“If the Universe Is Teeming with Aliens… Where Is Everybody?” -Stephen Webb

If stars, planets, and biological processes are so common in the Universe, then where is everyone?

Image credit: NASA / Space Shuttle Atlantis mission 110.

Here on Earth, we take for granted how easy it was for life to form. Our world has been around for some four-and-a-half billion years, and the oldest records of life go back to nearly the oldest rocks: 3.8 billion years ago.

But if we ran the "experiment" of having a Solar System similar to our own form in the Universe over and over again, how many times would we see life arise on Earth?

Image credit: © 2002, ReefNews, Inc.

And of those times, how often would we see intelligent life arise, and how long would such a civilization last in that phase?

In other words, we're asking about one of the biggest questions of them all: given our galaxy, with some 200-to-400 billion stars, all the planets around those stars, and a Universe with at least 200 billion Milky Way-like galaxies, how many of those worlds have life on them? How many of those have intelligent life on them? And how many of those have intelligent life on them at the same time we have intelligent life on ours?

For this week's throwback Thursday, go check out the entire amazing, in-depth answer at Medium, and then leave your comments here!