1. Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA

Correspondence to: T. Jacobson Correspondence and requests for materials should be addressed to T.J. (Email: jacobson@physics.umd.edu).

Abstract

Special relativity asserts that physical phenomena appear the same to all unaccelerated observers. This is called Lorentz symmetry and relates long wavelengths to short ones: if the symmetry is exact it implies that space-time must look the same at all length scales. Several approaches to quantum gravity, however, suggest that there may be a microscopic structure of space-time that leads to a violation of Lorentz symmetry. This might arise because of the discreteness¹ or non-commutivity² of space-time, or through the action of extra dimensions³. Here we determine a very strong constraint on a type of Lorentz violation that produces a maximum electron speed less than the speed of light. We use the observation of 100-MeV synchrotron radiation from the Crab nebula to improve the previous limit by a factor of 40 million, ruling out this type of Lorentz violation, and thereby providing an important constraint on theories of quantum gravity.