Thank you, Undidly and Bogle, for your comments. Following are my responses:

Undidly: You appear to believe that gravitation is caused by motion. It is not. It is fully accounted for by the field equations of Einstein's general theory of relativity. The presence of massive bodies distorts spacetime in their vicinity in a manner described by solutions to the Einstein field equations. This distortion in turn distorts the world lines of other bodies in the vicinity of the body causing the distortion. For example, it causes the planets of the solar system to orbit the sun in approximately elliptical paths.

Bogle: Your statement that "Take out the possibilites that are dependant on the coupling of space and time, i.e. GTR solutions that are not flat and all you have left is flat " is an example of circular reasoning. It is like saying that throwing away all of the items in a collection containing the item you want except the one you want will leave only the item you want, which is really too obvious to be worth mentioning, Would you like to try again to say whatever you were trying to say?

You asked, "How do we justify eliminating curved spacetime? The answer is that we cannot justify it. In fact WMAP measurements have been interpreted as eliminating it. My argument is I suspect that spacetime IS curved but so slightly that we have thus far not been able to detect the curvature.

You said, "Gravity has a cause. If we knew the cause, ---" We DO know the cause. See my second paragraph above, starting with "Undidly:".

Also, you seem to think that compressing a three-dimensional object can make it two-dimensional. Not true. No matter how thin you make a sheet of paper, it's still three-dimensional. A valid example of a two-dimensional object is a shadow: It has no thickness at all.