Once Before Time - Martin Bojowald [156]
10. Gamma ray bursts were first discovered by the Vela satellite of the U.S. military, which was deployed to detect putative Soviet nuclear explosions in space.
11. The motion of all the stars, however, is not confined to a fixed plane. A 3-D animation can be viewed at http://www.mpe.mpg.de/ir/GC/index.php.
6. BLACK HOLES
1. Passages in italics are fictitious and are meant to illustrate which speculations the mathematical foundation of modern physics forbids that might otherwise be possible.
2. For rotating black holes, which are not rotationally symmetric but are typical in the cosmos, there are nevertheless new phenomena. For instance, according to the Penrose process, objects passing near a rotating black hole can be accelerated at the expense of the black hole’s rotation rate; by stopping the rotation, one could in principle gain energy corresponding to up to 30 percent of the black hole mass. This is an enormous amount, as one can see if one considers that nuclear power relies on the transformation of a much lower percentage of the far smaller nuclear fuel mass.
3. Or drown, after several more years of global warming.
4. Unruh’s suggestion started with a harmless metaphorical illustration in a colloquium talk on black holes. By now, actual experiments are being performed in different versions.
5. Which is by no means to say that investigations of black body radiation cannot lead to important insights. Just Planck’s studies or the black body radiation of the cosmic microwave background need be mentioned here.
6. Here, initial contributions came, in different collaborations, from Kirill Krasnov, Carlo Rovelli, Abhay Ashtekar, John Baez, Alejandro Corichi, Romesh Kaul, and Parthasarathi Majumdar.
7. In parallel, similar investigations were undertaken by Leonardo Modesto as well as Viqar Husain and Oliver Winkler. More recently, Christian Böhmer and Kevin Vandersloot as well as Rodolfo Gambini and Jorge Pullin have turned to these questions.
7. THE ARROW OF TIME
1. An application of this principle is more realistic, but much more difficult, than that of ideal mathematical time; this is best expressed in the words of Peter Bergmann, who in the 1960s took the first steps toward this issue in relativity: “Such a question can, we are assured, always be answered from a sufficient set of initial data, though the performance of this task may call for considerable mathematical agility.” The theoretical description still remains to be completed; in recent times it has been pushed forward by, for instance, Carlo Rovelli and, building on his work, Bianca Dittrich. Julian Barbour also continues to tackle such questions.
8. COSMOGONY
1. Of interest is the usual picture with one healthy and one broken tusk as in figure 33, symbolizing the combination of perfection and chaos in the real world; see also chapter 11.
2. Pre-Socratic fragments are translated from the German quotations in Philosophie von Platon bis Nietzsche, Digitale Bibliothek, 3rd ed., vol. 2, (Berlin: Directmedia, 2002), and Hermann Diels, Die Fragmente der Vorsokratiker: Griechisch und Deutsch, 4th ed., vols. 1 and 2 (Berlin: Weidmannsche Buchhandlung, 1922), respectively.
3. At least this was the case in the early, innocent years of loop quantum cosmology. With promising results and higher stakes, the situation has changed: It has already been shown that singularities can be avoided; now the question is how space-time looks. This is a different issue, requiring a handle on more details that are easy to misinterpret. For instance, there were some discussions of the grand “quantum nature of the big bang,” in blissful ignorance of the fact that the model used as well as quantum states analyzed in this context were very special—too special, as it turned out, to reliably draw detailed conclusions about the big bang. Another example is the claim that “loop quantum cosmos are never singular,” a statement that tells it all about how contrived the contents are: The word