Oh my, this time they take on string theory. The episode is watchable at the link and is titled “Road to the Multiverse”.
Here are a few frame snaps. First the universe where religion never took hold. Since MacFarlane is a big old atheist it doesn’t surprise me that this would be the first universe the travel towards. I won’t tell you who painted the Sistine Chapel. But this one definitely comes from the Jetsons.
The Japanese themed universe. In this universe the U.S. never dropped the atom bombs on Japan so the Japanese just kept going.
And then the Flinstones universe.