Einstein wins again: Space satellite confirms weak equivalence principle

The idea that all objects fall at the same rate regardless of mass is known as the equivalence principle. David Scott illustrated this during a moonwalk. The two objects hit the dirt at the same time, after he dropped a falcon and hammer at the same time.

Albert Einstein's general theory of relativity is based on the weak equivalence principle, which has been tested many times. The equivalence principle has held up well over time. The most precise test of the equivalent principle to date has been achieved by the MICROSCOPE mission. There were additional papers in a special issue.

Testing, 1,2,3

John Philoponus was the first to argue that the speed at which an object falls has nothing to do with its weight.

The balls were rolled down inclined planes, which made it easier to measure their speed. Some of the balls were made of iron and others of wood. Galileo used his pulse to time the balls' travel. The balls would travel at the same rate regardless of the incline.

Galileo used a pendulum apparatus to measure the period of pendulums of different lengths. The method was favored by both Friedrich Bessel and IsaacNewton. The Moon is made of silicates, while the Earth is made of iron. NASA's laser lunar ranging experiments have confirmed that they fall at the same rate.

In the 19th century, Hungarian physicist Lornd Etvs combined a pendulum approach with a balance to create a pendulum that could be used to test the equivalence principle.

The foundation for Einstein's theory of relativity was laid out in his 1916 paper. The rules of quantum mechanics kick in when general relativity breaks down at the subatomic level. Physicists have been looking for violations of equivalency. New physics could help unify the two into a single theory.

It is possible to use matter-wave interferometry to test equivalency. Physicists at the time believed that the luminiferous aether was the source of the movement of the Earth. It's the same for matter.

Prior experiments used matter-wave interferometry to measure the free fall of two isotopes of the same atomic element. A group of physicists thought that there wasn't enough difference between their compositions to get the sensitivity they wanted. They used different elements in their version of the experiment. The atoms fell on two different paths. The interference pattern indicated that equivalence held to within 1 part.