Allais effect

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Not to be confused with the Allais paradox in economics, which is occasionally referred to as Allais effect.
Allais's paraconical pendulum
Photo taken during the French 1999 eclipse

The Allais effect refers to the alleged anomalous behavior of pendulums or gravimeters, which is sometimes purportedly observed during a solar eclipse. The effect was first reported as an anomalous precession of the plane of oscillation of a pendulum for the solar eclipse of June 30, 1954 by Maurice Allais, a French polymath who went on to win the Nobel Prize in Economics. He reported another observation of the effect during the solar eclipse of October 2, 1959.

Experimental observations[edit]

Various experiments have been performed in order to detect anomalous behavior during solar eclipses. Some observations gave positive results and some failed to detect any noticeable effect. The table below gives an overview of the different experiments.

Experimenter Date Place Device Result
M. Allais June 30, 1954 Saint-Germain-en-Laye, France Paraconical pendulum "The plane of oscillation of the paraconical pendulum approximately shifted 15 centesimal degr. during the eclipse." [1]
M. Allais October 2, 1959 Saint-Germain-en-Laye, France Paraconical pendulum "An analogous perturbation of amplitude approximately 10 grads has been observed" [2]
G. T. Jeverdan et al. February 15, 1961 Iași, Romania Foucault pendulum The oscillation period of the pendulum decreased by about 1 part in 2000 – the so-called ‘Jeverdan effect’,[3] but his report was not published in a mainstream English-language scientific journal.
L. Slichter et al. February 15, 1961 Florence, Italy Gravimeter "Gravity observations during the solar eclipse of February 15, 1961, failed to detect an associated gravitational signal" [4]
E. J. Saxl and M. Allen March 7, 1970 Harvard, Massachusetts Torsion pendulum Increase in the period of a torsion pendulum during the solar eclipse: "Quantitative observations made with a precise torsion pendulum show ... that the times required to traverse a fixed fraction of its total angular path vary markedly during the hours before the eclipse and during its first half, i.e., up to its midpoint." [5]
T. Kuusela July 22, 1990 Turku, Finland Torsion pendulum "Contrary to previous experiments, no increase in the period was observed".[6]

A published observation of what was initially claimed to be a possibly related anomalous gravitational effect (claimed variation of terrestrial gravitation as measured by a sensitive gravimeter) was by Wang et al. in 2000, for an experiment carried out in 1997 in a remote region of China during a total solar eclipse. Further observations which the same team performed in 2001 and 2002 during solar eclipses in Zambia and Australia appear to have yielded much weaker evidence of similar anomalies. However, the same authors later (2002 and 2003) published papers explaining that their observations could be explained by conventional phenomena such as temperature and pressure change caused by the eclipse. In their 2002 paper, they posited a more conventional explanation based on temperature changes causing ground tilting, but they suggested that this explanation was unlikely. In their 2003 paper (Flandern and Yang, 2003), on the other hand, the authors argued that atmospheric motion induced by temperature changes was both plausible and sufficient to explain the observed anomaly.

A published article on the topic in a mainstream scientific journal (Flandern, 2003) concludes that there have been "no unambiguous detections [of an Allais effect] within the past 30 years when consciousness of the importance of [experimental] controls was more widespread." This paper also suggests a mechanism that might cause slight gravitational variations during an eclipse (high speed high-altitude winds). They point out that "the gravitation anomaly discussed here is about a factor of 100,000 too small to explain the Allais excess pendulum precession… during eclipses" and from this conclude that the original Allais anomaly was merely due to poor controls.

A possible but yet controversial explanation is the so-called van Flandern–Yang hypothesis by van Flandern and Yang's article,[7] which conjecture the effect is due to the gravitational effect of an increased density spot in the upper atmosphere created by cooling during the solar eclipse.

A self-published review article by Chris Duif, which surveys the field of gravitational anomalies in general, concludes that the question remains open, and that such investigations should be pursued, in view of their relatively inexpensive nature and the enormous implications if genuine anomalies are actually confirmed – but the article has not undergone any peer review.

