[ExI] Complex numbers (was: new entry from symphony of science)

[John Clark]

On Nov 24, 2010, at 10:52 PM, Darren Greer wrote:

> I'm having trouble understanding how the square root of negative one could have a practical application beyond abstract mathematics. Or even in abstract mathematics, for that matter. 

The short answer is that the square root of negative one is essential if mathematically you want to calculate how things rotate. It you pair up a Imaginary Number(i) and a regular old Real Number you get a Complex Number, and you can make a one to one relationship between the way Complex numbers add subtract multiply and divide and the way things move in a two dimensional plane, and that is enormously important. Or you could put it another way, regular numbers that most people are familiar with just have a magnitude, but complex numbers have a magnitude AND a direction. 

Many thought the square root of negative one (i) didn't have much practical use until about 1860 when Maxwell used them in his famous equations to figure out how Electromagnetism worked. Today nearly all quantum mechanical equations have an"i" in them somewhere, and it might not be going too far to say that is the source of quantum weirdness. The Schrodinger equation is deterministic and describes the quantum wave function, but that function is an abstraction and is unobservable, to get something you can see you must square the wave function and that gives you the probability you will observe a particle at any spot; but Schrodinger's equation has an "i" in it and that means very different quantum wave functions can give the exact same probability distribution when you square it; remember with i you get weird stuff like i^2=i^6 =-1 and i^4=i^100=1.

 John K Clark


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