Malenfant brought her to what he called the muon laboratory. This was some way away from the accelerator ring itself; it seemed that beams of high-speed protons were drawn off from the ring and impacted into targets here.
And here they found Dan Ystebo, wearing a smeared white coat over a disreputable T-shirt, hunched over softscreens spread out on a trestle-table. The screens were covered with particle-decay images and charts of counts, none of which Emma could understand.
Dan’s broad face split into a grin. ‘Yo, Emma. Have you heard? …’
Malenfant said, ‘One step at a time. Tell her what you’re doing here, Dan.’
Dan took a breath. ‘Making neutrinos. We’re slamming the Tevatron’s protons into a target to make pions.’
‘Pions?’
‘A pion is a particle, a combination of a quark and its anti-quark, and it is unstable. Pions decay into, among other things, neutrinos. So we have our neutrino source. But it should also be a source of advanced neutrinos, neutrinos coming from the future, arriving in time to make our pions decay …’
‘Backward ripples,’ Emma said.
‘Exactly – hopefully modified, and containing some signal.’
‘How do you detect a neutrino?’
Malenfant grunted. ‘It isn’t easy. Neutrinos are useful to us in the first place because matter is all but transparent to them. But we have a full-scale neutrino detector: a ton of dense photographic emulsion, the stuff you use on a camera film. When charged particles travel through this shit they leave a trail, like a jet contrail.’
‘I thought neutrinos had no charge.’
‘They don’t,’ said Dan patiently. ‘So what you have to look for is a place where tracks come out but none go in. That’s where a Tevatron neutrino has hit some particle in our emulsion. You get it? You have a mass of counters and magnets downstream of the emulsion, and you measure the photons with a twenty-ton lead-glass detector array, and the results are stored on laser discs and analysed by the data acquisition software –’
He talked on, lapsing continually into jargon she couldn’t follow.
But then they started talking about the neutrinos themselves.
Neutrinos, it seemed, barely existed: no charge, no mass, just a scrap of energy with some kind of spooky quantum-mechanical spin, fleeing at the speed of light. Spinning ghosts indeed. Most of them had come out of the Big Bang – or the time just after, when the whole universe was a soup of hot subatomic particles. But neutrinos didn’t decay into anything else. And so there were neutrinos everywhere. All her life she would be immersed in a sea of neutrinos, a billion of them for every particle of ordinary matter, relics of that first millisecond.
At that thought she felt an odd tingle, as if she could feel the ancient, invisible fluid that poured through her.
Now humans had sent waves rippling over the surface of that transparent ocean. And the waves, it seemed, had come reflecting back.
Dan talked fast, as excited as she’d ever seen him. Malenfant watched, rigid with interest. ‘Essentially we’ve been producing millisecond neutrino pulses,’ Dan said. He produced a bar chart, a scrappy series of pillars, uneven in height. ‘Anyhow, up until yesterday, we were just picking up our own pulses, unmodified. Then – this.’
A new bar chart, showing a long series of many pulses. Some of the pulses, now, seemed to be missing, or were much reduced in size.
Dan picked out the gaps with a fat finger. ‘See? On average, these events seem to have around half the neutrino count of the others. So half the energy.’ He looked at Emma, trying to see if she understood. ‘This is exactly what we’d expect if somebody downstream has some way of suppressing the advanced-wave neutrinos. The apparent retarded neutrinos then would have only half the strength –’
‘But it’s such a small effect,’ Emma said. ‘You said yourself neutrinos are hard to detect. There must be other ways to explain this, without invoking beings from the future.’
‘That’s true,’ Dan said. ‘Though if this sustains itself long enough we’re going to be able to eliminate other causes. Anyhow, that’s not all. We have enough data now to show that the gaps repeat. In a pattern.’
Malenfant growled, ‘This is new to me. A repeating pattern. A signal?’
Dan rubbed his greasy hair. ‘I don’t see what else it could be.’
‘A signal,’ said Malenfant. ‘Damn. Then Cornelius was right.’
Emma felt cold, despite the metallic stuffiness of the chamber.
Dan produced a simplified summary of several periods of the pattern, a string of black circles and white circles. ‘Look at this. The blacks are full-strength pulses, the whites half-strength. You get a string of six white. Then a break of two black. Then an irregular pattern for twelve pulses. Then two black, six white, and a break. Then another set of twelve black-whites, “framed” by the two black and six white combination. I think we’re seeing delimiters around these two strings of twelve pulses. And this is what repeats: over and over. Sometimes there are minor differences, but we think that’s caused by the experimental uncertainty.’
Malenfant said, ‘If it’s a signal, what does it mean?’
Emma said, ‘Binary numbers. The signals are binary numbers.’
They both turned to her.
Malenfant said, ‘Huh? Binary numbers? Why?’
She smiled, exhausted, jetlag-disoriented. ‘Because signals like this always are.’
Dan was nodding. ‘Yes. Right. I should have thought of that. We have to learn to think like Cornelius. The downstreamers know us. Maybe they are us, our future selves. And they know we’ll expect binary.’ He grabbed a pad and scribbled out two strings of 1 and 0:
1 1 1 0 1 0 1 0 1 0 0 1
0 1 1 1 1 1 0 0 0 0 1 0
He sat back. ‘There.’
Malenfant squinted. ‘What’s it supposed to be?’
Emma found herself laughing. ‘Maybe it’s a Carl Sagan picture. A waving downstreamer.’ Shut up, Emma.
‘No,’ Dan said. ‘It’s too simple for that. They have to be numbers.’ He cleared his softscreen and began tapping in a simple conversion program. After a couple of minutes, he had it running.
3 7 5 3
1 9 8 6
They stared. Malenfant said, ‘What do they mean?’
Dan began to feed the raw neutrino counts through his conversion program, and the converted signals – live, as they were received in the film-emulsion detector – scrolled steadily up the screen.
3 7 5 3
1 9 8 6 3 7 5 3 1 9 8 6 3 7 5 3 1 9 8 6
‘Someone should call Cornelius,’ Dan said. ‘And –’
Malenfant said, ‘What?’
‘We only ran for a week before we picked this up. How did the downstreamers know when we were ready, when to switch on?’
Malenfant grinned. ‘Because they already knew when we’d be here.’
Emma didn’t share his evident glee at this result.
She felt dwarfed. She imagined the world wheeling around her, spinning as it carried her through darkness around the sun, around