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        Einstein's Cosmic Speed Limit

        This video focuses on one particularly interesting result from NASA’s Fermi Gamma-ray Telescope sky survey. In May of 2009, the highly sensitive telescope received two photons 900 milliseconds apart after a journey of 7 billion years -- meaning the photons traveled 7 billion light years and arrived at virtually the same moment. That result, described and animated in the video, offers support for one of Einstein’s predictions - that space-time is smooth -- thus discounting several competing theories that posit a “foamy” space-time structure that would have caused the two photons to arrive with a greater time separation.

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