# Loop quantum gravity Reference Libraries

String Theory -- A string theory is a physical model whose fundamental building blocks are extended objects (strings, membranes and higher-dimensional objects) rather than points. String theories are able to avoid problems, such as infinite energy density, associated with the presence of mathematical points in a physical theory. The term 'string theory' properly refers to both the 26...

Spacetime -- In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional manifold called spacetime (alternatively, space-time; see below). A point in spacetime may be referred to as an event. Each event has four coordinates (t, x, y, z). Just as the x, y, z coordinates of a point depend on the axes one is using, so...

- Any of various tropical Old World birds of the family Indicatoridae, some species of which lead people or animals to the nests of wild honeybees. The birds eat the wax and larvae that remain after the nest has been destroyed for its honey.