tailieunhanh - The Philosophy of Vacuum Part 7

The Philosophy of Vacuum Part 7. Physicists will find it extremely interesting, covering, as it does, technical subjects in an accessible way. For those with the necessary expertise, this book will provide an illuminating and authoritative exposition of a many-sided subject." -John D. Barrow, Times Literary Supplement. | Reflections on Ether 53 critique of ether runs something as follows considering the ether not as a single privileged frame but as a privileged class of frames the local inertial frames this ether enters into the causal nexus of the world it determines the kinematics of mass-energy distributions and is determined in turn by these distributions. In field theory the ether of mechanics is the metric tensor or perhaps it is the Ricci curvature in either case it is a tensor field. But what is of interest is that it is not a local field quantity in the sense of electromagnetism or any other particle fields for there is no reasonable definition of a local distribution of stress-energy. The tendency to read into general relativity a theory of physical fields is in conflict with the geometric basis of the theory. Einstein was fully aware of this difficulty. Shortly after his completion of the general relativity he attempted to define conservation laws for total energy and momentum in the process Einstein 1916 he was led to a local stress-energy tensor for the gravitational field as opposed to other particles or fields that might be present which was not a tensor density. Subsequently it was recognized that this stress-energy was indefinite and that all its components could be given arbitrary values at a given point Einstein 1918 . There were many motives for attempting a synthesis of gravity and electromagnetism the peculiar circumstance that neither the ether of mechanics nor the c-number fields of light in a singularity-free domain admits a reasonable definition of a stress-energy tensor could only have reinforced Einstein s conviction that the synthesis was necessary. Each appears the key to the other geometry determines the meaning of space-time relationships and the quantum theory governs the localization of energy. We know well enough that Einstein laboured on this task for the rest of his life. In effect he took the residue from the first-quantized ether what remains