Introduction
The second program called 'Canonical Quantum Gravity' theory has a very different parentage. Following the established mathematical techniques developed by Schroedinger and Dirac, Einstein's equation for gravity gets rewritten, and it is in this new form that it can be analyzed for a consistent set of 'operators' and 'states' following conventional quantum mechanics. This forces quantum gravity theory to come out looking like a respectable quantum theory, but in which the dynamics of 3-D geometries play a key role, and the new Hamiltonian formulation describes how a system, the complete 3-D geometry of the universe, changes from state to state. Whereas quantum mechanics depends on considering the histories of particles as they move through space-time, quantum gravity must, in addition, consider all possible geometries of space as they unfold in time.
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Gravitational waves are propagating gravitational fields, "ripples" in the curvature of space-time, generated by the motion of massive particles, such as two stars or two black holes orbiting each other. Gravitational waves cause a variable strain of space-time, which result in changes in the distance between points, with the size of the changes proportional to the distance between the points. Gravitational waves can be detected by devices which measure the induced length changes. Waves of different frequencies are caused by different motions of mass, and difference in the phases of the waves allow us to perceive the direction to the source and the shape of the matter that generated them. (Source: NASA-The Laser Interferometer Space Antenna (LISA).)
Citation
Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2008. "Gravity: Canonical Quantization." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published June 11, 2008].
<http://www.cosmosportal.org/articles/view/135635/>
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