The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics: Physics Today: Vol 62, No 5

Stephen was fond of this flexible notion of cosmological history that emerges from quantum cosmology. But how did inflation start and what selects a particular realization of inflation? Stephen discovered that early on there was a profound connection between the no boundary wave function and inflation . In a series of papers over many years he and his collaborators consolidated this connection, showing that the no boundary proposal predicts an early period of inflation. Thus, the no boundary proposal provides a foundation for inflationary cosmology.

• Just because something’s not ultimately real doesn’t mean it’s a hallucination.
• Accordingly, in order to eliminate such restrictions, Stephen set his mind to developing new techniques that might strengthen the existing results.
• In a paper, ‘Brane new world’, Stephen, working with Hertog and Reall, described the creation of such membrane cosmologies in the context of the no boundary proposal .
• A black hole is held to be surrounded by a glow of radiation called Hawking radiation, which is theorized to slowly take over the black hole and then eventually evaporate over incredible amounts of time.
• While in Switzerland in 1985, Stephen contracted pneumonia and a tracheotomy was necessary to save his life.

A distinct phase of Stephen’s career concerned investigations of classical black hole physics. The singularity theorems had clearly piqued his interest in black holes, as the Hawking–Penrose theorems include the result that a space-time that contains a marginally trapped surface must be singular. The result was interpreted as meaning that a black hole must contain a space-time singularity. At the start of this phase, many of the fundamental physical properties of black holes were not well understood. The singularity work up to 1972, including partial classical black hole uniqueness theorems and the area theorem, were consolidated in the text The large scale structure of space-time by Stephen and Ellis, which from then on served as a standard reference in the field .

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While the writing was in progress, various results on causality and black hole theory appeared, including Stephen’s crucial black hole area theorem, which had been inspired by earlier discussions with Penrose, and so substantial sections of the book were devoted to these topics. Some important themes of classical black hole theory, such as the four laws of black hole thermodynamics and the definitive uniqueness theorems, were not included because they were developed later. The advantage of these covariant methods is that they avoid treating as physical those perturbations that are merely due to coordinate transformations, providing a very clear view of gravitational wave propagation and absorption based on physically transparent variables.

The star gets smaller and denser until not even light escapes the irresistible tug of gravity; the star becomes a black hole. Within the region of blackness the star continues to collapse until it becomes infinitely small and infinitely dense—what mathematicians call a singularity—and the equations of physics break down. Page notes that Hawking is opening the door to a scenario so extreme “that anything in principle can get out of a black hole”. Although Hawking does not specify in his paper exactly how an apparent horizon would disappear, Page speculates that when it has shrunk to a certain size, at which the effects of both quantum mechanics and gravity combine, it is plausible that it could vanish. At that point, whatever was once trapped within the black hole would be released .

Gravitational radiation: an experimental digression

Following the successful Nuffield Workshop described in Section 12 , subsequent observations confirmed the resulting predictions which must count as one of the great triumphs of theoretical cosmology, connecting the universe’s earliest quantum evolution to the matter distribution today. As a consequence of the growth of fluctuations, the universe also exhibits arrows of time such as that characterized by the global increase in thermodynamic entropy. In his original paper, Stephen obtained the radiation by considering zero-point fluctuations Stephen Hawkings Radical Thinking in the initial vacuum state that were amplified by the collapse that formed the black hole. However, the fluctuations would receive a huge redshift just outside the horizon, so that the radiation seemed to come from modes that were initially far above the Planck frequency. The theory might break down at such high frequencies and so Stephen sought a mathematical treatment of black hole radiation as low energy particles leaking out of the horizon at late times, rather than as a high energy process during the collapse itself.

Unlike the entropy of other systems, however, black hole entropy is not extensive, being proportional to the horizon’s area A and not its volume. While in Switzerland in 1985, Stephen contracted pneumonia and a tracheotomy was necessary to save his life. Strangely, after this brush with death, the progression of his degenerative disease seemed to slow to a virtual halt. His tracheotomy prevented any form of speech so that acquiring a computerized speech synthesizer became a necessity. He was sustained, then and thereafter, by a team of helpers and personal assistants, as well as by the family. In the aftermath of this encounter with pneumonia, the Hawkings’ home was almost taken over by nurses and medical attendants, and he and Jane drifted apart.

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A further theme was classical black hole studies which started with the paper of 1971 and which led to the area theorem, uniqueness theorems and the four laws of black hole thermodynamics, discussed in section 7. Stephen next considered primordial nucleosynthesis https://www.wave-accounting.net/ in spatially homogeneous cosmologies in a paper with Roger Tayler . They considered how anisotropies in cosmology could increase helium production by primordial nucleosynthesis and so improve agreement with the helium-4 estimates of the time.