Once Before Time - Martin Bojowald [116]
As already mentioned, this picture remains to be supported by further calculations—required, for instance, for a quantitative estimate of the energies involved. Even though it is quite certain that the unfolding interior would radiate much more energy than the final stage of Hawking radiation, it could be just a small fraction of the whole of collapsed matter. It takes, after all, a long time for heavy black holes to evaporate. In this time, a large fraction of the total energy can already be emitted by the Hawking process, even though in brief intervals the radiation is only of low intensity. Before all these ingredients have been combined, the strength and brightness of a possible black hole explosion cannot yet be reliably estimated. But given the extremely high curvatures in the interior, far surpassing anything in the universe except the big bang itself, one must expect a gigantic event. Unfortunately (or perhaps luckily), we will have to wait a long time for this to happen in our universe. For now, black holes are protected from evaporation by cosmic background radiation, despite its weakness.
At first, the gravonomist on duty did not consider the speck of light in the black night sky exciting, but it was a welcome distraction in his otherwise dull routine. Eruptions of this kind had long lost their initially spectacular flair, even though they represented the sole remaining cosmic events visible to the naked eye. Everything else was long extinguished, after the expansion of the universe had made other galaxies and then even neighboring stars drift too far away. The unrelenting expansion had, however, also made the cosmic background radiation cool down more strongly, and at last facilitated the evaporation even of massive black holes. Long after collapse and compression, their matter now reappeared in immense explosions. They were the main sources of gravitational waves, whose detection by gravonomy had replaced the traditional mapping of the sky by astronomy.
Scientific investigations of the universe, however, became ever rarer, and gravonomy was tightly held by the military. The origin and fate of the universe, growing larger and emptier, appeared clear; thus scientific interest in gravitational waves and other, weak cosmic messages diminished. Instead, the old observatories served for military surveillance. After the depletion of traditional energy sources, the extraction of energy from black holes by the Penrose process became the last elixir of life. To that end, some of the naturally existing black holes had been artificially enlarged by a process which came to be called “horizon broadening.” Initially, as a by-product, humankind had used the opportunity to eliminate unpopular civilizations unfortunate enough to have settled near a black hole, but this practice was soon largely banned. Among all civilizations of the universe, as always, humanity had distinguished itself by its destructive power. It also had had the luck of having early in its history developed a successful theoretical description of space-time by general relativity. (By humans’ own fault, geo- and science-political circumstances had for several decades hampered their gravitational research, but these played no role in the following centuries.) This knowledge and its application was used by humankind to consolidate its dominance, after which they officially banned horizon broadening. Only a few rogue galaxies were still suspected of using horizon broadening, and they were monitored to detect the gravitational