The Einstein field equation is inconsistent unless we demand a divergence-free stress-energy tensor. This makes me think that Hoyle's steady-state cosmology is inconsistent with general relativity. But Hawking and Ellis has this at p. 90: I had always imagined that the C field was just some vague hand-waving by Hoyle. Is it really a field theory? Is everything perfectly OK in classical relativity if we allow such a field? Quantum-mechanically, is there really a reasonable field theory with such a field? I'm imagining a Dirac sea that isn't full. Not sure what state you would refer to as the vacuum. Are we talking about doing quantum mechanics with a spectrum of energy states that isn't bounded below? Don't Bad Things happen then? If we're creating negative-energy C-field quanta in the steady-state theory, where do they all end up? Can we detect them? Don't their gravitational fields cancel out the gravitational fields of the hydrogen atoms being created?