The Twelfth Notebook

He was reading his grandfather's twelfth notebook again, looking for anything he might have missed, when he found the letter.

It was folded inside the back cover, tucked into the gap between the cover and the lining, invisible unless you looked carefully. His grandfather's handwriting on the front said simply: For whoever finds the signal.

Nico's hands were not entirely steady when he unfolded it.

The letter was dated fourteen months ago, three months before his grandfather had died. It was three pages long and he read it slowly, twice, before he moved.

His grandfather had found the signal too. Eighteen months before Nico, sitting at the same console, looking at the same patch of sky. He had recorded it for six weeks and worked out the pattern and come to the same interpretation. He had contacted the same kinds of experts and received the same kinds of responses.

But he had also done something else. He had spent the last months of his life trying to do what nobody else had thought to do, which was to send something back.

The observatory had a radio transmitter, old and not especially powerful, that they used for communication with other amateur astronomers. His grandfather had spent weeks calculating the precise frequency and direction and had transmitted a response. The same pattern. Short short long short long long short. And after it, a new sequence, something of his own.

He had transmitted the first seventeen prime numbers in binary.

Prime numbers, he wrote in the letter, are the same in every mathematics. They are the proof that something understands numbers rather than simply generating them. If anything out there receives this and understands it, they will know we are here and that we are thinking.

Nico put the letter down on the console and looked at the equipment around him. The transmitter. The telescope. The notebooks on the shelf. The whole small, slightly draughty observatory that his grandfather had built and his mother ran and he had grown up in.

His grandfather had sat in this same chair and looked at this same signal and thought the same things and reached the same conclusions and done something about it.

And then he had written a letter to whoever would come next.

Nico read the last paragraph of the letter again.

It said: I do not know if anyone will answer. I do not know if anyone is there to answer. But I know that this signal is not natural and I know that someone made it and I know that the right response to something like that is not to file a report and move on. The right response is to reach back. So I reached back. If you are reading this, the signal is still there. That means something. Reach back again. Keep the conversation going. That is what we do.

Nico sat for a long time in the quiet observatory with his grandfather's letter in his hands.

Outside the window the sky was very clear, Sector Nine perfectly visible, forty-six light years of nothing between here and wherever the signal was coming from.

He got up and went to the transmitter.