Mass has different definitions. The moon’s orbit confirms two are equivalent

Two ways of looking at mass match, squaring with theories of Newton and Einstein

A photo of the moon as seen from Earth's orbit with the a blue haze at the bottom of the image.

Scientists used laser measurements of the moon’s orbit to compare two different types of mass, active and passive gravitational mass.


Mass is mass is mass.

Physicists have three different definitions of mass, all thought to be equivalent. Measurements of the distance between Earth and the moon confirm that two of those masses are one and the same to higher precision than ever before, physicists report July 13 in Physical Review Letters.