For more than 20 years, I have been thinking about human history in its cosmological context. That means seeing human history as part of the much larger histories of Earth and the universe as a whole. I call this â€œBig History.â€
Big History raises some big questions about our place in the universe and our future trajectory as a species. Above all, it forces us to ask: How unique are we humans? Are we alone in the universe? Or is it possible that there are many other humanlike or â€œhumanoidâ€ species? If so, is it possible that they, too, have historiesâ€”histories that might be similar in some ways to our own, histories from which we might even have something useful to learn?
We now have some scraps of evidence and some lines of thought that may help us think about such questions with some seriousness. And pursuing these questions is actually a great way of thinking about the future of our own species. Plus, such speculations are fun.
How rare are humanoids?
How likely is it that other humanlike species exist? What are the chances of being born into this universe as a human being or a humanlike creature rather than as a mote of intergalactic dust or a meteorite or a cockroach?
The Buddha once told his disciples: â€œImagine that the whole earth was covered in water, and that someone were to throw a wooden yoke with a hole in it on to the surface. And suppose that once in a hundred years, a blind turtle were to rise to the surface. What are the chances that it would put its head through the hole in the yoke?â€ His loyal disciples replied: â€œIt is very unlikely, Lord!â€
â€œWell,â€ said the Buddha, â€œit is equally unlikely that one might be born as a human being.â€ In a world that believed deeply in reincarnation, this was the Buddhaâ€™s way of saying that being born human is an extraordinarily rare privilege, and one to be valued.
Today, astrobiologists ask similar questions, but in a more modern form. How many humanlike civilizations could there be in the universe? And what are the chances of contacting some of them? They often ask this question using some form of what is known as the â€œDrake equation,â€ which was devised by the American astronomer Frank Drake in 1960. It looks like an equation, but it’s really a list of questions.
Here is a simplified version:
N = Nstars x Fplanets x Flife x Fhumanoids x Fnow.
N is what weâ€™re looking forâ€”the number of humanoid civilizations that might exist in our galaxy right now. (We ignore the rest of the universe.)
Nstars is an estimate of the number of stars in our galaxy, the Milky Way. Fplanets is an estimate of the fraction of stars that have planetary systems. Flife is an estimate of the fraction of planets that might have life on them. Fhumanoids is an estimate of the number of planets that might have humanoid civilizations. And the final term, Fnow, estimates the fraction of humanoid civilizations that might exist right now.
Of course, most of our answers are guesswork, but we have quite a lot more information than Frank Drake did. So let’s play with some numbers.
How many stars are there in the Milky Way? A good estimate is about 400 billion, though it could be a bit less or a bit more. If you were to count one star every second, it would take you about 11 days to count to the first million stars. It would take you about 32 years to count the first billion stars, and almost 13,000 years to count all 400 billion stars in our galaxy. That is more time than has passed since the end of the last ice age.
How many of these stars might have planets? In the last 20 years, astronomers have learned how to detect planets around nearby stars, and right now, the Kepler satellite is finding them by the bucketful. It looks as if at least 10 percent of all stars, or about 40 billion, might have planets and moons.
But how many of those planets are habitable? In our solar system, several planets and moons might have been habitable at some time, but we know for sure of only one habitable planet, our own. So let’s be conservative and estimate that there is, on average, one habitable planet in each planetary system, for a total of about 40 billion habitable planets.
How many might actually have life? Itâ€™s probably a similar number. We know that, on Earth, life appeared as soon as it was possible, as soon as it was cool enough for oceans to appear. That suggests that all habitable planets acquire a thin scum of bacteria. In other words, there could be 40 billion living planets in our galaxy. Calculations like these explain why most astrobiologists now believe that life is common in the universe.
Next we look for the fraction of living planets on which intelligent life evolved. But thatâ€™s not quite right. Your dog is intelligent; so is my neighbor’s cat. Humanoids are not just intelligent, and it takes more than raw intelligence to generate technologies, like the ability to transmit radio messages to other star systems. Complex technologies are built by the slow sharing of learned information by intelligent individuals over long periods of time. In other words, we’re looking for species that are intelligent and can also share their thoughts with great precision because they have a powerful language of some kind. This means they do not just learn as individuals; they can also learn collectively, so they can accumulate more and more information over time. I call this ability â€œcollective learning.â€ Itâ€™s so distinctive that Iâ€™m going to define humanoid species as species that are capable of collective learning. It doesnâ€™t matter what they look like.
