The Sound That Wasn't Sound

The gym still smelled like water and floor wax. Everyone else had gone home, and the ripple tank sat in the middle of the free-throw circle, half full, throwing wobbly light up onto the basketball hoop.

"Push it again," Maya said.

Soren tapped the edge of the tank with one finger. A ring spread out across the surface, and the light on the ceiling flexed, went bright at the edges, went dark in the middle.

"That's the whole demo," he said. "Waves need something to wiggle. Water wiggles. Air wiggles. Mr. Okafor said if you were standing on the moon and I screamed, you'd hear nothing."

"Because there's no air to carry it." Maya crouched so her eyes were level with the water. "So space is silent."

"Completely."

She watched the last ring die against the plastic wall. "Then what did they hear?"

"Who?"

"The people with the big detector. Mr. Okafor put it on the screen at the end and everyone was already packing up. There was a sound. A little swoop, like a bird going up." She hummed it. "Woop. He said two black holes made it."

Soren stopped coiling the extension cord. "Black holes are in space."

"Yeah."

"Space is silent."

"Yeah." Maya looked at him. "So how do you hear a thing that happened in a silent place?"

Soren sat down on the gym floor with the cord in his lap. This was the kind of thing that would keep him up, and he knew it, and he didn't mind. "Maybe they didn't hear it. Maybe they made it into a sound after. Like when they color the Mars photos."

"Then what was actually there?" Maya reached into the tank and pressed her palm flat against the bottom, feeling the water settle. "Something moved. Something got to the detector. If it wasn't sound, and it wasn't air, what came across?"

"Light comes across space. That's not silent, that's just, you know, invisible sound rules don't apply."

"It wasn't light either. He said the detector doesn't have a telescope. It's just two really long tunnels." She stood up, dripping. "Tunnels with a laser going down each one. Why would you need it to be long?"

Soren pulled his notebook out of his back pocket and drew two lines meeting in a corner, like an L. He tapped the end of each line. "You'd only need it long if you were measuring how long it is. A short thing, you can't tell if it got a tiny bit shorter. A long thing, maybe."

"Shorter," Maya repeated. She said it slowly. "You'd build a four-kilometer tunnel to check if it got shorter."

"By how much?"

"He said the number and it was insane. Smaller than a proton. Smaller than the inside of an atom."

Soren looked at his two lines. He put his pencil down in the water tray to wet the tip, out of habit, and then held it over the L. "Okay. Push the tank again."

Maya tapped it. The ring went out. They both watched the light stretch and squeeze on the ceiling.

"The water goes up and down," Soren said. "But watch the light. The light isn't going up and down. The pattern is getting wide and then narrow. Wide. Narrow."

"Because the water's shape is changing underneath it."

"The distance between the high parts is changing. That's what a wave is, really. Distance changing, over and over, and moving along." He stopped. His hand went very still over the paper, and then he wrote one word and underlined it twice. "Maya. What if the black holes didn't make a wave in something."

"What do you mean, in something. Everything's a wave in something. Water waves in water."

"Sound waves in air. Right. But what if there's nothing to wave in out there, so instead the wave is in the distance itself." He held up the notebook. The underlined word was DISTANCE. "The tunnels don't get shorter because something pushed the walls. They get shorter because how long a meter is changed. For a second. Then it changed back. Woop."

Maya went quiet. She was looking at the ripple tank, but she wasn't seeing the tank.

"Say it again," she said.

"Space stretched. Then it squeezed. The ruler and the thing you're measuring both changed, except the laser goes so far that it caught the difference before it evened out." Soren's voice went up at the end, not because he was unsure, but because he could feel how big it was getting. "It's not a sound. It's the shape of everything wobbling. They turned the wobble into a sound so we could hear it, but the real thing is worse. The real thing is the whole floor of the universe going like this." He pressed both hands into the water and let the rings crash into each other.

Maya crouched again, fast. "So when the detector caught it, the detector got longer and shorter."

"Yeah."

"And the people standing next to it."

Soren stopped.

"They got taller and shorter too," Maya said. "By a proton. Everybody in the building did. When the swoop happened, everyone reading the screen was a little bit stretched and they couldn't feel it because their eyeballs stretched the same amount as the thing they were looking at." She held her own hand up in front of her face and spread her fingers. "It went through the whole planet. It went through this gym. It went through us, before we were born, and nothing in us was built to notice."

"Two black holes," Soren said. "A billion years ago."

"And the only reason anybody knew is somebody built a ruler long enough and asked the right stupid question." Maya laughed, a little shaky. "Did it get shorter. What a question. Who wonders that."

Soren looked down at his soaked notebook, the word DISTANCE bleeding into the paper. "People like the ones who built the tunnel."

"People who don't fit," Maya said. "People who notice they're standing in a room and think, what if the room isn't holding still."

She tapped the tank one more time.

The ring went out across the water, and the light on the ceiling stretched wide and squeezed narrow, wide and narrow, all the way to the edge of the hoop.