"Project Hail Mary"

Andy Weir comes up with some truly great What-Ifs and follows through well. The science behind space travel part is solid, presumably, but there's a lot more hand-waving when it comes to astrophage biology.

• Let’s not jump to wild conclusions. Yes, the gravity is too high. Work from there and think of sensible answers.
  I could be in a centrifuge. It would have to be pretty big. But with Earth’s gravity providing 1 g, you could have these rooms at an angle running around a track or on the end of a long solid arm or something.
• I look down at my sheet toga. “I am the great philosopher Pendulus!”
• “It’s right,” she said. “The sun’s output will drop a full percent over the next nine years. In twenty years that figure will be five percent. This is bad. It’s really bad.”
• That other hatch in the lab—the one that leads farther up—that must be important. This is like being in a video game. Explore the area until you find a locked door, then look for the key. But instead of searching bookshelves and garbage cans, I have to search my mind. Because the “key” is my own name.
• “It lives on or near the surface of the sun. Does that sound like a water-based life-form to you?”
• “I did some back-of-the napkin math. And I’m pretty sure that light is how they move around.”
  Stratt raised an eyebrow. “I don’t follow.”
  “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.”
• She pinched her chin. “What would you call an organism that exists on a diet of stars?”
  I struggled to remember my Greek and Latin root words. “I think you’d call it ‘Astrophage.’ ”
• “Don’t be dramatic,” she said. “I’m just playing it safe. Imagine what would happen if I sent Astrophage to the most brilliant minds on the planet and it killed them all. In an instant we’d lose the very people we need the most right now. I can’t risk 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.”
• Back to the microscope. “Okay, you little reprobates. You’re radiation-proof, I’ll grant you that. But how about I stab you in the face?”
• Anyway, all this can only mean one thing: The Hail Mary isn’t going home. This is a one-way ticket. And I’m pretty sure these beetles are how I’m supposed to send information back to Earth.
  There’s no way I have a radio transmitter powerful enough to broadcast several light-years. I don’t know if that would even be possible to build. So instead, I have these little “beetle” ships with 5 terabytes of information each. They’ll fly back to Earth and broadcast their data.
• Point is: The inside of an Astrophage wasn’t much different from the inside of any single-celled organism you’d find on Earth. It used ATP, RNA transcription, and a whole host of other extremely familiar things. Some researchers speculated that it originated on Earth. Others postulated this specific set of molecules was the only way for life to occur and Astrophage evolved it independently. And a smaller, vocal faction suggested life might not have evolved on Earth at all, and that Astrophage and terrestrial life have a common ancestor.
• When light hits gas molecules, the electrons get all worked up. Then they calm down and re-emit the energy as light. But the frequency of the photons they emit is very specific to the molecules involved. Astronomers used this for decades to know what gases are out there far, far away. That’s what spectroscopy is all about.
• Light is a funny thing. Its wavelength defines what it can and can’t interact with. 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.
• Astrophage hang out on the surface of the sun gathering energy via heat. They store it internally in some way no one understands. Then, when they have enough, they migrate to Venus to breed, using that stored energy to fly through space using infrared light as a propellant. Lots of species migrate to breed. Why would Astrophage be any different?
• Anyway, once it “sees” Venus, it goes straight to it. The path it takes—straight away from the solar pole, then sharply turning toward Venus—that’s the Petrova line.
  Our heroic Astrophage reaches the upper atmosphere of Venus, collects the CO2 it needs, and can finally reproduce. After that, both parent and child return to the sun and the cycle begins anew.
• but there’s a clear pattern of ‘infection’ from star to star. We know when each star was infected and by which infected star. Our sun was infected by a star called WISE 0855–0714. That star was infected by Sirius, which was infected by Epsilon Eridani. From there, the trail goes cold.”
• “We have figured this out, yes,” said Dimitri. “With lasers. It was very illuminating experiment.”
  “Was that a pun?”
  “It was!”
  “Good one!”
  We both laughed. Stratt glared at us.
• Astrophage can, apparently, do this in either direction. It takes heat energy and somehow turns it into mass. Then when it wants the energy back, it turns that mass back into energy—in the form of Petrova-frequency light. And it uses that to propel itself along in space. So not only is it a perfect energy-storage medium, it’s a perfect spaceship engine.
• That means this journey took at least one thousand days. Over three years. Well, it takes light twelve years to make this trip, so it should take me a long time too.
  Oh, right. Relativity.
