I know that gravitational energy is a delicate topic in GR. It is true that the localisation of gravitational energy is not possible in GR but it should at least be possible to determine correctly the sign of the gravitational energy. I found the following article in arxiv.org, nl http://arxiv.org/PS_cache/gr-qc/pdf/0508/0508041.pdf in which it is mentioned that "it is known that gravitational energy is negative". Does someone know of a refereed paper or book where this is explained ? I would expect the gravitational energy to be positive. The energy carried by gravitational waves should also be positive, otherwise a rotating star system would speed up instead of slowing down when emitting gravitational waves. Also, if it were negative, one should expect some sort of antigravity effect with all kinds of strange consequences. Further, does someone know of a refereed paper or book where the total energy in the (static) gravitational field is calculated correctly ? According to Noether's theorem it should be possible to find a definite and clear answer to this.