Re: Lord D'Arcy and steam elevators

on 22/04/2006 11:29 pm, Zeborah at zeborah@xxxxxxxxx wrote:

Jonathan L Cunningham <spam@xxxxxxxxxxxxxxxxxxxx> wrote:

Nowadays, we have a similar puzzle: why there is any matter at all,
and why matter and anti-matter didn't cancel themselves out exactly.
<snip>
But reading popular science type books with a more questioning
approach lends itself to all sorts of half-baked ideas for SF short
stories ...

My half-baked idea, written up in a brilliant sf short story in high
school(1), was that matter and anti-matter weren't created evenly
through the universe, so that as the universe expanded, while much
matter and anti-matter did cancel themselves out, some also formed into
like pockets. So we ended up with a matter galaxy (ours) and an
anti-matter galaxy (the one my starship arrived in, where it made
contact with a local planet, chatted happily for a while via EM signals,
and then attempted to land their starship. Bang. Oops.)

Barring the idiocy of a spaceship reaching a distant galaxy but not
figuring out that everything around it is antimatter, is there any
reason why this couldn't happen to be true?

Is there evidence against it? Yes. The universe is old and lots of particles
have had time to travel between galaxies (e.g. photons, which is how we can
see those other galaxies...). Particles of antimatter coming from antimatter
galaxies would be expected to annihilate with particles of matter when they
arrived in matter galaxies, and vice versa, and we don't see this. In
particular, we're missing the very characteristic signature of
electron-positron annihilation, that is, gamma rays with an energy of 0.511
MeV. I believe this is what ruled out this theory as a serious scientific
hypothesis, way back when people thought it might be.

In fact, whole galaxies collide fairly frequently, so you'd expect to see
some spectacular annihilations going on, and you never do.

A few people are still apparently looking for evidence of antimatter
galaxies, but nobody's found anything.

Also, in the past, shortly after the big bang, everything was closer
together and moving faster, so there was much more mixing and it would have
been difficult to keep neighbouring regions so thoroughly distinct. (I don't
think this is a knock-down objection, though. You'd have to ask a real
cosmologist.)

Also, apart from statistical variations, which aren't big enough, there's no
particular reason why different parts of the universe _should_ start out
different. Why would they? Occam's Razor (or maybe the principle of
sufficient reaason) should make us suspicious of this idea, although
obviously if there were actual evidence in its favour, that would trump
Occam's Razor.

Tim

.

Relevant Pages

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