The duplication paradox emerges when time travelers exist in the same time and place as their past or future selves.

WSJ: The Four Rules of Time-Travel Movies

In 2008, economists Justin Wolfers and Betsey Stevenson, both of the University of Pennsylvania, published a paper where they reassessed the Easterlin paradox using new time-series data.

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But there's a paradox buried inside Paul's rise in the Republican field, a time bomb ticking away.

CNN: Will his 'Paulbots' torpedo Ron Paul in Iowa?

There might have been no better way for the chancellor to raise the money he wanted to raise, but the fact that he has made the job of the central bank harder - at the same time as insisting it take the lead in stimulating the recovery - is indeed a paradox.

BBC: Mervyn King still ne regrette rien

They tackled problems like "flash crowds" (which can overwhelm computers storing a Web page or videoclip that suddenly is popular around the world) and the "fat file paradox": Why does data traveling at the speed of light often take such a long time to make it across the country?

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