Albert Einstein's Theory of General Relativity changed our understanding of physics by revolutionizing our understanding of gravity and the structure of space-time. Prior to this theory, scientists believed that gravity was a force that acted at a distance between objects with mass, but Einstein proposed that it is actually the curvature of space-time caused by massive objects like planets and stars. According to his theory, objects move in straight lines through curved space-time, which gives rise to the effect we call "gravity". This idea has been confirmed through numerous experiments and observations over the years.
Einstein's theory also predicted several phenomena such as black holes, gravitational waves, and time dilation (the slowing down of time near massive objects), which were later observed or detected by scientists. The discovery of these phenomena has led to new areas of research in astrophysics and cosmology.