theoretical physicist; Professor, Department of Physics, University of California, Santa Barbara
Crisis At The Foundations Of Physics

What really keeps me awake at night (besides being sued by an unprincipled water developer in Utah—another story) is that we face a crisis within the deepest foundations of physics. The only way out seems to involve profound revision of fundamental physical principles.

But I'll begin the story with something I believe we shouldn't worry about—"firewalls," a radically deviant picture of black holes recently advocated by colleagues, in which an observer falling into a black hole burns up right at the horizon. The firewall picture—really a clever renaming of a previously known phenomenon—has provoked some recent controversy, which has begun reaching the press. If correct, it could well mean that the black hole at the center of our galaxy is not a black hole at all: instead it is the firewall at the center of the galaxy, and instantaneously destroys anyone or anything who ventures within about 12 million kilometers of its center.

I'm not worried this scenario is correct because it is too preposterous and removed from known physics, and I believe there are less preposterous alternatives. But, the fact that otherwise serious physicists have forwarded it is definitely symptomatic of the profound crisis that we face.



While serious people still consider modifying quantum mechanics, so far proposals to do so create much bigger problems. For example, it has been argued that Hawking's original proposed modification of quantum mechanics would imply a "firewall" exists for all observers, everywhere! Quantum mechanics appears to be remarkably resistant to sensible modification.


The basic statement of locality is that quantum information cannot propagate faster than the speed of light. At least as early as 1992, modification of locality to solve the problem of getting missing quantum information out of a black hole was proposed. Then, in the following years, a picture involving an even more radical form of nonlocality took shape. This picture was based on the holographic principle, and a new notion of complementarity, proposing that observations inside and outside a black hole are complementary in analogy to Bohr's complementarity of position and momentum measurements in quantum mechanics. Holography/complementarity were widely explored, and became accepted by a significant segment of the physics community.

What has become clear, in the past few years, is that a picture based on complementarity is not only apparently unnecessarily radical, but also likely inconsistent. While the jury of the physics community may still not have a final verdict on complementarity, new awareness of its apparent downfall has rekindled broader interest in the deep crisis that we face.

In a context where one or more supposed bedrock principles must be discarded, we obviously need to be a little crazy—but not too crazy! Complementarity is an extreme, and plausibly inconsistent, form of nonlocality. On the other hand, if quantum mechanics is to be saved, by allowing nonlocality inside a black hole, but you accept that quantum field theory holds everywhere outside a black hole, you encounter the firewall problem. Is there a less-crazy alternative? I believe so, in the form of a more "nonviolent" nonlocality that extends outside what we would describe as the black hole horizon, and transfers quantum information out. I say "would describe," because the horizon concept makes reference to a classical spacetime picture, which may well not be fundamentally correct. More could be said, but describing such nonlocality would violate editorial marching orders of this forum.

