Cosmic noon, the time when most stars formed, was about ten billion years ago. We are now in the long, long twilight of the universe. Our Sun is a mere four and half billion years old, and a large proportion of stars are much older, or have died long ago. So why did sapience not evolve long, long, long ago, and devour the universe? Why was the Earth not settled by intelligent space aliens shortly after it was formed?
Where is everyone?
One possible explanation is that interstellar travel is very hard. But it is not that hard. It just takes a very long time when compared to the lifetime of individuals, or even civilizations — but a very short time compared to evolutionary time, geological time, and the lifetimes of stars.
A civilization approaching Kardashev II, a civilization that harnesses enormous amounts of energy and builds very big things, can send travelers between the stars and even between the galaxies at a good fraction of the speed of light on beamed power, using known technology, merely requiring a much bigger scale than we can accomplish.
A lesser civilization, the civilization Musk is calling upon us to make real, can manage about 60 km/s, which can reach the nearest stars in twenty thousand years. This sounds daunting, but is entirely doable. We would have to move our DNA to some form of machine storage to avoid inbreeding depression and evolution to a specialized environment, so we would not be entirely human at the journey’s beginning, and rather less human at the journey’s end, but still, at the end, recognizably human, as we can recognize the humanity of the Stone Age artists who painted the walls of Altamira Cave.
If we can do it in principle, why did some other creature not do it in practice, while the Earth was still forming? Even if most species do not go into space for the obvious reasons, what explains no species going into space?
One creature might not want to grab all the matter and energy of the universe, out of laziness, or concern for other actual or potential species, or for alien and incomprehensible reasons, but some would desire the universe. One species might erect a one-world government that forbids far-flung travel and settlement, perhaps for fear of spawning distant and potentially hostile regimes it cannot control, but not every species would fall into this trap. Many a government would desire the stars, and more governments would be happy to see troublemakers off on a very long slow journey that might well end in their deaths.
So there is a great filter behind us, or ahead of us, and very likely both.
We live in an extremely unlikely solar system — a system with many very unusual features, and every unusual feature makes catastrophes that are likely to destroy all complex life less likely — and despite this we have had lots of catastrophes that went a fair way toward destroying all complex life on Earth. So those are a bunch of great filters we got through, great filters behind us.
However, if complex life does not get wiped out, what are the chances of intelligence — is that a great filter behind us?
Apparently not — the deuterostome clade diverged from the protostome clade about six hundred million years ago, but the most intelligent deuterostome (us) is only something like a few million years different in intelligence from the most intelligent protostome (the common octopus, Octopus vulgaris).
Similarly the synapsids diverged from the sauropsids a bit over three hundred million years ago, but the most intelligent synapsid (us) is only a few million years different in intelligence from the most intelligent sauropsid (crows). So intelligence evolved in each group at about the same rate, despite wildly different environments and body plans. As soon as multicellular animals start moving around and attacking and eating other animals, there is pressure to develop intelligence, and intelligence then develops. So you need a reasonably high oxygen atmosphere to give creatures the selective pressure to eat other complex creatures, but once you have an oxygen atmosphere, creatures will quickly evolve towards intelligence — well, quickly as measured by the standards of cosmic time. Maybe the development of high oxygen levels is a great filter, but Mars has trace oxygen in its air, and highly oxidizing soil, so oxygen
environments are probably not all that rare.
There is, however, an obvious great filter in our future
As our artifact extended phenotype becomes ever larger and more complex, it, and we, become ever more vulnerable to violence, and as we command more and more energy more and more precisely, we become ever more capable of violence.
Our capacity to end civilization, to end our species, and to end all life, becomes ever greater.
So we have to expand into space faster than we can destroy each other. Everyone planning to colonize Mars fears that humans on Earth are in for a dark age or extinction. And, in the event of a dark age, we long ago exhausted all resources that are accessible to low tech, except for resources that renew themselves within the human lifetime, like wood and bog iron.
A space dwelling civilization is a civilization where the equivalent of a truck driver has the equivalent of nukes and rods from God, the central government is very far away, and it is very difficult for the central government to know what is going on.
So, the upcoming great filter is virtue. We must create consensus on what is aggression, and what is not, consensus on whether when one person or organization does something another person or organization does not like, that person’s action constitutes refusing a good, or that person’s action constitutes inflicting a bad.
Great powers must stop engaging in political and military maneuvers to increase their capacity to inflict violence on other great powers, and political and military maneuvers to diminish the capacity of other great powers to inflict violence, because such maneuvers wind up getting out of hand, and result in two vast coalitions fighting a world war. Instead, we need the Peace of Westphalia and the Concert of Europe, when Christian Kings agreed not to try to tip the balance of power in favor of themselves and against other Christian Kings.
The Congress of Vienna and the Concert of Europe were explicitly about balance of power. However, the Peace of Westphalia was also implicitly about balance of power, in the sense that a King in one country would back a non-state religion in another country to undermine that country’s state religion, thereby increasing his power and diminishing another King’s power, in much the same style and for much the same motives as today the Global American Empire has been instigating color revolutions in other countries. The Peace of Westphalia, when translated to the modern events, amounts to “Stop instigating color revolution.” Among the governments the US color revolutioned was Ukraine, an operation which may well end in World War III. This was very much one Sovereign interfering in the religion of another, in that it was in substantial part fought over the gay parade and the Russian Orthodox Church, which was the sort of thing the Peace of Westphalia prohibits.
One may well argue that our state religion is good, and theirs is bad, thus meddling in favor of our state religion, in countries that fail to adhere to it, is righteous and good, and if another sovereign reacts to this reasonable activity with horrific and extraordinary violence, he is being wicked. Perhaps this is true, but history tells us that whether it is true or not, adherents of the other state religion are likely to doubt it and unlikely to be persuaded.
That is the upcoming great filter.