• The Blip-A spins in space. It rotates end-over-end, probably at the exact same rate as the Hail Mary. I guess they saw me spin up the centrifuge and figured it was another communication thing.
  Humanity’s first miscommunication with an intelligent alien race. Glad I could be a part of it.
• But there’s no reason aliens would follow the righty-tighty-lefty-loosey rule, is there?
  I turn the lid to the right and it rotates. My heart skips a beat!
• I close the inner airlock door with me inside and depressurize it. I spin the outer door’s hatch handle and push. It opens without resistance. The tunnel is a vacuum—at least, it is on my side of the divider.
  I think I see. This is a test. They had all the same concerns I had. Attach it, let me pressurize my half with my air, and see what happens. Either it works or it doesn’t. If it works, great! If not, they’ll try something else.
• “Okay, if that’s the case…” I hold up the handcuffs and count everything again. “Then this is two atoms, each with eight protons, connected to each other. Element number eight is oxygen. Two oxygens. O2! And it was in the Hail Mary ball.”
  I hold it toward Rocky. “You clever fellow, this is my atmosphere!”
• Unlike bats and dolphins, Eridians have passive sonar. They use ambient sound waves to resolve their environment instead of making a specific noise to track prey.
• the Fourier transform. It’s the most basic tool in sound-wave analysis and arguably the most important. There’s a lot of complicated math on how to make it happen, but the end result is this: if you run a sound wave through a Fourier transform, it will give you a list of the individual notes being played at the same time.
• Fortunately, Rocky speaks with musical chords. While it’s very difficult to make a computer turn human speech into text, it’s very easy to make a computer identify musical notes and find them in a table.
• I pluck it out of the air and take a sip of water. I start it spinning again. Still off-center but not as bad.
  I take more sips, do more spins, take more sips, and so on until my little device rotates perfectly around the marked center point.
  That means the mass of the water is equal to the mass of the ball.
  I pull out the sippy. I know the density of water—it’s 1 kilogram per liter. So all I need to know is the volume of this water to know its mass and therefore the mass of the metal ball.
• “You want me to observe you sleep?”
  “Yes. Want want want.”
  Through unspoken agreement, a tripled word means extreme emphasis.
• Eridians watch one another sleep. It’s a thing. I should be more culturally sensitive, but he threw shade when I talked to myself. “Eridians are unusual.”
• “Well,” I said. “He wants to pave a chunk of the Sahara Desert with blackpanels. Like…a quarter of the entire Sahara Desert!”
  “It’d be the biggest thing ever made by humanity,” he said. “It’d be starkly visible from space.”
• “As a breeder system it’s horrible,” I said. “Way less efficient and far lower yield than my system on the carrier’s reactor. But he didn’t design it for efficiency. He designed it for scalability.”
• I stare in shock.
  How can a civilization develop space travel without ever discovering radiation?
• “Waaaaaait,” I said. “We know Astrophage is always 96.415 degrees Celsius. Temperature is just the velocity of particles inside. So we should be able to calcu—”
  “Calculate the velocity of the particles inside,” she said. “Yes. We know the average velocity of the protons. And we know their mass, which means we know their kinetic energy. I know where you’re going with this and the answer is yes. It balances.”
• “Okay, so it makes neutrinos,” I said. “How does it turn them back into energy?”
  “That’s the easy part,” she said. “Neutrinos are what’s called Majorana particles. It means the neutrino is its own antiparticle. Basically, every time two neutrinos collide, it’s a matter-antimatter interaction. They annihilate and become photons. Two photons, actually, with the same wavelength and going opposite directions. And since the wavelength of a photon is based on the energy in the photon…”
  “The Petrova wavelength!” I yelped.
• But suffice it to say, neutrinos are famously hard to interact with. But for some reason, Astrophage has what we call ‘super cross-sectionality.’ That’s just a fancy term meaning nothing can quantum-tunnel through it.
• “Galactic cosmic rays,” she said. “And they’re not cosmic rays, right?”
  “Right. They’re just hydrogen ions—protons. But they’re going a lot faster. They’re going near the speed of light.”
• We’re dealing with such absurd scales of energy here, I tend to think in ‘New York City years’ of energy, which is about one-half of one gram of Astrophage.”
• “Nonsense,” she said. “Humanity has been accidentally causing global warming for a century. Let’s see what we can do when we really set our minds to it.”
• Planets get magnetic fields if the conditions are right. You have to have a molten-iron core, you have to be in the magnetic field of a star, and you have to be spinning. If all three of these things are true, you get a magnetic field.
