Unitary evolution makes pure state on one Cauchy surface evolve to pure state on another Cauchy surface. Outgoing Hawking radiation is the only subsystem on the late Cauchy surface. The requirement that Hawking radiation should be pure amounts to requiring purity of the subsystem when the total system is pure. We will see that this requirement will lead to firewall even in flat spacetime, and thus is invalid. Information is either stored in the entanglement between field modes inside black hole and the outgoing modes or stored in correlation between geometry and Hawking radiation when singularity is resolved by quantum gravity effects. We will give a simple argument that even in semi-classical regime, information is (at least partly) stored in correlation between geometry and Hawking radiation.

中文翻译：

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重访信息丢失悖论：告别防火墙？

酉演化使一个柯西面上的纯态演化为另一个柯西面上的纯态。传出的霍金辐射是晚柯西表面上唯一的子系统。当整个系统是纯的时，霍金辐射应该是纯的要求相当于要求子系统的纯。我们会看到，即使在平坦的时空中，这个要求也会导致防火墙，因此是无效的。信息要么存储在黑洞内部场模式和出射模式之间的纠缠中，要么存储在几何和霍金辐射之间的相关性中，当奇点被量子引力效应解决时。我们将给出一个简单的论点，即即使在半经典状态下，信息（至少部分地）存储在几何和霍金辐射之间的相关性中。