Project Hail Mary

by Andy Weir

I have a pendulum. Cool thing about pendulums: The time it takes for one to swing forward and backward—the period—won’t change, no matter how wide it swings. If it’s got a lot of energy, it’ll swing farther and faster, but the period will still be the same. This is what mechanical clocks take advantage of to keep time. That period ends up being driven by two things, and two things only: the length of the pendulum and gravity.

Another planet? But there isn’t any planet, moon, or asteroid in the solar system that has this much gravity. Earth is the largest solid object in the whole system. Sure, the gas giants are bigger, but unless I’m in a balloon floating around the winds of Jupiter, there’s just nowhere I could go to experience this force.

“Believe it or not, light has momentum,” I said. “It exerts a force. If you were out in space and you turned on a flashlight, you’d get a teeny, tiny amount of thrust from it.”

I scowled. “This isn’t some cheesy movie, Stratt. Pathogens evolve slowly over time to attack specific hosts. Astrophage has never even been on Earth before. There’s just no way it can ‘infect’ humans. Besides, it’s been a couple of days and I’m not dead. So send it out to the real scientists.”

Whatever their navigation system was, it was based on light. I suspected that would be the case. What else could you use in space? There’s no sound. No smell. It would have to be light, gravity, or electromagnetism. And light’s the easiest of those three to detect.

Planets don’t just reflect light. They also emit it. Everything emits light. The temperature of the object defines the wavelength of light emitted. Planets are no exception. So maybe Astrophage looked for Venus’s IR signature. It wouldn’t be as bright as Mercury’s, but it would be distinct—a different “color.”

Anything smaller than the wavelength is functionally nonexistent to that photon. That’s why there’s a mesh over the window of a microwave. The holes in the mesh are too small for microwaves to pass through. But visible light, with a much shorter wavelength, can go through freely. So you get to watch your food cook without melting your face off.

Do you believe in God? I know it’s a personal question. I do. And I think He was pretty awesome to make relativity a thing, don’t you? The faster you go, the less time you experience. It’s like He’s inviting us to explore the universe, you know?”

“Math is not thinking. Math is procedure. Memory is not thinking. Memory is storage. Thinking is thinking. Problem, solution. You and me think same speed. Why, question?” “Hmm.” I ponder it for a while. It’s a really good question. How come Rocky isn’t a thousand times smarter than me? Or a thousand times dumber? “Well … I have a theory for why we’re about the same intelligence. Maybe.” “Explain.” “Intelligence evolves to gives us an advantage over the other animals on our planet. But evolution is lazy. Once a problem is solved, the trait stops evolving. So you and me, we’re both just intelligent enough to be smarter than our planet’s other animals.” “We are much much smarter than animals.” “We’re as smart as evolution made us. So we’re the minimum intelligence needed to ensure we can dominate our planets.” He thinks it over. “I accept this. Still not explain why Earth intelligence evolve same level as Erid intelligence.” “Our intelligence is based on the animals’ intelligences. So what is animal intelligence based on? How smart do animals have to be?” “Smart enough to identify threat or prey in time to act.”

The hardest part about working with aliens and saving humanity from extinction is constantly having to come up with names for stuff.

When you get down to it, smell is just tasting at range.

Seems odd that a species could invent interstellar travel before inventing the transistor, but hey, Earth invented nuclear power, television, and even did several space launches before the transistor.

Nitrogen is utterly harmless and nearly inert in its gaseous state. It’s usually content to be N2, which barely wants to react with anything. Human bodies ignore the stuff despite every breath being 78 percent nitrogen.

“Humans are very different,” I say. “We get diseases all the time. We have very powerful immune systems. Also, we find cures for diseases in nature. The word is ‘antibiotics.’” “No understand,” he says. “Cures for diseases in nature, question? How, question?” “Other life on Earth evolved defenses against the same diseases. They emit chemicals that kill the disease without harming other cells. Humans eat those chemicals and they kill disease but not our human cells.” “Amaze. Erid no have this.” “It’s not a perfect system, though,” I say. “Antibiotics work very well at first, but then over the years, they become less and less effective. Eventually they barely work at all.” “Why, question?” “Diseases change. Antibiotics kill almost all the disease in the body, but some survive. By using antibiotics, humans are accidentally teaching diseases how to survive those antibiotics.”

“Yes. There’ll be wars. Fought for the same reason most wars in ancient times were fought for: food. They’d use religion or glory or whatever as an excuse, but it was always about food. Farmlands and people to work that land.

We tend to think of solid materials as magical barriers. But at the molecular scale they’re not. They’re strands of molecules or lattices of atoms or both. When you get down to the teeny, tiny realm, solid objects are more like thick jungles than brick walls.

That’s the difference between Taumoeba and nitrogen. The nitrogen is just moving in a line and bouncing off stuff like a tennis ball. It’s inert. But Taumoeba is like me. It has stimulus-response capabilities. It senses its environment and takes directed action based on that sensory input. We already know it can find Astrophage and move toward it. It definitely has senses. But nitrogen atoms are ruled by entropy. They won’t “exert effort” to do anything. I can walk uphill. But a tennis ball can only roll so far before it rolls back down.