I'm not sure if this is the place for this kind of thing, but I enjoy speculating about things like aliens and extraterrestrial intelligence.

In a lot of the wonderful sci-fi that human creativity has been able to dream of, we've conceived of star systems and galaxies that are fecund with intelligent life. There are sci fi universes like Star Wars, with empires spanning an entire galaxy. There are universes like Star Trek, which incorporate numerous sentient species over a large section of a galaxy. Then there's Doctor Who, which effectively covers the whole universe, with all its many galaxies, stars, and planets.

But what if, at least in our Milky Way, this is not, and will never be, the case? What if sentient life, and civilization as we know it, are rare enough that there aren't any spacefaring ETs out there at all?

There are several possible scenarios for this:

• Intelligent species, like our own, are simply incredibly rare. Even complex life could be rare. It could be that a planet like ours is a one-per-galaxy occurrence, perhaps with some exceptions. It could turn out to be rare that more than one such species arises within the same galaxy, and due to physical constraints, this results in contact between species occurring very, very rarely.

• There are numerous civilizations in the Milky Way, but none of them are sufficiently more advanced than us to have developed interstellar travel. Perhaps civilization frequently arises, but it's rare that it gets to our technological level. There could be species that are at the tech level of our ancient Romans. There's a possibility that species often wipe themselves out with nuclear weapons or other mishandled technologies during their development, creating a "bottleneck effect" reducing the number of societies that can survive past a 20th century level of technology.

• Few species, even at a high technology level, end up trying to pursue interstellar travel. If physics does indeed prevent FTL travel, and it's simply overwhelmingly difficult to make it very far away from a civilization's own solar system, it could be that other civilizations simply do not or cannot achieve a Star Wars or Star Trek level of interstellar mobility and exploration. Perhaps technological development, beyond the level we're at right now, ends up focusing more on things like artificial intelligence, virtual reality, and brain augmentation, rather than expanding out into the stars. Perhaps instead of going outward, the usual progression is to turn inward instead, creating vast artificial worlds using VR tech, brain-machine interfaces, and other technologies. It could be that using these kinds of technologies to create and explore infinite worlds, could supersede interest in space travel.

• Our galaxy doesn't have many sentients, but that isn't the case everywhere. For whatever reason, our galaxy is decidedly sparse when it comes to civilizations of sentient species. For all we know, M81 could have a Star Wars type of society, but in our own galaxy, we're the most advanced out of a total of ten civilized species.

I highly, highly doubt that we're alone in the universe. Across the vastness of known space and time, the odds seem low that we are, have always been, and will always be, the only sentient life. However, with the universe being as big as it is, even an average rate of one civilization per galaxy could make First Contact nearly impossible for most species to actually achieve. Especially if FTL travel, along with alternatives like warp drives, turned out to be totally impossible, it could turn out that contact between sentient species isn't something that happens very often.