Summary
The equivalence principle (EP) states that all massive objects fall at the same rate in a given gravitational field. This idea can be tested by measuring the difference in acceleration of two freely falling objects. Since the EP is the foundation of general relativity, our most precise theory of gravity, EP tests probe the relationship between gravity and the other fundamental forces. In addition, EP tests are sensitive to the existence of new particles that could comprise “dark matter,” the matter of unknown composition that has been observed in astronomical data but has not yet been detec
