Abstract
TIPLER has given a new definition for a black hole1. These objects had previously been properly defined only in asymptotically flat spacetimes2, but it seems unlikely that our Universe is one of these. One of the well known properties of a black hole, proved in asymptotically flat spacetimes, is that its ‘surface area’ can never decrease. By means of this new definition Tipler has shown that this area theorem may well not be true in our Universe. However, Tipler's definition is complicated, and it is not obvious that it corresponds to our usual concept of a black hole. I show here that it is equivalent to a definition that is both simpler and more clearly a formalisation of what we mean by a black hole.
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References
Tipler, F. J. Nature 270, 500 (1977).
Hawking, S. W. & Ellis, G. F. R. The Large Scale Structure of Space-Time (Cambridge University Press, 1973).
Geroch, R. P., Kronheimer, E. H. & Penrose, R. Proc. R. Soc. A327, 545 (1972).
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LEE, C. Definition of a black hole. Nature 275, 725 (1978). https://doi.org/10.1038/275725a0
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DOI: https://doi.org/10.1038/275725a0
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