John Smith wrote:
"If you are truly laughing that loudly, you ARE an idiot."

My Schaum`s Outline physics book by Frederick J. Bueche and Eugene Hecht
says on page 70:
"Energy can neither be created nor destroyed,---."

And on page 366 it says:
"If two coherent waves of the same amplitude are superposed, and
distructive interference (cancellation, darkness) occurs when the two
waves are 180 degrees out-of-phase. Total constructive interference
(reinforcement, brightness) occurs when they are in-phase."

Best regards, Richard Harrison, KB5WZI