Einstein's equivalence principle in cosmology

Understand

We study physical consequences of the Einstein equivalence principle (EEP) for a Hubble observer in FLRW universe.

• We introduce the local inertial coordinates with the help of a special conformal transformation.
• The local inertial metric is Minkowski-flat and materialized by a congruence of time-like geodesics of static observers.
• The static observers are equipped with the ideal clocks measuring the proper time that is synchronized with the clocks of the Hubble observer.