The answer was impossible, and that did not stop me.
The laboratory was mostly empty. The lights came on slowly, one bank at a time. Dust covered the reception desk, and someone had left a chair pulled out from a table, as if they had only stepped away. I found Lena's notebook on a bench, her handwriting filling the first pages. She had been trying to organize our treatment data. She had believed there was a way. So had I.
I worked, though not because I thought I could cure myself. I could not, not in time. I worked because there was one thing left that might still matter, and the name of it was time.
The idea was not mine. It belonged to two visiting physicists who had spent three summers in our laboratory years before, bolting a small sealed cavity into the wall of the secured room, because it was the quietest place in the building: no vibration, no drift in temperature, stable enough, they said, to hold a delicate state for years. Their subject was closed timelike curves, paths through spacetime that loop back on themselves. Einstein's equations permit them under extraordinary conditions, and nobody has ever built one. They never claimed to have a time machine. They wanted to know whether a tiny physical system, wound around such a loop, could carry a single signal backward. When they left they left a note, a folder of drawings, and the cavity, and we forgot about it the way you forget about a smoke detector.
The rule that governs a loop like theirs is cruel in its simplicity. It can return information only to the moment it was opened, and not an instant earlier. I could not choose when to speak to myself. The cavity had been set to open on a disturbance of its wall, any jolt at all, and in all the years it had sat there the wall had been disturbed exactly once, when a seal bolted to the same steel was broken. I thought of the sound. Small, almost nothing. That sound was the only door the loop had ever had.
That fixed everything. It meant I could not warn myself the week before, or the night before, or even the minute before. I would reach the boy in the instant his mother's hands lifted the lid, and no sooner. The physicists had wired the cavity to the room's own intercom, so that any signal would come out as sound through the speaker in the wall. It would be a handful of seconds at most. It would be information and nothing else, a voice, not a machine and not a body. Forcing it through would take every watt the building could give and would burn the cavity out. I could try once.
There was a second problem, and I will not pretend I solved it. If a message from my future reached my past, then the world I was dying in was either already the result of the boy having heard it, or it was not. The physicists had argued about this for three summers, over dinner, with salt shakers for particles. One school said there is only one history, and whatever I sent had already happened, so the world I was dying in was the proof of what he did. The other said the loop opens onto a history that has not happened yet, a neighboring one, and that nothing I sent could save anyone I loved. I could not tell which was true, and I am not sure I wanted to. If the first was right, I was already the evidence that he had failed. If the second was right, I was writing to someone else, a stranger who happened to have my face, in a world where it was still possible to be spared. In neither case could I know what he would do with a few seconds of my voice. The choice would still be his. That was the only part of the physics I trusted.