Time travel

Sorry, science-fiction fans: Time travel is impossible.  That is the sobering conclusion, anyway, of a Hong Kong-based team of physicists.  They found that the maximum speed of a single photon, the basic unit of light, “obeys the traffic law of the universe,” Agence France-Presse reports.  The photon cannot go faster than the speed of light—186,282 miles per second—and thus provides […]

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