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Q & A: Standard Model and strings

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Most recent answer: 10/22/2007
Q:
what is the "Standard Model" and the "string theory" i’ve been hearing very, very, very much about this year?
- Anonymous
A:
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

, and if that leaves you hungering for more information, you can read the real hard-core stuff at
.

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 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)

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