Albert Einstein showed nearly a century ago that light always travels at one speed--670 million m.p.h.--but his Special Theory of Relativity had an often overlooked qualifier: this blistering pace applies only in a vacuum. When it passes through air, say, or glass or water, light goes a bit slower.
Even Einstein would probably be taken aback, though, by experiments announced in Cambridge, Mass., last week: two teams of scientists have slowed light to a dead stop. The achievements, to be reported in this week's issue of Nature and next week's Physical Review Letters, could one day lead to a new...
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