The Longest Stick in the Universe

The pole was twelve meters long, which was ridiculous. Soren's mother had bought it for a clothesline project she never finished, and now it leaned against the back fence like a silver line drawn against the sky.

Maya stood at one end. Soren stood at the other.

"Push it," Soren said.

"I'm going to push it."

"Then push it."

Maya shoved her end of the pole. Soren felt it instantly. Or what seemed like instantly. He wrote down: felt immediate.

"See?" Maya called from the far end of the yard. "You felt it right away. The whole pole moves at once."

Soren frowned at the pole. "It felt instant. But twelve meters isn't very far."

"So?"

"So what if the pole were longer?"

This was the argument. It had started an hour ago over a video about communicating across space. Someone in the comments had written: just get a pole long enough to reach Mars and push it, the person on the other end would feel the push instantly, faster than light, faster than radio. Problem solved.

Maya had laughed at the comment. But then she stopped laughing. Then she got quiet in the way she got quiet when something didn't fit.

"It can't work," she had said. "But I can't say why."

Now they were in the yard with a twelve meter pole and no answers.

Soren held his end loosely. "Do it again. But this time, don't tell me when."

Maya waited. She counted to some number she didn't share. Then she pushed.

Soren felt it. "Now," he said.

But this time he was paying attention to something specific. Not whether he felt it, but how it felt.

"It wasn't a push," he said slowly. "It was more like a bump. Like something arrived."

Maya walked toward him, leaving her end of the pole resting on the grass. "What do you mean, arrived?"

"When you push a thing, the whole thing should just go. But it felt like your push showed up at my end. Like it traveled."

"Everything that moves travels."

"The pole didn't move, though. Your push moved. Through the pole."

Maya stared at him. She picked up a stick from the ground and held it between two fingers. She squeezed one end. "When I squeeze here, does the other end bulge out at exactly the same time?"

"It has to," Soren said. Then: "Doesn't it?"

"What is the stick made of?"

"Wood. Atoms."

"And what's between the atoms?"

"Space. Forces. Bonds."

Maya dropped the stick. She was getting that look, the one where her eyes went slightly past whatever she was looking at. "The atoms aren't touching. They're just near each other. Held by forces. Like tiny springs."

"Okay."

"So when I push this end, I'm pushing the first atoms. And they push the next atoms. And those push the next ones."

"Like dominoes," Soren said.

"Like dominoes," Maya repeated. "It's not instant. It can't be instant. It just looks instant because the pole is short and the wave is fast."

Soren picked up the aluminum pole. He held it to his ear and tapped the far end against the fence. The ping arrived bright and sharp, a sound traveling through metal. A wave.

"The push is a wave," he said. "A sound wave. Moving through the pole."

"So the person on Mars wouldn't feel the push at the speed of light. They'd feel it at the speed of sound in whatever the pole is made of."

"Which is way slower than light."

"Way, way slower than light."

They stood there. The sprinkler two yards over made its ticking sound. A plane drew a white line overhead.

Soren sat down on the grass. "But that means something else."

"What?"

"If the push is a wave, then while the wave is traveling, the front of the pole has moved but the back of the pole hasn't. The pole is shorter. It's compressed."

Maya sat down across from him. "The pole squishes."

"Every pole squishes. Every rod, every beam, every stick. When you push one end, the other end doesn't know yet. It can't know yet, because information can't travel infinitely fast. So for a tiny moment, the pole is being compressed and the back end is just sitting there, having no idea."

"So a perfectly rigid thing, a thing that can't compress at all, would have to transmit the push instantly."

"Which would be faster than light."

"Which isn't allowed."

"So a perfectly rigid thing can't exist," Soren said.

The sentence hung between them. Maya pulled grass out of the ground, one blade at a time.

"Anything you push, no matter how hard it is, no matter how solid it feels, it compresses. It has to. Diamond. Steel. Anything. Because otherwise you'd be sending information faster than the universe allows."

"The universe has a speed limit," Soren said, "and it applies to everything. Even the inside of a stick."

Maya lay back on the grass and looked up. The plane was gone. The contrail was already dissolving, its edges going soft, the straight line becoming something that wasn't a line anymore.

"You know what's strange?" she said. "It means that solid things aren't really solid. Not the way we think. They're squishy. Everything is squishy. We just can't see it because we're too slow and the waves are too fast."

"The aluminum pole is squishy."

"The ground is squishy."

"The Earth."

"The Earth is a little bit squishy."

Soren opened his notebook. Then he closed it. This was not a notebook moment. This was a lying on the grass moment.

He lay back next to Maya. Above them, the sky was the kind of blue that looked solid, that looked like a dome, that looked like something you could knock on and hear a sound come back. But it wasn't solid. It was just scattered light and empty space, all the way up, and the blue was a lie your eyes told you because the truth was too big.

Maya reached over and pushed his shoulder, gently.

He felt it. A compression, arriving. A wave through the matter of him, atom by atom by atom, faster than he could follow but not infinitely fast. Nothing was infinitely fast.

"Did you feel that?" Maya asked.

"Not yet," Soren said, grinning. "Give it a few billion atoms."