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Susskind wrote:
"Gerard and I had been talking on and off about black holes for a number of years by 1994. He and I seemed to be the only two people who were completely convinced that the basic quantum laws of information and entropy must be respected by black holes. Although I am sure we agreed about the substantive issues, we tended to think a little differently. Gerard wanted to think about it from an S-matrix point of view like in quantum field theory. He wanted to construct a unitary S-matrix that would evolve an in-going state to an out-going state on the horizon of a black hole. I certainly agreed that an S-matrix should exist but it seemed to me hopeless to actually compute it. I thought that trying to construct an S-matrix would be a lot harder than discovering the underlying microstructure. I had formulated the idea of Black Hole Complementarity which stated that from the outside perspective, the (stretched) horizon of a black hole is composed of microscopic degrees of freedom that absorb, thermalize, and re-emit all information. But I had also argued that from the infalling point of view, the horizon was just empty space with no special properties. Think of an observer in a free falling elevator: as long as the elevator is freely falling, and up till the point when it hits the ground, she won’t be able to tell the difference between the laws of physics inside the small elevator and those inside a space-ship out in space. So will, for an observer who is freely falling into a black hole, and up till the point when she is crushed by tidal forces or absorbed in the singularity, the physics around her be the physics of empty space. Yet we know that for an observer who stays outside or is trying to escape from the black hole – like in an accelerator that is going up –, the region near the horizon is strongly gravitating and in fact it has membrane-like properties like an electric surface resistivity of 377 ohms and viscosity. I argued that the discrepancy of the two different descriptions is only apparent – only in the case that we think in terms of some superobserver, who somehow has access to both the freely falling and the accelerated system near the black hole, do we get any contradictions. That such a description should be precluded is what I called Black Hole Complementarity. Like in quantum mechanics, where we can’t measure both position and momentum at the same time without disturbing the system, we can’t measure both the inside and the outside of the black hole without using signals of an energy of the order of the Planck scale. This way Black Hole Complementarity argues that the two seemingly contradictory views can be reconciled, if we just agree on which observable we decide to measure."
OK, at first sight the above is very plausible. However, there are some conceptual problems.
1) Alice is LIF (Frefo) and Bob is hovering static LNIF (Fido) and they are momentarily locally coincident just outside the horizon of a simple SSS black hole.
Alice is freely floating on a timelike geodesic with zero covariant tensor 4-acceleration.
Bob has his rocket engines firing and is standing "still" in curved spacetime with a g-force
g(r) = (c^2rs/r^2)(1- rs/r)^-1/2 ---> infinity as r --> rs+
r = rs + &r
&r/rs << 1
Bob sees blackbody radiation at Unruh temperature
T(r) ~ hg(r)/ckB
Indeed, Bob will catch fire from the intense heat.
Suppose Alice is very close, won't she catch fire also - I mean with a substantial probability the closer she is to Bob?
Of course Alice will see tensor fields that won't vanish if they don't vanish for Bob.
Alice sees tensor/spinor fields that are the tetrad map image of Bob's tensor/spinor fields.
Therefore, what Lenny says that Alice will only see empty space may not be true at all!
Einstein's Equivalence Principle does not demand that Alice see nothing unusual at the horizon. She will see Bob catch fire and die. She may catch fire herself.
She may never be able to pass through the event horizon at all? - we need to study this more carefully.
Suppose the virtual electron-positron plasma is stuck to the event horizon like so many tiny FIDOs they will then see Unruh radiation enough to make them jump from virtual to real pairs in a real electron-positron plasma that obviously Alice will also see.