General relativity has taught us that space and time should not be thought of as a static arena for other phenomena. Instead, they are dynamical players: the curvature of space and time tells matter how it should move, and matter influences spacetime’s curvature. But the lesson of quantum gravity and string theory in particular is more far-reaching: space and time do not have to exist at the very beginning – they are kind of illusions. Moreover, there can be many different illusionary geometries that emerge if we look at the same physical system.

Quantum mechanics guarantees that the concept of a completely smooth geometry is incompatible with quantum mechanics that make things fluctuate. But string theory goes much further. Geometric descriptions, such as general relativity, are only approximations valid at very long distances. At very short distances, comparable to the “length of the string” (string scale) or “the smallest meaningful black hole” (the Planck scale), physics does not admit a simple description in terms of usual geometry. Geometry is generalized to something much more grandiose, and the difference between geometry and matter disappears – this is the content of unification of gravity with other forces and matter.

— Emergent space and emergent time

— Lubos Motl

2012.06.01 Friday ACHK