很抱歉我对于您问的折射的问题,我才去翻书,在光学里有个Fermat's principle of least time.这个没有从微观水平上解释为什么,不过却能解释为什么因为折射率的不同会产生出射角和入射角的不同。如果您想知道微观水平上的解释,也许要看quantum optics方面的书(我没有读过,所以只能说也许)。
siccashq, thanks for your comments. :-) selfish genes is only one way of looking at the life. It is only metaphysics, not science. It could be totally explained in the opposite way. Please have a look of Denis Nobel's website about life:
http://www.musicoflife.co.uk/
and my blog:
http://www.sciencenet.cn/blog/user_content.aspx?id=8312