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Re: what would the subtle differences be???



JB: There would be subtle differences between the appearance of the
light from matter galaxies -- and antimatter galaxies. But no
astronomer has yet detected what he or she thinks is light from an
antimatter galaxy. Astronomers think it isn't likely that any distant
galaxies are made of antimatter -- because when antimatter and matter
interact, they turn into pure energy -- what we'd see as a colossal
explosion.
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Just what would those "subtile differences" be, does the list suppose????

None are known, but the possiblity exists that they exist. After all, no
one has ever knowingly seen light from antimatter atoms in the laboratory,
let alone done spectroscopy on them. The smart money is against finding
such differences in astronomical sources, however. It is expected that the
light emitted by antimatter galaxies would be indistinguishable from that
emitted by matter galaxies.

Another common error is made here which is much worse. Not only would an
antimatter-matter collision not result in an outburst of pure energy,
no such thing exists! Energy is an attribute of a physical system and,
as Feynman points out dramatically in his first volume of lectures, the
attribute itself does not have an independent existence!

If two macroscopic bodies which are charge conjugates* of one another
were to collide it is conceivable that the result could be a burst of
gamma rays. That result is not forbidden by conservation laws. Neither
is the ejection of a large number of particle-antiparticle pairs, say
many protons and as many antiprotons and similarly matched numbers of
electrons and positrons. The latter sort of result is, moreover, much
more probable in a realistic collision.

If two particles which are mutual charge conjugates collide the result
is usually a shower of photons and particle-antiparticle pairs. I was
privileged to see the first proton-antiproton "star" produced in a
nuclesar emulsion the day after it was found, in the office of my optics
professor, Gerson Goldhaber, back in 1955. The "points" were mostly
charged pi mesons, and pi mesons don't decay completely to photons. In
the first case (that of the macroscopic bodies) the bodies would
discorporate and disperse long before any large fraction of them had
participated in matter-antimatter annihilation.

Having trashed yet another piece of science fiction let's go back to
astronomy. Please forgive the digression. I'm distracted because I
became a grandfather yesterday!

Leigh

*That means that each is exactly like the other except for the
interchange of particles in one for antiparticles in the other.