Photo taken by John Walker during the Zambia 2001 eclipse

The Allais effect is a claimed anomalous precession of the plane of oscillation of a pendulum during a solar eclipse. It has been speculated to be unexplained by standard physical models of gravitation, but recent mainstream physics publications tend rather to posit conventional explanations for the reported observations.

The effect was first reported in 1954 by Maurice Allais, a French physicist who went on to win the Nobel Prize for Economics. He reported another observation of the effect during a 1959 solar eclipse.

Prof. Allais's explanation for this and other anomalies is that space evinces certain anisotropic characteristics, which he ascribes to the existence of an aether; he has elaborated these theories in his 1997 book "Anisotropie de l'Espace".

The most recent published observation of 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. In response to criticisms, the same authors later (2002 and 2003) published papers maintaining that their observations could not be explained by conventional phenomena such as temperature and pressure change caused by the eclipse, and that, although tilting of the ground due to temperature changes could, in the extreme, have been responsible, that hypothesis was unlikely. Further observations which the same team performed in 2001 and 2002 during solar eclipses in Zambia and Australia appear to have yielded evidence of similar anomalies.

Another anomalous effect during a solar eclipse, an increase in the period of a torsion pendulum, was reported by Saxl and Allen in 1970, but subsequent attempts to replicate this experiment (under different eclipse geometries and with much smaller pendulum bobs) failed to observe any effect (Kuusela, 1991; Jun, 1991). Jeverdan in Romania claimed to have observed anomalous pendulum behavior during a solar eclipse in 1961 (Jeverdan, 1981) - decrease of the period by about 1 part in 2000 - the so-called "Jeverdan effect", but his report was not published in a mainstream English-language scientific journal.

A recent 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 for which there is no observational evidence), but admits that "the gravitation anomaly discussed here is about a factor of 100,000 too small to explain the Allais excess pendulum precession... during eclipses".

A 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.

Exotic explanations for Allais and related effects have not gained significant traction among mainstream scientists.

References and external links

• Maurice Allais, "Should the Laws of Gravitation be Reconsidered?", Aero/Space Engineering 9, 46–55 (1959).
• Maurice Allais, "The Allais Effect and my Experiments with the Paraconical Pendulum 1954-1960" (Report for NASA, 1999), available at www.allais.info/allaisdox.htm
• Maurice Allais, "L'Anisotropie de l'Espace" ("The Anisotropy of Space"), Clement-Juglar, 1997, 800 pp. (no English version available)
• T. van Flandern and X. S. Yang, "Allais gravity and pendulum effects during solar eclipses explained," Phys. Rev. D 67, 022002 (2003).
• Qian-shen Wang, Xin-she Yang, Chuan-zhen Wu, Hong-gang Guo, Hong-chen Liu, and Chang-chai Hua, "Precise measurement of gravity variations during a total solar eclipse," Phys. Rev. D 62, 041101(R) (2000).
• X. S. Yang and Q. S. Wang, "Gravity anomaly during the Mohe total solar eclipse and new constraint on gravitational shielding parameter," Astrophysics and Space Science 282 (1), 245–253 (2002).
• Luo Jun, Li Jianguo, Zhang Xuerong, V. Liakhovets, M. Lomonosov, A. Ragyn, "Observation of 1990 solar eclipse by a torsion pendulum," Phys Rev. D. 44, 2611–2613 (1991).
• T. Kuusela, "Effect of the solar eclipse on the period of a torsion pendulum," Phys. Rev. D. 43, 2041–2043 (1991).
• Erwin J. Saxl and Mildred Allen, "1970 solar eclipse as 'seen' by a torsion pendulum," Phys. Rev. D. 3 (4), 823–825 (1971).
• G. T. Jeverdan, G. I. Rusu, and V. Antonescu, "Experiments using the Foucault pendulum during the solar eclipse of 15 February, 1961," Biblical Astronomer 1 (55), 18–20 (1981).
• Chris P. Duif, "A review of conventional explanations of anomalous observations during solar eclipses," arXiv gr-qc/0408023 v3 (8 Oct 2004). (Unpublished preprint claiming that Allais observations do not satisfy conventional explanations.)
• Dave Dooling, "French Nobel Laureate turns back clock", Science@NASA (Oct. 12, 1999). A 1999 NASA attempt to observe an Allais effect; no results are reported. No results were ever published.
• Thomas J. Goodey, "Professor Maurice Allais — a genius before his time — as are they all" (Web site claiming to be the internet base of researchers studying and publicizing the Allais effect; includes copies/translations of several of the above papers.)