pion, which is
made up of an up quark and an anti-down quark.
The model was solidified in the 1970's with the description of the
strong nuclear force placed on a firm theoretical basis (Gross,
Politzer, and Wilczek received the Nobel prize in 2004 for their work
on this part of the Standard Model); this is where the gluons come from
which hold the quarks together.
Further predictions were made in the 1960's and 1970's which
described how the weak force works, and how it really comes from the
same interaction as the electromagnetic force we all know and love. In
addition to photons, there are W and Z bosons, which were discovered in
1983 at CERN, and studied extinsively since.
You can find out more about the Standard Model at the
Particle Data Group's Educational Outreach Web Site, and if that leaves you hungering for more information, you can read the real hard-core stuff at
their main site for particle physicists.
I'm not a string theory expert -- a recent poplularization of
string theory, by one of its leading practitioners, was presented by
PBS's fine series, NOVA. Here's a
link
to the web site for their show, "The Elegant Universe". String theory
started out as an attempt to describe the strong interactions, but
ended up as a rather elegant way to unify the force of gravity into a
model which also includes the strong, and electroweak forces.
Tom
(published on 10/22/2007)
