Zero Point Energy doc
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| ZP OWER C ORPORATION PAGE OF 352 Z ERO P OINT E NERGY On the other side of each plate, though, the full range of photons can come briefly into existence. The net result is a difference in the radiation pressure -- the feeble force exerted by photons on other objects -- between the insides and the outsides of the two plates. This difference, which Dr Casimir predicted, pushes them slightly together. Detecting the Casimir force between large objects calls for subtlety. Previous attemtps have either failed to achieve sufficient accuracy or merely measured the force between a plate and an atom. Even Dr Lamoreaux's experiment did not manage to measure the force between two flat plates (the ideal test, because of the difficulty of keeping them perfectly parallel while less than a thousandth of a millimetre apart. Instead, he used one curved and one flat plate. The curved plate sat on amounting that was finely adjustable backwards and forwards. The flat one was atone end of a bar that was in turn suspended from a fibre -- an arrangement known as a torsion pendulum. The other end of the suspended bar formed part ofan electrical capacitor.This allowed the pendulum to beheld steady by applying slight changes to the voltage across the capacitor. By moving the curved plate to and fro, Dr Lamoreaux could change the Casimir force between the plates and make the pendulum try to rotate one way or the other. Then, by measuring the change in voltage needed to stop this from happening, he could workout the strength of the Casimir force. Since the whole assembly -- which sat inside a vacuum chamber -- was so sensitive that it could detect somebody standing nearby from the way his weight tilted the laboratory floor, a very accurate measurement was possible. The force betwccn the plates was gratifyingly small about that exerted by a speck ofdust lying on a bench top. Also gratifying was the cost of the experiment. Dr Lamoreaux’s setup (which began life as a student project) cost only a few hundred dollars. Not quite something for nothing, but in the world of physics, a close approximation. |