Space is big. Really big. You just won’t believe how vastly hugely mind-bogglingly big it is.
Pondering this fact, in 1950 Enrico Fermi over lunch posed the now famous question concerning extraterrestrial life: "Where is everybody?" He was right: Considering the size and age of the universe we should be up to our eyeballs in aliens. Where the hell are they?
So far, SETI (Search for ExtraTerrestrial Intelligence) has been a total bust: a complete and utter waste of time and money. And that's great!
As Robin Hanson pointed out in the mid 90's: If they would ever encounter an extraterrestrial transmission, we would be (statistically and royally) screwed, considering that we could hear a civilization approximately on our own level of development, but there is nobody more advanced visiting us.
Here is a question for you: What was the fastest ever man-made object?
You'd probably guess it's one of the Voyager probes - specifically Voyager-1 at currently almost 40,000 mph. And you'd be most certainly and hilariously wrong.
To zero in on the correct answer, you have to learn not to underestimate the curiosity (and nerdiness) of a bunch of nuclear scientists, having really, really big "toys" to play with.