They sent the Riemann Hypothesis at 0347 on the third morning, timed to coincide with the signal's usual arrival. It felt important to Solaris that the transmission go out at the same moment theirs came in — a conversation beginning in the same breath, rather than a reply delayed by caution.
The array transmitted for four minutes and seventeen seconds. Then it went quiet. Then, at 0351, the incoming signal arrived on schedule, the same twelve primes, the same offset sequence. As if their transmission had not yet traveled far enough to matter.
Of course. Light-speed delay. Solaris had known this intellectually. Knowing it and sitting with it in her body were different experiences. Whatever answered them — if anything answered — would not arrive for the equivalent time it had taken the original signal to reach them. Months. Possibly years. They had opened a conversation whose other half existed in a future they might not live to see.
"Well," said Reyes, standing at her shoulder as the incoming signal's confirmation light blinked steady on the board. "We've done it."
"We've started it," Solaris corrected. She watched the signal technician log the timestamp. "Starting and doing are different things. We won't know which this was for a long time."
She thought about the nineteen months of unanswered transmissions. The patience of whatever had been sending. She hoped patience was a thing they had in common. It seemed suddenly very important that it was.