donald (08/09/82)
Re: Doug's reply to my reply I am not arguing that "space" does not have physical properties or some sort of structure (although I suspect that arguments about the "structure" of space have all sorts of semantic ambiguities lurking in them). I'll ignore the messy question of what we mean by "space", "physical existence", and "real things", since I suspect what I mean is not what Doug means. However, the view espoused by Doug (I haven't read Davies' book) seems to harken back to the days when we believed that an absolute frame of reference: just replace "space" by "ether". In Newton's mechanics there is no absolute uniform motion, but there is absolute accelerated motion, because (it was argued) a spinning bucket of water has a concave surface, thus demonstrating that it is the bucket which is really spinning. Doug's interpretation of the inertial forces on the spinning ant (poor thing!) seem to imply absolute accelaration, since the wheel spins relative to the (absolute?) "structure of space". One of the ideas of General Relativity is to eliminate absolute accelarated motion, and it incorporates Mach's Principle to do this. The ant can be viewed as in an accelerated frame in which the radial pull experienced by the ant is due to centripetal force due to the spinning wheel. Alternatively, the ant and wheel can be viewed as a nonaccelerated frame by considering the wheel to be still and the rest of the universe spinning. The gravitational field generated by the rest of the universe spinning causes the radial pull on the ant. Both these views are exactly equivalent according the the Prin- ciple of Equivalence in the General theory. The inertial forces are not caused by the wheel spinning relative to "space itself". I don't know the context in which Doug quoted Davies' book, but the above explanation is the one you'll find in any relativity text. Perhaps Davies mentions it somewhere? Don Chan