But in Einstein's theory, the flow of time becomes a function of location, so the quickest path could now be an elliptical orbit or a plumb line to the ground.Įxperiments have tested the theory to higher and higher precision, but direct measurements of the gravitational redshift have had to struggle with the minimal size of the effect in Earth's gravitational field. In a flat geometry, the quickest route is a straight line. This insight means that what we think of as the influence of gravity - planets orbiting stars, for example, or an apple falling to Earth - is really matter following the quickest path through spacetime. Müller also noted that the experiment demonstrates very clearly "Einstein's profound insight, that gravity is a manifestation of curved space and time, which is among the greatest discoveries of humankind." So, as we use better and better clocks, we need to know the influence of gravity better." "But lifting a clock by 1 meter creates a change in the 16th digit. "If we used our best clocks, with 17-digit precision, in global positioning satellites, we could determine position to the millimeter," he said. "The paper that we are publishing in Nature uses two fundamental aspects of the quantum description of matter to perform one of the most precise tests of The General Theory of Relativity."įar from merely theoretical, the results have implications for Earth's global positioning satellite system, for precision timekeeping and for gravitational wave detectors, Müller said. Chu was one of the originators of the atom interferometer, which is based on his Nobel Prize-winning development of cold laser traps. "Two of the most important theories in all of physics are Quantum Mechanics and the General Theory of Relativity," noted Müller's collaborator, Steven Chu, a former UC Berkeley professor of physics and former director of Lawrence Berkeley National Laboratory (LBNL). The equations of general relativity predicted precisely the measured slowing of time, to an accuracy of about one part in 100 million (7x10-9) - 10,000 times more accurate than the measurements made 30 years ago using two hydrogen maser clocks, one on Earth and the other launched via rocket to a height of 10,000 kilometers. While the frequency of cesium matter waves is too high to measure, Müller and his colleagues used the interference between the cesium matter waves in the alternate realities to measure the resulting difference between their oscillations, and thus the redshift. In the other, the atom remains unmoved inside Earth's gravitational well, where time flies by less quickly. In one, the laser has pushed the atom up one-tenth of a millimeter - 4/1000 of an inch - giving it a tiny boost out of Earth's gravitational field. The laws of quantum mechanics step in, and each cesium atom enters two alternate realities, Müller said. When the cesium atom matter wave enters the experiment, it encounters a carefully tuned flash of laser light. The cesium atoms used in the experiment can be represented by matter waves that oscillate 3x1025 times per second, that is, 30 million billion billion times per second. Müller tested Einstein's theory by taking advantage of a tenet of quantum mechanics: that matter is both a particle and a wave. The phenomenon is often called the gravitational redshift because the oscillations of light waves slow down or become redder when tugged by gravity.Ī report describing the experiment appears in the Feb. "This experiment demonstrates that gravity changes the flow of time, a concept fundamental to the theory of general relativity," Müller said. The result shows once again how well Einstein's theory describes the real world, said Holger Müller, an assistant professor of physics at the University of California, Berkeley.
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