Erisian wrote:
So being a mathematician is a bit like being a quantum physicist - you have to be able to think inside out and upside down or do you just accept that it's a fact and work with it. I wasn't disputing your definitions, just trying to understand how it all works. I can almost see what you mean about 0.999 but how would you work out an equation who's answer is the square root of -1? What figures do you start with?
Hi Erisian,
Mathematics is a "game". You have set of rules, and if you follow them, you can "play" with them. Sometimes the rules "make sense" (intuitive) to us, sometimes they don't. But surprisingly, the rules that don't make sense to us (less intuitive), sometimes have applications in science and engineering. For example, we always think that two equal numbers, if multiplied, will give positive numbers. But that's because we don't deal with imaginary number in everyday life, that's why we have difficulty to accept it. People in the past also have difficulty to accept zero or negative number.
anyway, maybe the most useful application of i is this:
e^(i.x) = cosine x + i.sine x
where e is the euler number e = 2.718....... And so, anything which is periodic in nature, can be expressed as sine or cosine (if you remember, sine and cosine plots are periodic with period 2*pi), hence can be expressed in e^(ix). That's why imaginary number appears in science branches which deal often with waves/vibration. For example, lylejk said about power in ALTERNATING current (some kind of vibration). and then, quantum mechanics also uses imaginary number because it deals with some entity called WAVE FUNCTION (anyway it is some kind of wave). etc. Wave and vibration are everywhere, that's why i is used a lot.
You ask, an equation who's answer is the square root of -1? easy:
x^2 + 1 = 0
Then x = i. If I have this equation:
x^2 + 4 = 0
then x = 2.i. And so on
We invent new numbers system according to our needs. Prehistoric people use maths mainly to CALCULATE something. Hence they invent natural number: 1,2,3,..... But then what happens if I have 5 rabbits, and all of them are eaten by a lion? Hence they invent zero. But how do we define five minus ten? Hence negative numbers. but then if I have a rabbit, and I cut into two, I give one part to my friend, and I keep another part, how many rabbit that I have now? Hence fraction (rational numbers). Then irrational numbers. Then complex numbers, and so on, and so on; with each step is more sophisticated than before and less "intuitive".
Anyway, in mathematics, there are other numbers system which are more "weird" than imaginary numbers. For example, there is a system where a times b is NOT equal to b times a. There is a system where a times b is equal to MINUS b times a (the last one is called grassmann number, it is used in quantum field theory, which is one step more sophisticated than quantum mechanics) and so on
