... 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 number Author Year G (x10-11 m3Kg-1s-2) Accuracy % Deviation
from CODATA1 Cavendish H. 1798 6.74 ±0.05 +0.986 2 Reich F. 1838 6.63 ±0.06 -0.662 3 Baily F. 1843 6.62 ±0.07 -0.812 4 Cornu A, Baille J. 1873 6.63 ±0.017 -0.662 5 Jolly Ph. 1878 6.46 ±0.11 -3.209 6 Wilsing J. 1889 6.594 ±0.015 -1.202 7 Poynting J.H. 1891 6.70 ±0.04 +0.387 8 Boys C.V. 1895 6.658 ±0.007 -0.243 9 Eotvos R. 1896 6.657 ±0.013 -0.258 10 Brayn C.A. 1897 6.658 ±0.007 -0.243 11 Richarz F. & Krigar-Menzel O. 1898 6.683 ±0.011 +0.132 12 Burgess G.K. 1902 6.64 ±0.04 -0.512 13 Heyl P.R. 1928 6.6721 ±0.0073 -0.031 14 Heyl P.R. 1930 6.670 ±0.005 -0.063 15 Zaradnicek J. 1933 6.66 ±0.04 -0.213 16 Heyl P.,Chrzanowski 1942 6.673 ±0.003 -0.018 17 Rose R.D. et al. 1969 6.674 ±0.004 -0.003 18 Facy L., Pontikis C. 1972 6.6714 ±0.0006 -0.042 19 Renner Ya. 1974 6.670 ±0.008 -0.063 20 Karagioz et al 1975 6.668 ±0.002 -0.093 21 Luther et al 1975 6.6699 ±0.0014 -0.064 22 Koldewyn W., Faller J. 1976 6.57 ±0.17 -1.561 23 Sagitov M.U. et al 1977 6.6745 ±0.0008 +0.004 24 Luther G., Towler W. 1982 6.6726 ±0.0005 -0.024 25 Karagioz et al 1985 6.6730 ±0.0005 -0.018 26 Dousse & Rheme 1986 6.6722 ±0.0051 -0.030 27 Boer H. et al 1987 6.667 ±0.0007 -0.108 28 Karagioz et al 1986 6.6730 ±0.0003 -0.018 29 Karagioz et al 1987 6.6730 ±0.0005 -0.018 30 Karagioz et al 1988 6.6728 ±0.0003 -0.021 31 Karagioz et al 1989 6.6729 ±0.0002 -0.019 32 Saulnier M.S., Frisch D. 1989 6.65 ±0.09 -0.363 33 Karagioz et al 1990 6.6730 ±0.00009 -0.018 34 Schurr et al 1991 6.6613 ±0.0093 -0.193 35 Hubler et al 1992 6.6737 ±0.0051 -0.008 36 Izmailov et al 1992 6.6771 ±0.0004 +0.043 37 Michaelis et al 1993 6.71540 ±0.00008 +0.617 38 Hubler et al 1993 6.6698 ±0.0013 -0.066 39 Karagioz et al 1993 6.6729 ±0.0002 -0.019 40 Walesch et al 1994 6.6719 ±0.0008 -0.035 41 Fitzgerald & Armstrong 1994 6.6746 ±0.001 +0.006 42 Hubler et al 1994 6.6607 ±0.0032 -0.202 43 Hubler et al 1994 6.6779 ±0.0063 +0.055 44 Karagioz et al 1994 6.67285 ±0.00008 -0.020 45 Fitzgerald & Armstrong 1995 6.6656 ±0.0009 -0.129 46 Karagioz et al 1995 6.6729 ±0.0002 -0.019 47 Walesch et al 1995 6.6685 ±0.0011 -0.085 48 Michaelis et al 1996 6.7154 ±0.0008 +0.617 49 Karagioz et al 1996 6.6729 ±0.0005 -0.019 50 Bagley & Luther 1997 6.6740 ±0.0007 -0.003 51 Schurr, Nolting et al 1997 6.6754 ±0.0014 +0.018 52 Luo et al 1997 6.6699 ±0.0007 -0.064 53 Schwarz W. et al 1998 6.6873 ±0.0094 +0.196 54 Kleinvoss et al 1998 6.6735 ±0.0004 -0.011 55 Richman et al 1998 6.683 ±0.011 +0.132 56 Luo et al 1999 6.6699 ±0.0007 -0.064 57 Fitzgerald & Armstrong 1999 6.6742 ±0.0007 ±0.01 58 Richman S.J. et al 1999 6.6830 ±0.0011 +0.132 59 Schurr, Noltting et al 1999 6.6754 ±0.0015 +0.018 60 Gundlach & Merkowitz 1999 6.67422 ±0.00009 +0.0003 61 Quinn et al 2000 6.67559 ±0.00027 +0.021 -- PRESENT CODATA VALUE 2004 6.6742 ±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?
5 comments:
The idea that gravity fluctuates over time is one of the recurring jokes of Kurt Vonnegut's novel "Slapstick." Very funny stuff.
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.
hello thanks for the article.
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.
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.
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