One Friday each month, Dad, who was a physicist, would sit us around a table and set us a random topic of discussion. He’d listen and occasionally mediate, and then at the end he’d hand out a prize for the best ideas. Answers, he told us, weren’t important. To think, that was the important thing. The prizes weren’t particularly exciting by today’s standards – an Airfix model airplane once, a small electric motor and some circuits another time. Once there was a skateboard – that was misjudged. But the prizes, like all prizes, were icons – declarations of superiority.

Of the two of us, Rory was the genius. I was the impressionist – a fake. He had the beautiful brain. I had the right arrangement in my head, but it didn’t produce the same music. And Dad, though he loved us both, loved perfection and purity most of all. He loved maths. When he saw numerical puzzles, he somehow saw the Universe in a way that I couldn’t – but Rory could. Rory was a pure mind. But he was younger than me, so for a while I could mask the symptoms of his genius. I remember how urgent it was that I hold him back to give myself a chance of winning something. Maybe just love.

The Fermi paradox: that was the one, now I think back, that changed everything. You’ll know the one, Fermi, a physicist, asked about extraterrestrial life: If there are so many trillions of planets in the observable universe and billions of Earth-like planets among them, where are all the people? And why haven’t we heard from them?

When he set the discussion, Dad played at being the casual benign professor, as if the questions spontaneously occurred to him. But I’d known for some time that they came from the back of a monthly physics magazine. So I occasionally went to the local library when the new issue came out and had a quick preview. And one day there it was: Fermi. Rory loved space and astrophysics and there was no way of beating him without a head start. So, I cheated. For a week I read everything I could on the subject at the school library, and even spoke to the physics teacher after lessons.

The day of the test came and I remember Rory had been up in his room doing some computer programing. I had had to call him twice, to get him to come down.

‘So,’ Dad said when Rory floated in. ‘Where are all the aliens?’ He held up the prize. A lock knife with a dark, polished wood handle. I salivated as Rory rubbed his chin, oblivious.