We report the direct observation of optical precursors of heralded single photons with step- and square-modulated wave packets passing through cold atoms. Using electromagnetically induced transparency and the slow-light effect, we separate the single-photon precursor, which always travels at the speed of light in vacuum, from its delayed main wave packet. In the two-level superluminal medium, our result suggests that the causality holds for a single photon.
There was a demon that lived in the air. They said whoever challenged him would die. Their controls would freeze up, their planes would buffet wildly, and they would disintegrate. The demon lived at Mach 1 on the meter, seven hundred and fifty miles an hour, where the air could no longer move out of the way. He lived behind a barrier through which they said no man could ever pass. They called it the sound barrier.
If you start at the center and expand outwards, you've got 13 billion light years in each direction. (aka 26 billion.) That's only off by 50%, which isn't bad at that kind of scale.
And by a small amount, i mean a very, very small amount -- the black hole is absorbing more energy from ambient photons around it left over from the big bang than it is emitting in hawking radiation. It will take a very, very, very, very, very long time before any black holes lose any mass on balance from hawking radiation, except perhaps for very small ones (smaller black holes emit more radiation than larger ones
If you think you understand quantum mechanics, you don’t understand quantum mechanics. – Richard Feynman
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