‘Moving between timelines isn’t possible,’ I said. ‘I can show mathematically . . .’ But then I realised what I should have realised long ago, and would have if I hadn’t been so focused on other problems. ‘I’ve been doing it! That’s why I’m lying here with stitches in my side rather than with a hole right through me.’
‘You can do that?’ It was Eva’s turn to look surprised.
‘Not well enough, apparently.’ I touched my dressing and winced. ‘Tell me what happens. With the paradox, I mean.’
‘The divergence grows. It always grows. Slow or fast, but always more. The example with the fly – well, that might take a while for noticeable differences to accumulate, but they will. Wait long enough and cities will stand or fall on that small initial change. And if the timelines remain bound then the energy associated with those differences grows too, bubbling under the fabric of both realities.’
‘Until?’
‘Space-time itself starts to boil.’ She met my gaze with a level stare.
‘What does that mean?’
‘Local temporal distortions. In the year I’ve come from, some parts of the world can be microseconds ahead or behind others. London could be a microsecond ahead of Glasgow one month, a microsecond behind months later.’
‘Honestly, it doesn’t sound that apocalyptic. I was thinking you’d come back from the future to save us from an army of terminators hunting down the last dregs of humanity.’ I offered her a smile.
‘Think about it.’
I thought about it. ‘Um . . .’
‘The whole planet is—’
‘Moving! OK. Got it.’ Earth hurtles through space, orbiting the sun, which in turn orbits the centre of the galaxy at more than a hundred miles a second. Make different bits of the planet experience time at different rates and they would travel different distances. For microseconds’ difference, that might be a metre or so – enough to cause earthquakes, perhaps. If microseconds became milliseconds then the world would tear itself apart. ‘Pretty terminal then.’
‘Not as immediately terminal as the gas explosion that wrecks this ward.’ She stood and reached for my arm. ‘So we have to leave. Now!’
The contact between her hand and my arm made an unpleasant tingling and a crackling that sounded as if my flesh were crisping under her fingers. She helped me to sit, or forced me to, depending on your point of view.
‘You know this place is going to blow?’ I bit down on the pain in my side and slid my bare feet to the ground.
‘I know that it did. I’ve read the newspaper reports.’ Eva helped me to the end of the bed, the curtain slithering over us as I hobbled along, gasping. ‘You weren’t one of the casualties, but it’s different now. I’m here and everything is in flux.’
‘Shouldn’t— Ah! That hurt . . . Shouldn’t we warn someone?’ I limped out onto the ward, my whole side aching, the pain shooting through me with each step as my stitches pulled.
‘It’s you that the universe is trying to kill. If we get you out of here it probably won’t happen.’
I sank into the wheelchair with a gasp, sure that my wound was bleeding again. ‘But you said it had already happened.’
Eva looked at me as if I were an idiot. She dumped my clothes in my lap then went around the back to push the wheelchair. ‘This is a new timeline. When someone comes back they start a new timeline.’ She said it as if instructing a child, though she was a year or two older than me at most.
‘Demus remembers himself coming back. His timeline has his time travel baked into it, and as long as he doesn’t do anything incompatible with that experience he thinks he can change his own future by what he does in this here and now.’ I got it all out in a hurry, not caring if it made sense. Now that Eva had told me about the impending explosion I could visualise the fireball consuming the ward, withering skin and melting the flesh beneath. ‘You could push a little faster!’
‘I’m trying not to be notice—’
‘Hey! Hello? Where do you think you’re off to?’ A rather fierce nurse with short red hair and a thick Irish accent came up from behind to intercept us.
‘I’m just taking him for a little walk.’ Eva tried to steer around the nurse.
‘He shouldn’t even be out of bed!’ The nurse’s outrage grew. ‘He’s lost a lot of blood and been unconscious for a prolonged period. Let’s just hope he hasn’t ruptured any stitches with this foolishness!’
