For decades, physicists have conducted experimental tests of quantum entanglement, a phenomenon that Albert Einstein once dismissed as "spooky action at a distance." Despite Einstein's misgivings, the experiments have consistently found results compatible with quantum theory. Yet every experiment has been subject to one or more "loopholes," which would still allow for an explanation without the need for quantum mechanics. Arguably the most subtle and stubborn loophole is known as "freedom of choice," and concerns whether any unknown cause could have affected both the selection of measurements to be performed on the entangled particles, and the outcomes of those measurements. To address this loophole, one should obtain random numbers that can be expected to be uncorrelated with any aspect of the entanglement experiment. In a recent “Cosmic Bell” experiment, we used real-time astronomical observations of distant quasars as a classical source of binary numbers, to determine which measurements to perform on pairs of entangled particles. We found clear violations of Bell’s inequality, providing even more compelling evidnece that quantum entanglement is a robust feature of our world, and constraining certain types of alternative theories considerably more strongly than ever before.
Bio: David Kaiser is Germeshausen Professor of the History of Science and Professor of Physics at MIT. His physics research focuses on early-universe cosmology as well as on foundations of quantum theory. A Fellow of the American Physical Society, Kaiser has received MIT’s highest awards for excellence in teaching. His work has been featured in Science, Nature, the New York Times, and the New Yorker magazine, as well as in NOVA television programs, National Public Radio, and the BBC.