Albert Einstein’s theory of general relativity is the most accurate description of gravity that we have. It explains how objects move in response to gravity, and predicts the behavior of extremely massive objects, like black holes.
Einstein’s theory of general relativity is a theory of spacetime. In Newtonian physics, space and time are separate entities; in Einstein’s theory, they are combined into a single entity called spacetime. This means that gravity is not a force between masses, as Newton believed; instead, it is a property of spacetime itself.
The key idea behind general relativity is that the presence of mass or energy bends spacetime. The more mass or energy an object has, the more it bends spacetime around it. This explains why all objects fall at the same rate: they are all being pulled by the curvature of spacetime around Earth.
General relativity also explains why GPS devices need to take into account the effects of gravity when they calculate your location. GPS satellites orbit Earth at high speeds, so their clocks run faster than clocks on the ground. But because they are further from Earth’s center (and thus experience less gravitational pull), their clocks run slower than expected according to Newtonian physics. General relativity predicts this effect precisely, and without it, GPS would be inaccurate by about 10 kilometers!
Finally, general relativity has allowed us to make some incredible predictions about very massive objects, like black holes. Black holes are so massive that their gravitational pull prevents anything from escaping them – not even light! We can only see them indirectly, by observing how they interact with other objects in their vicinity.
But thanks to Einstein’s theory of general relativity, we now know that black holes exist – and we have even been able to observe them directly! In 2015, astronomers used data from the Event Horizon Telescope to create an image of a black hole for the first time ever. This landmark achievement would not have been possible without general relativity