Neurotic Void Melody said:
Fermi's paradox...why? Why does it keep getting brought up for anything other than mockery? It's based on so many simplistic assumptions it legitimately annoys me that some consider it relevant at all. It's the theoretical equivalent of looking at the outside of a huge expansive forest and going "Nope! Absolutely no-one could be here. Otherwise they'd have visited us already. we've even brought gifts and meat buffets...how could they not notice our grandeur by now??" I'd give him some credit however, for his time, if it were me there, I'd be illiterate and dead by 20. But now it seems no less silly than flat Earth belief.
Consider the scale.
The big bang happened around 13 billion years ago.
Our solar system formed around 4.5 billion years ago.
Life appeared between 3.5 and 4 billion years ago.
The cambrian explosion happened 0.5 billion years ago (500 million years)
The first hominids evolved 0.02 billion years ago (20 million years)
Modern homo sapiens evolved around 0.0002 billion years ago (200,000 years).
The first cities appeared around 0.00001‬ billion years ago (10,000 years)
So, let's assume the universe was pretty chaotic and hostile for a couple of billion years after the big bang. That still leaves us 6.5 billion years during which other habitable, life-supporting planets could have formed before earth. Let's say one of those planets produced intelligent life, and a mere one billion years ago, a pretty short time compared to the age of the universe, they launched their first space craft..
If that were the case, then at the time these aliens were making their first attempts at space travel, multicellular life doesn't exist on earth yet.
However huge the task of populating the galaxy might be does not matter much at this point. The aliens have inconceivable amount of time. Without some kind of faster than light propulsion, it will take them millions of years to colonize every star in the galaxy, but they have a billion years. Whatever setbacks, whatever political concerns or whatever local circumstances might block our alien super society from exponential expansion, the timeframe is so great that it is ultimately not going to matter. Heck, even extinction might not stop them, another species could simply evolve and do the same thing without really eating into the timeframe very much.
If you look at it in these terms, the question becomes less "why haven't these aliens come to visit us" and more "why can't we find evidence of their existence". Why doesn't every star in the sky have a dyson swarm? Why has our solar system not already been disassembled for its resources? Heck, even if aliens evolved in other galaxies, there's a decent chance we'd be able to see them because once they become advanced enough they should start leaving marks on the galaxy itself, and there's no reason we can imagine why they wouldn't become that advanced. Again, they have time. They have more time than we can possibly imagine.
Even worse, there are so many stars and, potentially, so many habitable planets in our galaxy that this should have happened many times. So even if our hypothetical aliens wanted to hide their presence out of some kind of respect for the prime directive, and could somehow sustain that belief for literal aeons across countless star systems where (assuming they were still recognizable as organic life) the inhabits would have long since ceased to be the same species, there should be so many aliens at this point that you'd think there would be some evidence of their presence.
The Fermi paradox isn't meant to indicate for certain that advanced alien civilizations don't exist. Heck, a billion year old civilization would be so unimaginably ancient that it may have long since stopped according with any technological or cultural paradigm we can imagine or observe. It's just pointing out something that is weird and incongruous.