Donald Moffitt - Genesis 01

hydrogen, depend on it,” Jao said, crowding in behind Smeth with a drink cradled in one fist. “Hi, Mim.”
    Trist followed, raising his eyes heavenward for Bram’s benefit.
    Smeth scowled. “That’s what the probe project is all about. The Nar want to build a probe that can reach the galactic center in a reasonable length of time. On the order of fifty thousand years. And it’s beginning to look more and more possible. And yes, we think we can do it by scooping up hydrogen atoms in space and squeezing the plasma to induce fusion.”
    “Don’t fail to tell him about exhaust velocities,” Jao prompted, winking at Bram.
    “Go ahead, have your fun,” Smeth said.
    Trist sighed. “The original idea,” he said, “was to collect interstellar hydrogen and use it both for reaction mass and for an energy source. But matter is matter, even when you strip it down, and even though you can expel it at velocities brushing the speed of light, all our studies indicated that there was a practical limiting factor of about ninety-eight percent.” He turned to Jao. “That about right?”
    “Yah. Ninety-eight percent. For plasma and all that junk.”
    “The ultimate exhaust velocity, by definition, would be provided by a pure photon drive. But that would require the total conversion of matter into energy, and we don’t know how to do that. So photon drives of the various sorts we’d been kicking around—mostly they boiled down to turning a fraction of the energy of matter into laser light—are inefficient.”
    “Yah, weak,” Jao said.
    “Now we come to the hadronic photon. Under certain circumstances, it’s possible to increase the energy of a photon by a factor of from one to ten billion. And when you do, it takes on the properties of a hadron. It acts as though it has mass, like a proton, for instance. It has energy and momentum that are conserved.”
    “First you have to pump all that energy into it,” Bram pointed out. “Ten billion times, did you say?”
    “Hey, not bad for a biologist,” Jao said. “Yah, all that has to come out of the ramjet fusion reaction in the first place.”
    “The point is,” Trist said, “that we don’t have to annihilate matter to get our beam of superphotons. It’s done strictly through electromagnetic interactions that we know how to handle. In theory, at least.”
    “What you do is you swat pulsed laser photons with a high-energy electron beam and scatter them a hundred eighty degrees,” Jao said. “They pick up the energy of the swat.”
    Trist nodded. “Then you focus the back-scattered photons—hadronic photons now—in the electromagnetic throat of the drive, and since they have a temporary nonzero mass, your vehicle not only gets a healthy kick, but gets it at the speed of light.”
    “Don’t forget to mention the four-wave conjugate mirrors,” Jao said, pulling at his sleeve.
    “Oh, those. Yes. That’s how we collect all those muscular photons that’re scattering in all directions and herd them into a tight beam.”
    “It all sounds wonderful,” Bram said. “I think.”
    “Of course, these aren’t real photons we’re talking about,” Trist said.
    “What?”
    “They’re virtual photons. They exist by courtesy of the uncertainty principle.”
    “Now you’ve lost me,” Bram said. “Mim, do you have any idea what he’s talking about?”
    “Not a clue,” she said, looking amused.
    “All physicists are crazy,” Jao said. “It’s a well-known fact.”
    Smeth gave a snort. “You two are crazy. I’ll grant that much.”
    “Jao’s right,” Trist said. “We’re all crazy, Smeth included. We believe in things that don’t exist. The hadronic photon has no right to be. It’s supposed to hold hands with another photon, so that momentum and energy can be balanced. But it doesn’t. It lives its brief solitary life, violating all the superstitions of quantum electrodynamics. The universe finds this a very unsatisfactory state of affairs. So our imaginary friend disappears before it can be detected. It materializes into a rho vector meson, which immediately decays into two pions, and those can be detected.”
    “But we don’t care by then,” Jao said with a redbearded grin. “Let the universe sort things out. By that time our mythical photon’s given its mythical kick to the vehicle.”
    “What’s this about the uncertainty principle?” Bram said.
    “That’s the beauty of it. The shorter the time the virtual photon exists, the