Black holes obey all laws of physics, including the laws of gravity. Their remarkable properties are in fact a direct consequence of gravity.
In 1687, Isaac Newton showed that all objects in the Universe attract each other through gravity. Gravity is actually one of the weakest forces known to
physics. In our daily life, other forces from electricity, magnetism, or pressure often exert a stronger influence. However, gravity shapes our Universe because
it makes itself felt over large distances. For example, Newton showed that his laws of gravity can explain the observed motions of the moons and planets in the
Albert Einstein refined our knowledge of gravity through his theory of general relativity. He first showed, based on the fact that light moves at a fixed
speed (671 million miles per hour), that space and time must be connected. Then in 1915, he showed that massive objects distort the four-dimensional space-time
continuum, and that it is this distortion that we perceive as gravity. Einstein's predictions have now been tested and verified through many different
experiments. For relatively weak gravitational fields, such as those here on Earth, the predictions of Einstein's and Newton's theories are nearly identical. But
for very strong gravitational fields, such as those encountered near black holes, Einstein's theory predicts many fascinating new phenomena.
The theory of general relativity continues to be tested with ever more accurate measurements, for example by NASA's Gravity Probe B satellite.