• You know what strong magnetic fields and thick atmospheres are really good at? Radiation protection.
  All life on Earth evolved to deal with radiation. Our DNA has error-correction built in because we’re constantly bombarded with radiation from the sun and from space in general.
• He turned back to me. “So here I am. Environmental activist. Climatologist. Antiwar crusader.” He looked out to sea. “And I’m ordering a nuclear strike on Antarctica.
• Eridians are, in effect, biological smelters... Rocky’s carapace is made of oxidized minerals. His bones are honeycombed metallic alloys.
• In short: Eridians are steam-powered... Oxygen to CO2, CO2 to oxygen, back and forth, always kept in balance. Rocky’s body is a little biosphere. All it needs is energy via food and airflow to dump heat.
• The Blip-A’s hull robot has removed the old tunnel and is installing a new one. <But no computers!!!!!>
• I’ve gone from “sole-surviving space explorer” to “guy with wacky new roommate.” It’ll be interesting to see how this plays out.
• “Hello!” Ilyukhina lunged forward and hugged Stratt. “I’m here to die for Earth! Pretty awesome, yes?!”
  I leaned to Dimitri. “Are all Russians crazy?”
  “Yes,” he said with a smile. “It is the only way to be Russian and happy at the same time.”
• “That’s your food?” I ask.
  “Social discomfort,” he says. “No talk.”
• Eridians never bothered to invent spacesuits. Why would they? Space is devoid of sensory input to them.
• “Oh my God!” I gasp. My heart just about beats out of my chest. “Astrophage has a predator!”
  There’s a whole biosphere at Adrian. Not just Astrophage. There’s even an active biosphere within the Petrova line.
• Adrian isn’t just some planet that Astrophage infected. It’s the Astrophage homeworld! And it’s the home of Astrophage’s predators.
• They don’t know about time dilation. Rocky doesn’t realize that Erid experienced a whole bunch more time than he did on that trip. They don’t know about length dilation. The distance to Tau Ceti will actually increase as you slow down relative to it—even if you’re still going toward it.
• Just like that, with minimal complication, Rocky had made a life-support system for Adrian life-forms—a system that didn’t need to know the conditions to provide in advance. It just maintains the status quo.
• This is one of those things I frequently have to explain to my students. Gravity doesn’t just “go away” when you’re in orbit. In fact, the gravity you experience in orbit is pretty much the same as you’d experience on the ground. The weightlessness that astronauts experience while in orbit comes from constantly falling. But the curvature of the Earth makes the ground go away at the same rate you fall. So you just fall forever.
• It’s simple, straightforward, elegant, and solves all the problems. The winch is powerful enough to lift the chain. It separates the links and lets them fall into the planet below. Having a long length of chain dangling down next to the one we’re pulling up would be a disaster. Imagine earbud wires getting tangled, then multiply that by 10 kilometers.
• I thought the hull couldn’t melt. It was cooled by Astrophage! But of course it can melt. Even if Astrophage is a perfect heat absorber (and it may be), the heat has to conduct through the metal before it can be absorbed. If the outer layer of the hull reaches its melting point faster than the heat can transmit through the thickness of the hull, the Astrophage can’t do anything about it.
  It all comes together. “Oh crap! The Astrophage in the fuel bay! It’s exposed to space! That means it can see Adrian! My fuel is migrating to Adrian to breed!”
• All that fuel blasting out into space…it didn’t politely leave along the ship’s long axis. It blew out at an angle, spinning us like a top. And the exploding fuel bays probably made things even worse.
• Well, I stopped the fuel leak, at least. There are no new thrust vectors acting on the ship. Now I just have to deal with the spin. I manage to get a breath in. The centrifugal force is less than the uncontrolled thrust force, but it’s still monumental. But hey, at least it pulls my arms toward the screen instead of away from it.
• After a few seconds, the force reduces dramatically. Much more manageable now. Less than 1 g, actually. All thanks to the magic of centrifuge math.
  The force you feel in a centrifuge is inverse to the square of the radius. By spooling out the cables, I made the radius go from 20 meters (half the length of the ship) to 75 meters (distance from the control room to the center of mass with full cable extension). I don’t know how much force I was dealing with before, but now it’s one-fourteenth as much as it was.
• My shoulders scream in pain. This is not a well-designed backpack with a properly distributed load. It’s 200 pounds of alien held up by two thin straps digging into my collarbones. And I just have to hope the melting point of the nylon tethers is higher than Rocky’s body temperature.
