Ferhmats principle

[Crash]

Soz if i got the dudes name wrong, I was wondering if any body knows of any good books/sites or has any good interpretations themselves into the principle of least time/most time?

I dont get what it means when "there is no change in the first order time, just a change in the second order time???

Im finding this principle very hard to pick up and would appreciate the help.

[Pangloss]

There's a brief description of Fermat's Principle on this web site at the Wikipedia:

 

http://en.wikipedia.org/wiki/Fermat%27s_principle

 

It's a good starting point because it links to a lot of other stuff so you can investigate a bit.

 

Others may have better links than I. Good luck.

[Crash]

In the explanation of the Principle (Feynman Lectures) where i read it stated, "the path in which the first order of time is not altered but the second order of time is"

 

I dont get that part, cheers for the help pangloss

[DerSpooky]

I think you meant that when you change the path of light by a very small amount there will ne no first order (substantial) change in the time it takes for light to follow the new path, only a second order (less substantial) change in time (approximately). Think about binomial series approximations. Feynman sums up in the next sentence that light follows a path that is surrounded other paths that take just a little bit different time to traverse, but not substantially.