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An Atomic Explosion
The Silence
Watching this film, there are many things to wonder (and worry) about, but one of the stranger moments is how the bomb bursts in complete silence. We see a sudden white flash. It makes the soldiers flinch. Then there’s a pause, a pregnant quiet that lasts for a beat, then another and then — there’s a roar. (“There it is! The ground wave!”), after which the sky above seems to go black and the air turns to fire.
Basic physics explains the pause. Because light travels quicker than sound, you see light first, you hear sound later. In most movies (even in government-released atomic bomb blast films), the sound is artificially time shifted to make the flash and the sound appear simultaneous.
‘A Long, Thundering Growl’
But that’s not what it’s like if you are actually there. Science historian Alex Wellerstein has found an undoctored and deeply frightening recording — which he just posted on Restricted Data; The Nuclear Secrecy Blog.
He got it, he says, from “a Russian correspondent” who was searching the U.S. National Archives. (Why not? Our past is open to all.) The Russian found a recording of an American atomic test in 1953, which shows an enormous flash of white, so white it blanks out the entire sky, then thick clouds of ash (or maybe dirt?) tumble up, a fireball appears — all of this in total quiet. Thirty seconds pass.
http://www.npr.org/blogs/krulwich/2012/07/16/156851175/five-men-agree-to-stand-directly-under-an-exploding-nuclear-bomb
Lamb and the Dragon 