Though there are plenty of Earth-like planets – enough to guarantee that there’s intelligent life out there – the Universe is so vast that the likelihood of finding them is vanishingly small. Aliens living, say, only ten million light years away would need to travel at the speed of light for ten million years before they reached us. Which means they’d have to leave their home planets before humans came into existence. And then head over to us on a huge cosmic gamble.

‘But what if they mastered interstellar travel?’ Rory asked.

I smiled.

‘Not possible,’ I said. ‘The amount of energy, even if somehow there was a way around the limits on the speed of light, you would need – would be – well – astronomical.’

‘But an advanced civilisation, with technology expanding in accordance with Moore’s Law, could tap the energy.’

‘What?’ I sneered. ‘Fusion?’

‘Well, maybe fusion. It doesn’t matter. If you could harvest all of the energy on the planet, that would probably be enough.’

‘Not enough. Not if you calculate the rate at which you’d be using the energy and multiply it by the distances you’d be covering.’ I knew this. I’d researched it. Type I civilisations. That’s what he had stumbled on, just from thinking.

Dad smiled and then winked at me.

Rory scratched his head.

‘Could harness the energy of your star. That would be enough.’

‘What?’

‘A planet would need a star to sustain life. If you could collect all of the sun’s power, that would be enough.’

And now through pure thought he’d stumbled on Type II civilisations. I stopped smiling.

‘You couldn’t do that. It’s impossible,’ I said.

Dad rubbed his hands and smiled at Rory.

‘Or is it?’ Dad said, arching an eyebrow at Rory.

Rory raised his eyebrow with his finger. It annoyed me that he couldn’t do it without physically pushing it with his finger.

‘Wait. What if you, I don’t know, built a thing around the sun that captured all of the energy, or most of it? Then you could have something that self-replicated using the sun’s energy.’

I pushed my chair back along the tile and stood up. I gave him a hate-filled look and left. Later, after I’d accused him of cheating and he’d convinced me that he hadn’t, he said, ‘Statistically speaking, the difference between winning and losing is that over the longer term, losers give up. You give up too quickly,’ he added plainly. He wasn’t being mean or smug or irritating; he was just saying it, as an observation.

‘And that’s how you win, is it?’ I snapped.

‘I don’t care about winning. You can have the knife,’ he said, holding it out to me.

‘Then what is it?’

‘It’s solving the equation. Sometimes you have to keep going to solve it. You give up. There’s no fight in you.’