Extra dimension in space

String theory, the most promising theory combining quantum mechanics and gravity, gives a concrete reason to think about extra dimensions. However, although the arrival of string theory in the physics world improved the respectability of extra dimensions, the idea of extra dimensions originated much earlier. Einstein's. theory of relativity opened the door to the possibility of extra dimensions of space.His theory of relativity describes gravity, but it doesn't tell us why we experience particular gravity we do. Einstein's theory does not favor any particular number of spatial dimensions. It works equally well for three or for or ten. Why , then, do there seem to be only three? Swedish mathematician Oskar Klein proposed that the extra dimension would be curled up in the form of a circle, and that it would be extremely small, just10-33cm, or one tenth of a millionth of a trillionth of a trillionth of a centimeter. This tiny rolled-up dimension would be everywhere: each point in space would have its own minuscule circle, 10-33 cm in size. This small quantity represents the Planck length that has relevance to gravity itself. Klein picked the Planck length because it is the only length that would naturally appear in a quantum theory of gravity, and gravity is connected to the shape of space. For now, all you to need to know about the Planck length is that it is extraordinarily, unfathomably small-far smaller than anything we would ever have a chance of detecting. It is about twenty-four orders of magnitude smaller than an atom and ninteen orders of magnitude smaller than a proton. It is easy to over-look anything as in miniscule as that. For Klein though, the thing that was undiscernibly small was not the thickness of an object, but a dimension itself.