Abstract
The central challenge in trying to resolve the firewall paradox is to identify excitations in the near-horizon zone of a black hole that can carry information without injuring a freely falling observer. By analyzing the problem from the point of view of a freely falling observer, I arrive at a simple proposal for the degrees of freedom that carry information out of the black hole. An infalling observer experiences the information-carrying modes as ingoing, negative energy excitations of the quantum fields. In these states, freely falling observers who fall in from infinity do not encounter a firewall, but freely falling observers who begin their free fall from a location close to the horizon are ``frozen'' by a flux of negative energy. When the black hole is ``mined,'' the number of information-carrying modes increases, increasing the negative energy flux in the infalling frame without violating the equivalence principle. Finally, I point out a loophole in recent arguments that an infalling observer must detect a violation of unitarity, effective field theory, or free infall.
Highlights
The firewall paradox introduced by Almheiri, Marolf, Polchinski, and Sully (AMPS) [1] is a wonderful tool for sharpening our understanding of black holes
Note the minus sign: a freely falling observer sees a negative energy density relative to Minkowski spacetime. Such negative energy densities are known to be possible in quantum field theory [3] and have been constructed in simple examples
I have pointed out what I believe is a significant loophole in the arguments that the infalling observer must detect a violation of unitarity, effective field theory, or free infall
Summary
The firewall paradox introduced by Almheiri, Marolf, Polchinski, and Sully (AMPS) [1] is a wonderful tool for sharpening our understanding of black holes. In order to use these states to avoid the firewall paradox, one must assume that most degrees of freedom in the zone of an old black hole are entangled with the stretched horizon rather than the early radiation. The data at large r can be evolved in all the way to the angular momentum barrier, but not into the zone This is a strong motivation to consider more carefully an essential feature of the AMPS argument: evolving back the outgoing Hawking radiation in order to obtain information about the quantum fields near the horizon. We encounter a different obstacle to stating the AMPS paradox: at least for a wide class of black holes, the behind-the-horizon partner of a mode with definite angular momentum does not fit into any single causal patch. I argue that the old, simple idea that any given observer can have it allunitarity, the equivalence principle, and effective field theory- is not yet ruled out
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