This is one of the few spots in Interstellar where the characters get the science wrong. Christopher Nolan knew that Brand’s argument was wrong, but he chose to retain these lines from Jonah’s draft of the screenplay. No scientist has perfect judgment.
Although Gargantua tries to suck asteroids and comets into itself, and planets and stars and small black holes too, it rarely succeeds. Why?
When far from Gargantua, any object has a large angular momentum,[23] unless its orbit is headed almost directly toward the black hole. That large angular momentum produces centrifugal forces that easily overwhelm Gargantua’s gravitational pull whenever the object’s orbit carries it near the black hole.
A typical orbit has a form like that in Figure 10.1. The object travels inward, pulled by Gargantua’s strong gravity. But before it reaches the horizon, centrifugal forces grow strong enough to fling the object back outward. This happens over and over again, almost endlessly.
The only thing that can intervene is an accidental near encounter with some other massive body (a small black hole or star or planet). The object swings around the other body on a slingshot trajectory (Chapter 7), and thereby is thrown into a new orbit around Gargantua with a changed angular momentum. The new orbit almost always has a large angular momentum, like the old one did, with centrifugal forces that save the object from Gargantua. Very rarely the new orbit carries the object almost directly toward Gargantua, with a small enough angular momentum that centrifugal forces can’t win, so the object plunges through Gargantua’s horizon.
Astrophysicists have carried out simulations of the simultaneous orbital motions of millions of stars around a gigantic black hole like Gargantua. Slingshots gradually change all the orbits and thereby change the density of stars (how many stars there are in some chosen volume). The star density near Gargantua does not go down; it grows. And the density of asteroids and comets will also grow. Random bombardment by asteroids and comets will become more frequent, not less frequent. The environment near Gargantua will become more dangerous for individual life forms, including humans, promoting faster evolution if enough individuals survive.
With Gargantua and its dangerous environment under our belts, let’s make a brief change of direction: to Earth and our solar system; to disaster on Earth and the extreme challenge of escaping disaster via interstellar travel.
III
DISASTER ON EARTH
11
Blight
In 2007, when Jonathan (Jonah) Nolan joined Interstellar as screenwriter, he set the movie in an era when human civilization is a pale remnant of today’s and is being dealt a final blow by blight. Later, when Jonah’s brother Christopher Nolan took over as director, he embraced this idea.
But Lynda Obst, Jonah, and I worried a bit about the scientific plausibility of Cooper’s world, as envisioned by Jonah: How could human civilization decline so far, yet seem so normal in many respects? And is it scientifically possible that a blight could wipe out all edible crops?
I don’t know much about blight, so we turned to experts for advice. I organized a dinner at the Caltech faculty club, the Athenaeum, on July 8, 2008. Great food. Superb wine. Jonah, Lynda, me, and four Caltech biologists with the right mixture of expertise: Elliot Meyerowitz, an expert on plants; Jared Leadbetter, an expert on the diverse microbes that degrade plants; Mel Simon, an expert on the cells that make up plants and how they are affected by microbes; and David Baltimore, a Nobel laureate with a broad perspective on all of biology. (Caltech is a wonderful place. Named the top university in the world by the Times of London in each of the last three years, it is small enough—just 300 professors, 1000 undergrads, and 1200 graduate students—that I know Caltech experts in all branches of science. It was easy to find and recruit the experts we needed for our Blight Dinner.)
As dinner began I placed a microphone at the center of our round table and recorded our two-and-a-half-hour, free-wheeling conversation. This chapter is based on that recording, but I’ve paraphrased what people said—and they checked and approved my paraphrasing.
Our final consensus, easily reached, is that Cooper’s world is scientifically possible, but not very likely. It is very unlikely to happen, but it could. That’s why I labeled this chapter for speculative.
Cooper’s World
Over wine and hors d’oevres, Jonah described his vision for Cooper’s world (Figure 11.1): Some combination of catastrophes has reduced the population of North America tenfold or more, and similarly on all other continents. We have become a largely agrarian society, struggling to feed and shelter ourselves. But ours is not a dystopia. Life is still tolerable and in some ways pleasant, with little amenities such as baseball continuing. However, we no longer think big. We no longer aspire to great things. We aspire to little more than just keeping life going.
Most of us think the catastrophes are finished, that we humans are securing ourselves in this new world and things may start improving. But in reality the blight is so lethal, and leaps so quickly from crop to crop, that the human race is doomed within the lifetime of Cooper’s grandchildren.
What Catastrophes?
What kind of catastrophes could have produced Cooper’s world? Our biologist experts offered a number of possible, but improbable, answers. Here are severaclass="underline"
Leadbetter: Today (2008) most people aren’t growing their own food. We’re dependent on a global system for growing and distributing food, and for distributing water. You could imagine that system breaking down due to some biological or geophysical catastrophe. As an example on a small scale, if there was no snow in the Sierra Nevada Mountains for a few consecutive years, there would be little drinking water in Los Angeles. Ten million people would be forced to migrate, and agricultural output in California would plummet. You can easily imagine much larger scale catastrophes. In Cooper’s world, with a vastly reduced population and a return to agrarian society, the production and distribution problems are lessened.
Simon: Another possible catastrophe: Over human history there has been a continual battle between us and pathogens (microbes that attack the human body or attack plants or other animals). We humans have developed a sophisticated immune system to deal with the pathogens that attack us directly. But the pathogens keep evolving and we’re always half a step behind them. At some point there could be a catastrophe where the pathogens change so fast that our immune systems can’t keep up.
23
The angular momentum is the object’s circumferential speed multiplied by its distance from Gargantua; and this angular momentum is important because it is constant along the object’s orbit, even if the orbit is complicated.