Racing Photons (IMAGE)

Stanford University

Racing Photons

Caption

In this illustration, one photon (purple) carries a million times the energy of another (yellow). Some theorists predict travel delays for higher-energy photons, which interact more strongly with the proposed frothy nature of space-time. Yet Fermi data on two photons from a gamma-ray burst fail to show this effect, eliminating some approaches to a new theory of gravity.

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NASA/Sonoma State University/Aurore Simonnet

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