Abstract

At a purely instrumental level, quantum theory is all about multiplication, addition and taking mod squares of complex numbers called probability amplitudes. The rules for combining amplitudes are deceptively simple. When two or more events are independent you multiply their respective probability amplitudes and when they are mutually exclusive you add them. Whenever you want to calculate probabilities you take mod squares of respective amplitudes. That’s it. If you are prepared to ignore the explanatory power of the theory (which you should not) the rest is just a set of convenient mathematical tools developed for the purpose of book-keeping of amplitudes. Thus we tabulate amplitudes into state vectors and unitary matrices, and place them in Hilbert spaces