NASA. Einstein's Cosmic Speed Limit

To find out more visit: http://www.nasa.gov/mission_pages/GLA... Want more? Subscribe to NASA on iTunes! http://phobos.apple.com/WebObjects/MZ... Or get tweeted by NASA: http://twitter.com/NASAGoddard In its first year of operations, NASA's Fermi Gamma-ray Space Telescope has mapped the entire sky with unprecedented resolution and sensitivity in gamma-rays, the highest-energy form of light. On May 10, 2009 a pair of gamma-ray photons reached Fermi only 900 milliseconds apart after traveling for 7 billion years. Fermis measurement gives us rare experimental evidence that space-time is smooth as Einstein predicted, and has shut the door on several approaches to gravity where space-time is foamy enough to interfere strongly with light.