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**Finkelstein's "unidirectional membrane" paper**

The "unidirectional membrane" interpretation of black-hole event horizons originated with this paper:

Finkelstein, Phys. Rev. 110, 965–967 (1958), "Past-Future Asymmetry of the Gravitational Field of a Point Particle," downloadable from his web page at https://www.physics.gatech.edu/user/david-finkelstein

The basic idea is that if you impose a bunch of reasonable conditions on the Schwarzschild spacetime, and try to eliminate all coordinate singularities, you have to break time-reversal symmetry. This was a point that I hadn't understood properly before -- I'd thought that the Schwarzschild spacetime was time-reversal symmetric, as it appears to be when you write the metric in the Schwarzschild coordinates.

I have a few questions about the paper:

1. He seems to be claiming uniqueness of the solution, but I don't see where he proves that...? He uses the term "analytic," and certainly for an analytic function defined in part of the complex plane, any analytic extension to the whole plane is unique. But this is calculus on a manifold, so ...?

2. He describes two classes of spacetimes that differ by time reversal, and speculates that "it is possible that the gravitational equations imply that all particles in one universe belong to the same class." Was his conjecture right? He also speculates about particle-antiparticle interpretations...was there any validity to that?

3. He ignores negative-mass solutions. Is there any other physical ground for ignoring them, besides the fact that they would violate energy conditions? I guess they couldn't form by collapse of known forms of matter. Could they conceivably have been produced in the Big Bang?

Thanks in advance!

-Ben