Fig. 3. (Color online) Local inertial frames in the Schwarzschild space-time. (Red) world-line of an observer O, fixed on Earth for example, is curved with respect to the local inertial frame (see also the inset). This means that the observer O is accelerating constantly, illustrating equivalence principle. The most left one quite deviates from local inertial frame due to high curvature around the horizon.
© NPSM
