…which you can read about here.
And this quote, in a nutshell, is why I don’t believe in aliens in the skies:
The technology and knowledge of a civilization only 1,000 years ahead of us could be as shocking to us as our world would be to a medieval person. A civilization 1 million years ahead of us might be as incomprehensible to us as human culture is to chimpanzees. And Planet X is 3.4 billion years ahead of us…
If they existed, they would have made their presence know in an unmistakable fashion by now. In a rather forceful manner.
If you are looking for aliens, wait about 50 to 100 years. Even if robots never become sentient, our biotechnological abilities will be able to permit us to make our own aliens right here on Earth. Throw in cybernetics, the desire for agelessness, flawless beauty, and perfect health, and the humans *cough* of 2500 are going to be definitely different from what we are today.
Now, the article posits Great Filters – massive challenges that make life impossible, makes sentient life impossible, or long-lived technological civilizations impossible.
Of course, as a believing Christian I will insist that the Great Filters are behind us, between the unlikelihood of 1) the universe existing 2) life existing 3) sentient existing. The possibility of my computer just randomly putting itself together last night is a good deal higher than some of these odds!