The Cost of a Bone

Soren broke his wrist falling off the low wall behind the science wing, which everyone agreed was an unscientific way to break a wrist.

Now he sat in the radiology waiting room with his arm wrapped and his good hand holding the X-ray printout the technician had let him keep. Maya leaned over the back of his chair to look.

The bones glowed pale against the black. Two long shapes in his forearm, a cluster of small ones at the wrist, all of it bright and clean.

"Why do they show up white," Maya said. It was not really a question. It was the start of one.

"Calcium," Soren said. "The tech told me. Bones are dense with calcium, so they block more of the X-rays. The white is where nothing got through."

"So the white is your calcium."

"The white is my calcium."

Maya was quiet. Soren knew the quiet. It was the quiet she got before she said something that turned the room sideways.

"Where did it come from," she said.

"Milk. Probably. Cheese."

"No. Before that."

A nurse called a name that wasn't theirs. Soren's father was at the desk arguing gently about a form. Soren looked at the bright bones in his arm and tried to follow Maya backward.

"The cow ate grass," he said slowly. "The grass pulled it out of the soil. The soil got it from rocks."

"And the rocks?"

"The rocks are just Earth. The Earth came from the stuff that made the Sun." He stopped. He had reached the edge of the part he knew, and he could feel there was more cliff past it.

Maya was already past the edge. "There's no calcium in a new universe," she said. "I read that. At the start there's only hydrogen and helium. The two lightest. That's the whole menu."

"So how do you get to calcium."

"You build it. Somewhere with enough pressure to jam small things into bigger things."

Soren turned that over. There was only one thing in the universe with that kind of pressure at its core.

"A star," he said.

His father finished at the desk and said it would be another twenty minutes, and did they want to wait inside or get air. Maya said air before Soren could answer. She was already moving.

The hospital had a flat roof terrace for visitors, gravel and a railing and a row of dark planters. It was after nine. The town's lights washed out most of the sky, but a few stars held on overhead, stubborn and small.

Soren held his X-ray up against the dark. The printout was nearly black, so the bones seemed to float among the real stars.

"Okay," he said. "Walk it forward. A star fuses hydrogen into helium. That's the part everyone knows. Then?"

"Then it runs low on hydrogen and starts fusing the helium," Maya said. "Into heavier stuff. Carbon. Oxygen." She counted on her fingers in the dark. "It keeps going. Each new fuel makes something heavier. Like floors in a building going down."

"And calcium's on one of those floors."

"Calcium's way down." She frowned. "But here's the thing that doesn't fit. A star can't make the heavy stuff and keep it. It's locked inside. Buried in the core."

Soren looked at the white wrist bones against the night. Locked inside. Buried in a core. He thought about the only way a buried thing gets out of a star.

"It has to break," he said.

Neither of them said anything for a moment.

"The star that made your calcium," Maya said, "already died. It made the calcium and then it blew itself apart and scattered it. And that had to happen before the Sun even existed. Before there was an Earth for the rocks to be in."

"So my arm is older than the Sun."

"The stuff in your arm is older than the Sun."

Soren lowered the printout. He could feel his pulse in the broken wrist, a small insistent beat under the wrapping. He thought about what was riding in that blood. Iron. Iron made the red. Iron was heavier than calcium, even further down the building, even harder to make.

"Maya," he said. "The iron in my blood. Same story?"

"Worse story. Iron's the last floor a star can build before it can't anymore. Past iron, fusing doesn't give energy back, it costs it. So iron's where the ordinary building stops." She paused. "Some of it comes from the explosion itself. The dying."

The pulse in his wrist kept going. Iron, made in a death, carrying oxygen made in a different death, looping through a kid sitting on a hospital roof with a broken arm.

"Every heavy thing in me," Soren said, testing each word, "is a receipt. From a star that's gone."

"From more than one," Maya said. "Your calcium and your iron probably came from different stars. Different explosions. Different times. All mixed into the same cloud that became us." She looked at him. "You're not from a star. You're from a crowd of them."

Soren had spent the whole evening feeling sorry about his wrist. The smallness of it. A wall, a bad landing, a stupid afternoon. He held the printout up again, and the bright bones sat among the real points of light, and he could not tell anymore which white was star and which white was him.

"That's why it's white," he said softly. "The calcium blocks the X-rays because it's heavy. It's heavy because something enormous made it heavy. The reason the picture works at all is the reason it had to come from a star."

Maya grinned at him in the dark. She loved when he closed the loop.

"There are people," Soren said, "who'd find it weird that I'm sitting on a roof with a broken arm thinking about this instead of just icing it."

"There are stars," Maya said, "that spent ten million years and their entire lives so that one day you'd have something to break. I think you're allowed."

Soren's father appeared in the doorway and called that they were ready for the cast.

Soren stood. He held the X-ray flat against his chest, over the iron going around inside him, and tipped his face up to the few stars the town hadn't drowned, looking for the ones that might have been close enough to count.