George Chapline just gave the most provoking and most bizarre colloquium we have seen at Harvard for years. (I guess that the talk would not be bizarre enough for Quantoken and perhaps not even for Arun, and I apologize if they will be disappointed by the amount of strangeness.) Chapline used to be a T.A. for Feynman's lectures, he was awarded by various awards, but his goal right now is to revolutionize our understanding of the strong gravitational fields.
His talk was based on various papers such as
Chapline admitted that every time he was giving a talk, people would think that he had lost his mind. This was the case until 2000 or so when he met Robert Laughlin who agreed with Laughlin completely. There is a difference however: Laughlin is a Nobel prize winner who became a big shot in condensed matter physics while Chapline is a field theorist. From an outsider such as Laughlin, some comments simply may sound a bit less embarassing because everyone knows that Laughlin just tries to extend his incredible success from condensed matter physics where he has achieved everything he could to completely different fields of human activity.
(I guess that many readers of mine have heard the rumors about a similar black hole talk by Laughlin at Stanford. Lenny Susskind jumped on him and defended rigorous and established physics vehemently. Thanks, Lenny.)According to the conventional wisdom of general relativity, a sufficiently massive object - even a sufficient amount of water - is guaranteed to collapse and nothing can prevent the black hole from being formed. The causal structure of spacetime is such that a horizon eventually appears. However, when the star is collapsing, it is absolutely unclear where the horizon actually is. We can only determine the position of the horizon - and divide the regions of space to the "interior" (the dark blue triangle on the figure below) and the "exterior" - if we know the future (which we can't know in advance).
Imagine that you draw a horizontal line (time slice) roughly 3 millimeters above the red word "horizon" in the figure. No one knows where the red line (the horizon itself) should be drawn. If you hide the future (the upper portion of the figure), you just don't know the difference between the interior and the exterior. The local physics near the horizon is otherwise completely indistinguishable from a regular piece of space. This is why nothing special may be happening near the horizon during the early stages of the existence of the horizon - unless you want to violate the rules of causality in the most drastic fashion.
(Jacques Distler just came to my office and told me the very same statement, including the Penrose diagram I can't draw for you so I will borrow it from France. Jacques could not resist and he wrote a very illuminating article about the same subject.)
Chapline's picture is very, very different. Let me highlight some of his basic points:
- He can't stand the idea that the role of space and time is somewhat reversed inside the black hole, and therefore it must be wrong, he thinks. (The "exchanged role" is just about the isometries that indeed become spacelike in the interior, and there is nothing paradoxical about it.)
- General relativity is incorrect, and Chapline uses the paper of Gödel as well as another, older, less famous paper to argue that GR is wrong and Einstein could have known it. (The closed time-like curves can't be formed because of other reasons even though the solution exists.)
- General relativity is also "inconsistent with quantum mechanics". (Don't expect some fancy arguments about string theory and loop divergences - the "problem" with GR is that it does not have a unique universal time which Chapline believes to be necessary for quantum mechanics. Well, it's not.)
- The component g_{00} of the metric, for example, can't continuously switch to the opposite sign as you cross the horizon. Instead, the decrease stops and bounces back. The behavior in the 1-inch vicinity of the would-be horizon is described by a highly quantum low-temperature quantum critical phenomenon. (This special treatment of the horizon violates causality and relativity, as explained above.)
- Consequently, horizons don't exist and black holes can't exist either; they're replaced by the "dark energy stars". (I am actually intrigued by the analysis of "nearly black holes" etc. but their properties are very different from those of Chapline's.)
- This also means that no gravitational collapse can ever end up as a black hole, and all collapses look like an explosion of supernovae which, Chapline believes, is supported by observations. (There are many objects that are almost certainly known to be black holes.)
- What about the black hole that we observe at the galactic center, for example? Chapline points out that the 511 keV lines show a lot of annihilation of electrons and positrons over there, and he argues that this confirms his model in which the dark energy star transmutes protons into positrons. (In reality, the radiation agrees with the models of a black hole sucking the stuff around.)
- All the effects associated with the black holes may be reproduced if we replace the speed of light by the speed of sound. One may study condensed matter systems where the speed of sound goes to zero and time stands still, and he proposes to create such a black hole in the laboratory.
(Incidentally, a Czech philosopher and the chairman of Mensa Czechoslovakia and Miss Internet Czech Republic Mr. Jan Fikáček has hypothesized that we only use the speed of light in special relativity because we prefer the vision over hearing. Blind people, he argued, would probably prefer to use the relativity of sound instead in which "c" stands for the speed of sound. Unfortunately, this independently thinking colleague of ours has not explained whether the blind people are allowed to use supersonic airplanes.)
In other words, Chapline did not like the idea about the horizon being a regular place in space. He did not explain how he wants to modify the laws of physics in such a way that his new critical behavior replacing the horizon suddenly turns on. He also sketched his condensed matter system where the speed of sound goes to zero and asked what happens. Bert Halperin answered but my guess is that during his next lecture, Chapline will repeat his remark that no one at all the famous universities he will have visited knew the answer.
