In this brilliant essay Charles Krauthammer discusses that question. And he steers it in a provocative way, one that shows why politics—more specifically, why getting politics right—is so important to any form of intelligent life.
Let me now write perhaps the second-most controversial statement I’ve ever written on Ricochet. The answer to the above question, I believe, is yes – that we humans are the only intelligent beings in the universe. (I believe my first-most controversial statement was that the BCS system in college football might be sort of okay.)
One reason I believe this is that the counter-theory is not falsifiable, in the sense argued by the great philosopher Karl Popper.
To explain this, let me first explain the opposite—that my theory is falsifiable. What this means is that I can imagine an observable event that would make me disbelieve my theory. One such event is simply that aliens visit our planet. Another is that we receive radar signals from a distant planet that unmistakably come from an intelligent source. E.g. suppose the signals, like those in the movie starring Jodie Foster, followed a pattern of prime numbers.
However, the same is not true with the opposite theory. That is, suppose you believe that we are not alone – that somewhere in the universe there are other intelligent beings. What event would make you believe that that is not true? I assert that you cannot imagine such an event. E.g., suppose we send additional spaceships to Mars that conclusively show that no life exists on that planet. You could simply respond, “Well that’s only one planet. It’s still possible that intelligent life exists elsewhere.” No matter what sort of experiment that a scientist conducts, you could respond with a similar statement.
As Popper explained, we should be skeptical of any theory that is not falsifiable.
A second reason is a form of the Fermi Paradox, which asks “If it’s so easy for intelligent beings to arise in the universe, where are they?”
Here are some quick calculations that I’ve done. Over the last 2000 years, human population growth has been about 0.16% a year. Suppose: (i) at least one civilization has existed for at least a billion years (The Earth is about 4.5 billion years old, while the universe is about 13.7 billion years old. If it is easy for intelligent life to arise, then at least one civilization must have arisen before the birth of Earth. If so, then that civilization, if it still exists, must be at least 4.5 billion years old.), and (ii) that civilization has experienced population growth similar to ours. If these two facts are true, then the population of that civilization would be more than 10^700,000. This is more than there are atoms in the universe.
Clearly, if it were easy for intelligent life to arise, and it grew at even a tiny fraction of human population growth, then—assuming such beings could invent technology to colonize other planets—such beings should exist in all corners of the universe. This clearly is not the case. It is one more reason that makes me skeptical that other intelligent life really exists in the universe.