Sunday, November 28, 2010

Gravitational Constant : Variations in Gravitational Constant G

g-apparatus ... This is a photograph of a simple big G apparatus used to indirectly determine the value for G. The value of the fundamental constant G has been of great interest for physicists for over 300 years and it has the longest history of measurements after the speed of light. In spite of the central importance of the universal gravitational constant, it is the least well defined of all the fundamental constants. Despite our modern technology, almost all measurements of G have used variations of the classical torsion balance technique as engineered by Cavendish during the 17th century.

The usual torsion balance basically consists of two masses connected by a horizontal rod suspended by a very thin fibre, referred to as the dumbbell. When two heavy attracting bodies are placed on opposite sides of the dumbbell, the dumbbell twists by a very small amount. The attracting bodies are then moved to the other side of the dumbbell and the dumbbell twists in the opposite direction. The magnitude of these twists is used to find G. Another common set-up variation to this technique, is to set the dumbbell into an oscillatory motion and measure the frequency of oscillation. The gravitational interaction between the dumbbell and the attracting bodies causes the oscillation frequency to change slightly when the attractors are moved to a different position and this frequency change determines G. This frequency shift method was used in the most precise measurement of G to date (reported in 1982) by Gabe Luther and William Towler from the National Bureau of Standards and the University of Virginia. Based on their measurement, CoData now lists G = 6.6742E-11Nm2/Kg2 and assigned a quite conservative uncertainty of 0.015%. Comparing this constant to other well known units of physics, the fractional uncertainty in G is still thousands of times larger. As a result, the mass of the Earth, the sun, the moon and all celestial bodies cannot be known to an accuracy greater than that of G, since all these quantities have been derived from the experimental G. The units of G are m3/Kg/sec2, so any error in the Kg unit will show up as an error in G. An uncertainty of 0.015% might seem quite small, but when applied to masses under consideration, for example earth's mass with a nominal mass of 5.972E24 Kg, it means that the actual mass could be higher by as much as 8.958E20 kg!, and that's why the mass of earth can only be given to three decimal places.

Variation evidence from readings spanning over 200 years

Data Set numberAuthorYearG (x10-11 m3Kg-1s-2)Accuracy% Deviation
1Cavendish H.17986.74±0.05+0.986
2Reich F.18386.63±0.06-0.662
3Baily F.18436.62±0.07-0.812
4Cornu A, Baille J.18736.63±0.017-0.662
5Jolly Ph.18786.46±0.11-3.209
6Wilsing J.18896.594±0.015-1.202
7Poynting J.H.18916.70±0.04+0.387
8Boys C.V.18956.658±0.007-0.243
9Eotvos R.18966.657±0.013-0.258
10Brayn C.A.18976.658±0.007-0.243
11Richarz F. & Krigar-Menzel O.18986.683±0.011+0.132
12Burgess G.K.19026.64±0.04-0.512
13Heyl P.R.19286.6721±0.0073-0.031
14Heyl P.R.19306.670±0.005-0.063
15Zaradnicek J.19336.66±0.04-0.213
16Heyl P.,Chrzanowski19426.673±0.003-0.018
17Rose R.D. et al.19696.674±0.004-0.003
18Facy L., Pontikis C.19726.6714±0.0006-0.042
19Renner Ya.19746.670±0.008-0.063
20Karagioz et al19756.668±0.002-0.093
21Luther et al19756.6699±0.0014-0.064
22Koldewyn W., Faller J.19766.57±0.17-1.561
23Sagitov M.U. et al19776.6745±0.0008+0.004
24Luther G., Towler W.19826.6726±0.0005-0.024
25Karagioz et al19856.6730±0.0005-0.018
26Dousse & Rheme19866.6722±0.0051-0.030
27Boer H. et al19876.667±0.0007-0.108
28Karagioz et al19866.6730±0.0003-0.018
29Karagioz et al19876.6730±0.0005-0.018
30Karagioz et al19886.6728±0.0003-0.021
31Karagioz et al19896.6729±0.0002-0.019
32Saulnier M.S., Frisch D.19896.65±0.09-0.363
33Karagioz et al19906.6730±0.00009-0.018
34Schurr et al19916.6613±0.0093-0.193
35Hubler et al19926.6737±0.0051-0.008
36Izmailov et al19926.6771±0.0004+0.043
37Michaelis et al19936.71540±0.00008+0.617
38Hubler et al19936.6698±0.0013-0.066
39Karagioz et al19936.6729±0.0002-0.019
40Walesch et al19946.6719±0.0008-0.035
41Fitzgerald & Armstrong19946.6746±0.001+0.006
42Hubler et al19946.6607±0.0032-0.202
43Hubler et al19946.6779±0.0063+0.055
44Karagioz et al19946.67285±0.00008-0.020
45Fitzgerald & Armstrong19956.6656±0.0009-0.129
46Karagioz et al19956.6729±0.0002-0.019
47Walesch et al19956.6685±0.0011-0.085
48Michaelis et al19966.7154±0.0008+0.617
49Karagioz et al19966.6729±0.0005-0.019
50Bagley & Luther19976.6740±0.0007-0.003
51Schurr, Nolting et al19976.6754±0.0014+0.018
52Luo et al19976.6699±0.0007-0.064
53Schwarz W. et al19986.6873±0.0094+0.196
54Kleinvoss et al19986.6735±0.0004-0.011
55Richman et al19986.683±0.011+0.132
56Luo et al19996.6699±0.0007-0.064
57Fitzgerald & Armstrong19996.6742±0.0007±0.01
58Richman S.J. et al19996.6830±0.0011+0.132
59Schurr, Noltting et al19996.6754±0.0015+0.018
60Gundlach & Merkowitz19996.67422±0.00009+0.0003
61Quinn et al20006.67559±0.00027+0.021
--PRESENT CODATA VALUE20046.6742±0.001±0.0150

