Time. Stephen Baxter

energy goes into the retarded wave.’

      ‘It’s kind of beautiful,’ Malenfant said. ‘You have to imagine all these ghostly wave echoes travelling backward and forward in time, perfectly synchronized, all working together to mimic an ordinary radio wave.’

      Emma had an unwelcome image of atoms sparsely spread through some dark, dismal future, somehow emitting photons in a mysterious choreography, and those photons converging on Earth, gathering in strength, until they fell to the ground here and now, around her …

      ‘The problem is,’ Cornelius said gently, ‘Feynman’s argument, if you think about it, rests on assumptions about the distribution of matter in the future of the universe. You have to suppose that every photon leaving our transmitters will be absorbed by matter somewhere – maybe in billions of years from now. But what if that isn’t true? The universe isn’t some cloud of gas. It’s lumpy, and it’s expanding. And it seems to be getting more transparent.’

      Dan said, ‘We thought it was possible that not all the advanced waves cancel out perfectly. Hence all this. We use the radio dishes here to send millisecond-pulse microwave radiation into space. Then we vary the rig: we send out pulses into a dead-end absorber. And we monitor the power output. Remember the advanced waves are supposed to contribute to the energy of the retarded wave, by Feynman’s theory. If the universe isn’t a perfect absorber –’

      ‘Then there would be a difference in the two cases,’ Emma said.

      ‘Yeah. We ought to see a variation, a millisecond wiggle, when we beam into space, because the echo effect isn’t perfect. And we hope to detect any message in those returning advanced echoes – if somebody downstream has figured out a way to modify them.

      ‘We pick cloudless nights, and we aim out of the plane of the Galaxy, so we miss everything we can see. We figure that only one per cent of the power will be absorbed by the atmosphere, and only three per cent by the Galaxy environment. The rest ought to make it – spreading out, ever more thinly – to intergalactic space.’

      Cornelius said, ‘Of course we can be sure that whatever message we do receive will be meaningful to us.’ He looked around; his skin seemed to glow in the starlight. ‘I mean, to the four of us, personally. For they know we are sitting here, planning this.’

      Emma shivered again. ‘And did you find anything?’

      ‘Not to a part in a billion,’ said Cornelius.

      There was silence, save for a distant wind rustling ink-black trees.

      Emma found she had been holding her breath. She let it out gently. Of course not, Emma. What did you expect?

      ‘Crying shame,’ said Dan Ystebo, and he reached for another beer. ‘Of course experiments like this have been run before. You can find them in the literature. Schmidt in 1980. Partridge, Newman a few years earlier. Always negative … Which is why,’ he said slowly, ‘we’re considering other options.’

      Emma said, ‘What other options?’

      Cornelius said, ‘We must use something else – something that isn’t absorbed so easily as photons. A long mean free path length. Neutrinos.’

      ‘The spinning ghosts.’ Dan belched, and took a pull at his beer. ‘Nothing absorbs neutrinos.’

      Emma frowned, only vaguely aware what a neutrino was. ‘So how do you make a neutrino transmitter? Is it expensive?’

      Cornelius laughed. ‘You could say that.’ He counted the ways on his hands. ‘You set off a new Big Bang. You spark a supernova explosion. You turn a massive nuclear power plant on and off. You create a high-energy collision in a particle accelerator …’

      Malenfant nodded. ‘Emma, I was going to tell you. I need you to find me an accelerator.’

      Enough, she thought.

      Emma stood and drew Malenfant aside. ‘Malenfant, face it. You’re being spun a line by Cornelius here, who has nothing to show you, nothing but shithead arguments based on weird statistics and games with techno toys. He’s spinning some kind of schizoid web, and he’s drawing you into it. It has to stop here before –’

      He snapped, ‘If something goes wrong in the cockpit you don’t give up. You try something else. And then another thing. Again and again until you find something that works. Have a little faith, Emma.’ Emma opened her mouth, but he had already turned back to Dan Ystebo. ‘Now tell me how we detect these damn neutrons.’

      ‘Neutrinos, Malenfant …’

      Cornelius leaned over to Emma. ‘The Wheeler-Feynman stuff may seem spooky to you. It seems spooky to me: the idea of radio waves passing back and forth through time … But it’s actually fundamental to our reality.

      ‘Why is there a direction to time at all? Why does the future feel different from the past? Some of us believe it’s because the universe is not symmetrical. At one end there is the Big Bang, a point of infinite compression. And at the other there is the endless expansion, infinite dilution. They couldn’t be more different.

      ‘We can figure out the structure to the universe by making observations, expressing it in such terms. But what difference does it make to an electron? How does it “know” that the forward-in-time radio waves are the “correct” ones to emit?

      ‘Maybe it’s because of those back-in-time echoes. Perhaps an electron can tell where it is in time – and which way it’s facing. And that’s how come the forward-in-time waves are the ones that make sense.

      ‘All this is analogy and anthropomorphism. Of course electrons don’t “know” anything. I could say, more formally, that the Wheeler-Feynman theory provides a way for the boundary conditions of the universe to impose a selection effect on retarded waves. But that would just be blinding you with science; and we wouldn’t want that, would we?’ He was smiling, his teeth white. He was toying with her, she realized.

      Malenfant and Ystebo talked on, slightly drunk, eager. It seemed to Emma that their voices rose up into the sky, small and meaningless, and far above the stars wheeled, unconcerned.

      Bill Tybee:

      Tuesday.

      Well, June, I had my meeting with Principal Bradfield. She’s still determined she won’t take Tom back.

      At least I found out a little more.

      Tom, well, he isn’t the only one. The only supersmart kid, I mean. There are three others they’ve identified at the school, and a couple more they’re suspicious about. That makes it a couple per thousand, and that’s about right.

      It seems this is some kind of nationwide phenomenon. Maybe global.

      But the numbers are uncertain. The kids are usually identified only when they get to school.

      The Principal says they are disruptive. If you have one of them in a class they get bored and impatient and distract everybody else. If there is more than one, they kind of hook up together and start doing their own projects, even using their own private language, the Principal says, until you can’t control them anyhow.

      And then there’s the violence. The Principal wasn’t about to say so but I got the impression some of the teachers aren’t prepared to protect the kids properly.

      I asked the Principal, why us? But she didn’t have an answer.

      Nobody knows why these kids are emerging anyhow. Maybe some environmental thing, or something in the food, or some radiation effect that hit them in the womb. It’s just chance it happened to be us.

      Anyhow the school board are looking at some other solution for Tom. Maybe he’ll have a teacher at home. We might even get an e-teacher, but I don’t know how good they are. I did read in the paper there have been proposals for some