How related is Number Theory to Physics?

[Calabi_Yau]

As I've read and been told, you can never know too much mathematics when you study physics, and I think I read it somewhere here. I have also read that cutting-edge theories like M-Theory need most likely a new the invention of a new type of mathematics to be developed.

But my question is, how does number theory relate to physics? I would like to know its direct, or indirect applications, how did the Fermat's Last Theorem proof have possiby contributed to our understanding of the universe? I imagine there is much more to number theory than that, as my knowledge about the subject does not go much further than a bit of modular arithmetics.

This is by no means a rant against number theory, I'm only asking it because I am becoming very interested in it, and would like to know more about its pratical usefulness.

 

[Whovian]

Hmm. I, personally, don't know, but I can guess that a lot of the applications of NT are to be found in quantum mechanics.

 

[mathman]

One major application of number theory is in cryptography.

http://www.math.ucsd.edu/~ebender/DiscreteText1/NT.pdf

Also google "cryptography number theory" to get more.