Fermi Paradox is the discrepancy between rough predictions of expected frequency of alien encounters, and us not having detected a single one. Simply put: where are the aliens?
There have been many hypotheses as to what the answer is. Perhaps life is not as common in the Universe as we would think. Or maybe aliens are everywhere, but we cannot detect them due to their advanced stealth technology. Maybe aliens observe us from a large distance, but feel no need to interact with us.
One of the major hypotheses is the "Great Filter": that at some point every civilisation faces an issue making it unable to ever expand far beyond its planet. It could be that every civilisation develops a technology that leads it to exterminating itself - for example, a very powerful weapon of mass destruction, or a synthetic virus, or an artificial intelligence that rebels and genocides its creators. It also could be simply that the interstellar travel is unfeasible for a variety of reasons, and so every civilisation ends up stuck in its star system forever.
I personally like the theory that every civilisation eventually develops a very powerful AI that, through logical argumentation humans cannot comprehend, comes to the conclusion that all life is evil, and exterminates its creators, followed by self-destruction.
But recently I have been leaning towards a more optimistic scenario. Let us call it the "virtual retreat" hypothesis.
As our technology develops, so does our ability to build realistic virtual worlds. At some point, say, 1000 years from now, our virtual worlds can become nearly as realistic as our real world. We will be able to design any virtual world we could possibly like, and experience it in a very realistic way, with all 5 senses simulated. They would be nearly indistinguishable from the real world.
At that point, it becomes very tempting to escape our limited real life into a virtual world of our dreams. Our body could be infinitely preserved inside life support machines, while we are free to live in much nicer simulated worlds forever.
It is possible that eventually the entire population escapes into the virtual reality this way. The real world becomes irrelevant, as everyone virtually lives their dreams. Nobody has any incentive to ever leave their home planet, because everyone has already achieved everything they could possibly want.
So there could be billions civilisations out there, all consisting of nothing more but underground capsules with living organisms inside experiencing endless virtual bliss.
Do you think this hypothesis is realistic? And even if it is not, do you think such an end to a civilisation would be a good one? Is it better to live in a perfectly made virtual reality, or in the real world?