away from wherever it was pointing. Think of the indium nucleus as a little arrow that gets knocked to the side. If all the little arrows were pointing in one direction before the tachyons arrived, then they would get disordered. That would be noticeable and—”
“I see, I see,” Peterson said disdainfully. Renfrew wondered if he had overdone that bit about little arrows. It would be fatal if Peterson thought he was talking down to him—which of course he was.
“That’s some other fellow’s indium, I suppose?”
Renfrew held his breath. This was the tricky part. “Yes. An experiment operating in the year 1963,” he said slowly.
Peterson said drily, “I read the preliminary report. These prelims are often deceptive, but I understood that. The technical staff tell me it makes sense, but I can’t believe some of the things you’ve written. This business of altering the past—”
“Look, there’s this fellow Markham coming—he’ll put you straight on that.”
“If he can.”
“Right. See, the reason nobody’s even tried to send messages back is an obvious one, once you think of it. We can build a transmitter, see, but there’s no receiver. Nobody in the past ever built one.”
Peterson frowned. “Well, of course—”
Renfrew went on enthusiastically. “We’ve built one, naturally, to do our preliminary experiments. But the people back in 1963 didn’t know about tachyons. So the trick is to interfere with something they’re already doing. That’s the ticket.”
“Um.”
“We try to concentrate bursts of tachyons and aim them just so—”
“Hold on,” Peterson said, putting up a hand. “Aim for what? Where is 1963?”
“Quite far away, as it works out. Since 1963, the earth’s been going round the sun, while the sun itself is revolving around the hub of the galaxy, and so on. Add that up and you find 1963 is pretty distant.”
“Relative to what?”
“Well, relative to the center of mass of the local group of galaxies, of course. Mind, the local group is moving, too, relative to the frame of reference provided by the microwave radiation background, and—”
“Look, skip the jargon, can’t you? You’re saying 1963 is in the sky somewhere?”
“Quite so. We send out a beam of tachyons to hit that spot. We sweep the volume of space occupied by the earth at that particular time.”
“Sounds impossible.”
Renfrew measured his words. “I think not. The trick is creating tachyons with essentially infinite speed—”
Peterson made a wry, tired smile. “Ah—‘essentially infinite’? Comic technical talk.”
“I mean, with unmeasurably high velocity,” Renfrew said precisely. “Sorry for the terminology, if that’s what bothers you.”
“Well, look, I’m only trying to understand.”
“Yes, yes, sorry, I may have jumped the gun there.” Renfrew visibly composed himself for a fresh attack. “Mind, the essential trick here is to get these high-velocity tachyons. Then, if we can hit the right spot in space, we can send a message back quite a way.”
“These tachyon beams will go straight through a star?”
Renfrew frowned. “We don’t know, actually. There’s a possibility that other reactions—between these tachyons and other nuclei besides indium—will be fairly strong. There’s no data on those cross sections yet. If they are, a planet or a star getting in the way could be trouble.”
“But you’ve tried simpler tests? I read in the report—”
“Yes, yes, they’ve been very successful.”
“Well, still—” Peterson gestured at the maze of equipment. “This strikes me as a fine physics sort of experiment. Commendable. But—” he shook his head “—well, I’m amazed you got the money for this.”
Renfrew’s face tightened. “It’s not all that bloody much.”
Peterson sighed. “Look here, Dr. Renfrew, I’ll be frank with you. I’m down here to evaluate this for the Council, because some pretty big names have said it makes some sort of sense. I don’t feel I have the technical background to evaluate this properly. No one on the Council has. We’re ecologists and biologists and systems people for the most part.”
“Should be broader based.”
“Granted, yes. Our idea in the past has been to bring in specialists as they’re needed.”
Gruffly: “So reach Davies at King’s College in London. He’s keen on this and—”
“There isn’t time for that. We’re looking for emergency measures.”
Renfrew said slowly, “It’s that bad?”
Peterson paused, as though he had given away too much. “Yes. Looks so.”
“I can move fast, if that’s your idea,” Renfrew said briskly.
“You may have to.”
“It would be better if we got a whole new generation of equipment in here,” Renfrew took in the lab with a hand wave. “The Americans have developed new electronics gear that would improve matters. To be really sure we got through, we need the Americans