Life in general may be common, but humanoid species are probably rare. I say this because there are so many evolutionary steps between a bacterium and a humanoid. The evolution of species with large brains, capable of sophisticated communication, is not necessarily that unlikely, but it will surely take a long time. On our planet, it took almost 4 billion years to evolve a humanoid species, Homo sapiens. Thatâ€™s almost a third of the age of the universe.
So to evolve humanoids, you don’t just need a habitable planet, you need a habitable planet that can stay habitable for billions of years. That’s tough. The planet’s orbit must stay stable, its sun must not throw tantrums, its fellow planets must stay well behaved, and there must be no nearby supernovae. Above all, the planet’s surface must stay in the narrow range of temperatures at which water can exist in liquid form. Our neighboring planets, Mars and Venus, show how hard this is. Both may once have been habitable, but on Venus, a build-up of greenhouse gases eventually boiled away all the oceans, while Mars lost its blanket of greenhouse gases and got too cold for life to flourish.
All this could mean we are the only humanoid species in the galaxy, or even the entire universe. But I don’t think so. After all, we’ve already estimated that the same evolutionary processes that eventually gave rise to us may have started up in 40 billion star systems just in our galaxy.
So let’s take a wild guess that humanoid species eventually evolve on one of 1,000 planets with life. On the figures we have already given, that would mean that 40 million humanoid species have evolved in our galaxy. Thatâ€™s a lot of humanoids.
Of course, what really interests us is how many exist right now. To estimate that, we need to guess how long a typical humanoid civilization lasts. Now this may seem an impossible question, but our definition of humanoids as species capable of collective learning actually gives us some important clues about what a typical humanoid history might look like.
Humanoid histories: Stage 1
We can imagine members of a young humanoid species sharing ideas and building a repertoire of new technologies. These will help them get more resources from their environments, so their populations will rise and there will be more humanoids to share more ideas. This is stage 1 of their history, a sort of species childhood. During this stage, members of the species slowly learn how amazingly creative they can be as they share ideas.
As technologies accumulate, synergies will develop between different technologies and regionsâ€”just as, on our planet, writing and then printing synergized technological change. As these synergies multiply, the pace of innovation will accelerate until, suddenly, the species will acquire the power to transform its home planet. The members of this species will have become world changers. They will have entered a second stage in their history.
On our own planet, human numbers took off after the end of the last ice age, rising by about 1,000 times, while human consumption of energy has increased by perhaps 50,000 times in the same period. But most new technologies, from fossil fuels to the Internet, arrived in a burst during the last 200 years, and they have made us a planet-changing species, the first species in the 4 billion year history of the planet that had such power. We entered stage 2 of our history about 200 years ago.
Humanoid histories: Stage 2
We should expect that most humanoid species will reach this second stage, and we should also expect that they will do so at about the time that they become visible to other humanoid civilizations because, by now, they will surely be able to transmit radio messages to other star systems.
Stage 2 marks a dramatic and dangerous crisis in the history of humanoid civilizations. It is a sort of species adolescence. Reveling in its growing power, the species will swagger. The danger is that it will now have so much power that it could ruin its own world.
A post-World War II novel by Walter Miller, A Canticle for Leibowicz, captures these dangers well. It begins in a dark-age world that we soon realize is centuries in the future, after a nuclear war called the â€œFlame Deluge.â€ Strange manuscripts have been discovered, which will turn out to be texts on nuclear physics. We move forward 600 years, and old technologies are being re-discovered. Then we move forward another 600 years, and humans have learned once again how to make nuclear weapons. And once again, they use them.
Sadly, the â€œFlame Delugeâ€ is not the only catastrophic ending to stage 2 of our history that we can imagine. Most endings are less dramatic, involving a sort of slow ecological strangulation of the biosphere on which we depend. Today, the sheer variety and scale of our technologies are beginning to disturb ancient balances. We are acidifying our oceans, carbonating our atmosphere, and driving other species to extinction at a terrifying rate.
