Scientists say that a perpetual motion machine is physically impossible, but a research team at the University of California Berkeley has just outlined an idea that comes pretty damn close. By proposing a 4D "space-time crystal," the engineers have designed a device that would operate at its lowest quantum energy state and exhibit a clock-like persistence that would theoretically exist even after the universe is exhausted of all its energy, the so-called heat death. Normally, crystals are comprised of atoms that are arranged in an orderly, repeating three-dimensional pattern. Earlier this year, however, MIT's Nobel-prize winning physicist Frank Wilcze outlined...