“Where are they?” famously asked Italian physicist Enrico Fermi in the 1950s. By “they,” he meant space aliens. Fermi figured that if the galaxy contained space-faring civilizations it would only take them a few tens of millions of years to populate it. So why hasn’t there been a saucer-landing-take-me-to-your leader moment already? This is the Fermi Paradox.
In 1961, American astronomer Frank Drake devised an equation in which he tried to estimate the number of technological civilizations that might exist in our galaxy. Depending on the values plugged into it, the galaxy could be brimming with extra-terrestrials or we might be its only technologically advanced denizens.
It turns out new parameterisation of Drake’s equation suggests that we humans may be alone in the universe.
Seems unlikely – but who really knows? It is an interesting question though because it has important consequences depending on how noisy we are and whether we do have neighbours. These themes have been explored by some of my favorite authors:
Alastair Reynolds in his Revelation Space series posited the idea that the universe was predisposed to teem with life, but that space faring species were being hunted down and destroyed by a robotic intelligence called the inhibitors.
Alastair Reynolds in Pushing Ice had the idea that the universe was teeming with life but that the time frames were on such a scale that intelligent life seldom coincided with other intelligent life.
Liu Cixin in his three bodied problem trilogy posited the idea that the universe was caught in a Malthusian trap and advanced civilisations hid from each other and immediately destroyed any lessor civilisation that inadvertently revealed itself.
David Weber in his Safehold series has an alien species – the Gbaba – exterminating any and all signs of intelligent life in the galaxy. In his Honor Harrington series humans are the most technologically advanced species in the galaxy.
Then there is a magnificent short story by Michael Shaara – All the way back – where as a result of an ancient war Earth is located in a portion of the galaxy known as the desert where all other inhabitable planets were destroyed.
All up a fairly pessimistic take on either why we find no evidence of other intelligent life in the universe and/or why we should be quiet in our own search through the universe. All good reading (less so Weber – I have stopped reading him through annoyance at his abuse of his readership) and probably a lot more interesting than the most plausible explanations being that the lightspeed limit is binding, and lifting intelligent life out of a gravity well on a large scale isn’t particularly economically viable.