The idea of extra dimensions beyond the usual four is far from new.\u00a0 In the 1920s, Kaluza and Klein postulated an extra dimension in an attempt to unify the theory of gravity with electromagnetism.\u00a0 While not completely successful, the idea continues. Modern string theory requires 10 spatial dimensions to maintain mathematical consistency.\u00a0\u00a0 There are also attempts to use large extra dimensions to solve the hierarchy problem\u00a0 — the large ratio between the electroweak and Planck\u00a0 energy scales,\u00a0 which is manifested by the weakness of gravity in relation to the other forces.<\/p>\n
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\u00a0\u00a0\u00a0\u00a0\u00a0 In the standard approach to string theory, the extra dimensions exist as finite curled up (“compactified”) spatial dimensions with sizes on the order of the Planck length (10^-35 meters).\u00a0 In 1998, Arkani-Hamed, Dimopoulos and Dvali proposed that these could be as large as 100 microns to a millimeter, if ordinary matter (standard model particles) is confined to a three-dimensional\u00a0 membrane (or “brane”) within the multi-dimensional space (or “bulk”). The spreading out of gravitational field lines in the bulk would then explain the apparent weakness of gravity.<\/p>\n
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\u00a0\u00a0\u00a0\u00a0 Whether large or small, one can ask why the extra dimensions\u00a0 are the size that they are — why don’t they expand or contract like the ordinary\u00a0 dimensions?\u00a0 The usual answer is that there is some dynamical mechanism (vaguely specified) which stabilizes them.\u00a0 Whatever that mechanism, we should expect the size of the extra dimensions to respond, even if only slightly, to the presence of mass.\u00a0 Gravity and light (unless it is confined to a brane) propagating through space should ‘sense’ the changing size of the extra dimensions. This should cause phenomena such as bending or retardation of light or gravity waves.<\/p>\n
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\u00a0\u00a0\u00a0\u00a0\u00a0 The behavior of waves traveling through inhomogeneous extra dimensions will be investigated.\u00a0 An attempt will be made to use the results to constrain theories of extra dimensions.<\/p>\n","protected":false},"excerpt":{"rendered":"
Cameron McBride\u00a0 with Glenn StarkmanThe Propagation of Light and Gravity through Matter-filled Spacetime with Stabilized Compactified Extra Dimensions<\/p>\n
The idea of extra dimensions beyond the usual four is far from new.\u00a0 In the 1920s, Kaluza and Klein postulated an extra dimension in an attempt to unify the theory of gravity with electromagnetism.\u00a0 While not completely successful, the idea continues. Modern string theory requires 10 spatial dimensions to maintain mathematical consistency.\u00a0\u00a0 There are also attempts to use large extra dimensions to solve the hierarchy problem\u00a0 — the large ratio between the electroweak and Planck\u00a0 energy scales,\u00a0 which is manifested by the weakness of gravity in relation to the other forces.<\/p>\n