Publications

Abstract

Slowly rotating collapsing spherical shells have flat spaces inside and the inertial frames there rotate at relative to infinity. As first shown by Lindblom and Brill the inertial axes within the shell rotate rigidly without time delays from one point to another. Although the rotation rate of the inertial axes is changing the axes are inertial, therefore relative to them there is neither an (Euler) fictitious force nor any other. However, Euler and other fictitious forces arise in the frame which is at rest with respect to infinity. An observer at the centre who looks in one direction , say) fixed to infinity will see that the sky appears to rotate and can compare its apparent rotation with that of the local inertial frame and of the shell itself. In contrast, in the electromagnetic analogue there is a time delay in the propagation of the magnetic field inside a rotating collapsing charged shell in flat space. We demonstrate this time delay by devising a null experiment in which the Larmor precession of a charged oscillator would be exactly cancelled by the rotation of the inertial frame but for the delay. In the `combined' problem of a collapsing charged shell we show that, due to the coupling of electromagnetic and gravitational perturbations, the instantaneous rotation of inertial frames inside the shell can be caused by pure electric currents in a non-rotating shell.