Number of superstring theories

Theoretical physicists were troubled by the existence of five separate string theories. …

Please note that the number of superstring theories given above is only a high-level classification; the actual number of mathematically distinct theories which are compatible with observation and would therefore have to be examined to find the one that correctly describes nature is currently believed to be at least 10^500 (a one with five hundred zeroes).

— Wikipedia on Superstring theory

2010.07.16 Friday ACHK