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Rupert Sheldrake recently had a TEDx presentation removed from the TEDx web-site, for making various controversial claims, basically calling all of science into doubt. I am highly skeptical about nearly all of them, most seem particularly cranky and mystical.

The most interesting to me is the claim that the gravitational constant (G) changes over time, or space. In particular, he claims that the estimate is obtained by different labs making measurements on different days, and taking the average, and then the International Committee on Metrology takes an average of averages to decide the "value of big G" (I imagine that they actually just make an estimate of the value). Sheldrake argues that if we looked at the raw data, we might begin seeing patterns (e.g. correlations between changes at different labs indicating that the errors in G are not actually measurement errors, but real, meaningful fluctuations (on a daily or annual scale), but that "no one has done this ... because G is a constant".

So the question is: is there any strong evidence for or against G being a difficult-to-measure constant, rather than being a fluctuating value?

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    Is he saying "what if that isn't a measurement error..." or is he claiming that it isn't measurement error?
    – user5582
    May 29, 2013 at 0:26
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    It reads very much as if he is simply asking a huge 'what if' question, and pointing out that because of our assumptions we aren't following up on the possibility that G might vary. I don't think there is a real skeptical claim to debunk.
    – DJClayworth
    May 29, 2013 at 1:55
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    While this is a good skeptical question, not sure if we have the requisite expertise to answer it here. I'd be interested in an answer, but maybe you would have better luck at Physics.SE?
    – Larian LeQuella
    May 29, 2013 at 2:32
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    With regards to the question, saying that he "basically calling all of science into doubt." is a bit of an exaggeration. When I saw the talk and from what I have read of his recent work he's basically beating the drum to remind people not to allow the scientific community to become too dogmatic in their thinking not that science or the scientific method is wrong. In other-words, we should avoid rejecting something that goes against the current dogma, for example quasicrylstals
    – rjzii
    May 29, 2013 at 12:52
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    Sheldrake is not claiming that scientists are trying to hide anything. Most skeptics don't claim that the pope is hiding evidence that God doesn't exist. Sheldrake is claiming that those scientists hold certain beliefs as dogma and therefore don't really investigate them with the scientific method because they think they already know the answer. Thy guy had a blog titled "Science is a method, not a position."
    – Christian
    May 29, 2013 at 18:08

2 Answers 2

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At this time the Gravitational Constant is regarded as a constant with problematic/low accuracy by physicists. From University of Washington Big G Measurement:

Since Cavendish first measured Newton's Gravitational constant 200 years ago, "Big G" remains one of the most elusive constants in physics. The value of big G tells us how much gravitational force acts between two masses separated by a known distance. In Einstein's language of general relativity, it tells us the amount of space-time curvature due to a given mass. Together with Planck's constant and the speed of light it is considered to be one of the most fundamental constants in nature. Big G is a necessary ingredient in determining the mass of the earth, the moon, the sun and the other planets.

Several measurements in the past decade did not succeed in improving our knowledge of big G's value. To the contrary, the variation between different measurements forced the CODATA committee, which determines the internationally accepted standard values, to increase the uncertainty from 0.013% for the value quoted in 1987 to the twelve times larger uncertainty of 0.15% for the 1998 "official" value. This situation is an embarrassment to modern physics, considering that the intrinsic strength of electromagnetism, for instance, is known 2.5 million times more precisely and is steadily being improved. (The situation of G becomes more understandable if one considers the weakness of gravity: the total gravitational force twisting on the pendulum of a typical Cavendish torsion balance is only equivalent to the weight of a bacteria and that small force must be measured very precisely.)

Since we are talking about physics, this is true to the best of our current understanding.

The question of how/why do we know that G (and other constants) are indeed constant was addressed in Physics.SE: What is the proof that the universal constants (G, ℏ, …) are really constant in time and space?

Regarding the claim that the data isn't made public. I couldn't find any evidence that labs are constantly remeasuring and updating G and I couldn't find that this data is hidden. The data is made public through journal articles. Also, the value is not updated constantly as the National Institute of Standards and Technology published a figure that was last updated at 2010.

Here are 4 different values for G from different sources:

When plotted in a graph with error bars, we have the following:

Graph of Gravitational Constant Measurements

So measurements are not constantly done, the "official" value is not updated regularly, and the results of the measurements are published.

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    @vartec, what I meant to show is that the physicist community does change its mind, like shown with quasicrystals and with Einstein's famous quote against quantum mechanics (there are other example, but they are less world changing than quasicrystals and quantum mechanics). Or in other words, If Sheldrake has any scientific evidence to his hypothesis he should conduct the research and present the results to the scientific community. The answer is not "G is forever constant", but like all scientific truths it's "G is a constant to the best of our current knowledge".
    – SIMEL
    May 29, 2013 at 11:30
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    No, he's right that the number is "decided" as an average of several independent measures that show slightly different numbers. What he is postulating is that there is a periodic change in the value of G. What physicists say is that Gravity is the weakest of the 4 fundamental forces, so it's harder to measure it, so we have greater error in its measurement. It's like trying to understand what a person standing right next to you is saying, vs. understanding someone who is 200 meters from you with his back turned. In order to prove he's right he needs to do the research, which he didn't do.
    – SIMEL
    May 29, 2013 at 16:45
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    @RobZ, something else is going on, it's called the 3 other fundamental forces. The Gravitational force is really weak compared to them, so it's very hard to measure it. Everyone is aware of this, and that's why the measures for this constant are so inaccurate. There is also a theory that backs up that G is a constant. At this point he needs to bring proofs to the table.
    – SIMEL
    May 29, 2013 at 21:49
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    @Christian The stable shape and period of orbits is evidence. We have quality records of the planetary orbits going back thousands of years. Physicists don't need to talk about this stuff because it is bleeding obvious. Obvious enough that anyone who passed first semester college physics could check it, if they cared to.
    – dmckee --- ex-moderator kitten
    May 29, 2013 at 23:58
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    @dmckee : (3) No answer of physics stackexchange mentions either orbits or shapes. This one doesn't either. You are basically saying that both answers don't provide us with the real evidence because of which physicits to believe that G is constant. If that conclusion is so easy why don't you write up an answer that shows every one that G doesn't fluctuate by 0.01% using the data we have from shapes and orbits?
    – Christian
    May 30, 2013 at 8:10
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According to Measurements of Newton's gravitational constant and the length of day Europhysics Letters (2015) vol. 110:

About a dozen measurements of Newton's gravitational constant, G, since 1962 have yielded values that differ by far more than their reported random plus systematic errors. We find that these values for G are oscillatory in nature, with a period of [P = 5.899 +/- 0.062 yr]

An article in response, Recent measurements of the gravitational constant as a function of time Physical Review D (2015) vol. 91 adds and corrects some data, but still finds a better fit to the time-varying model with 5.9 year period. It concludes:

The situation is disturbing—clearly either some strange influence is affecting most G measurements or, probably more likely, the measurements have unrecognized large systematic errors. The need for new measurements is clear.

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    This result from Anderson is not well regarded. Wikipedia has a reasonable summary: "This response notes that Anderson et al. not only omitted measurements, they also used the time of publication not the time the experiments were performed. A plot with estimated time of measurement from contacting original authors seriously degrades the length of day correlation. Also taking the data collected over a decade by Karagioz and Izmailov shows no correlation with length of day measurements..." You can read more in the article on G.
    – KAI
    Apr 18, 2016 at 22:19
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    @KAI That whole passage from Wikipedia "This response notes..." is referring to the second article in my answer.
    – DavePhD
    Apr 18, 2016 at 23:43

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