For three days in April, 2005, I was a speaker and panelist at the NASA-sponsored “Physics for the 3rd Millennium II Conference” in Huntsville, Alabama, where twelve of us, including two Nobel Laureates, were invited to give 50-minute lectures about cutting-edge physics to an audience of NASA engineers, teachers, students, parents, and other interested attendees. In this column, I want to tell you about the work described in one of the talks, given by Dr. George Chapline of the Lawrence Livermore Laboratory.
The issue that Chapline addressed had previously been brought into sharp focus in a science fiction story, Poul Anderson’s widely reprinted “Kyrie”, in which an intelligent energy-being falls into a black hole while in telepathic contact with a nun in a nearby spaceship. Near the event horizon of the black hole where time stops due to gravitational time dilation, the being is trapped in agony, presumably for all eternity.
If a collapsing star has enough mass, the star cannot be stabilized by repulsion from the strong interaction, and so it collapses to a black hole. According to Einstein’s general relativity, as one approaches such a collapsed star, the increasing gravity field causes time to slow down until, on a surface called the “event horizon,” time stops altogether and an infalling object “freezes” there. Curiously, the general relativity description of a fall through the event-horizon depends on the situation of the observer. As viewed by an outside observer, time effectively comes to a halt for the infalling object, so that it appears to freeze at the event horizon. However, from the viewpoint of the unfortunate observer who is falling through the event horizon and into the black hole, nothing unusual happens as the event horizon is crossed except that contact with the external universe is cut off.
Chapline argues that it is unreasonable that time comes to a halt in the external reference frame, while producing no observable consequences in the infalling observer’s frame. He suggests that quantum effects should become important near the event horizon.
This suggestion goes against the conventional wisdom. Since the 1950s, there has been a general agreement among the physicist practitioners of general relativity that quantum effects should become significant only at very small distance scales, and that quantum mechanics can be comfortably ignored elsewhere. Chapline raises objections to this rule. He argues that the infinite time dilation at the event horizon of a black hole creates a situation in which quantum effects are needed, even though it is a macroscopic system. Further, he points out that quantum mechanics (which in its current formulation is not compatible with general relativity) requires some universal time standard, so that clocks can be synchronized and cross-referenced everywhere in a system. The behavior of time near the event horizon prevents such synchronization. If general relativity tries to stop the clocks, Chapline argues that quantum mechanics will “fix” this problem by producing a phase transition in the infalling matter as the event horizon is approached.
To decide what should happen when quantum mechanics takes over, he considers an analogous situation, well described by quantum mechanics, which occurs in a vertical column of superfluid helium that has more pressure at the bottom than the top of the column due to the weight of the upper liquid. In such a situation, there is some particular vertical height at which the speed of sound in the liquid goes to zero. The sound waves encountering this zero-sound-velocity “barrier” should behave in a way that is analogous to the black hole situation in which the infalling particles attempt to cross the infinite time dilation barrier.
In the superfluid case, when the sound waves come within a critical distance of the barrier, two things happen. First, the relation that the product of frequency times wavelength equals wave speed breaks down, and second, waves above a certain frequency become unstable, and their energy is dissipated in the liquid. Chapline suggests that a similar scenario should happen near the event horizon, and that in particular, the infalling particles, as they approach the event horizon, will become unstable. First the heavy particles like protons will decay into lighter particles like positrons and mesons, and then the quarks and leptons themselves will dissipate into the vacuum, raising the energy of the vacuum as they become “dark energy.” In other words, he hypothesizes that inside the event horizon, there are no particles, but only a dark-energy region where the cosmological constant is much larger than it is in the external world.
As we have discussed in previous columns (for example, “Our Runaway Universe and Einstein’s Cosmological Constant”, Analog, May 1999), in general relativity, the dark energy of the vacuum creates a negative pressure that drives the accelerating expansion of the universe. Behind the event horizon, in Chapline’s scenario, the accumulating dark energy would create a large negative pressure that stabilizes the star, so that it never becomes a black hole, as that label is presently understood. Instead, the collapsed object becomes a dark-energy star.
Therefore, according to Chapline, there are no black holes in our universe, only dark-energy stars that contract to some definite size at which they are stabilized by the negative pressure of the dark energy inside. This provides a new mechanism that prevents a collapsing star from progressing all the way to an information-destroying singularity. Instead, the phase change to dark energy would produce a stable system of finite size, with no singularities to worry about. Further, the supposed “evaporation” of black holes by the Hawking radiation process (which has never been observed) does not happen, because the quantum processes manifest themselves in a different way. It’s also interesting to note that the supposed thermodynamic connection between string theory and the surfaces of black holes, which has recently been publicized as a great triumph for string theory, may be based on questionable physics.
