I know that the Gravitational constant was discovered by
Newton (He did, right?).
Is it a quantum measurement? I mean’ since its small, doesn’t it conform to the laws of quantum mechanics?
BTW does G represent the force of one graviton, or Planck
Mass, or what?
The value for G, the universal gravitational constant, is generally credited to Henry Cavendish in an experiment performed in 1798.
However, this site gives some interesting details of the experiment, and indicates that the apparatus was designed by John Michell, a geologist who also invented the torsion balance. (This is a key component of the apparatus used by Cavendish.) Also, while G may be calculated from Cavendish’s results, he apparently did not do the calculation himself.
The modern value for G is 6.67259(85) x 10[sup]-11[/sup] N m[sup]2[/sup]/kg[sup]2[/sup].
It does not represent the force of anything. It does not have force units. From the units it does have, though, it indicates that the force of gravity between two 1-kg particles that are separated by a distance of 1 meter is experimentally determined to be 6.67 x 10[sup]-11[/sup] N. I know of no theory that explains why this constant has the value it does.
I don’t know of any quantum connections, but would be interested to know of any. (I also don’t know of the connections, if any, with General Relativity.)
Newton deduced that there was a Gravitational Constant, but he couldn’t determine its value, nor the mass of any of the bodies in the solar system. He could, however, determine the product of G and M for many bodies. Cavendish, as noted, was the first to perform an experiment to measure it. Basically, you take two bowling balls in a laboratory, put them a known distace apart, and measure the force between them. As you can imagine, this is very difficult to do, with the result that of all the common fundamental constants, G is the one for which we have the least precise value.
Not only is G not a quantum quantity, there aren’t even any theories yet which can consistently incorporate both gravity and quantum mechanics. You’re thinking that it must be quantum, since the value is so small, but that’s not really accurate. To say that the value is small, you have to compare it to something, but there’s not really anything to compare it to. It’s small compared to the units that we humans are accustomed to working with, but then, what’s so special about us and our units? In fact, folks like myself who work General Relativity, the modern theory of gravity, typically use units where G=1, for convenience. In GR, one can think of G as describing the extent to which matter affects spacetime, but the net result is much the same as in Newton’s theory.
Scientific American had an interesting article on gravity last year. As usual with quantum physics, string theory and multiple dimensions, it’s both simpler and more complicated than one suspects.
Rats, they don’t have that article online. Check it out in your local library. I found it really interesting. August 2000 issue http://www.sciam.com/2000/0800issue/0800quicksummary.html