Friday, July 29, 2005

History of Gravity and the Equivalence Principle



History rerun on bar ringings?


That's it: the bar is in place.


Our word gravity and its more precise derivative gravitation come from the Latin word gravitas, from gravis (heavy), which in turn comes from a still more ancient root word thought to have existed because of numerous cognates in related languages. For example, compare the Old English word grafan (grave), the Old Slavic pogreti (to bury), the Sanskrit guru (weighty, venerable), and Greek barus (heavy, grievous) among others. These words have common meanings of heaviness, importance, seriousness, dignity, grimness; the modern, physical sense of a field of attraction did not appear until Newton's time. Indeed, for Galileo, Newton, and scientists up to the beginning of the twentieth century, gravity was no more than an empty name for the phenomenon, a fact that they were well aware of.


1 comment:

nigel said...

In the standard model, the Higgs boson is postulated to cause inertial mass, which by Einstein’s equivalence principle is also gravitational mass.

Recently, Quantoken pointed out on Lubos' blog that the usual approach to quantum gravity, invoking gravitons as a mediator by analogy to the photon mediator in QED, may contradict Einstein's equivalence principle. The graviton involved in gravity would also have to occur in all inertial accelerations.

This naturally leads to a pressure type approach to quantum gravity.

LeSage around 1748 first came up with a prediction based on a pressure shielding mechanism for gravity which had begun in Newton's time, and LeSage used it to predict that - since gravity depends on the matter inside the earth and not just the surface area - the atom muct be mainly 'empty'. This was verified eventually by x-rays and radioactivity.

If there is a pressure in space masses will be pushed together by mutual shielding. The contraction effect in general relativity compresses the earth’s radius by 1.5 mm; by the same pressure effect for inertial mass in motion, you get the FitzGerald contraction in the direction of motion (the drag on moving objects is simply the increase in mass that occurs as speed rises). The gravitational contraction is radial only, not affecting the circumference, so there a difference between the true radius and that calculated by Euclidean geometry. Thus curved space using non-Euclidean geometry, or you can seek the physical basis of the pressure in the surrounding universe.

I worked on this subject at Gloucestershire university and authored a paper: 'Solution to a Problem with General Relativity', CERN Document Server paper preprint EXT-2004-007. This was published in the April 2003 issue of 'Electronics World' (click on my name).

Pressures seem to result from the big bang. The recession varies from 0 to c with distance while corresponding times vary from 15,000 million years towards zero, so the matter of the universe has an effective outward acceleration of c divided by the age of the universe. This acceleration, a = c/t, is small, about 10^-10 ms^-2. But by Newton's 2rd law, the actual outward force, when properly allowing for the varying effective density of the observed universe as a function of spacetime, is large and by Newton's 3rd law it has an equal and opposite reaction, inward Higgs field pressure. The shielding of this pressure numerically predicts gravity quite well. To model both forces as pressure effects, you need find you need two pressures: virtual radiation pressure for charge and Higgs field for mass.

Photon radiation: this causes electromagnetic force in a similar way but is much stronger because in addition to the big bang effect, the potential adds up between similar charges like cells in a battery or displacement current between capacitor plates. The charges are randomly distributed so any straight line summation will encounter similar numbers of both charges and cancel out completely. The correct summation is a zig-zag so the effective sum is the square root of the number of charges in the universe times the gravity force: this predicts the strength of Coulomb's law quite accurately. Similar charges exchange extra energy and recoil apart, while opposite charges partly shield one another and are pushed together by a very slightly similar force due to the surrounding expanding universe.

If you have a big bang with speeds increasing in spacetime
v = dR/dt = RH,
(where H is Hubble constant) that means acceleration of
a = dv/dt = [d(RH)] / [dR / (RH)] = RH^2,
so there is outward force (by F = ma), due to the big bang universe around my apple, which means by Newton's 3rd law that there equal and opposite reaction of higgs bosons (inward force divided by area is the Higg’s field pressure).

This inward force is carried by the fabric of space around matter, so the inward pressure (force / area) goes as the inverse-square law, causing gravitation since the earth below the apple partially shields the pressure from the downward direction. The correct force of gravity turns out to be
F = mMG/r^2,
where
G = (3/4) H^2 / (pi x density x e cubed)
= 6.7 x 10^-11,
which is a factor of half e cubed = 10 times off the value that the critical density suggests. Put another way, this mechanism proves the cause of gravity while correcting the formula for the 'critical density' by the factor half e-cube, so the dark matter problem disappears and there is a direct comparison possible between the measured force of gravity and the big bang expansion and density data. The result is correct to within 2% for experimental data, which is fortuitous due to the error bars on the data, but it is a useful test.