Einstein actually imagined a man in a falling elevator, he felt no gravitational force.Once again Einstein’s genius mpelled him to take things at face value. If the orbiting astronaut feels no force, it is only someone outside the shuttle , observing or imaging the astronaut’s position from afar, who would come up with the idea of a force emanating from the Earth and holding in orbit the shuttle. Einstein supposed that the astronaut’s point of view and not the observer’s, was correct. Why postulate the existence of a force called gravit, when no force is felt. An astronaut orbiting the Earth clearing is not moving in straightline, therefore a force is needed. Einstein would respond, what is there to tell the astronaut, who feel no deflecting force. The astronaut has no way to telling the differencebetween being in a shuttleorbiting the Erath or in one sailing through empty space in what an outside observer would call a stright line. From the astronaut’s point of view, a circular orbit around the Earth is indistinguishable from a stright line, and Einstein resolution of the puzzle was radical, he redefined what a straight line mean. Empty space devoid of mass , is a flat space, and in it a straight line is a straight line, but around the Earth, because of the presence of the Earth mass, space is curved, and a straight line is a circle.
The Last Contradiction by David Lindley