Allais Effect

The Allais effect is the alleged anomalous behaviour of pendulums or gravimeters sometimes purportedly observed during a solar eclipse. It was first reported as an anomalous precession of the plane of oscillation of a Foucault pendulum during the solar eclipse of 30 June 1954 by Maurice Allais, who reported another observation during the eclipse of 2 October 1959 using the Paraconical Pendulum he invented. The source states that the veracity of the effect remains controversial, as testing has frequently met with inconsistent or ambiguous results over more than five decades.

The dynamic-versus-static distinction

Allais emphasised the "dynamic character" of the effects he observed. In his own words, quoted in the source:

The observed effects are only seen when the pendulum is moving. They are not connected with the intensity of weight (gravimetry), but with the variation of weight (or of inertia) in the space swept by the pendulum. Actually, while the movement of the plane of oscillation of the pendulum is inexplicable by the theory of gravitation, the deviations from the vertical are explained perfectly by that theory. The deviations from the vertical […] correspond to a static phenomenon, while my experiments correspond to a dynamic phenomenon.

This distinction separates the claimed anomaly from ordinary gravimetric measurements: the effect is claimed to appear in the variation of weight or inertia across the space swept by a moving pendulum, not in the intensity of weight at a point.

Reported positive results

• Jeverdan, Rusu and Antonescu (15 February 1961) — Romanian physicists monitoring a Foucault pendulum reported a change in oscillation period during the eclipse, the so-called Jeverdan–Rusu–Antonescu effect (or Jeverdan effect). They proposed either a lunar screening effect on the Sun's gravitational attraction or diffraction of gravitational waves.
• Saxl and Allen (7 March 1970) — reported strong anomalous changes in the period of a torsion pendulum and concluded that "gravitational theory needs to be modified."
• Savrov (1991 Mexico, 1994 Brazil) — reported increased rotational velocity of the oscillation plane in the direction of the Foucault effect during eclipses, but could not confirm Allais's claimed diurnal periodicity.
• Atomic clock and gravimeter anomalies — reported by teams during eclipses in China (1992), India (1995) and China (1997), which the source says could not be attributed to tidal effects, gravimeter drift, or high-frequency noise.
• Romanian team (22 September 2006 annular eclipse) — reported confirmation of the Allais and Jeverdan–Rusu–Antonescu effects, with a "quantization" of the paraconical pendulum's behaviour.
• Ukrainian and Romanian teams (1 August 2008) — three teams hundreds of kilometres apart, using five miniature torsion balances, two short ball-borne pendulums and a long Foucault pendulum, all reported "unexplained and mutually correlated disturbances."
• Pugach and Olenici (26 January 2009 annular eclipse) — reported the same significant correlation between light torsion balances and a Foucault pendulum, this time outside the umbra.
• Underground salt-mine experiment (1 June 2011 partial eclipse) — reported similar anomalies with a Foucault pendulum and a very light torsion balance in a disused salt mine with minimal interference.

Reported negative or inconclusive results

• Slichter (15 February 1961, Florence) — a gravimeter failed to detect an associated gravitational signal.
• Finland and Belomorsk (22 July 1990) — no anomalous period increase of a torsion pendulum was detected independently by either team.
• NASA 1999 international campaign (11 August 1999) — coordinated by NASA's Marshall Space Flight Center across seven countries. Allais criticised the observation period as "much too short […] to detect anomalies properly"; the lead supervisor left NASA with the data and the study was never published.
• Yang and Van Flandern — concluded 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," and that "the gravitation anomaly discussed here is about a factor of 100,000 too small to explain the Allais excess pendulum precession […] during eclipses," attributing the original anomaly to poor controls.
• China 2009 (22 July 2009) — eight gravimeters and two pendulums across six sites; no result published in any academic journal.
• Argentina 2010 (11 July 2010) — an automated Foucault pendulum found no evidence of a precession change, with an upper bound of < 0.3 degree per hour.

Proposed explanations

Several single-author proposals appear in the source, none presented as established:

• Anisotropic Dark Flow Acceleration (Bjarne Lorenzen, 2017) — a kinematic analysis of 21 Allais effect measurements, calculating an anisotropic acceleration of around 35 μGal (3.5×10⁻⁷ m/s²) directed in the same direction as Dark Flow.
• Gravitomagnetic tensor (Delso J) — the gravitomagnetic tensor is proposed to generate the extra force needed to explain the anomalous pendulum behaviour.
• Gravitational tilt / circular anisotropy (J. D. Francis) — an additional law of gravity in which the horizontal direction of gravitational tilt rotates with varying magnitude, producing horizontal torque.
• Gravitational shielding / screening — the hypothesis that the Moon screens the Sun's gravitational attraction during an eclipse, tested by Slichter and constrained by Yang and Wang (2002).
• Upper-atmosphere air-density spot (Yang and Van Flandern) — cooling winds during the eclipse create a denser spot in the upper atmosphere whose gravitational effect perturbs the pendulum.

Open questions

• The source is a secondary compilation; primary papers should be consulted before treating any result as established.
• The NASA 1999 data remain unpublished — a genuine gap.
• No independent replication of the paraconical pendulum specifically is claimed beyond the named teams' own reports.
• The positive and negative results are not reconciled by the source.

Related pages

• Maurice Allais
• Paraconical Pendulum
• Aether Anisotropy (Allais)
• Allais Effect Claims vs. Evidence: Positive Reports, Negative Results and the Unpublished NASA Study
• research-method