Equivalence of Active and Passive Gravitational Mass Tested with Lunar Laser Ranging

Area of Science:

• Physics
• Astronomy
• Geophysics

Background:

• The equivalence principle is a cornerstone of modern physics, stating that gravitational and inertial mass are equivalent.
• Lunar Laser Ranging (LLR) has been used since 1969 to precisely measure Earth-Moon distances.
• Previous experiments have set limits on violations of the equivalence principle.

Purpose of the Study:

• To test the equivalence of passive and active gravitational mass (m_a/m_p) using Lunar Laser Ranging (LLR) data.
• To establish new, stringent limits on potential violations of the equivalence principle for aluminum and iron.

Main Methods:

• Analysis of long-term Lunar Laser Ranging (LLR) data collected from Earth-based observatories to the Moon's retro-reflectors.
• Utilizing the Moon's orbital dynamics and the gravitational interaction with Earth, influenced by the Sun's gravity.
• Comparing the predicted orbital behavior with observed data to detect minute discrepancies indicative of mass-equivalence violation.

Main Results:

• A new, improved limit for the ratio of active to passive gravitational mass (m_a/m_p) was determined to be 3.9×10^{-14}.
• This limit is approximately 100 times more precise than previous experimental results, such as those by Bartlett and Van Buren (1986).
• The enhanced precision is attributed to the extensive duration and quality of the accumulated LLR data.

Conclusions:

• The study provides strong experimental support for the equivalence principle at unprecedented levels of precision.
• No violation of the equivalence of active and passive gravitational mass was detected for aluminum and iron within the achieved limit.
• The continued collection and analysis of LLR data offer a powerful tool for fundamental physics tests.