During the solar eclipse of January 26, 2009, a correlation was found between anomalous behavior of a pendulum and torsion balances, located at two different points outside the shadow zone.[8]

Eight gravimeters and two pendulums were deployed across six monitoring sites in China for the solar eclipse of July 22, 2009.[9] Although one of the scientists involved claimed in an interview to have observed an Allais effect,[10] the result has not been published in any mainstream peer-reviewed scientific journal.

An automated Foucault pendulum was used by H.R. Salva and found no evidence for a precession change of the pendulum's oscillation plane (<0.3 degree / hour) during the Solar eclipse of July 11, 2010.[11]


Maurice Allais states that the eclipse effect is related to a gravitational anomaly, that is inexplicable in the framework of the currently admitted theory of gravitation, without giving any explanation of his own.[12] Allais’s explanation for another anomaly (the lunisolar periodicity in variations of the azimuth of a pendulum) is that space evinces certain anisotropic characteristics, which he ascribes to motion through an aether which is partially entrained by planetary bodies. He has presented this hypothesis in his 1997 book L’Anisotropie de l’espace. This explanation has not gained significant traction amongst mainstream scientists.

After analysis of Foucault pendulum data during the solar eclipse of July 11, 1991, L. Savrov suggested that the "pendulum responded to the remanent shock wave at the maximum of the total eclipse phase".[13]


  1. ^ Maurice Allais, Should the Laws of Gravitation be Reconsidered?, Aero/Space Engineering 9, 46–55 (1959)
  2. ^ Maurice Allais, "Maurice Allais, L'Anisotropie de l'Espace ("The Anisotropy of Space"), Clement-Juglar, 1997
  3. ^ G. T. Jeverdan, G. I. Rusu and V. I. Antonescu, "Date preliminare asupra comportarii unui pendul Foucault in timpul eclipsei de soare de la 15 februarie 1961", Analele Științifice ale Universității "Al. I. Cuza" of Iași, section I, tom VII, anul 1961, Fasc.2, p. 457
  4. ^ Slichter L. B., Caputo M. and Hager C. L., An experiment concerning gravitational shielding, Journal of Gravitational Research 70, 1965, 1541-1551
  5. ^ Saxl E. and Allen M., 1970 solar eclipse as "seen" by a torsion pendulum, Phys. Rev. D, vol. 3, no. 4, pp. 823-825 (1971)
  6. ^ Kuusela T., Effect of the solar eclipse on the period of a torsion pendulum, Phys. Rev. D 43, 2041–2043 (1991)
  7. ^ T. van Flandern and X. S. Yang, "Allais gravity and pendulum effects during solar eclipses explained," Phys. Rev. D 67, 022002 (2003).
  8. ^ A. F. Pugach and D. Olenici, “Observations of Correlated Behavior of Two Light Torsion Balances and a Paraconical Pendulum in Separate Locations during the Solar Eclipse of January 26th, 2009,” Advances in Astronomy, vol. 2012, Article ID 263818, 6 pages, 2012. doi:10.1155/2012/263818
  9. ^ " July eclipse is best chance to look for gravity anomaly", New Scientist, 2009-07-19
  10. ^ "Eclipse at Sheshan Hill", The Atlantic, 2009–07
  11. ^ H.R. Salva, Searching the Allais effect during the total sun eclipse of 11 July 2010, Phys. Rev. D 83, 067302 (2011) doi:10.1103/PhysRevD.83.067302
  12. ^ Maurice Allais, "Maurice Allais, L'Anisotropie de l'Espace ("The Anisotropy of Space"), Clement-Juglar, 1997, p.169, footnote 2
  13. ^ Savrov, L. A. "Improved determination of variation of rate of rotation of oscillation plane of a paraconic pendulum during the solar eclipse in Mexico on July 11, 1991." Measurement Techniques 52.4 (2009): 339-343.

External links[edit]