If you say our solar system may have had aliens pass by, you're an eccentric.
If you say aliens landed on earth, you're a crank.
Why is the sanity of the claimant inversely proportional to the distance of aliens from Earth?
It's not about sanity, it's just about understanding how much evidence certain claims require to be considered likely.
Modern thinking is it's more likely there were civs that thrived, but they are all dead now. - https://www.youtube.com/watch?v=o9kbcGfX35M
https://www.cnet.com/news/nasa-spacecraft-discovers-the-univ...
It takes a long, long time to get anywhere, because light moves at a relative crawl compared to the distances between stars, so it would be a long and energy-intensive process to visit another planet, especially given how hard it would be to detect a civilization there before you departed. The Earth didn't emit much of a signal on radio waves until about 1900, so even if the aliens were only sixty light years away and could move at the speed of light, they'd have had to launch just as soon as they got some signals.
Ah, but FTL, you say. But nothing. FTL implies Closed Timelike Curves: time travel, or the informational equivalent, with all of the logical paradoxes that can entail. I'd sooner believe in breaking the conservation of mass-energy than beating the speed of light.
1) FTL implies CTCs, that means paradoxes. How are those going to be resolved? Because the Cosmic Censor stuff never quite makes sense -- exactly what mechanism is going to forbid you from opening the message that says, "Do not send this message back in time?"
2) Again allowing for FTL ... where are the self-replicating machines spreading across the cosmos? Pop to another star system, pop to another galaxy, or even a local cluster. They should have already been there. The universe is vast. Most species will realize that this is a terrible ass idea, but there's always a lunatic in a large enough crowd, and it'll be a pretty large crowd.
Nobody ever deals with these points. People want FTL to be true because, well, Star Trek (or Star Wars, or Farscape, take your pick). It's a bit dull, plodding along at some small fraction of c, but the universe doesn't have to be exciting for us. And I'm not going to bet otherwise.
2, didn't the universe itself expand faster than light during inflation? what does relativity have to say about that? if we can't use relativity to explain inflation, why do we so comfortably use it to forbid FTL?
2) None of the matter in the universe was expanding, the spacetime was. You're not the first person to think of this. Probably the first question that popped into anyone's mind when variants of the concept were being kicked around. Anyway, the expansion doesn't generate CTCs because there's no information and/or matter to circle around, it's just the stretch between these.
Now, you'll probably ask about -- well, why can't we shrink spacetime selectively to get around all of that? Ah, that requires some exotic matter, matter with negative mass-energy. No, anti-matter does not have negative mass-energy (first thing people reach for). In fact, we've never found anything with negative mass-energy and that concept itself raises a ton of fun paradoxes which I could get into. And you still get CTCs.
There's probably a large tree of arguments out there on the Internet somewhere which addresses all of these common objections.
We also don't know that I can't use that device to go back in time to the start of the universe and change all of the physical laws so that the previous contraption cannot work.
But what are the odds? What would you bet on?
Who is to say that I cannot write an AI in under 1,000 lines of C? We don't know what we don't know. By all means, pursue that line of inquiry if you feel that the odds are with you.
It's just not a useful heuristic for deciding what to spend your resources (time, money, effort, energy, etc.) on.
To be sure there are nuts working in their garages on various projects, but in the scientific community, nobody is holding their breath on these fantastic breakthroughs.
All the speed of light problems can be ameliorated. The entire galaxy could be visited (if not colonized) in a relatively short amount of time by something like a Von Neumann probe at even 0.01c. The 'aliens' needn't be biological.
The answer is it probably is somewhat arbitrary but maybe related to human psychological proximity and the fear response. The most common response to fear is denial and so questioning the credibility of those people providing information that could provoke fear is a form of denial. The closer the object of fear the more fear therefore the more denial perhaps.