A Brick Wall?

There are two more possibilities worth pointing out. One is that the horizon is not penetrable. In other words, from the viewpoints of an infalling system, the horizon bounces everything out. A freely falling observer would encounter a “brick wall” just above the horizon.

The reason that this was never seriously entertained, especially by relativists, is that it badly violates the equivalence principle. Since the near horizon region of a Schwarzschild black hole is essentially flat space-time, any violent disturbance to a freely falling system would violate the second law of nature in the Introduction. Even more convincing is the fact that the horizon of a black hole formed by a light-like shell forms before the shell gets to the center.

Finally, the quantum Xerox principle closes out the last possibility. The information conservation principle requires all information to be returned to the outside in Hawking radiation. The equivalence principle, on the other hand, requires information to freely pass through the horizon. The quantum Xerox principle precludes both happening. In other words, the horizon cannot duplicate information, and send one copy into the black hole while sending a second copy out. Evidently we have come to an impasse. It seems that some law of nature must break down, at least for some observer.