by Thorne, Kip
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 several:
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.
Baltimore: For example, the AIDS virus could quickly evolve into a far more contagious form, one transmitted by coughing or breathing instead of sex.
Simon: The Earth’s ice caps, melting due to global warming, could release a long-dormant lethal pathogen from before the last ice age.
Leadbetter: Yet another scenario: People could panic about global warming. The warming is largely caused by increasing carbon dioxide in the atmosphere. To save us, they might fertilize the Earth’s oceans to produce algae that will eat much of the atmosphere’s carbon dioxide via photosynthesis. A lot of iron, thrown into the oceans, could do the job. But there might be catastrophic unintended side effects. You might get some new kinds of algae that produce toxins (poison chemicals, not deadly life-forms) that poison the oceans. There would be a massive kill off of fish and plant life. Human civilization depends heavily on the oceans. This could be catastrophic for humans. Is it impossible? Not at all. Experiments have been done where iron was thrown locally into the ocean to produce algae—so much algae that it could be seen from space as green spots (Figure 11.2). Some of the algae that bloomed were of types never before known to science! We were lucky: the new algae were not noxious, but they might have been.
Fig. 11.2. Map of chlorophyll concentration (algae) after dumping 100 tons of iron sulphate into the ocean off the coast of British Columbia. Iron-stimulated algae growth produced the high algae concentration inside the dashed ellipse. [From Giovanni/Goddard Earth Sciences Data and Information Services Center/NASA.]
Meyerowitz: Ultraviolet light, streaming through our atmosphere’s ozone hole, could mutate your enormous bloom of algae so it creates new pathogens. These pathogens could wipe out plants in the ocean, and then jump to land and start wiping out crops.
Baltimore: When faced with catastrophes like these, our only hope for dealing with them is advanced science and technology. If, politically, we don’t invest in science and technology, or we hobble them by anti-intellectual ideologies such as denial of evolution, the very source of these catastrophes, we may find ourselves without the solutions we need.
And then there is blight—the consequence of many of these scenarios.
Blight
Blight is a general term for most any disease in a plant that is caused by a pathogen.
Baltimore: If you want something to wipe out humanity, there might be no better way than a blight that attacks plants. We are dependent on plants to eat. Yes, we can eat animals or fish instead, but they ate plants.
Meyerowitz: It might be sufficient for the blight just to kill off the grasses and nothing else. Grasses are the basis of most of our agriculture: rice, corn, barley, sorghum, wheat. And most animals that we eat feed on grasses.
Meyerowitz: We already live in a world where 50 percent of the food grown is destroyed by pathogens, and it’s much higher than that in Africa. Fungi, bacteria, viruses, . . . they all can be pathogens. The East Coast used to be covered with chestnut trees. They are no more. They were killed by a blight. The species of banana preferred by most people in the eighteenth century was wiped out by a blight. The replacement species, the Cavendish banana, today is being threatened by blight.
Kip: I thought that blights are specialists that attack only one narrow group of plants and don’t jump to others.
Leadbetter: There are also generalist blights. There seems to be a tradeoff between being a generalist that attacks many species and a specialist that attacks only a few. For the specialist blight, the lethality can be turned up really high; it can knock out, say, 99 percent of a very specific group of plants. For the generalist, the range of plants attacked is much broader, but its lethality for any one plant in that range might be much smaller. That’s a pattern we see again and again in Nature.
Lynda: Could you have a generalist blight that becomes much more lethal?
Meyerowitz: Something like that has happened before. Early in the Earth’s history, when cyanobacteria started making oxygen, thereby changing radically the composition of the Earth’s atmosphere, they managed to kill most everything else on Earth.
Leadbetter: But the oxygen was a lethal byproduct, a poison, produced by the cyanobacteria; not a generalist pathogen.
Baltimore: We may not have seen it, but I can imagine a very lethal specialist pathogen becoming a lethal generalist. It could spread the range of plants it attacks with the help of an insect that carries it to many species. A Japanese beetle, for example, which eats something like two hundred different plant species, could infect many species with the pathogen it carries, and the pathogen might adapt to attack those species, lethally.
Meyerowitz: I can conceive of a totally lethal generalist: a pathogen that attacks chloroplasts. Chloroplasts are something that all plants have in common. They are crucial to photosynthesis (the process where a plant combines sunlight with carbon dioxide from the air, and water from its roots, to produce carbohydrates that it needs for growth). Without chloroplasts, a plant will die. Now suppose that some new pathogen evolves, for example in the oceans, that attacks chloroplasts. It could wipe out all algae and plant life in the oceans, and jump to the land where it wipes out all land plants. So everything becomes a desert. This is possible; I see nothing to prevent it. But it’s not very plausible. It is unlikely ever to happen, but it could be a basis for Cooper’s world.
