I was studying the double slit experiment and started wondering what exactly does happen to the wave when its in the slit that makes it diffract or not? I toyed around with http://www.falstad.com/ripple/ but could not figure what exactly goes on that makes things as they are. While trying to answer myself two additional questions came up: Does light require an EM field to travel through or does it create its own? Is light nothing more than a ripple through the EM field and if so how do we quantise it? Wouldnt it have a continuous nature (I know it doesnt) because of that?