Einstein was right yet again

[John Clark]

The "MICROSCOPE" experiment was devised to test Einstein's equivalence principle with 100 times greater precision than had ever been achieved before, the idea that all objects fall in a gravitational field at exactly the same speed. MICROSCOPE consisted of a 402 gram platinum cylinder inside a 300 gram titanium outer cylinder that was in orbit for 2 1/2 years. Any deviations from the equivalence principle would cause the two cylinders to move relative to each other, but no such movement was detected, so any violation of the equivalency principle must be less than one part in a thousand trillion or 10^15. An even more precise satellite, MICROSCOPE-2, is planned to be launched by 2030 and it will test it to one part in 10^18.

MICROSCOPE Mission: Final Results of the Test of the Equivalence Principle

John K Clark    See what's on my new list at  Extropolis

rwe

[Lawrence Crowell]

Well yawn, what else would we expect? I do though wonder how they account for the differential gravitational acceleration due to tidal interaction and Weyl curvature.

LC

[Brent Meeker]

Earlier, Earth based tests of the equivalence principle tried a lot of different materials (without much theoretical justification).




Robert Dicke, who did the most accurate Etovos type measurements used aluminum and gold masses.

An obvious problem of the satellite tests is that one tends to be limited to two materials.  I looked at one of the MICROSCOPE series of papers about the design of the satellite, to see why they selected titanium and platinum.  This what I found:

The choice of the materials is a trade-off between the machining laboratory know-how and the theoretical motivation [43, 55].  Titanium and platinum differ mainly from the neutron excess over the atomic mass (N-Z)/A and a little from the nuclear electrostatic energy Z(Z-1)/(N+Z)^(1/3).

I wonder what other criterion might drive the material selection?

Brent

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