Einstein predicted the existence of the gravitational waves in 1915,this theory came to be proven only recently in February 2016 when the LIGO (Laser Interferometer Gravitational-Wave Observatory )detectors in Louisiana ,USA detected a change in length of the tube detector equal to about one-thousandth of the width of a proton, a revolutionary discovery for our times . This phenomenon is based on spacetime. Einstein said that space and time can be merged to form the single continuum of spacetime which can be imagined like a mesh or a net in the universe, the mesh containing the three axes of length, breadth and depth and also the fourth axis of time together forming the spacetime continuum. This mesh is curved by the presence of mass or energy forming a crater in spacetime, greater the mass of the body larger the crater, all other inferior masses tend to fall in this crater, a phenomenon known as gravitation.
Fig. 1 Spacetime