The existence of extra-terrestrial life is, statistically, almost guaranteed. The biological necessities for life are not as quite as specific as often portrayed, with extremophile organisms surviving everything extreme ionizing radiation and drying (in Tardigrades) to reproducing in freezing temperatures (Colwellia p.). The “habitable zone” is likely wider and more dynamic than currently believed. The idea that life on Earth may have even first originated from space, carried on meteoroids, is even suggested by the handedness (chirality) of amino acids, according to NASA.
The fact we are not alone in an unbelievably large universe is pretty well accepted, with even the former Pope, Benedict XVI being open to the idea. The increasing recognition of life on other planets, even potentially under the surface of Mars, has led some to combine these facts with the speculation of past alien contact with humans. If this happened, it certainly didn’t happen in the way most imagine.
Most imagine beings from another planet flying to Earth in some type of craft powered by some highly efficient zero-point energy source. This fits nicely with the typical alien conspiracy theories.
Firstly, the idea of biologicals (or living beings) touring the universe is largely irrational. The evolution of any species has primarily selected for those who can best survive on their home planet, and cosmic rays outside one’s sun’s protection would most certainly decimate DNA during long voyages. Not to mention that despite advances in stem cells, eternal life is likely out of reach for any living organism. Once the ETs did then make it to a new system, and manage to retain their cognitive functioning, they would have to be able to deal with the type of radiation given off by this system’s sun and the atmosphere of any planets they land on. The relaying of any new information would also then be centralized in this one craft, and dependant on the pilots surviving and gathering data. If there is other sentient life out there, more advanced than us, they will have likely come to the solution I am about to propose for solving this problem.
To solve the problems created by sending either individuals or a group to explore space, one would instead use self-replicating AI probes. This would entail creating probes capable of learning, sharing their knowledge within the network, and self-replicating. “Daughter” probes would preferably be linked via quantum entanglement to quickly exchange and share information with each other and, if still surviving, the species that created them.
“I don’t think the human race will survive the next thousand years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I’m an optimist. We will reach out to the stars.”
Stephen Hawking, interview with Daily Telegraph, 2001
To effectively scout for another planet, which may be a necessary step considering the propensity for technological civilizations to destroy their own environments, it would be beneficial to create scouting networks with redundant mechanisms for transferring data to avoid significant loss if a single one is destroyed. Making the probes self-replicating, with a bias for reproducing on uninhabited moons, minimizes initial resources and maximizes potential reach. Their capacity for learning and sharing enables the each generation to be increasingly effective, and each probe would also represent an increase in processing power. A civilization capable of intergalactic travel is surely capable of thinking this far ahead.
If humans had contact with space faring civilizations in the past, it was likely not with biological entities. Independent of the reasons above, as Stephan Hawking noted; “If aliens visit us, the outcome would be much as when Columbus landed in America.” A multi-node AI would have access to records of human history, and the experience of all other probes: it would have learned that the most gain, coupled with the least risk, rests in being largely benign or non-committally helpful.
Of course, independent of the success of the probes, the continued survival of their biological creators is likely tied to the survival of their biosphere. The ability to successfully relocate and reproduce on a new planet is not guaranteed, and if civilizations do tend to lead to ecocide, space may be filled with microorganisms, sentient probes, the few civilizations that managed to maintain the habitability of their worlds (or have other viable options like a 2nd planet), and the slowly decaying remains of the civilizations that never made it that far.