Is there any evidence that the Chapline view of collapsed stars is correct? Perhaps so. There have been several space-based X-ray and gamma ray telescopes launched in recent years, and the resolution and sensitivity of these instruments has been improving, year by year. When these instruments look in the direction of our galactic center, they observe a remarkable and puzzling thing. There is a stream of antimatter electrons, the so-called “Positron Fountain,” coming from the galactic center region and producing a large quantity of 511-keV annihilation radiation there. This is probably related to another observation, of the population of charged particles in cosmic rays, which show that above a certain energy (~500 MeV) there is a definite excess of positrons over electrons in the population of charged particles reaching the solar system. These preferences for positrons are a mystery, since fundamental interactions, e.g. electron-positron pair creation, produce matter and antimatter electrons in an even-handed way, favoring neither one nor the other.
Chapline suggests that these positron-favoring phenomena are the result of enhanced proton decay as the particles become unstable near the event horizons of dark-energy stars. In the 1980s, there were predictions from grand unified theories that the proton might be intrinsically unstable, and that in the fullness of time it might decay, for example, to a positron and one or more pi mesons. Subsequent experimental attempts to observe such decays have failed, thereby falsifying the simplest versions of grand unification theories and setting fairly low upper limits on the probability that a proton might decay in vacuum. However, in the vicinity of an event horizon, Chapline suggests that the decay rate of the proton is greatly enhanced, so that there is a much higher probability of proton decay. Some fraction of the positrons from such decays, particularly those with high energies, should escape the strong gravity field of the collapsed star, perhaps accounting for the observed positron cosmic ray abundance and the positron fountain at the galactic center. Chapline also makes the case that destabilization of infalling matter could account for the energy distributions observed in gamma ray bursts.
Chapline further suggests that the dark matter in our universe might be an artifact of the same physics. Perhaps our normal vacuum is already close to the quantum transition point between normal vacuum and the dark energy continuum, with dark matter showing up in the vacuum because of the close proximity to the transition conditions. His papers are not specific enough to convince me that this would have the properties needed to account for the concentrations of dark matter near galactic clusters, but it’s an interesting idea.
However, we might ask whether all of the recent publicity about the “observation” of black holes at the centers of our own and other galaxies contradicts these ideas. Doesn’t the observation of black holes preclude the existence of dark-energy stars?
No, it doesn’t. The label “black hole” is now conventionally attached to any collapsed astronomical object heavier than a neutron star. The observations mentioned concern the accelerations of nearby stars and the existence of an accretion disk around the objects. Necessarily, there is no observational evidence of what lies inside the event horizons of the objects. Thus, the astronomical observations would be consistent with either a black hole or a dark energy star.
Since this is a science fiction magazine, let’s suppose that Chapline is correct and consider the SF implications of his new twist on collapsed stars. First, all the SF that involves penetrating through the event horizon of a black hole is invalidated. For example, Fred Pohl’s Heechee in his Gateway series would not have been able to burrow behind the event horizon of an assembled low-tidal-force black hole, because when they approached the horizon, the Heechee populace would be converted into dark energy.
But it does bring up some interesting questions. Suppose that by some mechanism (a wormhole?) one could reach the interior of a dark-energy star. How does the flow of time work inside the event horizon? Would the interior be a completely hostile environment? Could matter exist inside, if it didn’t have to come in through the event horizon? Would the high cosmological constant there induce a “Big Rip” in any matter present? Would the laws of physics there be those we understand? Could one “drain” the accumulated dark-energy through a wormhole and use it as an inexhaustible energy source?
Perhaps, if Chapline’s ideas can withstand observational tests and theoretical scrutiny, we may learn the answers to some of these questions.
AV Columns Online: Electronic reprints of over 120 “The Alternate View” columns by John G. Cramer, previously published in Analog, are available online at: http://www.npl.washington.edu/av. The preprints referenced below can be obtained at: http://www.arxiv.org.
“Dark Energy Stars,” G. Chapline, Proceedings of the Texas Conference on Relativistic Astrophysics, Stanford, CA, December 12-17, (2004), preprint astro-ph/0503200
“Have Nucleon Decays Already Been Seen?” J. Barbierii and G. Chapline, Phys Lett. B 590, 8, (2004);
“Quantum Phase Transitions and the Breakdown of Classical General Relativity”, G. Chapline, E. Hohlfeld, R. B. Laughlin, D. I. Santiago, Int. J. Mod. Phys. A18 3587-90 (2003), preprint gr-qc/0012094.