Renfrew’s experiment makes sense? All this talk of loops and not being able to close switches …”
“Sure it’ll work.” Markham accepted a glass dark with the thick stout. The manager placed Peterson’s ale carefully before him and began, “Sir, I want to apol—”
Peterson waved him into silence, impatient to hear Markham. “Perfectly all right,” he said quickly.
Markham eyed the manager’s retreating back. “Very effective. Do they teach that in the best schools?”
Peterson smiled. “Of course. There’s lecture, then field trips to representative restaurants. You have to get the wrist action just right.”
Markham saluted with the stout. After this silent toast he said, “Oh yes, Renfrew. What Wheeler and Feynmann didn’t notice was that if you send a message back which has nothing to do with shutting off the transmitter, there’s no problem. Say I want to place a bet on a horse race. I’ve resolved that I’ll send the results of the race back in time to a friend. I do. In the past, my friend places a bet and makes money. That doesn’t change the outcome of the race. Afterward, my friend gives me some of the winnings. His handing over the money won’t stop me from sending the information—in fact, I can easily arrange it so I only get the money after I’ve sent the message.”
“No paradox.”
“Right. So you can change the past, but only if you don’t try to make a paradox. If you try, the experiment hangs up in that stuck-in-between state.”
Peterson frowned. “But what’s it like? I mean, what does the world seem like if you can change it round?”
Markham said lightly, “Nobody knows. Nobody’s ever tried it before.”
“There were no tachyon transmitters until now.”
“And no reason to try to reach the past, either.”
“Let me get this straight. How’s Renfrew going to avoid creating a paradox? If he gives them a lot of information, they’ll solve the problem and there’ll be no reason for him to send the message.”
“That’s the trick. Avoid the paradox, or you’ll get a stuck switch. So Renfrew will send a piece of the vital information—enough to get research started, but not enough to solve the problem utterly.”
“But what’ll it be like for us? The world will change round us?”
Markham chewed at his lower lip. “I think so. We’ll be in a different state. The problem will be reduced, the oceans not so badly off.”
“But what is this state? I mean, us sitting here? We know the oceans are in trouble.”
“Do we? How do we know this isn’t the result of the experiment we’re about to do? That is, if Renfrew hadn’t existed and thought of this idea, maybe we’d be worse off. The problem with causal loops is that our notion of time doesn’t accept them. But think of that stuck switch again.”
Peterson shook his head as though to clear it. “It’s hard to think about.”
“Like tying time in knots,” Markham conceded. “What I’ve given you is an interpretation of the mathematics. We know tachyons are real; what we don’t know is what they imply.”
Peterson looked around at the Whim, now mostly deserted. “Strange, to think of this as being an outcome of what we haven’t done yet. All looped together, like a hooked rug.” He blinked, thinking of the past, when he had eaten here. “That coal stove—how long have they had that?”
“Years, I suppose. Seems like a sort of trademark. Keeps the place warm in winter, and it’s cheaper than gas or electricity. Besides, they can cook at any time of day, not just the power hours. And it gives the customers something to watch while they’re waiting for their orders.”
“Yes, coal’s the long-term fuel for old England,” Peterson murmured, apparently more to himself than Markham. “Bulky though.”
“When were you a student here?”
“In the ’70s. I haven’t been back very often.”
“Have things changed much?”
Peterson smiled reminiscently. “I dare say my rooms haven’t changed much. Picturesque view of the river and all my clothes get moldy from the damp …” He shook off his mood. “I’ll have to be getting back to London soon.”
They elbowed through the students to the door and out into the street. The June sunshine was dazzling after the pub’s dark interior. They stood for a moment, blinking, on the narrow sidewalk. Pedestrians stepped off into the street to walk past them and cyclists swerved around the pedestrians with a trilling of bells. They turned left and strolled back towards King’s Parade. On the corner opposite the church, they paused to look in the windows