On 21st January 2014, David Garner led a discussion entitled "Firewalls". We debated the validity of conclusions drawn about black hole event horizons in the controversial AMPS paper.
The black hole information paradox arises from the observation that while pure states may fall into a black hole, Hawking radiation is a thermal ensemble of mixed states. Unitary evolution does not allow for pure states to evolve into mixed states. Therefore one must either reject unitarity or dismiss thermal Hawking radiation.
As the setting for a firewall discussion, one assume unitary evolution inside the black hole and (approximate) QFT in curved spacetime some distance outside the black hole. The firewall conjecture claims that these assumptions imply the existence of extremely high energy particles living on the event horizon. These would be invisible to an outside observer, but would burn any infalling objects to a crisp. AMPS argue that the early and late radiation from the black hole are entangled. The blueshift of the early radiation propagated backwards in time manifests itself as highly energetic later radiation.
The following resources are available.
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The following papers and blog post are useful background reading.
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