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"The speed of light is constant… or so Einstein would have us believe. But he was wrong (well – he was right in a way – in a vacuum yes, the speed of light is constant). In 2006 scientists fired a laser into a tube laced with the rare element erbium – before the entire pulse entered the tube, part of it appeared at the other end and raced backward faster than the speed of light. In 1999, Harvard scientists slowed light to a mere 38 mph by shooting it through supercooled matter."

from The List Universe

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