That's cos they keep changing their theories. As far as I see physics (speaking as a chemistry teacher / geologist) - every time someone comes up with data that puts Einstein's ideas into doubt, the physicists run away to their slide rules and try to make the maths work. Adding another (imaginary) dimension to the universe does the trick mathematically, but that then means they have to install fudge factors, which normally involves changing the universe's mass, or rate of expansion, its age, or the existence of other, new particles. I think we're currently up to .... what ... 16 dimensions by some reckoning.
I tease my physics colleagues by referring to the subject as "mathematics and make-believe."
Bosonic string theory suggests 26...up to now.








