Prompt: Do you believe in aliens? Why or why not?
Since I assume we're talking life on other planets, I'm going to point out that actually I think this is a surprisingly complex question.
First up: is there life on other planets? Well, it's hard to guess what the odds might be when our sample size is basically just our own solar system, but even if the odds of life developing on a planet are vanishingly slim, there are still a lot of planets out there. So if I have to guess, I'm going to say, "Yeah, probably."
The same goes for intelligent life: it just seems unlikely to me that Earth is the only place in the entire Universe where this has happened. Intelligence isn't a fixed quality and honestly, human beings are frequently very bad at recognizing it when it doesn't look the way we expect, but intelligent life in general? "Yeah, probably."
So that brings us to the next question: do I believe in aliens who actively travel through space, and do I think they've visited Earth? And the answer, again, is complicated.
Because yes, we know as an absolute fact that aliens have visited Mars and left evidence of their advanced technology there. We know, because we are the aliens who did that. So we know that if intelligent life exists, it is possible for it to travel to other planets. We've done it ourselves.
So why aren't there aliens everywhere? Why haven't we seen any, met any, shaken appendages with any? I suspect it's because the universe is truly, ridiculously vast, and the speed of light is an absolute limit. Otherwise, whatever species first developed a trick for faster-than-light travel -- and statistically, it wouldn't have been us and it was probably a very long time ago -- would have been able to spread freely across the galaxy, at the very least. (This line of thinking is based on several questionable assumptions, but it's the one that seems reasonable to me.)
In case you need more #CosmologyFunFacts to break your brain, did you know that there are distant galaxies that are currently receding from us faster than the speed of light (due to cosmic expansion), and ALWAYS HAVE BEEN, and yet we have pictures of them? 🙃 https://t.co/R1XaddwVXq— Katie Mack (@AstroKatie) April 23, 2022
So yeah, I think that alien life probably exists, and I think it's even possible that we might someday make contact with it -- but that would require a concentrated effort to transport human beings across mind-numbing distances to a large enough number of worlds to find it. (Or, alternatively, an alien race that had made a concentrated effort to transport its species to enough different worlds that they finally happened upon us.) And given our biases, we still might fail to realize that what we'd encountered was intelligent or even alive.
...Which is honestly a little more cynical and depressing than I meant be when I started writing this out.
So let me just add that if I'm wrong about Earth never having been visited by extraterrestrials -- if you, yourself, are an extraterrestrial and happen to be reading this -- well, I believe in you, Alien Buddy. You've got this. You can get things done! So go on out there and have a really good day.