cos everytime you halve the length of string avialable you go up an octave... eg the e string, when the string is at full length ie open, you've got E, at 12th fret (which is half the length of the string), you've got another E but an octave higher, at 24th fret, that's half of the left over distance, ie it's at 1/4 length, you have another E again an octave higher, at 32 nd fret, that's half the left over length, so that's 1/8th length left, you have another ocatave...
So at 1/16th, 1/32, 1/64, 1/128, 1/256, 1/512, 1/1024.... 1/infinity, you have an E, so you've got (in theory an infinite number of notes)...
but the main problem is that the bridge pickup isn't that close to the bride, so you cant get to those really really high octaves... another problem is human hearing range, anything over 20000hertz and you cant hear it... and the reason you cant get infinite, is because at some point you'll reach down to the size of atoms (not very good for sounds on thier own :D lol), and then sub atomic particles, and then????????????????...