" Each day, the moon’s gravitational field tugs at the earth as it rotates underneath. At CERN, this tiny stress caused the total length of the LEP tunnel to stretch and contract by about a millimeter (one-twenty-fifth of an inch) every day. Not such a big deal in a seventeen-mile-long beam pipe, but enough to cause a tiny fluctuation in the energy of the electrons and positrons—one that was easily detectable by the high-precision instruments. After some initial puzzlement at the daily energy variations, the CERN physicists quickly figured out what was going on. "

― Sean Carroll , The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads Us to the Edge of a New World