N.15 A tenth of a googol in uni­verses

There is an oft-cited story go­ing around that the many worlds in­ter­pre­ta­tion im­plies the ex­is­tence of 10$\POW9,{99}$ worlds, and this num­ber ap­par­ently comes from Everett, III him­self. It is of­ten used to ar­gue that the many-worlds in­ter­pre­ta­tion is just not cred­i­ble. How­ever, the truth is that the ex­is­tence of in­fi­nitely many worlds, (or prac­ti­cally speak­ing in­fi­nitely many of them, maybe, if space and time would turn out to be dis­crete and fi­nite), is a ba­sic re­quire­ment of quan­tum me­chan­ics it­self, re­gard­less of in­ter­pre­ta­tion. Everett, III can­not be blamed for that, just for com­ing up with the lu­di­crous num­ber of 10$\POW9,{99}$ to de­scribe in­fin­ity.