Institute for Advanced Study Astrophysics Seminar

It is quite simple to build a Newtonian dynamics without Newton's absolute space which nevertheless gives exactly the same relative motions of the bodies as Newton's dynamics when the latter is applied in a non-rotating Universe like ours. The small Machian effects discovered in General Relativity by Einstein have now been worked out even when the effects are strong. However they are not just due to matter and its motion. The energy and angular momentum of swirling gravitational waves can accelerate and rotate the inertial frame far from the wave itself just as the energy and angular momentum of a rotating shell of matter rotates ('instantaneously'!) the inertal frame in the flat space far inside it. Gravitational waves have no matter tensor; thus the matter tensor in the Universe is not the only source of inertia; it is energy, not matter, that matters. Arguments are given suggesting that space-time may disappear as its energy content is removed. In the presence of a lambda term this only works if the value of lambda depends on some positive power of the energy content of the Universe rather than being a fundamental constant.