Cosmic race ends in a tie

Result puts limit on how ‘lumpy’ space-time can be.
A race between two energetic photons that began more than 7 billion years ago and spanned half the cosmos has ended in a virtual dead heat. The result, if it stands up to scrutiny, would tighten the limits, suggested by some theories, on how ‘lumpy’ space-time can be. The work, to be presented on 11 January at the 219th meeting of the American Astronomical Society in Austin, Texas, by Robert Nemiroff of the Michigan Technological University in Houghton and his colleagues, relies on an analysis of a short-lived, powerful stellar explosion known as a γ-ray burst that was recorded by NASA’s Fermi Gamma-ray Space Telescope in May 2009 and dubbed GRB 090510A. The study focused on two photons, one with an energy of 25 gigaelectronvolts (GeV) and another of about 1.5 GeV, which were separated by just 0.00136 seconds. READ MORE