From: Robert J. Bradbury (bradbury@www.aeiveos.com)
Date: Wed Aug 18 1999 - 16:55:18 MDT
> Clint O'Dell <clintodell@hotmail.com> wrote:
Re: anti/normal-matter galaxy collissions
> It would be quite scary! I assume that the side with the most matter of its
> type would win.
Yes, for those cases where the matter encounters its anti-matter.
However, galaxies are mostly empty space. I think the average
density is something like 1 atom per cubic meter (someone correct
me if they know better). That is why a ramjet collector for
interstellar travel needs to be huge. When galaxies, of normal
matter, collide now, most of the material (stars, molecular clouds)
passes through untouched. The gravitational distortions do change
orbits though, sometimes creating collisions. (Think about Jupiter
distorting comet/asteroid orbits throwing them at the Earth; its
similar with the gravity of the entire galaxy and the stars orbiting
in them).
> Is there a way that our side can gain an advantage so that
> were not annihilated?!
Well, since the general view is that anti-matter galaxies don't
exist, we may not have to worry about it. If that turns out to
be true, then we need a really big computer (like a Matrioshka
Brain) to compute all the gravitational trajectories and recomend
one that lets us (and our star) avoid colliding with something.
> Since annihilation produces pure energy would that hold the
> two universes apart in a rhythmic pattern for a while?
If enough annihilation were occuring, you would get a fair
amount of photon pressure that would provide outward momentum
to particles that intercepted it. This would clear out
the gas clouds fairly easily but probably wouldn't have much
effect on the stars or black holes.
> I'm picturing power much greater than a supernova.
Yes, these would be quasars & blazars, but current theories
can account for these objects without having to resort to
anti/normal-matter galactic collisions.
> How can an anti-matter galaxy and a posi-matter(?) galaxy co-exist?
By not getting in each others way. :-)
> Is this because there is nothing between the galaxies? All empty space?
There is belief that there may be atomic or molecular hydrogen in
the space between galaxies, but the density is very low. All you
need is for relatively energetic events in a galaxy (supernovas,
star collisions, black holes eating matter, etc.) to give atoms or
small molecules enough energy to be traveling faster than the
galactic escape velocity and you can kiss them goodbye.
> Not to be million questions or anything but if disaster is possible its
> probably worth while to prepare for it now.
Well, I think we should balance our perspectives with regard to
disasters... I would make up the "worry list" as follows:
Motor vehicles, falls, poisonings, fires, drowning, suffocation, and
of course firearms.
Once you have finished not driving, climbing, eating, drinking,
swimming, bathing, breathing and playing with guns, you should
be concerned with:
- the weather (floods, hurricanes, typhoons, blizzards, snow, hail,
lightening);
- airplanes (if you aren't in them when they crash, you can always
be under them);
- trains (in 'em or in front of 'em);
- contagious diseases (tuberculosis, malaria, cholera, etc);
- the Earth (earthquakes, volcanoes, rockslides, mudslides,
glaciers, etc.);
After you get finished with all of those, we can discuss the
extraterrestrial hazards (or events we should be concerned about),
in approximate order of significance, I would say are:
- a meteor(asteroid) strike
- a comet strike
- a nearby (< 10 LY?) supernova
- being consumed by a superintelligence or getting in the
way of a superintelligence construction project
- the sun becoming a red giant star and boiling all water off Earth
- the formation of a nearby blackhole
- a nearby stellar collision
- the low mass stars die out
- planets become detached from stars (which are dead)
- stars become detached from galaxies (which are dead except for the
blackholes)
- gravitational radiation causes all orbits to decay (which doesn't
matter much since everything is dead anyway).
- the evaporation of all of the black holes from Hawking radiation
- all solid matter becomes effectively liquid
- all matter decays into iron
- all matter (presumably liquid iron) collapses into black holes
(which has the interesting effect of "resetting" the black hole
evaporation clock).
Just guessing, I would put
- a collision between matter/anti-matter galaxies
someplace in the middle of the ET hazard list.
Robert
P.S. [For those who want to quibble on the details, ~50% of the
prioritization are from Dyson's 1979 "Time Without End" paper.
So read that before you put me up against the wall to shoot me.]
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