From: scerir (scerir@libero.it)
Date: Tue Mar 12 2002 - 00:51:20 MST
Dickey, Michael F
> Would the universe be curved in the absence of matter?
John Archibald Wheeler and Ignazio Ciufolini [1]
D.W. Sciama [2] and D.J. Raine [3] pointed out that
no solution of Einstein's field equation can give a
reasonable account (i.e. of inertia) if the geometry
nowhere displays an identifiable _center of mass_.
That's because without _other_ masses there is no way
to measure distances (and no way to define inertia).
But (ref. [1], p. 297] these days to think of material
masses as the ultimate primordial entity and space-time
geometry as derivative (from those masses) is wrong.
Space-time geometry, in and by itself, defines the location
of the mass, its velocity, its acceleration, the local
inertial frame, and therefore its inertia.
Thus there are models of 'empty' universes (just the mass-energy
of gravitational waves) in which, in example, there is gravitation
and also inertia (the Taub model [4]).
[1] in "Gravitation and Inertia", Princeton U.P., 1995, page 296.
[2] in "Physical Foundations of General Relativity", Doubleday,
London, 1969.
[3] in "Mach's principle and space-time structure", Rep. Prog. Phys.,
44:1152-1195 (1981).
[4] A.H. Taub, "Empty space-times admitting a three parameter group
of motions", Ann. Math., 53:472-490 (1951).
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