Stephen Hawking discusses the "Breakthrough Starshot" space exploration initiative during a news conference Tuesday at One World Observatory in New York City. Bryan Bedder/Getty Images for Breakthrough Prize Foundation hide caption

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Stephen Hawking's Plan For Interstellar Travel Has Some Earthly Obstacles

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An image from the European Southern Observatory shows the sky around the bright star Alpha Centauri — which appears so large because of the telescope optics and photographic emulsion — taken from photos in the Digitized Sky Survey 2. Alpha Centauri is the closest star system to Earth's solar system. ESO/Digitized Sky Survey 2/Davide De Martin hide caption

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This artist's impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus. M. Kornmesser/ESO hide caption

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British cosmologist Stephen Hawking gives a talk to workers at Cedars-Sinai Medical Center in Los Angeles on April 9. Eric Reed/Cedars-Sinai/AP hide caption

toggle caption Eric Reed/Cedars-Sinai/AP