🚀 go-pugleaf

In article <25319@dog.ee.lbl.gov> sichase@csa3.lbl.gov (SCOTT I CHASE) writes:

> >Could you be more specific? If you mean the coupling constants coming
> >together, theoretically they should, and experimentally they do.
> 
> I don't agree on either point.  "Theoretically they should" is questionable.
> You certainly can construct unification schemes where two of the coupling 
> constants come together at one mass scale and the combined pair comes
> together with the third at another, can't you?  As far as I understand it,
> there is no strong reason to expect otherwise.

I agree with Scott.  First of all, we should always remember that the
only reason we think that the coupling constants should become equal
at a single point is a theoretical prejudice.  Specifically, we have a
theory (the SU(3)xSU(2)xU(1) model) which works quite well every time
that we have tested it experimentally; theorists, however, find it
ugly that there are three independent coupling constants, and prefer a
model based on a simple group, which only has a single coupling
constant.  I happen to share this prejudice, but at some point it's
wise to step back and remember that nature doesn't necessarily have to
work the way that theoretical physicists think is pretty.

Second, as Scott points out, even if all of the coupling constants do
become equal at some scale, this does not mean that they have to come
together at the same point; we could have two of them unify at one
point, and then meet the third (and, perhaps, a fourth, and...) at
some other point.  This, in fact, is the generic case; it is only the
very simplest of "grand unified theories" in which all of the
constants come together simultaneously.  

And, of course, it is very misleading to talk about "experimental"
evidence on the question of whether or not the coupling constants
become equal.  We can't do experiments at 10^15 GeV, so we have to
infer the physics at that scale from what we know at, say, 10^2 GeV,
and we have to make assumptions about what's going on at intermediate
scales.  Extrapolating over 13 orders of magnitude is a notoriously
dangerous business...
--
Matthew Austern              I dreamt I was being followed by a roving band 
(510) 644-2618               of young Republicans, all wearing the same suit,
matt@physics.berkeley.edu    taunting me and shouting, "Politically correct
austern@theorm.lbl.gov       multiculturist scum!"... They were going to make
austern@lbl.bitnet	     me kiss Jesse Helms's picture when I woke up.