Allais effect
Alleged pendulum anomaly during solar eclipses, first reported by Maurice Allais.
Wikipedia / Wikimedia Commons
The Allais effect is a disputed phenomenon in which pendulums or gravimeters are said to behave unusually during a solar eclipse. It was first noted by Maurice Allais, a French polymath and later Nobel laureate in economics, who observed an unexpected shift in the oscillation plane of a Foucault pendulum during the eclipse of June 30, 1954. Allais also reported a similar effect during the eclipse of October 2, 1959, using a paraconical pendulum he had invented. That work earned him the 1959 Galabert Prize from the French Astronautical Society and recognition as a laureate of the U.S. Gravity Research Foundation for a 1959 memoir on gravity. Over more than fifty years, attempts to confirm the effect have produced inconsistent or ambiguous results, leaving its validity contested.
Allais stressed that the effects he observed were dynamic, not static: they appeared only when the pendulum was moving and were linked to changes in weight or inertia across the pendulum’s path, not to the intensity of gravity itself. While deviations from the vertical could be explained by standard gravitational theory, the movement of the pendulum’s oscillation plane could not. Other researchers have explored whether the Moon might shield, absorb, or bend the Sun’s gravitational field during an eclipse. Some experiments have detected small, seemingly real variations in gravity-dependent devices within the eclipse’s umbra, while others have found no noticeable effect.
In 1961, Romanian physicist Gheorghe Jeverdan and colleagues observed both the Allais effect and a change in a Foucault pendulum’s oscillation period during the February 15 solar eclipse. They proposed two explanations: either the Moon screens the Sun’s gravitational pull, indirectly increasing Earth’s attraction (a phenomenon possibly linked to tides), or gravitational waves are diffracted, altering Earth’s gravity. Erwin Saxl and Mildred Allen reported strong anomalous changes in a torsion pendulum’s period during the March 7, 1970 eclipse, concluding that gravitational theory required modification. Leonid Savrov of the Sternberg Astronomical Institute built a paraconical pendulum to test the effect during the July 11, 1991 eclipse in Mexico and the November 3, 1994 eclipse in Brazil. He did not confirm Allais’s claim of daily periodicity in the pendulum’s motion but noted an increase in the rotation speed of its os
- field
- Gravitational physics, pendulum dynamics
- known_for
- Reporting anomalous pendulum behavior during solar eclipses
- first_reported_by
- Maurice Allais
- first_observation_date
- June 30, 1954
- status
- Controversial; inconsistent experimental results
Lore & Background
Maurice Allais, a French polymath and Nobel laureate in Economics, first reported the effect during the solar eclipse of June 30, 1954, observing an anomalous precession of a Foucault pendulum. He later reported another observation during the solar eclipse of October 2, 1959 using the paraconical pendulum he invented. This study earned him the 1959 Galabert Prize of the French Astronautical Society and made him a laureate of the U.S. Gravity Research Foundation for his 1959 memoir on gravity. Allais emphasized the 'dynamic character' of the effects, stating they are only seen when the pendulum is moving and are not connected with the intensity of weight but with the variation of weight or inertia in the space swept by the pendulum.
Reader's Guide
The Allais effect has been tested by numerous researchers over more than five decades, with results ranging from positive to inconclusive or negative. Romanian physicist Gheorghe Jeverdan et al. observed the effect and a change in oscillation period during the solar eclipse of February 15, 1961. Erwin Saxl and Mildred Allen reported strong anomalous changes in a torsion pendulum during the eclipse of March 7, 1970. Dr. Leonid Savrov observed an increase in rotational velocity of the pendulum oscillation plane during eclipses in 1991 and 1994. However, other experiments, such as those by Louis B. Slichter in 1961 and teams in Finland and the USSR in 1990, failed to detect any effect. A coordinated international effort for the total solar eclipse of August 11, 1999 was criticized by Allais for too short observation periods, and the NASA study was never published. Later analyses by Xin-She Yang and Tom Van Flandern concluded there have been no unambiguous detections within the past 30 years when experimental controls were more widespread, and suggested the original anomaly may have been due to poor controls. The effect remains unexplained within standard gravitational theory, with Allais himself proposing an aether hypothesis involving anisotropic characteristics of space.
Did You Know?
- The effect was first reported by Maurice Allais during the solar eclipse of June 30, 1954 using a Foucault pendulum.
- Allais invented the paraconical pendulum and used it to observe the effect during the solar eclipse of October 2, 1959.
- Romanian physicist Gheorghe Jeverdan et al. observed both the Allais effect and a change in oscillation period during the solar eclipse of February 15, 1961.
- A coordinated international test during the total solar eclipse of August 11, 1999 was never published after the lead supervisor left NASA with the gathered data.
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