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Clocking the direction of space - the breaking of Lorentz symmetry can cause different points in space–time to have a preferred direction (red arrows). If the direction of space is the same at all points in the Earth's orbit, experiments on board the International Space Station (ISS) should be able to measure the magnitude of the Lorentz-breaking effect. For instance, the orientation of atoms in an atomic clock on board the ISS (blue arrow) will change with respect to the red arrows as the ISS orbits the Earth. This would modify the energy levels of the atoms and therefore cause the clock rate to change cyclically.