I reread each story with that in mind, and so far as I know everything still fits with current knowledge. A few things have even gained in plausibility. For example, when I wrote “Rogueworld” we had no direct evidence of any extra-solar planets. Now reports come in every month or two of another world around some other star, based not on direct observation of the planet but on small observed perturbations in the apparent position of the star itself. The idea of vacuum energy extraction, first introduced to science fiction in “All the Colors of the Vacuum,” has proceeded from wild science fiction idea to funded research. Black holes, which at the time I wrote “Killing Vector” were purely theoretical entities, form a standard part of modern cosmology. A big black hole, about 2.5 million times the mass of the Sun, is believed to lie at the center of our own galaxy. Radiating black holes, which in 1977 were another way-out idea, are now firmly accepted. The Oort cloud, described in “The Manna Hunt,” is a standard part of today’s physical model of the extended Solar System.
So has there been nothing new in science in the past twenty years? Not at all. Molecular biology has changed so fast and so much since the 1970s that the field seen from that earlier point of view is almost unrecognizable, and the biggest changes still lie in the future. Computers have become smaller, more powerful, and ubiquitous, beyond what anyone predicted twenty years ago. We also stand today on the verge of quantum computation, which takes advantage of the fact that at the quantum level a system can exist in several states simultaneously. The long-term potential of that development is staggering.
Finally, in the very week that I write this, a report has appeared of the first successful experiment in “quantum teleportation.” Via a process known as “entanglement,” which couples the quantum state of two widely separated systems, a Caltech team “teleported” a pattern of information from one location to another, independent of the speed of light. If there isn’t a new hard SF story in that report, I don’t know where you’ll find one.
Kernels, black holes, and singularities.
Kernels feature most prominently in the first chronicle, but they are assumed and used in all the others, too. A kernel is actually a Ker-N-le, which is shorthand for Kerr-Newman black hole.
To explain Kerr-Newman black holes, it is best to follow McAndrew’s technique, and go back a long way in time. We begin in 1915. In that year, Albert Einstein published the field equations of general relativity in their present form. He had been trying different possible formulations since about 1908, but he was not satisfied with any of them before the 1915 set. His final statement consisted of ten coupled, nonlinear, partial differential equations, relating the curvature of space-time to the presence of matter.
The equations are very elegant and can be written down in tensor form as a single short line of algebra. But written out in full they are horrendously long and complex — so much so that Einstein himself did not expect to see any exact solutions, and thus perhaps didn’t look very hard. When Karl Schwarzschild, just the next year, produced an exact solution to the “one-body problem” (he found the gravitational field produced by an isolated mass particle), Einstein was reportedly quite surprised.
This “Schwarzschild solution” was for many years considered mathematically interesting, but of no real physical importance. People were much more interested in looking at approximate solutions of Einstein’s field equations that could provide possible tests of the theory. Everyone wanted to compare Einstein’s ideas on gravity with those introduced two hundred and fifty years earlier by Isaac Newton, to see where there might be detectible differences. The “strong field” case covered by the Schwarzschild solution seemed less relevant to the real world.
For the next twenty years, little was discovered to lead us toward kernels. Soon after Schwarzschild published his solution, Reissner and Nordstrom solved the general relativity equations for a spherical mass particle that also carried an electric charge. This included the Schwarzschild solution as a special case, but it was considered to have no physical significance and it too remained a mathematical curiosity.
The situation finally changed in 1939. In that year, Oppenheimer and Snyder were studying the collapse of a star under gravitational forces — a situation which certainly did have physical significance, since it is a common stellar occurrence.
Two remarks made in their summary are worth quoting directly: “Unless fission due to rotation, the radiation of mass, or the blowing off of mass by radiation, reduce the star’s mass to the order of the sun, this contraction will continue indefinitely.” In other words, not only can a star collapse, but if it is heavy enough there is no way that the collapse and contraction can be stopped. And “the radius of the star approaches asymptotically its gravitational radius; light from the surface of the star is progressively reddened, and can escape over a progressively narrower range of angles.” This is the first modern picture of a black hole, a body with a gravitational field so strong that light cannot escape from it. (We have to say “modern picture” because before 1800 it had been noted as a curiosity that a sufficiently massive body could have an escape velocity from its surface that exceeded the speed of light; in a sense, the black hole was predicted more than two hundred years ago.)
Notice that the collapsing body does not have to contract indefinitely if it is the size of the Sun or smaller, so we do not have to worry that the Earth, say, or the Moon, will shrink indefinitely to become a black hole. Notice also that there is a reference to the “gravitational radius” of the black hole. This was something that came straight out of the Schwarzschild solution, the distance where the reddening of light became infinite, so that any light coming from inside that radius could never be seen by an outside observer. Since the gravitational radius for the Sun is only about three kilometers, if the Sun were squeezed down to this size conditions inside the collapsed body defy the imagination. The density of matter must be about twenty billion tons per cubic centimeter.
You might think that Oppenheimer and Snyder’s paper, with its apparently bizarre conclusions, would have produced a sensation. In fact, it aroused little notice for a long time. It too was looked at as a mathematical oddity, a result that physicists needn’t take too seriously.
What was going on here? The Schwarzschild solution had been left on the shelf for a generation, and now the Oppenheimer results were in their turn regarded with no more than mild interest.
One could argue that in the 1920s the attention of leading physicists was elsewhere, as they tried to drink from the fire-hose flood of theory and experiment that established quantum theory. But what about the 1940s and 1950s? Why didn’t whole groups of physicists explore the consequences for general relativity and astrophysics of an indefinitely collapsing stellar mass?
Various explanations could be offered, but I favor one that can be stated in a single word: Einstein. He was a gigantic figure, stretching out over everything in physics for the first half of this century. Even now, he casts an enormous shadow over the whole field. Until his death in 1955, researchers in general relativity and gravitation felt a constant awareness of his presence, of his genius peering over their shoulder. If Einstein had not been able to penetrate the mystery, went the unspoken argument, what chance do the rest of us have? Not until after his death was there a resurgence of interest and spectacular progress in general relativity. And it was one of the leaders of that resurgence, John Wheeler, who in 1958 provided the inspired name for the Schwarzschild solution needed to capture everyone’s fancy: the black hole.