The Milky Way is 100,000 light-years across. So at least that long assuming we can ever attain near-light-speed travel (unlikely). And due to cosmic inflation, many other galaxies are receeding at faster than light speed, so we could never get there.
There could be a lot of intelligent life (as intelligent as us, maybe more so) that can never realistically travel beyond their local star systems, and we'd never notice them.
The Milky Way is 100,000 light-years across. So at least that long assuming we can ever attain near-light-speed travel (unlikely). And due to cosmic inflation, many other galaxies are receeding at faster than light speed, so we could never get there.
There could be a lot of intelligent life (as intelligent as us, maybe more so) that can never realistically travel beyond their local star systems, and we'd never notice them.