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Go with the flow.

Unable to reach Felix by phone, Bruno hobbled across the street to his physicist friend's house and waved the insulting cheque at him. “What's the joke, Felix?”

Long retired, Bruno still recalled the joys of plumbing: the craft of figuring pipes, often well beyond necessity, by eye alone, in quality iron, copper or even plastic connections. It had been a while since anyone had asked him to do repairs, or even make a job estimate. But now a cheque had arrived, with a post-it “thank you” from his lifelong friend attached to the return invoice.

Felix gave him a confused look. “But ... but you did the job while I was away.”

“I did not,” Bruno said.

“Have you ... forgotten?” Felix asked the sudden stranger.

“I didn't send this invoice,” Bruno said.

“I'll see about it,” Felix said coldly, closing the door.

A month later, the scene played out again at Felix's door, with Bruno waving invoice and cheque for bathtub fixtures he had not installed.

A third time, Felix said more warmly, “No denying these invoices, with our signatures on each. So who's joshing us, Bruno?”

“Maybe it's you,” Bruno said.

“Not you, Bruno?” Felix asked. “Did we both forget?”

Bruno rubbed his bad knee and leaned back on the sofa as they stared at the paperwork on the coffee table in front of them.

“You know, Bruno,” Felix said, “I'm only a so-so physicist, but I have a wild idea about all this.”


“You're slipping, Bruno,” he said.


“Through your sum over histories.”

“My what?”

“Across the probabilities. Some version of you did all this work.”

“And you paid me,” Bruno said, saddened by his friend's covering up what might be signs of delusion and mental decline.

Credit: JACEY

“We can check it out,” Felix said.

They went to his bathroom and looked under the sink, where the new drain and water connections glistened with prideful workmanship; then at the immaculate workmanship in the shower and bath. Felix leaned down under the sink and fondled the drain and water-supply connections. “Ah, yes, nice and dry,” he said happily, looking around at the floor. “But look here,” he said suddenly, and picked up a long grey hair from the floor. “I'm sure this is yours!” He held the hair up to the light as he stood up and said, “You know, Bruno, if this proves out, you'll be famous in physics, more than I could ever be. It's classic Feynman and Schrödinger.”

“Is one hair any proof?” asked Bruno.

“One is enough ... and I'll do the mathematics,” Felix said.

“Maybe there'll be another invoice,” said Bruno warily.

Felix sighed. “Yes, a paper with all the right maths and one hair won't do. It could have got here a number of ways, and the rest is words. We'll see if it happens again, but even that won't be enough.”

“There's not much we can do at the moment,” Bruno said, hoping that a delay might rid his overworked friend of delusions.

“Moments ...” Felix mused with a glint in his eyes. “Think of all the infinite diverging moments, each one going its own way at every juncture, every minute of the day, at every fraction of a second, throughout all the galaxies!”

“But why — why would all this be happening ... to us?” Bruno asked, humouring his friend.

“Why does anything happen in the quantum realm? No one knows why, except that it does and can be described, even predicted and made useful in technologies. To ask why seems a useless question.”

Bruno asked: “But why are we able to notice it?”

“A slip of some kind,” Felix said.

“But this ... this spilling up from the small to the large ...”

“The small is affecting the large.”

“Are these divergences common?” Bruno asked.

“They might be finite sets.”

Demoralized, Bruno went home and slept badly, dreaming of the objects in his friend's realm of work — a vast grey infinity of spaceless distances and winking points far removed from the undersides of sinks. He woke up thinking that the one domain could have nothing to do with the other, despite the fact that the visible world depended on an invisible realm.

He got up and worked on the page proofs of the new edition of his physics text, which suddenly looked unfamiliar, as if someone else had written it; but finally he settled into its long-worked-over familiarities. “Probabilities are like the thin pages of an infinite book,” he wrote in the margin of the manuscript, “and sometimes they stick together, even flow into each other. This may very well be the reality that makes human choices possible, escaping a hard determinism through a form of limited chaos ...”

Clever thought, he told himself.

Sticky stuff.

Some world pages stuck, others didn't. Smiling, he picked up a book and riffled the pages, imagining plumbing analogies to the structure of the Universe ...

There was an annoying knock on his door, and Bruno resented the early interruption.

He opened the door, and saw Felix, his old school friend, with toolbox in hand.

“Well, here I am,” Felix said with a smile, looking happy. “Hope you didn't break your kitchen sink just to get me to visit.”

Bruno was puzzled for an instant, then stepped aside as the plumber hobbled in.

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Zebrowski, G. Sticky. Nature 495, 544 (2013).

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