I like Greg Egan's formula for stories of coming up with a "small" change to fundamental physics, and then follow all of the consequences to their logical conclusions to build the world. It's <
https://tvtropes.org/pmwiki/pmwiki.php/Mohs/OneBigLie> to a T. And I really like the "Science" pages on his website that explain these worlds, which a bunch of his books have, including this one (where there are 8 long-lived generations of leptons),
Orthogonal (where the time dimension is spacelike), and
Dichronauts (where one of the space dimensions is timelike).