If you took a look at one of the previous posts on how to remember the Laplacian in different forms by using a metric, you will notice that the form of the Laplacian that we get is:
But in Jackson’s Classical Electrodynamics, III edition he notes the following:
This is an interesting form of the Laplacian that perhaps not everyone has encountered. This can obtained from the known form by making the substitution and simplifying. The steps to which have been outlined below:
To understand why this is true, we must start with the Fundamental Theorem of Vector calculus. If is a conservative field ( i.e ), then
What this means is that the value is dependent only on the initial and final positions. The path that you take to get from A to B is not important.
Now if the path of integration is a closed loop, then points A and B are the same, and therefore:
Now that we are clear about this, according to Stokes theorem the same integral for a closed region can be represented in another form:
From this we get that Curl = for a conservative field (i.e ). Therefore when a conservative field is operated on by a curl operator (), it yields 0.
Bravo Prof.Ghrist! Beautifully said 😀