He was a tallish man with mild eyes who spent his free time, to the extent he had any, devising a complexity-based architectural system, full of shapes and curves he described as “natural.” He lived in Croydon, and his wife, who was older than him by a decade, had two children from her previous marriage. Perhaps as a reminder of his Los Alamos past, Tate favoured bowling shirts, horn-rimmed glasses and a careful haircut which made him look like Buddy Holly.

“We can slow down the rate at which the q-bits pick up phase. We’re actually doing better than Kielpinski there—I’ve had factors of four and up this week.”

He shrugged.

“After that, noise wins. No q-bit. No quantum computer.”

“And that’s it?”

“That’s it.” Tate took off his glasses and rubbed the bridge of his nose. “Oh. There was one thing.”

“What?”

“Come and look at this.”

Tate had installed a thirty-inch superflat display on a credenza at the back of the room. He did something to a keyboard and it lit up an icy blue colour. Somewhere off in its parallel mazes, the Beowulf system began modelling the decoherence-free subspace—the Kielpinski space—of an ion-pair. Its filmy, energetic extensions reminded Kearney of the aurora borealis. “We’ve seen this before,” he said.

“Watch, though,” Tate warned him. “Just before it decays. I’ve slowed it down about a million times, but it’s still hard to catch—there!”

A cascade of fractals like a bird’s wing, so tiny Kearney barely noticed it. But the female oriental, whose sensory-motor uptake times had been engineered by different biological considerations, was off his shoulder in an instant. She approached the screen, which was now blank, and batted it repeatedly with her front paws, stopping every so often to look into them as though she expected to have caught something. After a moment the male cat came out from wherever it had been hiding and tried to join in. She looked down at it, chattering angrily.

Tate laughed and switched the display off.

“She does that every time,” he said.

“She can see something we can’t. Whatever it is goes on after the part we can see.”

“There’s not really anything there at all.”

“Run it again.”

“It’s just some artefact,” Tate insisted. “It’s not in the actual data. I wouldn’t have shown you if I thought it was.”

Kearney laughed.

“That’s encouraging,” he said. “Will it slow down any further?”

“I could try, I suppose. But why bother? It’s a bug.”