In 1990 I wrote a bit of fluff for Scientific American about whether our cosmos might be just one in an “infinitude,” as several theories of physics implied. I titled my piece “Here a Universe, There a Universe . . .” and kept the tone light, because I didn’t want readers to take these cosmic conjectures too seriously. After all, there was no way of proving, or disproving, the existence of other universes.*

Today, physicists still lack evidence of other universes, or even good ideas for obtaining evidence. Many nonetheless insist our cosmos really is just a mote of dust in a vast “multiverse.” One especially eloquent and passionate multiverse theorist is Sean Carroll. His faith in the multiverse stems from his faith in quantum mechanics, which he sees as our best account of reality.

To read more, click here.