Re: Anti-matter questions (fwd)

["Paul Camp" <pjcamp@coastal.edu>]

> > Also is there still postulated an "anti-universe" someplace since there
> > is always antimatter produced when energy is converted to matter? If not,
> > where did the anti-matter go?
>
> There is no reason to believe in the existence of an anti-universe.
> There may be large isolates of antimatter in our observable universe.
> Many physicists feel there are not, but there might be no observable
> consequences if they do exist. 

There are some observable consequences. If both matter and antimatter 
galaxies existed in the same cluster, there should be strong gamma 
emissions which are not observed. So if there is a significant amount 
of antimatter in the universe, it must be segregated from the matter 
on scales at least as large as 10^12 solar masses which would be 
difficult to account for cosmologically. 

> Whenever a physical reaction occurs it
> must do so in a manner that conserves baryons and leptons. 

That could not always have been the case else the universe would not 
have a baryon-antibaryon asymmetry. Of course, as far as known, 
experimentally confirmed physical law goes, this is correct. However, 
Sakharov pointed out (in 1967, a decade *before* grand unification 
attempts) that in order for the universe to have evolved a baryon 
asymmetry, several conditions would have to be satisfied:

1. Baryon number violation. If all interactions involve baryon 
conservation then the present observed asymmetry can only reflect 
asymmetric initial conditions. Note that most GUTS predict this 
effect.

2. C and CP violation. In the absence of this condition, Baryon 
nonconservation reactions will produce baryon and antibaryon excesses 
at the same rate. This condition is necessary to give the reactions 
an "arrow" in one direction.

3. Nonequilibrium conditions. In equilibrium, all the chemical 
potentials associated with nonconserved quantum numbers vanish. 
Masses of particles and antiparticles are guaranteed to be equal due 
to CPT invariance. This implies that the number of baryons equals the 
number of antibaryons. (Kolb and Turner's The Early Universe has the 
details of all this.)

Having pointed out that *something* must be asymmetric to give us the 
universe we see, one must also hasten to add that nobody really knows 
what it was. As far as known physical law is concerned, Leigh is 
right on target. Everything else is speculation. However, I can't 
miss a chance to refer to Sakharov's paper since I think it is one of 
the most remarkable examples of prescience I've ever seen.


 
Paul J. Camp                   "The Beauty of the Universe
Assistant Professor of Physics  consists not only of unity
Coastal Carolina University     in variety but also of 
Conway, SC   29528              variety in unity.
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