These speculations give us a sense of the kinds of nightmare scenarios that could keep a biologist awake at night. In Interstellar, the focus is a lethal generalist blight running rampant over the Earth. But Professor Brand has a secondary worry: humankind’s running out of oxygen to breathe.
12
Gasping for Oxygen
Early in Interstellar Professor Brand says to Cooper: “Earth’s atmosphere is 80 percent nitrogen. We don’t even breathe nitrogen. Blight does. And as it thrives, our air gets less and less oxygen. The last people to starve will be the first to suffocate. And your daughter’s generation will be the last to survive on Earth.”
Is there any basis in science for the Professor’s prediction?
This question lies at the interface of two branches of science: biology and geophysics. So I asked the biologists at our Blight Dinner, particularly Elliot Meyerowitz, and I asked two geophysicists, Caltech professors Gerald Wasserburg (an expert on the origin and history of the Earth, M
oon, and solar system) and Yuk Yung (an expert on the physics and chemistry of our Earth’s atmosphere, and the atmospheres of other planets). From them, and from technical articles they pointed me to, I learned the following.
Creating and Destroying Breathable Oxygen
The oxygen we breathe is O2: a molecule made of two oxygen atoms, bound together by electrons. There is lots of oxygen on Earth in other forms: carbon dioxide, water, minerals in the Earth’s crust, to name a few. But our bodies can’t use that oxygen until some organism liberates it and converts it to O2.
The atmosphere’s O2 is destroyed by breathing, burning, and decay. When we breathe in O2 our bodies combine it with carbon to form carbon dioxide, CO2, releasing lots of energy that our bodies use. When wood is burned, the flames rapidly combine the atmosphere’s O2 with the wood’s carbon to form CO2, which generates the heat that keeps the burning going. When dead plants decay on the forest floor, their carbon is slowly combined with the atmosphere’s O2 to form CO2 and heat.
The atmosphere’s O2 is created primarily by photosynthesis: chloroplasts in plants24 (Chapter 11) use energy from sunlight to split CO2 into C and O2. The O2 is liberated into the Earth’s atmosphere, while the plants combine the carbon with hydrogen and oxygen from water to form the carbohydrates that they need for growth.
O2 Destruction and CO2 Poisoning
Suppose evolution creates a pathogen that destroys chloroplasts, as speculated by Elliot Meyerowitz at the end of the last chapter. Photosynthesis ends, not all at once, but gradually as plants die out. O2 is no longer being created, but it is still being destroyed by breathing, burning, and decay—primarily decay, it turns out. Fortunately for the remaining humans, there is not enough decaying plant life on the Earth’s surface to swallow up all the O2.
Most of the decay will be finished after thirty years, and only about 1 percent of the O2 will be used up. There is still plenty for Cooper’s children and grandchildren to breathe, if they can find anything to eat.
But that 1 percent of the atmospheric O2 will have been converted into carbon dioxide, which means 0.2 percent of the atmosphere will then be CO2 (since most of the atmosphere is nitrogen). That’s enough CO2 to make breathing unpleasant for highly sensitive people and perhaps drive the Earth’s temperature up (via the greenhouse effect) by 10 degrees Celsius (18 degrees Fahrenheit)—unpleasant for everyone, to put it mildly!
To make everyone’s breathing uncomfortable and induce drowsiness, ten times more atmospheric O2 would have to be converted into CO2; and to kill most everyone by CO2 poisoning, an additional five times more would have to be converted, a factor of fifty in all. I have not found a plausible mechanism for this.
So is Professor Brand wrong? (Even theoretical physicists can make mistakes. Especially theoretical physicists. I know; I am one.) Probably yes, he is wrong, but conceivably no. The Professor could be right, but it would require geophysicists’ understanding of ocean bottoms to be severely flawed.
There is undecayed organic material on the ocean bottoms as well as on land. Geophysicists estimate that the amount on ocean bottoms is about one-twentieth that on land. If they are wrong and there is fifty times more on the ocean bottoms than on land, and if there is a mechanism to quickly dredge it up, then its decay to produce CO2 could leave everyone gasping for oxygen and dying of CO2 poisoning.
Now, once every many thousand years, an instability triggers the ocean to turn over. Water from the surface sinks to the bottom and drives bottom water to the surface. It is conceivable that in Cooper’s era there is such an overturn so vigorous that the upwelling bottom water brings with itself most of the ocean bottoms’ organic material. Suddenly exposed to the atmosphere, this material could decay, converting atmospheric O2 into lethal amounts of CO2.
Conceivable, yes. But highly improbable on two counts: highly unlikely that there is 1000 times more undecayed ocean-bottom organic material than geophysicists think, and highly unlikely that a sufficiently vigorous oceanic overturn will occur.25
Nevertheless, in Interstellar the Earth is surely dying and humanity must find a new home. The solar system, aside from Earth, is inhospitable, so the search is on, beyond our solar system.
