[kolbe]

Well, firstly, we should define what "sigma" means. Most people interpret it as it relates to the Normal Distribution.

In that case, a +10 sigma event will occur with probability 4.26361e-81. Each year consists of about 3.1536e+22 femtoseconds, which are 1e-6 the length of a nanosecond, which is the smallest unit of time I've ever heard mentioned in Finance. So, even on that time scale, and with millions of derivatives and securities, I'm not seeing much possibility for a 10 sigma event.