How far away is Proxima Centauri, the closest star to our sun? But a mere 4 lightyears.
20190306/https://en.wikipedia.org/wiki/Proxima_Centauri
Here, there is a lot of interesting discussion about why our Earth-ball we live on is so extremely unlikely to be found elsewhere in the Universe. Most of the Universe is either too barren or too violent to be reasonably stable for complex life to flourish.
20190306/https://en.wikipedia.org/wiki/Rare_Earth_hypothesis
This is an interesting concept to reach Proxima Centauri. Build a light sail and propel it with Earth-stationed lasers.
20190309/https://en.wikipedia.org/wiki/Breakthrough_Starshot