• A bunch of oxygen just passed over very hot metal pipes no thicker than a human hair. They burned. That’s the smoke I saw coming out of Rocky’s vents. His radiator was literally on fire.
  Jesus.
  The whole organ must be completely full of soot and other combustion products. And the capillaries will be coated in oxides, which ruin heat conductivity. Heck, oxides are insulators. The worst-possible outcome.
• I hit the sweet spot. All of a sudden, Rocky’s carapace vents belch out black smoke. The nasty dust and debris that built up when he was on fire. It’s intensely satisfying. Like that feeling when you blast an air duster into an old computer.
• “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.”
• “Yeah! Think about it. Gravity is what determines how fast an animal can run. Higher gravity, more time spent in contact with the ground. Faster movement. I think animal intelligence, ultimately, has to be faster than gravity.”
• We have two planets to deal with here. No, not Earth and Erid. Those are just the planets we live on. The planets we care about right now are Venus and Threeworld. That’s where Astrophage is breeding out of control.
• But I don’t want to say “Planet Three” all the time, so I’ve named it Threeworld.
  The hardest part about working with aliens and saving humanity from extinction is constantly having to come up with names for stuff.
• Venus’s atmosphere is 0.02 atmospheres at around the 70 kilometer mark, and the temperature there is about minus 100 degrees Celsius (thanks, infinite supply of reference material!). So that’s the temperature I have the Venus analog experiment set to.
• But while it took a long time to explain sight to Rocky, smell was easy. Because Eridians do have a sense of taste. When you get down to it, smell is just tasting at range.
• Working with Rocky is like having the world’s best engineer from 1950 on the ship with me.
  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.
• Rocky was mindful of that when he zeroed out our rotation. Now we have that under control and I can do EVAs in zero g like God intended.
• “Yes,” I say. “We don’t need to understand why or how nitrogen kills Taumoeba. We just need to breed nitrogen-resistant Taumoeba.”
• It meant another hole in my hull, but at this point I trust Rocky to do any engineering task. Heck, if he wanted to do open-heart surgery on me, I’d probably let him. The guy is amazing at this stuff. <literally 工具人>
• The pyros don’t just open a clamp. They shear the bolts clean off. And they don’t care about the damage to the mounting points.
  I spend a lot of time un-suiciding this suicide mission.
• “On Earth, we have a scary, deadly creature called a spider. You look like one of those. Just so you know.”
  “Good. Proud. I am scary space monster. You are leaky space blob.” He points to the breeder tanks. “Check tanks!”
• But after a few months, the Petrovascope won’t be able to see the light anymore. Not because the light is too dim—it’s a very sensitive instrument. It won’t be able to see him because our relative velocities will cause a red-shift in the light coming off his drives. It won’t be the Petrova wavelength anymore when it gets to me.
• What? Would I do a ridiculous amount of relativistic math to calculate our relative velocity at any given moment as perceived by my inertial reference frame and then do Lorentz transformations to figure out when the light from his engines will drop out of the Petrovascope’s perception range? Just so I know how much longer I can see my friend in the distance? Wouldn’t that be kind of pathetic?
  Yeah.
• What if Taumoeba can, for lack of a better description, work their way around the molecules of xenonite? What if there’s no hole at all?
  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.
• Yes, I made a strain of Taumoeba that could survive nitrogen. But evolution doesn’t care what I want. And it doesn’t do just one thing at a time. I bred up a bunch of Taumoeba that evolved to survive…in xenonite breeder tanks.
• So that’s what I’m left with. Option 1: Go home a hero and save all of humanity. Option 2: Go to Erid, save an alien species, and starve to death shortly after.
• I have everything I need for the best radar ever! To heck with my built-in radar system, with its measly emitter and sensors. I have spin drives and a Petrovascope! I can throw 900 terawatts of IR light out the back of my ship and see if any of it bounces back with the Petrovascope—an instrument carefully designed to detect even the smallest amounts of that exact frequency of light!
• And that means the object I’m tracking is also on an escape vector. You know what objects in a solar system don’t do? They don’t escape the star’s gravity. Anything going fast enough to escape did so billions of years ago. Whatever this is, it’s no normal asteroid.
• Anyway, it means I can finally eat meat. Yes, that’s right, I’m eating human meat. But it’s my own meat, and I don’t feel bad about it. Spend a decade eating nothing but odd-tasting, vaguely sweet vitamin shakes and then see if you’ll turn down a burger.
  I love meburgers. I eat one every day.