" Einstein brilliantly realized that it would be possible to patch together a comprehensive theory of gravity from free falling reference frames, treating each as it were at rest. Within each framework, he noted, each object would move in a straight line unless deflected by external forces. However, when viewed from another framework, those straight lines might appear curved. That is why we see bodies taking curved paths because of gravity- because we are viewing their motion from our framework, not theirs. "

― Paul Halpern , Einstein's Dice and Schrödinger's Cat: How Two Great Minds Battled Quantum Randomness to Create a Unified Theory of Physics