There are, by various estimates, several trillion planets within the local group of galaxies including our own Milky Way. Many of these are within the habitable zone of their stars. So if life finds a way, where are the alien civilizations?
This is the crux of what is known as the Fermi paradox, which posits that if life is fairly common in the Universe, humans should have collected credible evidence for the existence of extraterrestrial civilizations by now. People who think about this paradox believe there may be some "filter" which limits or entirely prevents an advanced civilization from sending out probes or even life-bearing spacecraft to nearby stars.
Philip Johnston is someone who thinks a lot about the Fermi paradox. A mathematician and physicist from the United Kingdom, Johnston has gained some notoriety lately in the space community as one of the biggest proponents of orbital data centers. He co-founded Starcloud in 2024 to develop such data centers, and the company is presently valued at $2.3 billion.
