I assume you, like me, have had endless thoughts about other life in the universe. The universe is infinitely big, right? And there are more observable stars than grains of sand on Earth? That’s… uncomfortable. Clearly, there isn’t only other life in the universe but lots of it. So why aren’t we aware of it?
One of my favorite theories is that other life is at such a different scale that we don’t even notice it. Like if you’re a bug born on the branch of a tree and you live three days, do you consider this tree you live on a living creature? No, it’s just the ground beneath your bug feet, largely unchanging in not just your life but your parent’s and children’s lives as well. Similarly, us humans are born on Earth, recent accelerations in climate change notwithstanding, largely Earth is unchanging in the few generations were closest to. But zooming out over a long a longer period of time (and size?), the Earth is very dynamic, with its shifting plates and oceans, weather systems, ice ages, and such. Clearly alive, as it were. As alive as a tree is to us mere humans.
So maybe alien life is either so big (the Earth is a spec of dirt in its toenail) or so slow (the life span of aliens is more like millions of our years) that our version of life doesn’t register on our scales of what we expect life to be.
The most comfortable theory is that life is so extraordinarily difficult to produce that we’re among very very few to ever happen. Plus travel is limited to light speed, so even if we wanted to visit each other, the time that takes is life-prohibitive.
Another fairly comfortable theory is that maybe life isn’t that hard to produce, but that the universe is fairly young, and we just happen to be some of the first to have broken through. So we haven’t met any aliens yet just because they are (all?) trailing us in evolution.
Less comfortable is the Zoo hypothesis. Why haven’t we met any aliens? Because, essentially, they keep us in a zoo.
The hypothesis states that alien life intentionally avoids communication with Earth to allow for natural evolution and sociocultural development, and avoiding interplanetary contamination, similarly to people observing animals at a zoo. The hypothesis seeks to explain the apparent absence of extraterrestrial life despite its generally accepted plausibility and hence the reasonable expectation of its existence.
Maybe there is lots of life out there, all mingling with each other at cool interplanetary jazz bars and such, but we’re just not invited because there is some consortium of life that intentionally keeps Earth in a zoo. Seems just as plausible as any other theory.