In classical general relativity, gravity is mediated by a field (the metric field) that both influences and is influenced by everything else, in accordance with the action principle. The way we translate mathematically-formulated principles into words is, at least to some degree, a matter of taste. On the other hand, an inverse square law suggests a "force" carried by particles (gravitons) due strictly to geometric considerations. it still seems to me that general relativity says that gravity is not a force in the "true" sense of the word. This is discussed in "Introduction to the Effective Field Theory Description of Gravity". (No third-derivatives, for example.) This, in turn, can be inferred using the idea that general relativity itself is probably just an approximation to something deeper that current experiments are unable to resolve. The "action" in the action principle shouldn't involve any more than second-derivatives. Loosely translated, this means that if we take all the "stuff" in the universe and distort it all together in some smooth but otherwise arbitrary way, then we haven't actually changed anything at all (because we distorted all the stuff the same way, and the only things that matter are stuff compared to other stuff). The list of "things" in the universe should include the metric field.ĭiffeomorphism invariance. Loosely translated, this says that if thing A influences thing B, then thing B must also influence thing A in a related way. The structure of general relativity can actually be deduced from a few simple principles that don't explicitly refer to any kind of inverse square law (this is supposed to be a non-technical rendition of Lovelock's theorem): A new foundation is adopted, and the original foundation becomes a prediction instead. This is a common theme in physics: the principles that were once regarded as fundamental are later regarded as mere approximations to something deeper. However, in hindsight, general relativity now stands on its own as our fundamental model of gravity, and the inverse square law is better regarded as one of the many correct predictions of general relativity. In this sense, the inverse square law played an important role in testing general relativity. The signal is detected by a supercon-ducting differential accelerometer, making a highly sensitive sensor of the gravity force generated by the source mass.If general relativity didn't reproduce Newton's model of gravity (the inverse square law) in the low-speed weak-gravity approximation, then general relativity would have been ruled out, because we already know that Newton's model is an excellent approximation under those conditions. Two test masses, also disk-shaped, are suspended on the two sides of the source mass at a distance of 100 μm to 1 mm. To minimize Newtonian errors, ISLES employs a near-null source of gravity, a circular disk of large diameter-to-thickness ratio. The low-damping magnetic levitation, combined with a low-noise SQUID, leads to extremely low intrinsic noise in the detector. As designed, the experiment will be cooled to less than 2 K in NASA’s low temperature facility the LTMPF, allowing superconducting magnetic levitation in microgravity to obtain very soft, low-loss suspension of the test masses. The measures to be applied for reducing the effects of disturbances will be described in this presentation. To accomplish these goals on the rather noisy International Space Station, the experiment is set up to provide immunity from the vibrations and other common-mode accelerations. ISLES will be sensitive enough to detect axions with the strongest allowed coupling and to test the string-theory prediction with R⩾5 μ m. The objective of ISLES (inverse-square law experiment in space) is to perform a null test of Newton’s law on the ISS with a resolution of one part in 10 5 at ranges from 100 μm to 1 mm.
0 Comments
Leave a Reply. |