Sheldon Glashow, theoretical physicist and Nobel Laureate, Boston University: "When an object emits light, say, a flashlight, it gets lighter."
This podcast was produced by David Levin and Lexi Krock. Audio editing by David Levin. NOVA is produced by WGBH in Boston. Major funding for NOVA is provided by Google.
For more on E = mc2, visit http://www.pbs.org/nova/einstein
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