We review certain emergent notions on the nature of space-time from noncommutative geometry and their radical implications. These ideas of space-time are suggested from developments in fuzzy physics, string theory, and deformation quantization. The review focuses on the ideas coming from fuzzy physics. We find models of quantum space-time like fuzzy S 4 on which states cannot be localized, but which fluctuate into other manifolds like CP 3 . New uncertainty principles concerning such lack of localizability on quantum space-times are formulated. Such investigations show the possibility of formulating and answering questions like the probability of finding a point of a quantum manifold in a state localized on another one. Additional striking possibilities indicated by these developments is the (generic) failure of CPT theorem and the conventional spin-statistics connection. They even suggest that Planck's 'constant' may not be a constant, but an operator which does not commute with all observables. All these novel possibilities arise within the rules of conventional quantum physics, and with no serious input from gravity physics.
Space-time in quantum physicsThe point of departure from classical to quantum physics is the algebra ´Ì £ ɵ of functions on the classical phase space T £ Q. According to Dirac, quantization can be achieved by replacing a function f in this algebra by an operatorf and equating i times the Poisson bracket between functions to the commutator between the corresponding operators.In classical physics, the functions f commute, so ´Ì £ ɵ is a commutative algebra.But the corresponding quantum algebraˆ is not commutative. Dynamics is onˆ . So quantum physics is a noncommutative dynamics.A particular aspect of this dynamics is fuzzy phase space where we cannot localize points, and which has an attendent effective ultraviolet cut-off: The number of states in a phase space volume V is infinite in classical physics and V 2d in quantum physics when the phase space is of dimension 2d. The emergence of this cut-off from quantization is of particular importance for the program of fuzzy physics [1].This brings us to the focus of our talk. In quantum physics, the commutative algebra of functions on phase space is deformed to a noncommutative algebra, leading to a 'noncommutative phase space'. Such deformations, characteristic of quantum theory, are now appearing in different approaches to fundamental physics. The talk will focus on a few such selected approaches and their implications. 359