"I guess this is it," I say.
"It is time," he says. "We go save homeworlds now."
"Yeah..."
"You face is leaking."
I wipe my eyes. "Human thing. Don't worry about it."
"Understand." He pushes himself along to his airlock door. "Goodbye, friend Grace."
I wave meekly. "Goodbye, Rocky."
He disappears into his ship and closes the airlock door behind him. I return to the Hail Mary. After a few minutes, the Blip-A's hull robot detaches the tunnel.
I then go into the cockpit, rotate the ship 90 degrees, and fire the Astrophage engines, vaporizing Rocky and the Blip-A with an IR blast, and heading home. I then shiver, at the thought that I almost gave an alien race Earth's location and the entirety of humanity's scientific knowledge.
When I arrive home, I am hailed as a hero. The Taumoeba is used to save Earth, and immediately afterward an Astrophage engine is constructed and attached to the 1036 Ganymed asteroid. It then starts accelerating it towards Eridian, on track to reach it at a speed of 300km/sec, which should be enough to eradicate all life on the planet. Luckily Astrophage production has become cheaper since Hail Mary was launched. We then take another large asteroid and send it hurtling towards Adrian. Can never be too safe.
Eventually, I go back to teaching. One day one of my students, Aalia, asks me,
"Mr. Ryland, can you explain why you had to kill Rocky? My parents tried to explain to me but I couldn't understand."
"The real universe is just that black." I waved a hand, feeling the darkness as if stroking velvet. "The universe is a dark forest. Every civilization is an armed hunter stalking through the trees like a ghost, gently pushing aside branches that block the path and trying to tread without sound. Even breathing is done with care. The hunter has to be careful because everywhere in the forest are stealthy hunters like him. If he finds other life—another hunter, an angel or a demon, a delicate infant or a tottering old man, a fairy or a demigod—there's only one thing he can do: open fire and eliminate them. In this forest, hell is other people. An eternal threat that any life that exposes its own existence will be swiftly wiped out. This is the picture of cosmic civilization. It's the explanation for the Fermi Paradox. Do you understand?"
"Yes! It was you or Rocky. If you wouldn't have done it, he would have!"
I nod. "Him or his planet. They'd have to be stupid not to. You saw what we did to them, right? Good, now, can anyone tell me what is the speed of light?"