Credit: Stuart McLachlan

He was ninety-eight, and this last summer had been hard on him. I embraced him. "Jiji-san. I've missed you."

His cheek pressed against my ribs. He seemed smaller than I remembered. "It's good to see you," he said, speaking with the slight Japanese accent he retained from childhood. "Have you done well in your studies?"

I paused. Jiji-san sometimes forgot that I've graduated. We did longevity testing a few years ago. The doctors told us he had Alzheimer's V, an incurable subtype. They gave him a med patch to slow its progress. I checked his upper arm just below his sleeve. The patch was still there. It looked like Jiji-san was remembering to wear it, or perhaps Yukio reminded him.

"My research is going well," I told him. "But I came here to see you."

"Let me make you some tea, David," said Jiji-san, starting to kneel to grab his cane. "Have a seat." His hand wavered as he reached, shifting his balance.

I caught Jiji-san and steadied him. "I'll make the tea," I said, picking up his cane. "You sit down. I'll bring it in here."

"Sit down, David."

"No. I'll make the tea. Please."

"You're too young to make tea," he said, and his eyes sparkled.

I laughed. "All right, but I'm coming in there with you."

In the kitchen, Jiji-san placed two gold-leaf teacups in the beverage machine and ordered hot water. After a moment, Yukio said, "The water is ready." Liquid poured into the teacups. Jiji-san placed a bag of green tea in each cup. He handed me mine and bowed slightly.

"Your tea," he said.

"My thanks," I said, completing our modern tea ceremony. Jiji-san and I had been drinking tea together as long as I could remember. I breathed the fragrant steam and relaxed. For a while I could forget the biggest problem in modern astrophysics.

My grandfather gestured towards the kitchen table, and we sat across from each other. The lamplight cast blocky patterns across the black tablecloth. Coloured square papers lay scattered across the table.
A menagerie of angular creations stood near the kitchen window.

"I see you've brought out your origami again," I said, smiling. "I haven't done any in years. I used to love this. I think about it sometimes when I'm working on…" I broke off, realising I was thinking about wormholes again. "Stop it", I chided myself. "Pay attention to Jiji-san."

"Do you still remember any of the patterns I taught you?"

"I'm not sure. I might." I moved my teacup aside. I took a piece of silver-foiled paper and creased it, corner to corner. Then I unfolded it and touched the points cleanly into the centre. My hands remembered the patterns, even if my mind didn't. They were shaping the paper into something I'd recognise soon. Kinaesthetic memory, of course – but it felt like a new way of thinking. A revelation.

"Ah, you remember," he said.

"I do, on some level."

"The best origami is done when the mind leaves."

It was then that I knew why I kept thinking about work. I needed Jiji-san's help. I needed him to see what I couldn't – what no one could see. It felt strange to appeal to him; his expertise was in AI development, not hypertopology. But some part of me, my five-year-old self, knew that Jiji-san could fix anything. If he could turn spilled juice into art, he could solve the riddle of the Om's wormholes.

"Jiji-san?"

"Yes?"

"You asked about my research. Would you like to hear about it?"

"Always, David."

Yukio asked, "Shall I sleep for a while as you talk?"

I considered. Yukio was unlikely to help; he was less advanced than my companions at the Centre. Besides, Yukio was vulnerable to hackers and electro-torture. Then again, Jiji-san was just as vulnerable. More so, in some ways. I looked away, uncomfortable. "That won't be necessary, Yukio. Just keep our discussion private."

"Confidentiality assured," Yukio said, and fell silent. I believed him. My grandfather had built pathological honesty into self-replicating artificial intelligence as one of their limitations. It helped prevent an AI takeover. They had the simplicity of Buddhist monks: power without ambition. Yukio collected Zen koans, which he contemplated often. I asked him once if he was upset about the laws forbidding self-replicating AIs in android bodies. He said he'd never desired to be anything other than what he was; he was incapable of it. I remember wondering whether his limitations bothered him, and then realising he couldn't comprehend that either.

"What are you working on?" my grandfather asked me.

I held up my paper and examined it. I couldn't remember where the next fold went – in fact, I wasn't even sure what I was making. "Well, you know I studied hypertopology in graduate school."

"Folding space is what your grandma called it."

"Yes, at its most basic. Like the way this corner touches the centre – you could say that space folds through another dimension. At one point people assumed that dimension must be time, back when this was all just a playful idea. But no one could ever manipulate it. Popular culture theorised travel over vast distances, like leaping across the paper, but no one could actually manipulate space-time that way. They were called wormholes then, and the name stuck, even though they've turned out different from how we imagined them."