* * *
24 Chloroplasts and photosynthesis also occur in algae, and in cyanobacteria in the ocean, both of which I treat as plant life in my simplified description. (In some sense, cyanobacteria are a form of chloroplast.)
25 For some quantitative details and explanations of the huge uncertainties in the geophysical estimates, see Some Technical Notes at the end of the book.
13
Interstellar Travel
Professor Brand tells Cooper, in their first meeting, that the Lazarus missions have been sent out to search for new homes for humanity. Cooper responds, “There’s no planet in our solar system that can support life, and it’d take a thousand years to reach the nearest star. That doesn’t even qualify as futile. Where did you send them, Professor?”
The worse-than-futile challenge, if you don’t have a wormhole, is obvious when you realize just how far it is to the nearest stars (Figure 13.1).
Distances to Nearest Stars
The nearest star (other than our Sun) thought to have a habitable planet is Tau Ceti, 11.9 light-years from Earth, so traveling at light speed you would need 11.9 years to reach it. If there are any habitable planets closer than that, they can’t be much closer.
To get some sense of just how far Tau Ceti is compared to more familiar things, let’s scale its distance down enormously. Imagine it as the distance from New York City to Perth, Australia, about halfway around the world.
Fig. 13.1. All the stars within 12 light-years of Earth. The Sun, Proxima Centauri, and Tau Ceti are circled in yellow, purple, and red. [I adapted this map from Richard Powell’s www.atlasoftheuniverse.com.]
The very nearest star other than the Sun is Proxima Centauri, 4.24 light-years from Earth, but there is no evidence it has habitable planets. With Tau Ceti’s distance imagined as New York to Perth, then Proxima Centauri’s is like New York to Berlin. It’s not a lot closer than Tau Ceti!
For comparison, the most distant unmanned spacecraft that humans have sent into interstellar space is Voyager 1, now about 18 light-hours from Earth. It has been traveling for thirty-seven years to get there. With Tau Ceti’s distance imagined as New York to Perth, then Earth to Voyager 1 is about 3 kilometers (2 miles): the distance from the Empire State Building to the southern end of Greenwich Village. That’s hugely less than New York to Perth.
The Earth to Saturn is even smaller: 200 meters, two east-west blocks in New York City, from the Empire State Building to Park Avenue. The Earth to Mars is just 20 meters; and the Earth to the Moon (the greatest distance humans have ever yet traveled) is just 7 centimeters—about two and a half inches!
Compare what we have achieved in going to the Moon, two and a half inches, with the challenge of going halfway around the world. That’s the leap of technology required to take humans to habitable planets outside our solar system!
Travel Times with Twenty-First-Century Technology
Voyager 1 is traveling out of the solar system at 17 kilometers per second, having been boosted by gravitational slingshots around Jupiter and Saturn. In Interstellar, the Endurance travels from Earth to Saturn in two years, at an average speed of about 20 kilometers per second. The fastest speed I think rocket technology plus solar system slingshots are likely to achieve in this, the twenty-first century, is about 300 kilometers per second.
At that 300 kilometers per second, we would need 5000 years to reach Proxima Centauri and 13,000 years to reach Tau Ceti. Not a pleasant prospect!
To get there far faster in the tweny-first century, you need something like a wormhole (Chapter 14).
Far-Future Technology
Technically savvy scientists and engineers have put much effort into conceiving far-future
technologies that might make possible near-light-speed travel. You can learn a lot about their ideas by browsing the web. It will take many centuries for humans to make any of those ideas real, I think. But they do convince me that ultra-advanced civilizations are likely to travel between the stars at a tenth the speed of light or faster.
Here are three far-out examples of near-light-speed propulsion that intrigue me.
Thermonuclear Fusion
Thermonuclear fusion is the most conventional of the three ideas. R&D to develop controlled-fusion power plants on Earth was initiated in the 1950s, and full success will not come until the 2050s. A full century of R&D! That’s a realistic measure of the difficulties.
And what will fusion power plants in 2050 mean for spacecraft propulsion by fusion? The most practical designs may achieve 100 kilometers per second, and conceivably 300 kilometers per second by the end of this century. A whole new approach to harnessing fusion will be required for reaching near light speed.
A simple calculation shows fusion’s possibility: When two deuterium (heavy hydrogen) atoms are fused to form a helium atom, 0.0064 (nearly 1 percent) of their rest mass gets converted into energy. If this were all transformed to kinetic energy (energy of motion) of the helium atom, the atom would move at about one-tenth the speed of light.26 This suggests that, if we could convert all the fusion energy of deuterium fuel into ordered motion of a spacecraft, we could achieve a spacecraft speed of roughly 1/10 the speed of light—and somewhat higher if we are clever.
In 1968 Freeman Dyson, a brilliant physicist for whom I have great respect, described and analyzed a crude propulsion system that, in the hands of a sufficiently advanced civilization, could achieve this.