From David Giles
Of course the Universe is spinning! Every free-floating particle or celestial body or galaxy is rotating, and I hope no one these days would ask the question asked by Ernst Mach in 1893, “relative to what?” (13 July, p 17).
An accelerometer attached to a spinning flywheel would show an acceleration – the spring pulling inwards to stop the weight flying off tangentially. The flywheel could be in deep space with no visible reference point.
Don, Tasmania
