  Almheiri, Marolf, Polchinski, and Sully, recently claimed that once a black
hole has radiated more than half its initial entropy (the Page time), the
horizon is replaced by a "firewall" at which infalling observers burn up, in
apparent violation of the equivalence principle and the postulates of black
hole complementarity. In this paper I review the arguments for firewalls, and
give a slightly different interpretation of them. According to this
interpretation the horizon has standard properties, but the singularity is
non-standard. The growing entanglement of the black hole with Hawking radiation
causes the singularity to migrate toward the horizon, and eventually intersect
it at the page time. The resulting collision of the singularity with the
horizon leads to the firewall. Complementarity applies to the horizon and not
to the singular firewall.
  Almheiri, Marolf, Polchinski, and Sully conjecture that firewalls form much
earlier then the Page time; namely at the scrambling time. I argue that there
is no reason to believe this generalization, and good reason to think it is
wrong.
  For most of this paper I will assume that the firewall argument is correct.
In the last section before the conclusion I will describe reasons for having
reservations.