Is it possible that most humanoid species destroy themselves during stage 2 of their histories? Do humanoid species flicker in and out of existence like galactic fireflies? Is stage 2 a natural Armageddon for most humanoid species?
If so, then our chances of contacting other humanoids before they self-destruct are very very small. If we guess that humanoid civilizations normally destroy themselves within 200 years of entering stage 2, we can calculate, using the figures we’ve already given, that at any one time there is only likely to be one or two humanoid species in the entire galaxy. As messages between them will normally take hundreds or thousands of years, they will never even know how tragically similar their histories were.
Humanoid histories: Stage 3
Letâ€™s hope we have been too pessimistic. After all Fnow is the one term in the Drake equation over which we have some control, and humanoid species are, by our definition, prodigious learners. Letâ€™s imagine that most of these species learn quickly enough to survive the dangers of stage 2. Then they enter a third stage in their histories. Stage 3 will be very different because most of the dangers of stage 2 will have been solved, and the species will have developed a more sustainable relationship with its planet. So it may then flourish for tens or even hundreds of thousands of years.
Indeed, it is beginning to look as if getting to stage three might be the greatest challenge facing any humanoid species.
How do they get there? There are two things that will surely have to happen. Like drivers approaching an accident, they will have to see the dangers, and they will have to swerve to avoid them.
Seeing the dangers should not be too hard for such a fiendishly clever species. In fact, during my own lifetime, I have watched our own species learn very fast about a lot of the dangers of stage 2.
Making the first atom bomb, for example, was a powerful wake-up call. On July 16, 1945, as he watched the first test at the Trinity test site, J.R. Oppenheimer, the scientific director of the Manhattan Project, remembered the words of the Hindu god, Vishnu, from the Baghavad Gita: â€œI am become Death, the Destroyer of Worlds.â€ Three weeks later, an atomic bomb was dropped on Hiroshima. It killed 80,000 people immediately, and as many more in the next 12 months. Our species had begun to learn the meaning of the â€œFlame Deluge.â€ Since then, we have learned about the many other dangers that arise from our astonishing technological creativity.
Changing direction may be more difficult, partly because there are so many of us. Imagine trying to swerve in a semi-trailer with 7 billion drivers. But at least we know which direction to turn: away from the path of endlessly increasing consumption of scarce resources. We need to shift from the obese, resource-hungry technologies of stage 2 toward lightweight, knowledge- and service-based economies.
Here, there is good news to report. Population growth is slowing throughout the world. Can we also slow consumption? To do that, we will need all our technological creativity, to create new and more lightweight forms of manufacturing. As I was writing this, I learned of the creation of an electric motor the size of a single molecule. It can spin 50 times a second around an axis made from a single sulfur atom. How clever is that! This nano-pump gives us a hint of the nearly weightless technologies we will need in stage 3.
We will also need to rethink our ideas of the â€œgood life.â€ But this shouldn’t be too hard. In our private lives, we already understand that beyond a certain point, ever-increasing consumption is a recipe for bloat rather than happiness; if one meal is good, that doesnâ€™t mean you should immediately eat 10 more. And beyond a certain level, most of the ingredients of well beingâ€”friendship, laughter, health, natural beauty, creativityâ€”donâ€™t cost much. Growth in creativity and well-being is not the same as growth in consumption.
Will we change direction in time?
One reason for thinking hard about how rare we are is that the exercise might give us the perspective we will need to get to stage 3. After all, if we are alone in the universe, then we must get to stage 3 to ensure that our descendants can also enjoy the unique privilege of being human. But getting there also becomes a sort of cosmological duty because, if weâ€™re really alone, we are the conscience and consciousness of the universe. So our demise as a species would amount to a sort of cosmological suicide.
What if we are not alone? What if most humanoid species manage to get to stage 3? That would greatly increase our chances of encountering each other. If, say, most humanoid species exist for at least 200,000 years after entering stage 3, that should mean, on our figures, that there are almost 2,000 in the galaxy right now!
Oh, for an inter-galactic telegram saying: â€œYes, you can! We did it!â€ Perhaps that would give us the inspiration we need to reach stage 3 by assuring us that we are not entirely alone in this vast universe.
Adapted from a presentation at the Global Future 2045 International Congress in Moscow.