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.
There are plenty of theoretical indications, though, that General Relativity isnât the end of the story of spacetime. And in fact, much as I like General Relativity as an abstract theory, Iâve come to suspect it may actually have led us on a century-long detour in understanding the true nature of space and time. Iâve been thinking about the physics of space and time for a little more than 40 years now. At the beginning, as a young theoretical physicist, I mostly just assumed Einsteinâs whole mathematical setup of Special and General Relativityâand got on with my work in quantum field theory, cosmology, etc. on that basis.