Permafrost(16)

I grinned at their insouciance.

“You’re both taking this way too casually.”

“We’ve had lot of time to get used to what we’re doing,” Margaret said with an apologetic smile, as if they were being bad hosts by not making more of their experiment. “Even time travel becomes normal when it’s your day job.”

“You constructed this apparatus?” I asked, nodding at the upright cylinder.

“Put it together from parts, more accurately,” Margaret said. “But it certainly didn’t exist in any significant form until we assembled it here. You’re wondering how far back we could have sent those electrons?”

“I’m thinking that a minute doesn’t really buy you anything. Time to cheat the stock markets, if there were still stock markets. But not to solve Director Cho’s food crisis.”

“If we eliminated every source of noise, we could go back fourteen months, the day we first put the apparatus together. Fourteen months would help us in small ways—we could transmit knowledge that would help speed up the development of the experiment, warning us from blind alleys and dead ends. In practise, though, we’re nowhere near that. Twelve hours is our effective limit with this setup.”

“And on the Admiral Nerva?”

“A little further back,” Antti said.

I approached the experiment, wanting to get a closer look at the instrumentation. Along the way my clean-room garment brushed against a pen and clipboard lying on one of adjoining benches. The pen clanged to the floor.

I stared down at it, shaking my head slowly.

“That didn’t just happen.”

“There’s your noise spike,” Antti said, stooping down and picking up the pen, then setting it back on the bench as if this was a completely mundane happening. “Congratulations, Valentina. You just made a small alteration to the past.”

I looked at Margaret’s apparatus, thinking hard, and trying to show that I wasn’t totally disorientated by what had just transpired.

“What if another noise spike showed in that trace, and we switched off the experiment immediately?”

“Then you’d be grandfathering,” Margaret said. “Sending a causal change upstream, which in turn affects the downstream reality. A true paradox, albeit a relatively mild one. But I can easily demonstrate a low-level paradox without turning off the experiment.” Her eyes flicked to a wall clock, a digital counter in a black surround. “In sixty seconds I’ll drop this pen again.”

I returned my gaze to the noise trace. Immediately a similar spike appeared, and after a few seconds the brackets and statistical parameters appeared.

“All right . . .” I said, eyeing Margaret carefully.

Margaret walked softly to another bench and picked up a second pen. Now she held them both, one in each hand. “You see one spike at the moment, agreed?”

“Agreed.”

“That’s because our downstream reality reflects an upstream case in which I dropped only one pen, as I promised. That’s a closed loop, paradox-free. But I’m going to violate it, by dropping two pens.”

The single spike was drifting to the left, now about thirty seconds downstream of our present position. I thought about what would happen when we caught up with the future moment in which Margaret had dropped only one pen. Now there would be two acoustic events, and the Luba Pairs would respond accordingly. The digital trace would have to show two noise spikes, instead of the one that was still visible.

But it hadn’t.

Something will happen, I thought, to preserve the present condition. Margaret would drop one pen and it would hit the floor just like the one I’d dropped. But the second would hit her shoe, muffling its impact, so that there was still only one acoustic event. Even that would be weird. But there’d be no paradox, no grandfathering.

The digital clock showed sixty seconds since Margaret picked up the first pen. She dropped it, waited a second, then dropped the second. Both pens had hit the floor, as loudly as the first time.

“We’ve modified the upstream condition,” Margaret said. “The past will now adjust itself to reflect this. But it doesn’t happen instantly. We call it causal-lag, a sort of inertia or stickiness.”

“It’s an outgrowth of your mother’s work,” Antti put in.

“We’re now in a superposition of histories,” Margaret continued. “There’s the fading state, in which there was just one noise event, and the rising state, in which there are two events. Gradually the rising state will supplant the fading one. Our minds are easily capable of perceiving both histories, until the new condition becomes dominant.”

My attention returned to the noise readout. The original spike was still there, but a fresh prominence was rising out of the noise to its right, like a second peak thrusting up from a mountain range. This new spike quickly became as significant as the first, bracketed and annotated. These were noise events that had already been recorded on the system ninety seconds ago.

I blinked.

There was a fuzziness to my thoughts, like the first pleasant stages of drunkenness.

I remembered that there had been one spike. I also remembered that there had always been two. My brain was holding two histories within itself, and it was no different, no stranger, no more paradoxical, than crossing my eyes and seeing two slightly offset versions of the same scene.