You can have a herniated disc in any part of your spine. But most herniated discs affect the lower back (lumbar spine). Some happen in the neck (cervical spine) and, more rarely, in the upper back (thoracic spine). Wear and tear of the disc. As you age, your discs dry out and aren't as flexible.
General relativity is a theory of gravitation that was developed by Albert Einstein between 1907 and 1915. According to general relativity, the observed gravitational effect between masses results from their warping of spacetime. By the beginning of the 20th century, Newton's law of universal gravitation had been accepted for more than two hundred years as a valid description of the gravitational force between masses.
Special relativity is perhaps one of the least intuitive theories ever conceived in the history of science, yet it is central to physics. In E = mc 2 Einstein concluded that mass (m) and kinetic energy (E) are equal, since the speed of light (c 2) is constant. In other words, mass can be changed into energy, and energy can be changed into mass.