The official CODATA value for G in 1986 was given as G= (6,67259±0.00085)x10-11 m3Kg-1s-2 and was based on the Luther and Towler determination in 1982. However, the value of G has been recently called into question by new measurements from respected research teams in Germany, New Zealand, and Russia in order to try to settle this issue. The new values using the best laboratory equipment to-date disagreed wildly to the point that many are doubting about the constancy of this parameter and some are even postulating entirely new forces to explain these gravitational anomalies. For example, in 1996, a team from the German Institute of Standards led by W. Michaelis obtained a value for G that is 0.6% higher than the accepted value; another group from the University of Wuppertal in Germany led by Hinrich Meyer found a value that is 0.06% lower, and in 1995, Mark Fitzgerald and collaborators at Measurement Standards Laboratory of New Zealand measured a value that is 0.13% lower. The Russian group found a curious space and time variation of G of up to +0.7%. In the early 1980s, Frank Stacey and his colleagues measured G in deep mines and bore holes in Australia. Their value was about 1% higher than currently accepted. ...

Interestingly, I was just reading about the large mammals that cropped up when the dinosaurs died out and I was wondering why they didn't get crushed under their own weight. Here's a strange idea that offers an explanation for that and a few other mysteries:

Dinosaurs would be crushed by their own weight under our present gravitational force

Interesting claim. I don't know about that... They had pretty strong bones. Anyway, this web site proposes periodic large fast changes in the force of gravity (G).
Another consequence of such big variation in mass of all objects within the solar system, is that while the planets themselves increase in mass, gravity can possibly crush them into higher density planets. Bigger animals will have less chance to survive as their bodies collapse due to their weight, and animals start getting smaller. In the case where the value of G changes abruptly, only the small 'versions' survive. Scientists are now convinced that what we refer to as birds, are in fact the survivors of the small scale dinasours. This can also explain a lot of known history of unsolved evolution facts. When on the next 112 million year cycle, mass starts to diminish again, Earth's density will decrease, possibly Earth itself would expand in radius, explaining why continents' coastlines are almost a perfect fit to each other, and could once cover the whole surface of a smaller earth. Animals grow taller and bigger as their muscles would be able to lift bigger bodies, and for us humans, building up temples with huge rocks, without any impossible machinery, would be like playing with blocks! Does this solve another mystery?

via Gravitational Constant : Variations in Gravitational Constant G.

For those who don't know me, I don't believe everything I post on this blog. I post things I want to check out, things I find interesting, and things I'd like feedback on from the experts out there who stop by.

What do you think about this variable G idea?


Patrick said...

The idea that gravity fluctuates over time is one of the recurring jokes of Kurt Vonnegut's novel "Slapstick." Very funny stuff.

Sam said...

Well, it really doesn't fluctuate. Gravity is a natural property of mass. Also to be considered is that gravity is different depending on where one is when measuring it. The top of the Himalayas will have a different reading than deep within a mine shaft. Also, this line: "explaining why continents’ coastlines are almost a perfect fit to each other," is a horribly backward conclusion. There are multiple reasons the coastlines "fit," and they are all a part of the one answer, which is, obviously, plate tectonics. (North America, some may be surprised to know, was once at the equator and oriented ninety degrees clockwise to its current orientation. It was also under water for millions and millions of years. "[A]nd could once cover the whole surface of a smaller earth," is, again, just ridiculous, as it completely ignores the existence of oceanic plates.) There may be something to glean from "variable G," but I don't see it yet. Looks much more like pseudo-science to me; something devised by someone with very little actual scientific knowledge.

Marcie Levay said...

hello thanks for the article.

Al said...

I don't believe G could have changed in the past. As far as I know there is no evidence of this or an explanation of how it could happen.
However, changes to the Earth's surface gravity could, and I believe did, change. No need to inject Earth expansion or to try to negate plate tectonics.
One theory posits that when the continents coalesced to form Pangea, the cores were forced off center to "balance" the rotational effects of the continental consolidation. Clearly, if this happened, there would have been an unequal surface gravity at different points on the Earth.

Xeno said...

It makes sense that the force of gravity varies with different amounts of mass in different places, as the curvature of space-time varies with mass, but if space time is visualized as a 2D sheet, what happens when that sheet is folded and two folds are next to each other? It seems to me G would change in that case because the nearby fold would accelerate you in a new direction and cancel out or increase the effect of G caused by the local space-time warp. This would explain how there could be an axis in space along which G varies. In other words, big folds in space time would make distant mass have effects on local G beyond what is predicted currently in our vision of a 4D universe.