Eva pressed forward with determination until my toes were against the nurse’s shins. I started to wonder if I could smell gas . . . or was smelling things that weren’t there a symptom of concussion? I didn’t know if I’d hit my head on the way down, but it certainly ached.
‘Look, if it’s dangerous moving him out of the bed, then it’s dangerous moving him back in, and he clearly needs a rest before you do it.’ Eva shoved the wheelchair, forcing the woman out of our path. ‘We’ll be back in twenty minutes.’ And with the nurse’s protests falling around us we banged through the doors at the end of the ward.
We found ourselves in one of those endless hospital corridors that vanish into the distance until the curvature of the Earth takes them from view. Eva sped us along it towards a distant exit.
‘So, we escaped the gas explosion or prevented it. I’m safe. Well, safer . . . in less immediate danger . . .’
‘Critical but stable.’ Eva put it in medical terms since we were still in the hospital.
‘But the world . . . two worlds . . . maybe more, are going to end because of the spreading effects of some paradox that is . . . going to happen soon?’
‘Yes.’ Eva kept up a steady pace, the exit less distant now. ‘It happens on Thursday. It sounds as if I’m not the only one with an interest in it either. How many of us have you seen?’
‘Just two. You and . . . uh . . . me.’
‘Well, that’s two more than most people meet.’
‘Only future me didn’t come back to avoid any paradox . . .’
‘But . . . why else he would come back?’ Eva sounded surprised. ‘Unless he just wanted to split off a new timeline and live in it . . .’
‘It’s complicated,’ I said. ‘There’s a girl and—’
‘Helen?’ Eva asked.
‘You know Helen? I knew it! She’s your sister, right? Right?’
Eva stopped just short of the main doors and came to stand before me. ‘He’s come back because of Helen?’
‘No. He’s come back for a girl called Mia. But something went wrong and he’s here in June rather than back in January. But if he gets to January and if he sticks to what he remembers he reckons he can change what happens after he left, and save her life.’ I raised a hand before she started lecturing me on how things worked. ‘It’s not how it’s supposed to work but there’s something special about his timeline. A kind of feedback loop got frozen in. Perhaps whatever caused that is the same thing that left your timeline tangled with another one. I’m guessing his timeline is the one that’s got fused with yours.’
Eva returned to pushing me in silence. A thoughtful silence. Just the low rumble of hospital life and the clack clack clack of her shoes as she took me ever closer to the sun-bright exit.
‘So, why is the universe trying to kill me?’ I asked.
‘Like any semi-stable system, the universe is a low-energy solution to an equation. Paradox is an unstable high-energy solution and the universe tries to configure itself to regain the low-energy solution. That means tearing up the affected timelines. Or making sure they never happen. There’s nothing personal about it. It’s just physics.’
A visitor held the doors wide as we passed through into the open air.
‘You’re saying I cause the paradox.’
‘Bingo.’
I grabbed the wheels and brought the chair to a halt. I tried to swivel round but my side hurt too much, so I settled for craning my neck to look at her.
‘Who are you?’ I held up the book from my lap. I realised now that the handwriting
in the dedication was what had been troubling me. It looked familiar. ‘And who gave you this?’
Eva paled and her cheek twitched again. She tried to speak but her voice came out as a strangled whisper. ‘You did . . . Dad.’
CHAPTER 14
In the space of one day I’d had a psychopath invade my home, an idiot stab me with a sword, had my leukaemia return and at sixteen years of age I’d met my eighteen-year-old daughter.
Eva wheeled me through the streets of Cambridge with no apparent destination in mind. It was an arrangement that saved us both from meeting each other’s eyes and seeing the confusion of our own emotions mirrored there.
I had a lot of questions. The only difficulty was asking them. ‘So . . .’ The words dried up on my tongue for the fourth or fifth time. ‘So, Helen is your mother?’
‘Yes.’
It explained why they looked like sisters.
‘And I’m . . .’
‘My dad. Yes.’