Chapline also hates the idea that the black holes emit the Hawking radiation, and that the neutral ones have negative specific heat. In order to show that the string theorists are the only physicists today who take this important piece of physics seriously, he argued that the string theorists never read Kittel's book (I suppose it is either Elementary Statistical Physics or Introduction to Solid State Physics) because otherwise they would have known from page 11 that a negative heat capacity is impossible.
Well, the reality is that the negative heat capacity is only impossible for stable forms of matter that can live in thermal equilibrium. Black holes are gravitational examples of unstable objects that decay via the Hawking mechanism, but there also exist non-gravitational examples. The thermal equilibrium in general is not possible in the gravitational context - because of the Jeans instability.
While I am open minded about new subtle and possibly non-local and acausal physical phenomena that may happen below the black hole horizon (and that may be instrumental to resolve the black hole information paradox) a long time after the black hole becomes "stabilized", in terms of Schwarzschild's coordinates, I am not open minded about the causal structure of spacetime before the black hole is fully formed, and about the counting of the black hole thermodynamic parameters.
The causal structure is guaranteed by the rules of special relativity that have been tested in detail - and for which there are no good reasons to violate them in a drastical way. And the temperature and the entropy were first calculated by Hawking who followed Bekenstein, but then they were also reproduced by completely independent methods from the microscopic counting of string theory - a calculation that was definitely not guaranteed to give the same results but it did. That is a pretty strong double argument.
Someone asked whether Chapline's new picture of the black hole also requires one to alter the membrane paradigm by Kip Thorne, in which the horizon is viewed as a superconducting membrane, and the answer was that the speaker did not know what the paradigm was.Reductionism and emergent phenomena
This may be a good context to mention another topic: the relation between condensed matter physics and fundamental physics, if you allow me to call it this way. In other words, the cold war between reductionism and the emergent phenomena. What do I think about it?
First of all, the emergent phenomena are great, they definitely exist, and their understanding is important for our correct qualitative - and in most aspects also quantitative - description of lots of the phenomena we observe. Also, the insights and methods used in condensed matter physics often become important in particle physics and most of us must learn many of them in one way or another.
On the other hand, we can and we should always ask what is the mathematically and quantitatively exact description of what we're doing. We can always ask what is the truth once we're unsatisfied with any kind of qualitative, fuzzy argument. If gravity is an emergent phenomenon - and of course, in string theory it is emergent to a large extent - we should always ask what is it emerging from.
If we try to deepen our understanding, we always inevitably end up with some kind of mathematically sharp theory. In the case of quantum gravity and particle physics, the previous sentence is equivalent to the well-known fact that all roads lead to string theory, a mathematically sound and unique combination of the methods from quantum field theory and general relativity. The statement that the phenomena we observe are "emergent" is always superficial in nature and it cannot be the final answer, by definition. Such a statement may be compatible with a partial understanding of the important aspects of the truth, but it is incompatible with the search for the ultimate and exact truth itself.
The emergent phenomena have their important role in the scheme of things, but the very words "emergent phenomena" can't be used as the ultimate answer to any exact enough question.
Gravity from condensed matter physics
A particular example of the application of "emergent phenomena" beyond the realm of their validity was the attempt to explain gravity as an emergent phenomenon based on some spin-2 bound states of quasiparticles near the Fermi liquid - the type of work that was done by Zhang and others. In reality, the existence of such bound states was never really justified, and if there were any evidence that such bound states could have existed, such arguments would have allowed not only for the spin-2 "gravitons" but also for higher-spin particles that simply should not exist.
There are many theorems that show that gravity can't be constructed in one way or another, that the interactions are incompatible with higher-spin gauge symmetries, and all things like that. Such no-go theorems are sometimes circumvented by string/M-theory, but it always involves a non-trivial feature of string/M-theory that was not anticipated before and that violates some of the more or less hidden assumptions.
All these vague arguments about gravity being constructed as a solid state system only existed at the level of free particles and there were never hints that the interactions of these particles shall reproduce general relativity. Given the fact that the very reason for introducing gravity is that it is an interaction, the failure to reproduce the interactions is pretty serious.
But even a priori, is there any reason to believe such pictures and pursue them? I think that the primary motivation for such attempts is to satisfy our old instincts that everything, including the most mysterious objects such as those in high-energy physics and quantum gravity, must eventually be "made" of the things we know from the everyday life such as water, wine, bread, and butter.
These objects are macroscopic, slow, low-energy, and with the exception of wine, they are also predictable and deterministic.
In my humble opinion, this approach may be good to entertain ourselves and our non-physics friends, but it is a misguided approach to theoretical physics - and I don't mean just fundamental physics right now but any physics that transcends our everyday lives - simply because theoretical physics has become less intuitive and more mathematically abstract, and it had to be so. And it will be so in the future. And it is one of the symptoms of a true conceptual progress. The humans have been trained to comprehend phenomena associated with classical, non-relativistic, low-energy physics - and it should not be unexpected that the intuition fails if we try to understand quantum, relativistic, high-energy, unusual phenomena that go beyond the realm of validity of our naive approximations.
