The Wrong Way Round

The trouble started because Soren wanted the ice pops to be perfect.

Not good. Perfect. Smooth, with no big crunchy crystals in them, the kind you got from the store. He had read that the secret was temperature, so he and Maya filled two batches of mango juice, set them side by side, and waited.

One batch they cooled in the fridge first. The other they left warm, fresh off the stove, because Soren had heated the juice to dissolve the sugar and hadn't gotten around to cooling it yet.

"The cold one wins," Soren said. "Obviously. It's already partway there."

Maya didn't answer. She was looking at the two trays through the frosted freezer door like she was watching a race.

Forty minutes later she opened it and poked both.

"Soren."

"What."

"The hot one's frozen. The cold one's still slushy."

He came over and pushed the cold tray with one finger. It gave, soft and wet. He pushed the warm tray. It was solid. He pushed it again, harder, like the ice pop might be tricking him.

"That's the wrong way round," he said.

"I know."

"That's completely the wrong way round. Cold water is closer to freezing. It has less distance to fall. It should win every time."

"I know," Maya said again. She wasn't arguing with him. She was just looking at the trays with her head tipped, the way she did when something didn't fit and she hadn't caught up to why yet.

Soren got his notebook. He wrote down the start temperatures, guessing, and the time, and then he wrote: HOT FROZE FIRST. He underlined it. Then he stared at the underline like it had insulted him.

"We measured wrong," he said. "Or the trays are different. Or the freezer is colder on that side."

"So swap them," Maya said.

They did the whole thing again. New juice. They swapped which side each tray went on. They used the same kind of tray, twins, checked twice. Soren cooled one batch in the fridge until it was genuinely cold, cold enough to fog the glass, and the other they poured in steaming.

This time Maya set a timer and they didn't open the door.

When the timer went, the steaming one was frozen. The cold one wasn't.

Soren sat down on the kitchen floor.

"It did it again," he said. "It did the impossible thing again, in exactly the same direction."

"Then it isn't a mistake," Maya said. "Mistakes go different ways. This keeps going the same way."

That was the thing that got him. A mistake was random. You measured wrong high one time and low the next. But this had picked a side and stayed there. Hot, every time. Hot, when hot made no sense.

Maya was already pulling out her phone. She typed: hot water freezes faster than cold. She fully expected to find the website that told her she was being silly.

Instead she found a name. Erasto Mpemba.

"He was a student," she read out. "In Tanzania. They were making ice cream in school, and you were supposed to cool your mix before you put it in the freezer, and he was in a hurry so he put his in hot. And his froze first. Before everybody who did it right."

"How old was he?" Soren asked.

"Thirteen." Maya kept reading, faster now. "And he asked his teacher why, and the teacher told him he was confused. That he must have used the wrong tray, or the wrong time. The teacher said, that's not physics, that's Mpemba's physics. Like it was a joke. Like he was the only person in the world dumb enough to see it."

Soren had gone very still.

"But he kept saying it," Maya said. "He wouldn't drop it. And then a real physicist came to give a talk at his school, and Mpemba asked him, in front of everybody. Why does hot water freeze faster than cold. And everybody laughed at him. The other students laughed."

"And the physicist?"

"The physicist went home and tried it." Maya looked up. "And it happened to him too. So they wrote it down together. The student and the scientist. It's got the kid's name on it. The Mpemba effect."

Soren looked at the two trays on the counter, one solid, one slush, sitting there breaking the rule in front of him.

"So a grownup explained why it happens," he said. "Eventually. Right?"

Maya scrolled. She scrolled again. Her thumb slowed down.

"No," she said.

"What do you mean, no."

"I mean no. They have guesses. Maybe the hot water evaporates a little, so there's less to freeze. " She set the phone down. "They have a bunch of maybes. Nobody has the answer. Not the teacher who laughed. Not the physicist. Not anybody. Right now. Tonight."

Soren picked up his notebook. He looked at where he'd written HOT FROZE FIRST and underlined it like he was wrong.

He wasn't wrong.

"So when we did it," he said slowly, "and got the answer that's supposed to be impossible. We weren't behind everyone who knows."

"No," Maya said.

"We were standing exactly where the scientists are standing."

"Yeah," Maya said. "At the part nobody's figured out."

Soren got up off the floor. He opened the freezer and felt the cold pour out over his hands, and he looked at the warm tray, the one that should have lost and didn't, the one that broke the rule the same way every single time and dared him to say why.

"Do it again," he said. "But this time let's measure the evaporation. Weigh the trays before and after. If the hot one loses water, that's a maybe we can check ourselves."

Maya was already reaching for the kettle.

"And if it doesn't lose enough to matter," she said, "then it's something else, and we don't know what either."

"Good," Soren said.

Maya stopped. "Good?"

"Good," he said again. "It means there's still room."

They filled two trays, one cold and one steaming, and Maya set them side by side on the kitchen scale, watching the numbers settle, while the kettle ticked and cooled behind them.