Pedagoguery

In past columns, I have written about the fundamental conflict between general relativity and quantum mechanics. Perhaps no phenomenon exemplifies that conflict more than black holes. Here we have the essence of general relativity; a region of space where gravity is absolutely dominant, yet quantum effect can be quite important. Recently, a scientist name Chapline at Lawrence Livermore National Laboratory came up with an hypothesis that may fundamentally change the understood nature of black holes.

To fully understand Chapline's concept, we have to review black holes themselves as understood by general relativity. When matter is compressed to a particular point, defined by its mass and denoted the Swartzchild radius after the German physicist who first solved general relativity's equations for this case, something strange happens. The surface at the Swartzchild radius becomes a surface of infinite redshift – no matter or energy can escape to the outside from inside. Time and space change places inside that surface. By this, it means that the radial direction inside becomes timelike; you can only move in one direction along that dimension, and you cannot fully control your movement in that dimension. Just like normally, you move forward in time, and can control your “time velocity” only by moving faster or slower (to induce time dilation) in the other dimensions. Inside the black hole, you will move toward the center, the only question is how fast. For quantum mechanics, this is a problem, because quantum mechanics requires some kind of universal time. In a classical black hole, the time inside the event horizon is totally separate from that outside. Why does quantum mechanics require universal time? It is due to something called quantum entanglement. Let's say that there is a particle that decays into two photons. The photons are emitted in opposite directions and the quantum spins of the photons have opposite parity. Given these conditions, if you measure the spin parity of one of the photons, you instantaneously know the spin parity of the other. It doesn't matter if the other photon is half way across the universe – the information of its spin parity is instantly known to you. Einstein himself called this “spooky action at a distance.” But what is the concept of “instantly” if one of the photons got sucked into a black hole? The whole concept breaks down.

Another quality of black holes within general relativity is that they destroy information. Given a black hole, you can tell only three things about it: It's mass, its electric charge, and its rate of rotation. All other information that went into its making is lost. Destruction of information, however is a clear violation of quantum mechanics. In quantum mechanics, information can be transformed, but never destroyed. Stephen Hawking himself believed that black holes could destroy quantum information until recently, when he figured a way that the information could be “encoded” into the event horizon itself. In order to do this, he had to invoke quantum concepts, so our understanding of black holes has changed.

So, what did Chapline come up with? He first considered a form of condensed matter confined in a vertical tube. At a certain depth in this tube, the speed of sound in the material shrinks to zero. This is conceptually equivalent to an event horizon. So, he though, what if space is something akin to this condensed matter state? If subjected to enough stress, which the collapse process could easily do, perhaps it changes phase in some way, similar to how water can flash to vapor when subjected to enough heat. This other phase of space would be characterized by a vastly higher vacuum energy – one that would be high enough to counteract the gravitational pull of the collapsing matter, but not enough to reverse it. What is produced is a dark energy star.

The boundary between these two phases of space would have some unusual properties. Any particles above a certain energy threshold, which would include all quarks and gluons inside nucleons, which impact this surface, decay. A quark, for example, would decay into a positron and two antiquarks. The antiquarks would then annihilate with quarks inside the star, but the positron would be reflected back. Less energetic particles would fall through the surface, be bent around by the internal geodesic, and eventually thrown out in a different direction. An interesting observation is that this phenomenon would produce an excess of positrons from black holes. Such an excess is observed emanating from the core of our galaxy, where a super massive black hole is though to reside. Furthermore, the energy spectrum of these positrons matches closely with that predicted by this theory.

Another potential coup for this theory is a possible explanation for dark matter. If the normal state of space is close to the transition point to this high dark energy phase, it is possible that large quantities of microscopic dark energy stars were created in the primordial universe. If that is the case, they could easily have persisted to this day. Unlike microscopic black holes, they would not decay via Hawking radiation because the surface is fundamentally different from the event horizon of a black hole. So, these microscopic dark energy stars could easily constitute dark matter.

Is the theory correct? No one knows at this time. It has the advantages that it fully agrees with quantum mechanics, does not require any new fundamental particles, and explains the excess of positrons from the center of our galaxy. Beyond that, it is rather difficult to test, given the lack of black holes in our vicinity (something we should perhaps be thankful for). It remains an intriguing idea that we will perhaps be able to test one day.

Next issue I will talk about six common misconceptions about the big bang.