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It took 100 years, but scientists say they have proved Albert Einstein’s theory that gravitational waves exist. The waves were predicted as part of Einstein’s General Theory of Relativity, published in 1916. The idea is that there are waves in space, caused by energetic and violent events. These waves shrink and stretch the space-time of the universe. Now a group of scientists, including ones from Caltech, MIT and the LIGO Scientific Collaboration say they have found these gravitational waves. Imagine throwing a rock into a pond. When the rock hits the flat surface of the water, it creates small waves, or ripples. The gravitational waves are like the ripples moving out from where the rock hits the water. The waves expand and contract space and time as they move through outer space. And when they reach Earth, the waves pass through, and contract and expand the planet as the wave goes by. These are not large waves. They are very, very small, which is why it took so long to find them. For years, scientists have also been watching two black holes in another solar system. They were spinning around each other and finally crashed. When they hit each other, it was with such power and force, that gravitational waves moved through the universe. Those waves, traveling at the speed of light, finally reached Earth, some 1.3 billion years later. These are the waves that the scientists announced they found.