The Cup That Would Not Stay Full

Maya's aunt Priya worked nights at the place that made the cold, and the cold was colder than anything Maya had a word for.

"Two more dewars," Priya called from across the loading bay, her voice echoing off the concrete. "Then I drive you both home. Do not touch the silver tanks. They will take the skin off your fingers."

"We know," Maya said. They had been told four times.

Soren was crouched by a small glass-walled chamber on the test bench, the one Priya called the demo rig. Inside it sat a tiny open cup, no bigger than a thimble, half full of clear liquid. A frost of cold rolled off the whole apparatus in slow sheets.

"That's helium," Soren said. "She said it gets to two Kelvin in there. Two degrees above the coldest anything can be."

"Okay," said Maya. She leaned in until her breath fogged the outer glass. "Then why is the cup emptying."

"It's not. Nothing's pouring out."

"It's emptying, Soren. Look at the line."

He looked at the line. The little surface of liquid inside the thimble was lower than it had been thirty seconds ago. No drip. No splash. The cup was simply, quietly, losing what was in it.

"Maybe it's boiling off," he said. "Cold stuff boils. Into gas."

"Then where's the gas going? The chamber's sealed." Maya pressed her cheek nearly to the glass. "And look at the bottom. There's liquid in the bottom of the big dish. Outside the cup. How did it get outside the cup?"

Soren got down level with her so his eyes were at the height of the thimble's rim. For a while neither of them said anything.

"Maya. The rim's wet."

"What?"

"All the way up the inside wall. And over the top. And down the outside." He spoke slowly "There's a film of it. Going up the wall."

"Up," Maya repeated.

"Up. Against the wall, over the lip, down the other side. It's climbing out."

Maya sat back on her heels. "Liquids don't climb out of cups."

"This one is."

They watched the line in the thimble drop again, the tiniest amount. Somewhere a pump hummed. Priya thumped a tank into place behind them and swore softly at a frozen valve.

"Okay," Maya said. "Try this. If it climbs walls, it doesn't care about gravity the way water does."

"It cares. It's just—" Soren stopped. "Water climbs a little. Up the side of a glass. The edge curves up, you've seen it. There's a tiny pull between the liquid and the wall. But friction stops it. Stickiness. It can only climb a hair before its own weight drags it back."

"So take the friction away," Maya said.

Soren went very quiet, then said it out loud. "If there's no friction at all, the climbing never stops. The pull up the wall just—keeps winning. Forever. It walks right over the edge."

"There's no such thing as no friction."

"There is in there." He pointed at the chamber without touching it. "That's why it's so cold. She said below some exact temperature it changes. Becomes something else. A super-something."

"Superfluid," Priya said, appearing behind them with a clipboard, not looking up from it. "Below two point one seven Kelvin. Don't put your hands on the glass." She turned a page. "It's the only liquid that does that. Climbs. We hate it, actually. You cannot keep the stuff in a container. It finds every gap."

"Every gap," Maya said.

"Holes a gas couldn't fit through, it pours straight out. No friction, see. Friction's what makes a thing too big for a hole. Take that away and it just slips between the atoms." Priya clicked her pen. "Beautiful and a complete nuisance. One more tank." She walked off.

Maya and Soren looked at each other.

"It goes through holes too small for gas," Soren said, like he needed to hear himself say it.

"And it climbs out of any cup," said Maya.

"And—" Soren stopped. He was staring at something else in the rig now, a small clear ring of the liquid that Priya had set spinning earlier with a stir, a slow circular drift inside a groove of the dish. "Maya. How long has that been turning."

"The little circle?"

"It was going when we got here. She stirred it before we sat down." He checked his wrist, though he had no watch, an old habit. "That was twenty minutes ago. Easy."

Maya watched the ring of liquid drift around its groove. Around. And around. Exactly as fast as before. Not slowing. Not even a little.

"Stir water," she said. "It stops."

"In seconds."

"Stir this."

"It doesn't stop." Soren's voice had gone thin. "There's nothing to stop it. Friction is the thing that stops things. And in there, for that liquid, there is no friction. So it would keep going—"

"Don't say forever."

"It would keep going forever. If you kept it cold, that ring would still be turning after we're old. After everybody's old. The same circle, the same speed."

Maya put her hand near the glass and remembered, and pulled it back.

"So everything that ever stops," she said slowly, "only stops because of friction."

"Yeah."

"A ball rolling. A swing. The merry-go-round. Everything I've ever watched slow down and stop. It only stopped because something was rubbing."

"Yeah."

"And that—" she nodded at the silent, endless ring, "—is what motion is like when nothing rubs. That's the real thing. Underneath. All the stopping was just stuff getting in the way."

Soren had his notebook open. His pencil moved, then stopped, hovering over the page, because the circle in the glass had not stopped and he could not make the pencil draw a thing that ended.

The thimble inside the chamber was empty now. Every drop had walked up its own walls and over the edge while they argued, and pooled in the dish below, and joined the ring, and the ring went around, and around, patient as a planet, taking its time the way a thing takes time when it has all of time and intends to use every bit of it.

Behind them Priya dropped the last tank into its cradle and said they could go. Neither of them moved. The little circle kept turning.