Monday, November 2, 2009

7.3 Billion-Year Race

Two types of gamma-ray photons emitted after a star crash long before the Earth was formed have reached the Fermi Space Telescope. After traveling 7.3 billion light years, the photons met at the detector within nine tenths of a second, affirming (with caveats) the constancy of light and rejecting some alternative theories of gravity. Physicist Peter Michelson is quoted in Science Daily, "To one part in 100 million billion, these two photons traveled at the same speed. Einstein still rules."

(image credit: illustration of two photons of different energies, NASA/Sonoma State University/Aurore Simonnet, via