The proposal was written on a single sheet of paper, which Vance had printed out and placed in the center of the conference table with the deliberate formality of a man presenting a legal document.
Solaris read it twice. Then she looked up.
"You want to send them a problem we don't know the answer to."
"Not any problem," Vance said. He was animated in a way that suppressed grief sometimes produced — the particular manic clarity of a man who had found something to think about more important than what he was trying not to think about. "The Riemann Hypothesis. Unsolved for a hundred and seventy years. If they're mathematically sophisticated enough to initiate a prime-number handshake, they may be sophisticated enough to have solved it. And if they have, and if they respond with the proof—"
"Then we have a proof of the Riemann Hypothesis," said Dr. Chen, the mission's chief mathematician, in a tone that suggested she had not yet decided whether this was the best or worst day of her professional life.
"More importantly," Vance continued, "we learn something about their cognitive range. Their willingness to share knowledge. Whether contact, for them, means exchange or just announcement." He sat back. "It's also a message that can't be misinterpreted as hostile. Mathematics doesn't have a threatening form."
Admiral Reyes turned his glass in a slow circle on the table. "Unless their relationship with mathematics is entirely different from ours," he said. "In which case we have no idea what we'd be communicating."
The room was quiet for a moment.
"That's always been true," Solaris said. "We've just been pretending it wasn't."