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n2doc

(47,953 posts)
Fri Jun 20, 2014, 12:42 PM Jun 2014

Quantum method closes in on gravitational constant

Physicists have used the quantum nature of matter to obtain a highly precise value for the universal gravitational constant, the 'big G' that appears in Isaac Newton's law of how gravity pulls together everything, from planets to apples. Although the technique still needs refinements, physicists believe that in the future it will beat the precision of conventional methods — and hopefully solve apparent discrepancies between measurements that have long puzzled physicists.


In a study described today in Nature, researchers measured the minuscule gravitational tug between rubidium atoms and a 516-kilogram array of tungsten cylinders. The uncertainty in the latest measurement is 150 parts per million, or 0.015% — only slightly larger than that of the conventional method of determining G, which is to quantify the mutual pull of two macroscopic masses.

The measurement is “a marvellous experimental achievement and an important contribution to the knowledge of G”, says Holger Müller, a physicist at the University of California, Berkeley, who was not involved in the study.

The technique, which exploits the ability of matter particles such as atoms to behave as waves, could provide fresh insight on a problem that has frustrated physicists for years. The conventional method measures the torque caused by gravitational attraction on the weights attached to a rotating balance, an experiment that was first conducted by English scientist Henry Cavendish in 1798. But despite the increasing precision of some 300 modern-day experiments using Cavendish's set-up, different labs have found slightly different values for G, and in recent years the discrepancy has widened rather than narrowed (see 'G-whizzes disagree over gravity').



more

http://www.nature.com/news/quantum-method-closes-in-on-gravitational-constant-1.15427

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Quantum method closes in on gravitational constant (Original Post) n2doc Jun 2014 OP
I can tell you from personal experience jimlup Jun 2014 #1
I don't think it's between individual atoms caraher Jun 2014 #2

jimlup

(7,968 posts)
1. I can tell you from personal experience
Fri Jun 20, 2014, 07:13 PM
Jun 2014

that the traditional way of measuring big G is very tedious. This is fascinating. Hard to believe that they can measure the gravitational attraction between atoms but I guess the mass is small it is really just the attraction of the lead spheres experiment scaled way down.

caraher

(6,276 posts)
2. I don't think it's between individual atoms
Mon Jun 23, 2014, 10:08 PM
Jun 2014

From some skimming it looks like what it boils down to is looking at differences in atom interferometer signals induced by a heavy (100+ kg) test mass. The quantum-ness is the precision with which an interferometric technique can detect subtle changes in the interaction of atoms with its gravitational environment.

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