Why haven’t we encountered or even heard from civilizations beyond our solar system? If there are any, there probably hasn’t been enough time yet for contact.
There’re some widely held and tested ideas about our existence, most of them can be expressed as numbers, really big ones, but easy to talk about.
The universe is around 14 billion years old and the earth is less than 5 billion years old.
It’s safe to say the universe contains at least at least 100 billion galaxies. Our galaxy, the Milky Way which is pretty ordinary, contains somewhere between 100 to 400 billion stars. How many of those are like our sun with a life-friendly rock circling it? There’re probably a few out there, when the numbers are that big.
Look at this another way, consider the life of the universe as if it occurred over the course of one year – starting with the Big Bang ringing in the new year.
Our sun doesn’t appear until September 1st, followed by the earth on September 11th. Single-cell life pops up on September 30th, but there’re no multi-cellular life until lunchtime on December 14th.
Dinosaurs are only around for three days(!) starting on December 27th.
People don’t show up until 11:39 pm on December 31st. Greek philosophers were flourishing just 5 seconds before the year’s end. You get the picture.
We humans just recently have gotten to the party, and the timeline for another (off earth) civilization developed enough to contact us is probably about like our timeline. Given the distances to cover it seems unlikely that we’ll contact anyone else soon.
Traveling to one edge of the universe, if you could travel as fast as light does, would take billions of years (just getting to the nearest large cluster of galaxies would take about 60 million years).
What about if there are other older universes? Hard to say.