Josh Caldwell is an astrophysicist at the University of Central Florida.

We now know the answers to some of those questions pretty well.

So we know how many stars are in the Milky Way galaxy.

We know a pretty good census of what kinds of stars there are that might develop life.

We know a lot more now than we did even a few decades ago about how many planets there are.

So a whole bunch of those parameters, we've got actual numbers that we really know.

Or maybe they're out there, and these aliens just don't want to be found.

Or maybe civilizations never actually get to that point, and that gets to this concept called the Great Filter, which says something happens that prevents life from getting to the point where it could colonize the galaxy, so to speak.