Transcript: Collapsed stellar objects offer the best chance to test Einstein’s Theory of General Relativity. General Relativity is based on the idea that acceleration due to gravity is not distinguishable from acceleration due to any other force. The consequence of this idea is that gravity distorts both space and time. For example, if someone were to fall into a black hole, as seen from afar, they would take an infinite amount of time to reach the event horizon, their clock slowing down asymptotically as they reach the event horizon. For the person falling in, however, it would take only a finite time, and they would see no difference in their clocks. Mass tells light how to move as well because light has an equivalent mass by E = mc2, and so gravity deflects light. These subtle interactions are hard to detect in a situation of normal masses like planets and stars like the Sun, but when stars collapse and densities rise by factors of millions, as happens in the late stages of stellar evolution, the effects of General Relativity can become measurable.