Another prospect is that intelligent life inevitably destroys itself. Until recently, our choices for total self-destruction were restricted to nuclear weapons. But we are on the verge of increasing our fleet to contain genetically engineered viruses.
And consider the threats posed by nanomachines, tiny self-replicating robots encoded to convert matter into more robots. Picture a tiny robot, no larger than the width of a human hair, programmed to deliver some useful function, designed to build a copy of it, using materials from its environment. Now you have two machines, and both can make copies, giving us four machines. But what if this development got out of control? The nanomachines could quickly devour the entire Earth, transforming it, along with everyone on the planet, into “grey goo.” British astrophysicist Martin Rees debates these and other disastrous possibilities in his book, Our Final Hour. Have all our possible alien guests surrendered to self-destruction?
Or is it probable that the galaxy actually does contain other forms of intelligent life, but something stops contact with us? Here we enter the land of more hypothetical ideas. (Translation: when a researcher says “hypothetical,” it in fact means “a very stimulating concept that’s only one step removed from total nonsense.”)
Among the more hypothetical prospects: maybe the galaxy is a dangerous place, full of robotic probes sent out by unfriendly ETs to wipe out any rivalry, so everyone else is in hiding. Maybe we actually should not have put a thorough description of the location of our solar system on our own space probes. It’s a bad notion to reach out and attempt to touch ET when we might get a call from the Alien instead.
An even stranger proposal is that superior civilizations have decided not to communicate with lesser creatures such as ourselves, so that we live in a kind of intergalactic zoo, with a “Do not talk to the animals” board.
Some have even proposed that we live in a huge computer simulation, Just like The Matrix.
A lengthier list of prospects (along with a sceptical discussion) has been assembled by astrophysicist Milan Ćirković.
Without more data, the Fermi paradox will continue, for now, unsettled, and many of the suggested solutions will have to be categorized as “speculative.” And now you know precisely what that means.