Friday began with a lecture by Mike Brotherton about galaxies. He began with a little history, about William Herschel's attempt to determine the Sun's position within the Milky Way galaxy by counting the stars in different portions of the sky. This gave a decent rough approximation of the shape, but vastly underestimated the size and put the Sun right in the middle. The discovery of Cepheid variables — stars which brighten and dim on a regular pattern which is proportional to their luminosity — gave astronomers a yardstick to measure the Milky Way and find our proper position halfway between the core and the edge.
   
He went on to describe types of galaxies and their structure. One result which startled astronomers was their measurement of star velocities within the Milky Way. Stars don't orbit according to Kepler's laws, which means the bulk of the galaxy's mass is not concentrated in the center. But the stars obviously are most numerous there. From this the conclusion arises that the bulk of the galaxy's mass is not in stars. Nor is it in clouds of dust and gas, because astronomers can make a good estimate of that. So where is it?

That's the origin of what's known as "dark matter." Apparently most of the mass of the Universe is not the matter we see every day. It's shadowy, invisible stuff which doesn't interact with other matter. Dark matter carries no electrical charge or nuclear force, which means it can't form atoms or solid bodies. It's just ghostlike particles, slipping unaffected through the empty space within atoms. But dark matter does have mass.

Having briefed us on normal boring old galaxies, Dr. Brotherton moved on to his personal specialty: active galaxies. Colliding galaxies, cannibal galaxies, galaxies that shoot out giant beams of radiation. It seems likely that there are entire galaxies — and remember, these are swirls of billions of stars — in which the radiation flux from the active core is too high for any life to evolve. Think about that: uncounted billions of planets, some no doubt exactly like Earth in size and temperature, but forever doomed to sterility.

After a lunch break we had The Talk from Dr. Stratmann: sex and reproduction in space. This is a subject which is almost entirely theoretical. Despite the fact that mixed crews have been making long-duration space flights since the 1970s, nobody's talking. What little data we do have comes from rats and fish.

As doctors tend to do, Dr. Stratmann focused on the dangers and difficulties of orbital sex. Like sex in cars or while skydiving, it's difficult, awkward, and hazardous — and that probably won't stand in anybody's way. (One married pair of astronauts flew on a Shuttle mission, and I can't help but think their fellow crew members must have been absolutely relentless. "Are you two going to do it? You're sure you're not going to do it? We'll clear out the flight deck if you want to do it. When are you going to do it?" They may have gone ahead just to get some peace.)

Reproduction is a bit more fraught, what with the dangers of microgravity and radiation already mentioned in his previous lecture. If humans ever want to establish a genuinely permanent presence in space, self-sustaining and not dependent on Earth, it will have to include some kind of artificial gravity and radiation protection as good as high-altitude places on Earth. (Or the inhabitants will have to be so modified that we may not see them as human.)

After that we heard from Stanley Schmidt on how to make imaginary science seem rigorous and plausible. He used his novels Sins of the Fathers and Lifeboat Earth as worked examples. Both depended on a wave of the magic wand, in the form of a faster-than-light interstellar drive. But other than that he tried to be as realistic as possible in describing the Herculean task of propelling the Earth out of the galaxy to escape an apocalyptic catastrophe.

He made an important point: science in a work of fiction doesn't have to be real as long as it's realistic. His characters build devices capable of moving the Earth, but they still have to cope with the side effects — oceans shifting, the landscape becoming an icy wasteland as the Sun gets left behind, the problems of feeding humanity and keeping order on the long journey.

This is one of the things that draws me to science fiction. I love the sensation of reading a book (or seeing a movie) and thinking "Yes, that's what it would be like." It's a rare feeling, but when it happens it's like biting into a perfectly ripe peach after a day working in the summer heat.

The day wrapped up with a guest lecture by Dr. Ruben Gamboa of the University of Wyoming's computer science department. Although his ostensible title was "Computing in Astronomy" he quickly tossed that subject aside. Of course we use computers in astronomy. We use computers for everything. Topic exhausted.

His real subject was on what computer science actually studies, including the question of computability. Which problems can be solved by computers, and if there are any which cannot, can humans solve them? Alan Turing devised a theoretical computer to test the concept of computability, known of course as the "Turing Machine." Are humans Turing Machines? Either answer is important. If we aren't — if we don't operate according to algorithms which can be modeled (however complicated and unconscious those algorithms may be) — then that means there's really something about human minds which computers will never copy. That's certainly a big deal.

And if the reverse is true, it's an equally big deal. We may someday be able to create minds that equal or exceed human intellects.

As Walt Kelly said in another context, "Either way, it's a mighty sobering thought."

That night Mike Brotherton hosted a party for the workshop and some University colleagues. Food and drink were consumed, small talk was made, and I won't go into detail.