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.
Einstein's general theory of relativity explains gravity as the curvature of space-time. This concept can be pictured by imagining space-time as a rubber sheet. The balls on the rubber sheet bend the sheet around them, somewhat as matter bends space-time in its vicinity.