Gravity was known to humans long before the present-day picture of four fundamental interactions was formed. The nature of gravity is fundamental to our understanding of our solar system, the galaxy and the structure and evolution of the Universe. It was Newton who first understood that gravity not only dictates the fall of apples and all bodies on Earth, but also planetary motion in our solar system and the sun itself are govern by the same physical principles. On the larger scales the effects of gravity are even more pronounced, guiding the evolution of the galaxies, galactic clusters and ultimately determining the fate of the Universe. Presently the Einstein’s general theory of relativity is a key to the understanding a wide range of phenomena, spanning from the dynamics of compact astrophysical objects such as neutron stars and black holes, to cosmology, where the Universe itself is the object of study. Its striking predictions include gravitational lensing and waves, and only black holes have not yet been directly confirmed.
