Einstein, for his GR theory he made a last important effort to make it valid also for rotating objects. So consider the following thought experiment. There is an observer A standing at the North Pole and another observer B sitting on a platform, turning clockwise once every 24 hours, both with a camera. The earth is hollow, with little gravity and a thin crust, turning like the normal earth. At the equator there is a man sending short laser pulses through an hole in the earth crust to the opposite side, about 12.000 km away. It takes 40 msec. for the pulses the reach the other side and inside the hollow earth there is a bit of fog as to show the course of the laser beam. During the 40 msec. objects at the equator move on for about 18 meters. At the North Pole there is also a hole in the crust. Both A and B make a pictures during the laser beam crossing the inner earth. Now, considering the rotating earth as a reference frame for GR, observer A sees the laser beam going straight. But B in rotation gets a picture from a laser beam slightly bent. But then, consider B as part of the non-rotating universe, following the laser beam with his camera, he should find a straight line. Because why should light bent when there is no gravity involved. How to solve this dilemma.