Bonn 2025 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 32: Atom & Ion Clocks and Metrology II

Q 32.3: Talk

Wednesday, March 12, 2025, 11:45–12:00, HS Botanik

High precision test of the equivalence of active, passive, and gravitating mass — •Claus Lämmerzahl and Eva Hackmann — ZARM, University of Bremen, Germany

The kilogram is one of the basic physical units. It has been given by the Paris prototype consisting of platinum and Iridium. Recently, within the new SI (Systeme International) the kilogram has been defined through the setting of the Planck constant.

While the Plack constant is unique, the operational definition of mass has a variety of aspects which need not be equivalent: We can define an inertial mass appearing on the "right" hand side of Newton’s third axiom through, e.g, scattering processes, we have a passive gravitational mass which is the weight of a body in an external gravitational field, and we have the active gravitational or gravitating mass which creates a gravitational field. These three definitions are independent and in principle may lead to completely different quantities. However, high precision tests prove that these three masses are equivalent to very high precision.

Here we report on the basics notions, describe theoretical and metrological aspects as well as experimental implications of a hypothetical non-equivalence of these masses, and highlight the recent experimental progress on testing the equivalence of these masses achieved with Lunar Laser Ranging and with the MICROSCPE space mission, and outline future planned tests.

Keywords: definition of mass; equivalence principle; experimental gravitation; metrology