Four Hundred Years Late

The signal had been travelling for four hundred and six years when it reached the listening station at Tycho, and Dr. Ada Forsell was forty-nine years old when they told her it would be her life's work to answer it. She remembered the room. She would always remember the room, the way you remember the room in which you were told something that divided your life into a before and an after. It was an ordinary briefing room on the lunar farside, grey and warm and slightly too small, and the station director had a way of folding her hands that Ada had come to understand meant the news was large. "It's structured," the director said. "That's the first thing, and it's the thing that matters. We have looked at it every way we know how, and it is not pulsars and it is not a quasar and it is not us. It has structure. It repeats. It has — Ada, it has what looks like grammar. It is a message, and it was sent on purpose, and it was sent to anyone who might be listening." Ada had spent her whole career on the edge of this moment without ever quite believing it would arrive. She was a linguist; specifically, she was a linguist of the impossible kind, the kind who studied the deep structure of how meaning might be built by minds that were not human minds, a discipline that for most of its history had been the study of a thing that had never once been observed. People had been kind about it. People are always kind about a discipline that has no object. She had felt the kindness like a draught. "Where," she said. Her voice came out steady. She was proud of that, later. The director brought up the star. It was an unremarkable star, a quiet yellow-orange star in a quiet part of the sky, and the director let it sit on the display for a moment before she said the rest. "That's the source. And that's the second thing, and it's the hard thing." The director unfolded her hands and folded them the other way. "The signal is four hundred and six years old. That's how far it had to travel. We can confirm the source, and we can confirm something else about the source, because we have four centuries of observation of that star sitting in the archives." She paused. "It went out, Ada. The star. Three hundred and ninety years ago — sixteen years after this signal left it — it went through a stellar event that nothing in a biosphere survives. Whoever sent this message has been dead, by our reckoning, for the better part of four centuries." Ada looked at the quiet star that was not there anymore. "Then there's no one to answer," she said. "That's the conclusion most people in this building have reached, yes." "But you didn't bring me to the moon to tell me there's no one to answer." Ada was a linguist; she heard the shape of a sentence the way a mason hears the shape of a stone. "You used the word work. My life's work. You don't say that about a message to the dead." The director smiled, very slightly, the smile of someone who had hoped the person across from her would catch exactly that. "The signal is structured," she said. "Which means we may, with effort, with years, learn to read it. And a message built carefully enough to be readable by strangers is, very often, a message that contains the means of its own reply — a key, an address, a frequency. We think this one does. We think that buried in four hundred years of structured light there are instructions for how to answer." She let it land. "And here is the thing, Ada, here is the whole of why you are on the moon. If we crack it, and if we send a reply — the reply travels at the speed of light, the same as the signal did. Four hundred years out. And if anything is still there to hear it, or anything ever will be, then any answer to our answer is another four hundred years coming home." Ada did the arithmetic. It was not difficult arithmetic. It was only enormous. "A single exchange," she said slowly. "One message, and one reply, and one reply to the reply. Twelve hundred years, end to end. Longer than any human institution has ever lasted. Longer than most languages." "Longer than most languages," the director agreed. "Which is the third thing, and the reason it has to be you, and the reason I am sorry. Because the work of answering this signal is not a project, Ada. A project has an end. This has no end you will live to see. We are asking you to give the rest of your life — every year of it, all of it — to composing one half of a conversation whose other half will be spoken to people not yet born, in a year you cannot imagine, about a star that has been dark for four hundred years." She unfolded her hands a final time. "We are asking you to write a letter you will never see answered. And we needed to ask someone who would understand, completely, what that costs, before she said yes." Ada Forsell sat in the small grey room and looked at the light of a dead star, and felt her life divide, cleanly, into the part that came before this and the part that would now come after. "Tell me everything you know about the grammar," she said. "And then find me somewhere quiet to work. It seems I am going to be here a while."