Free Dark Lightning (Thunder and Lightning) by John Varley Page B

admitted to us, during our first visit to the bridge, that he knew it was silly, but there was just something that fundamentally bugged him about an eight-mile-long ship hurtling through space near the speed of light with no one at the stick.
    So there has been someone “at the stick” continually for all my life. Shifts are six hours, or until one is formally relieved.
    The ceiling of the bridge is a clear dome, inscribed with lines of declination and right ascension so that it doesn’t seem invisible, so that you don’t get the sense of sitting on the naked rock of
Rolling Thunder
’s bow.
    Well . . . actually not.
    It’s a superdef screen. Far from being in the actual bow, there was still a quarter of a mile of solid rock over our heads.
    You hear about “empty interstellar space,” but it’s not really empty. Compared to inter
planetary
space, it’s pretty thin, but compared to inter
galactic
space, it’s thick as pea soup. The density varies, but the average is one molecule per cubic centimeter. That’s one million molecules per cubic meter, nine hundred thousand of them hydrogen, and ninety thousand of them helium. Even considering the considerable surface area of the ship, that’s not enough to slow us down. If we turned off the engines right now, the ship would continue going at the same velocity forever, for all practical purposes.
    However, at .77c—143,000 miles per second and change—that stuff would impact with a hell of a lot of power. I don’t understand it all, but I think that it would hit with the power of gamma rays.
    The other 1 percent in that cubic meter is dust. Not the sort that forms dust bunnies under your bed, but particles of just about anything, chiefly silicates, carbon, water, and iron. I think of it as wet rocks. Some of the gas and dust can be very hot. I don’t understand how that can be, since the median “temperature of interstellar space” is three degrees above absolute zero. Papa says don’t worry about it, it’s just a confusion of terminology. As in all things physical, I take his word for it.
    Some of that dust isn’t much bigger than the gas molecules, but some of it is
enormous
, relatively speaking. Up to a tenth of a micrometer. That’s one ten-millionth of a meter, which is pretty damn tiny, looked at one way, but when it’s arriving at three-quarters of the speed of light, even if there are only a few of the “big” ones in every cubic meter, we are moving through . . . well, I don’t know the number, but it’s an incredible volume of space every second. It can all add up.
    However, all that is mooted by the presence of the Shield.
    Captain Broussard is a belt-and-suspenders guy. The thickness of the rock at the bow would be more than enough to protect us from radiation and any damage from incoming dust. It would probably take a billion years for that dust to ablate a few inches. But out in front of us, traveling at the same speed we are, is a silver squeezer bubble, something like half a million miles across. It is held permanently at the same distance from us by one of Papa’s mysterious fields. It is absolutely invulnerable to anything anyone has yet discovered. Molecules and dust grains bounce off it, leaving a wide tube of space in its wake that is, as far as we know, the most perfect vacuum that exists anywhere in the universe. That tube will eventually close up, but
Rolling Thunder
will have passed through it long before that.
    So in reality,
nothing
is impacting the bow of the ship.
    I once asked my uncle why we needed to have all that rock between the Bridge and the surface.
    “What if the Shield fails?” he said.
    In the century we have been using them, no bubble has ever failed. But that’s my uncle Travis. A cautious man.
    —
    I recognized the watch-stander, in her uniform. She had graduated from the Bayouville School two years ahead of me and been the captain of the Gators skypool team when Polly and I joined. She was reading