Re: Basic Unification Question

frisbieinstein@xxxxxxxxx wrote:
> I know that the electromagnetic, strong, and weak forces have been
> unified. Is it true that all "forces" except gravity fall under this
> theory?

Let us not be hasty. The common wisdom is that the electromagnetic and
weak forces have been unified into the so-called electroweak theory.
This is usually said because when electroweak theory is written in a
standard form (the Yang-Mills form), the the individual components of
the electroweak force field do not correspond separately to the
electromagnetic and weak forces, these are mixed together. However, in
this sense, the strong force still stands apart.

There are attempts to construct grand unified theories (GUTs) that
unify the electroweak and strong forces. However, AFAIK, none of them
have been completely successful. For example. the SU(5) GUT works quite
well, except that it predicts the decay of the proton, which we do not
see. I think it also only accounts for a neutrino of a single chirality
(I don't remember whether it is a right- or left-handed one), which
also gets screwed up if the neutrino has mass, which is what we seem to
observe. There are many other GUT proposals, most of which I'm not
familiar with.

Hope this helps.

Igor

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