In The Beginning

(A Tribute to Maxwell)

In the beginning, God said unto his angels: “Let Us create electromagnetic radiation.”
“Use the vector potential!” they said.
“Ah,” God replied, “but the vector potential is not gauge invariant.”
“Then use the field tensor!” they tried again.
“But,” God replied, “the field tensor is not Lorentz invariant.”
“Well,” the angels said at last, “the self-contraction of the field tensor is both gauge and Lorentz invariant!”
And God saw that it was the Lagrangian field density, and that it was good.
Then there was light!

[...Maxwell's equations written the right way...]

—Kerson Huang, 1980

George R. Welch
21 January 1996
5 March 2012