As much as I liked the idea of making babies with Helen, it seemed rather unlikely given how things had been going so far. Plus where did that leave things with me and Mia? And were these the kind of things I wanted to discuss with my daughter . . . who was older than me. Had I been a good father to her? Why was it Eva standing in front of me . . . well, behind me . . . rather than the older me who had watched her grow? Why hadn’t the me from her timeline returned instead?
We were heading into the old part of town towards the main colleges and the river, the streets growing more crowded, our going slower. Clearly returning me to the hospital was not on Eva’s to-do list. I wondered how she was at changing dressings and taking stitches out.
I attracted a few stares as we went, my bare legs and feet emerging from the hospital gown, very pale in the sunlight. My head ached worse than the wound in my side, and thinking clearly was proving difficult.
I decided to start with something easy. ‘What were those things you were running away from, and where did you go?’
‘What things? When?’
‘The first time we met. You called me by name. Asked for my help.’
‘When?’ she repeated.
‘You know. When I came to see Halligan that first time, back in February.’
‘Really?’ She sounded surprised. ‘I go back further?’
‘I . . . uh . . . guess so?’
‘Well, I haven’t done it yet. That’s your past, my future.’
I ran a palm over my forehead, trying to press the ache out of my brain. It was easier to get my head around it on paper in the form of an equation. Words made it more complicated. Living it made it even harder to understand. Especially with mild concussion. ‘OK. I guess we’ll understand that bit when the time comes . . . again . . . or something.’
Eva wheeled me on in silence for a while, not speaking again until we passed the Gothic glory of King’s College and its chapel, towering to one side like an over-decorated stone cake. We came to a halt on the lawns leading down to the Cam.
‘So,’ Eva said. It seemed to be a family habit. She came and sat cross-legged on the grass in front of me. ‘So.’
‘Did I send you back?’
Eva shook her head, eyes on the grass.
Puzzled, I tried again. ‘Did I tell you not to come?’
Eva shook her head again, biting her lip. ‘I thought I would be better at this . . .’ Her voice sounded choked.
‘Better at what?’
‘Until the hospital just now, I’d never spoken to you before.’ She rubbed her shoulder while she spoke, as if offering herself comfort. ‘You died, Dad. You died when I was a baby. And . . .’ A sob, a gasp for air, then the words came quickly. ‘And I’ve spent a lifetime in your shadow, looking back at where you stood. The great Nicholas Hayes. The Time Lord who gave humanity the key to the TARDIS. And I worked to find a way back to you. I worked so hard to use that damn key. I thought . . .’
‘You thought it would be different. That I would recognise you. That somehow I would say the right thing, know what to do, make up for all those missing years.’ She’d told me I was going to die young. That I would marry Helen and make a child who I would never see grow. It should have cut me too deeply to care about anything else, but right then and there I cared more about making this right for her than I did about how wrong it was for me. And it wasn’t the selfless love of a father for his child. I already knew this scene we were acting out. I knew it from the other side, had imagined it a thousand times. Four years earlier my own father had left the house and never returned. There had been few days since that one when I hadn’t wished for that morning back: for the twelve-year-old me to have noticed him at breakfast. To have unwrapped myself from whatever nonsense had been on my mind and to have seen my father, truly seen him, for the last time. Maybe I could have somehow stood myself between him and that train he thought he needed to catch. Maybe now, if I went back, I would know the right words to say, might be able to unveil enough new wonder in the world to make him want to stay, make him want to fight his cancer. So, yes, I knew the sort of thing she needed from me, just not how to give it to her. ‘I’m sorry I wasn’t there for you.’
Eva looked up, eyes bright above a forced smile. ‘Well, you’re here now.’
We probably should have hugged or something, but we were Hayeses and nobody in my family had been given to hugging for generations. Instead we talked mathematics.
‘If I die when you’re a baby – and I have to say that I’m really not on board with that at all – how do I manage to find time to solve time travel? Demus told me it would take twenty years to iron out all the wrinkles. Or . . . do Helen and I wait a long time before we . . . I mean . . . when were you born?’
