Lots of explanatory emails pouring in. This one is briefer and more lucid than most:

Mr. Goldberg;
I’m not even going to try to outmath Derbyshire, but there is simpler explanation of the concept of multiple universes.
1. The multiple Universes exist regardless of your conscious or unconscious decision to choose Bud Lite over Bud. Your selection does not create the Universe. Instead…
2. You only perceive the Universe you selected.
It’s akin to climbing a tree – all the branches in the tree exist before you start to climb, but your selection of which branches to climb determines your ultimate location in the tree.
So you did not create the moon and the stars by choosing your beer; instead, your choice of beer tells you which stars and moon you see.
The reason has to do with the concept of time. We perceive time as unidirectional. We can’t go back and undo a decision. If we could, we would have the ability to go back and explore the alternatives, and our memory would be cluttered with the paths we retreated from.
BTW, the movie “The Butterfly Effect” nibbles at the edge of this concept. The protagonist is capable of going back and undoing certain decisions and events. The movie is decent, and Ashton Kutchner does a decent job as the protagonist. BTW, those around him eventually perceive him as insane, because he can remember the paths that he retreated from.

Me: I have some problems with this, too. But I’ve got to finish a column. The multiverse will still be here when I get back.