In this 30 minute-long science video from the talented Isaac Arthur, we investigate the multiverse as one of the potential explanations for the Fermi Paradox (a.k.a. where is anybody?).
That is to say, the same basic premise as the Stephen Baxter and Terry Pratchett books, The Long Earth, where humanity discovers a possibly infinite series of parallel worlds that are similar to Earth, which can be reached by using a cheap device called a Stepper.
In such a world you don’t explore the galaxy, you just move sideways to colonise unoccupied Earths where humanity never arose.