‘You’re sure you want to know all this?’
‘I know a future where I live for another twenty-five years. And I saw a whole bunch where I didn’t survive past lunchtime and died skewered on a sword in a stupid accident. So sure, tell me about one where I get to be with Helen and have a daughter.’
‘OK . . .’ She spoke slowly, picking her words with care as if knowing that all of them came with sharp edges. ‘I was born in 1989.’
‘Woah! I was quick off the mark! Or will be . . .’ A father at nineteen. Mother would not approve.
‘You and Mum weren’t sure you were still fertile after the chemo, and it looked as if you were likely to have more rounds of treatment. She said you both decided to try while there was still hope.’
‘There’s always hope, Eva.’ I quoted Demus.
‘Well . . .’ She sniffed and wiped her nose. Her mascara had run. ‘There was hope. You got me! And two years later you died.’
‘Aged twenty-one?’
Eva nodded.
‘The leukaemia?’
Another nod.
I took a while to chew that one over. ‘But . . . you didn’t come back just to meet me, or at least not only for that?’ Time travel was a big deal. It wasn’t something you did for personal tourism, even if the sights and destinations included lost relatives. ‘Did you?’
‘No,’ she admitted. ‘I had a bigger reason too.’
‘You came to escape the paradox breakdown?’ Even that seemed wrong, to run away by herself, leaving behind everyone she’d ever known.
‘I came to stop it happening. I’m not entirely sure it can be done yet, but if it can, this is the time and place to do it. I just need to take some more measurements, do some more calculations. I’m going to need help, though, and now it turns out I’ve got two dads right here in this city. Maybe that’s enough to help me save two worlds.’
I couldn’t help but grin at that. At the sheer craziness of it. I wondered what Demus would make of this daughter he’d never had. It might seem even stranger to him than it did to me. We sat for a while in the sunshine saying nothing, bees in the clover, white clouds dotting a blue sky.
‘And when have you come back from?’ I asked at last.
‘2007.’
‘How’s th
at possible, though? I mean . . . you said I died aged twenty-one. I couldn’t have worked out all the theory in five years, could I?’
Eva shrugged. ‘You broke the back of it. You’re famous as hell! And a bunch of other mathematicians carried on where you left off. Halligan led a team that did a lot of the remaining work. Uncle Bob, I call him. He died the year before I came back. Choked on a fishbone.’
‘Uncle Bob? You knew him like twenty years in the future?’
‘Sure. I worked with him. Here at Cambridge.’
The light slowly dawned. ‘It was you. You finished off my work!’
Eva shook her head. ‘Nope. I’ve been working on something else.’
‘What, then?’
She tapped her chest and for the first time I noticed that written in white across her black T-shirt were a collection of closed integrals. The notation didn’t make a lot of sense.
‘Are those tensors?’ I asked.
She nodded.
‘And those look like terms you find in work on turbulence.’ I frowned. ‘And that looks suspiciously like the generator for the Mandlebrot set . . .’
Another nod.
‘Tell me . . .’
So she did. At first she just talked, and later she took a pen and a pad of paper from her bag and began to write, page after page of tightly packed equations. Before long I started to see the forms rise from the notebook, the multidimensional shapes that cast their shadows on the paper below. Eva saw them too. I could tell it from the way she hardly glanced at the page as she wrote, but looked into space with a defocused gaze as though she were sketching what she saw.
‘Slow down.’ I’d never said that before. Not about mathematics. Even Halligan crawled compared to the speed I wanted him to go at when we discussed this stuff. With Halligan I would slowly reveal the inner workings of the mathematical universe, piece by glowing piece, while he steadfastly laboured through the dead ink on the page as if it were the secret itself rather than just being the grass rippling in the wake of some larger truth passing him by. With Eva I sat amazed while she spun and juggled structures of such grandeur and complexity that I strained to see the whole of them. ‘These are the foundations, aren’t they?’
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