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How did you come up with the idea for the book?<\/strong><\/p>\nI was thinking about what we would do if, with our current morals, beliefs and ideas, we had a mass-conversion fuel. Not in some weird future, but like right now. We could be colonizing the solar system. We could have cities on Mars.<\/p>\n
Just to clarify: A mass-conversion fuel is something that stores a huge amount of energy in a relatively tiny amount of mass, like with nuclear power. It\u2019s far more efficient than a fuel that requires combustion, like gasoline.<\/strong><\/p>\nI was thinking about that, and how to explain how we might get that technology. People could invent the mass-conversion fuel, but that seemed like a MacGuffin. Maybe they find a crashed alien spaceship \u2014 but the other technology on that ship would be more interesting. What if we found some alien fuel independent of a ship? But then you use it, and it\u2019s gone. So you have to be able to make more fuel with the fuel itself. What if it absorbs energy and makes more of itself? That sounded a lot like life.<\/p>\n
There has to be a reason that fuel ended up on Earth. If you\u2019re a mold or something, you\u2019d need to basically live on the surface of a star to get enough energy to do that. So I made astrophage, which is like an algae. But instead of living in the ocean, it lives on a star and spores out to other stars.<\/p>\n
I had my excuse for how astrophage ended up in our solar system, how humans had access to it and how we could reproduce it. But I had to make sure none of it got on our own sun, because that would be catastrophic.<\/p>\n<\/div>\n<\/div>\n
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The astrophage would consume too much of the sun\u2019s energy, eventually throwing Earth into another ice age.<\/strong><\/p>\nAnd then I realized that was the story. Forget about my city on Mars or the politics between planets \u2014 that problem was the story. I just needed a solution that involved an interstellar trip. And I worked from there.<\/p>\n
You strove for scientific accuracy when writing \u201cProject Hail Mary.\u201d What was it like adapting that for the big screen?<\/strong><\/p>\nIt\u2019s a matter of space and time. You really have to abbreviate. Sci-fi writers don\u2019t need to explain in so much detail that it enables readers to solve problems. They just need enough to understand the plot.<\/p>\n<\/div>\n<\/div>\n
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For the movie, a lot of it was just kind of a \u201cHey, trust us \u2014 hopefully you believe us when we tell you that if you accelerate at 1.5 g for this long, you experience about four years of time while Earth had 13.\u201d The viewers take our word for it.<\/p>\n
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Mr. Weir at Comic-Con San Diego last summer.<\/span>Credit…<\/span>Matt Winkelmeyer\/Getty Images<\/span><\/span><\/span><\/figcaption><\/figure>\n<\/div>\nIt sounds like you worked through that math yourself.<\/strong><\/p>\nI did. I found the equations for the rocket stuff online. That\u2019s how I got that you need two million kilograms of astrophage for a 100,000-kilogram spaceship \u2014 although that got scaled up in the movie.<\/p>\n
Eridians don\u2019t understand relativity, so I also calculated how to get from Erid to Tau Ceti, the star where Rocky and Dr. Grace meet, without accounting for it. I do calculations wrong by mistake all the time, so I might as well do them on purpose.<\/p>\n
I\u2019m proud that the only true violation of physics in the story is something you have to go down to the quantum level to find. Trillions of neutrinos, tiny particles that rarely interact with matter, pass through us every second. But astrophage can store neutrinos using a made-up property I called \u201csuper cross-sectionality.\u201d They don\u2019t bother trying to explain this in the film.<\/p>\n
Why make Rocky incompatible with an Earthlike environment?<\/strong><\/p>\nA lot of space opera-style stories are the great era of exploration in the 1700s projected into a science-fiction setting. The Enterprise goes out and visits strange new worlds, like how Marco Polo visited the Orient. When he met people from the Orient, they could be in the same room and breathe the same air and eat the same food, because they were also human. So if you want to evoke that feeling, you make those concessions with the aliens.<\/p>\n<\/div>\n<\/div>\n
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But I didn\u2019t want to do that. I mean, shoot, there are things on Earth that have incompatible environments. If you swap the locations of a shark and a camel, they\u2019re both going to die.<\/p>\n
I didn\u2019t set out for Rocky to be as alien as possible. What I did was not have any restrictions on my speculative evolution of what this alien is like.<\/p>\n
What was that process like?<\/strong><\/p>\nWhen I wrote \u201cProject Hail Mary,\u201d it was believed that there was an exoplanet very, very close to a star system called 40-Eridani. (Now it looks like the planet might not actually be there at all.) For the plot, I needed life based on liquid water. So I asked, how can you have liquid water on a planet so close to its star?<\/p>\n
The water would boil off unless there was a high atmospheric pressure. Drive up the pressure, and you drive up the boiling point of water. So I knew the planet had to have a thick atmosphere and really hot water.<\/p>\n
A star will blast the atmosphere off a planet that\u2019s too close. It helps if the atmosphere is made of heavy molecules, like Venus with its carbon dioxide. For Erid, I decided on ammonia. I also decided that Erid had a magnetic field. Both of those keep the atmosphere from blasting off.<\/p>\n<\/div>\n<\/div>\n