In science fiction, especially involving interstellar space travel, we often see aliens. Often, but not always. And this is something we wonder today. How many civilisations are there in space? How far are they from us? Will we ever encounter any alien civilisations on other planets?
In Star Trek, the population density of the galaxy is very high. Pretty much any star system with a planet in the Goldilocks zone has life and possibly a civilisation. Alpha Centauri has life, but not a native civilisation. Vulcan, Andor, and Tellar are all fairly close to Earth. Life is everywhere.
In the book that I’m reading now, Redemption Ark (Revelation Space), the galaxy is fairly empty. There have been civilisations, but they’re few and far between and happen at different times. But there’s a reason for it, and that’s explained in the book.
In my own Ariadne universe, I hint at other civilisations, but I don’t go into it so much, because all the action takes place on one planet. At least for now.
In these three, the mode of transportation is also different. In Star Trek, they have warp engines that take their ships out of normal space in a warp bubble, and propel that bubble through space many times the speed of light. No relativistic effects are experienced. In Revelation Space, the spacecraft are able to travel at nearly the speed of light, and there are major relativistic effects. But in Ariadne, I use a modified warp system that is unable to pass the speed of light. However, they use sleeper ships, so the effects of relativity are not felt, but the people also don’t age. In Star Trek, thanks to the form of propulsion, they are able to meet many different civilisations and visit many planets without any difficulties. In Revelation Space and Ariadne, the speeds are not enough to make regular interstellar travel practical.
I find that both kinds have their place in science fiction. I enjoy reading and watching science fiction that use either one. Which do you prefer? Let me know in the comments below.
I Read Encyclopedias for Fun 
Slow travel/all the action happening on one world, versus fast and easy travel and lots of adventures on lots of planets? I don’t have a preference; both kinds of stories can be enjoyable.
Every time someone comes up with yet more data to plug into the Drake Equation, it seems more and more that a heavily populated galaxy is the way to go… but then again, perhaps there’s a reason why the galaxy has all these excellent planets but no one lives there.
I can’t wait for the James Webb telescope to be up and running. It’ll really expand our knowledge of extrasolar planets. Kepler has been great, but we need more direct observations of planets. That will help a lot.
And yes, both kinds of stories are enjoyable.