The End of Time: The Next Revolution in Physics

Dynamics Without Dynamics (p. 258) In this section I refer to investigations by various authors. Their studies will be found in the bibliography. Physicists really interested in the semiclassical approach may also like to consult the review article by Vilenkin (1989), the paper by Brout (1987), the final part of Zeh (1992, 1999) and the introductory article by Kiefer (1997). The fullest account of my own ideas is Barbour (1994a).

CHAPTER 19: LATENT HISTORIES AND WAVE POCKETS

Schrödinger’s Heroic Failure (p. 278) In the first draft of this book I included a long section on the very interesting interpretation of quantum mechanics advanced originally by de Broglie, and revived by Bohm, whose 1952 paper I strongly recommend to physicists together with Peter Holland’s book (Holland 1993). With regret I omitted it, as I felt that it made this book too long, especially since I believe that the interpretation does not really solve the problem. However, I particularly value the way in which it shows that all the results of quantum mechanics can be obtained in a framework in which positions are taken as basic. This made the theory attractive to John Bell, as we shall see in the next chapters.

CHAPTER 20: THE CREATION OF RECORDS

The Creation of Records: First Mechanism (1) (p. 284) Bell’s paper can be found in his collected publications Speakable and Unspeakable in Quantum Mechanics.

(2) (p. 284) Mott’s paper is reproduced in Wheeler and Zurek (1983). Heisenberg’s treatment is in his Physical Principles of Quantum Theory. I am very grateful to Jim Hartle, who first drew my attention to Mott’s paper. At that time he was considering seriously an interpretation of quantum cosmology that is quite close to my own present position. He has since backed away somewhat, and now advocates an interpretation of quantum mechanics in which history is the fundamental concept. I should also like to express my thanks here to Dieter Zeh. Zeh, who was in this business long before me, also made me realize the importance of Mott’s work, and, crucially, alerted me to Bell’s paper. There are not many physicists who take the challenge of timelessness utterly seriously, but Dieter Zeh and his student Claus Kiefer, from both of whom I have gained and learned much, are two of them.

CHAPTER 21: THE MANY-INSTANTS INTERPRETATION

Bell’s ‘Many-Worlds’ Interpretation (p. 299) In his ‘cosmological interpretation’ of quantum mechanics, Bell combined elements derived from both Everett and the de Broglie-Bohm interpretation (see the note to Chapter 19). In fact, Bell’s account of his mixed interpretation is rather terse, and can be misunderstood. I am most grateful to Fay Dowker and Harvey Brown for drawing my attention to an error I made in reporting Bell’s idea in my first draft of this book. In this section I follow their interpretation of Bell, which I am sure is what he did mean.

The Many-Instants Interpretation (p. 302) I hope I have made it clear that probability ‘to be experienced’ or ‘to exist’ is a problematic concept. If consciousness is determined by structure, the consciousness is already in the Nows and must be experienced irrespective of their probabilities. What role remains for probabilities? It is a very difficult issue. Probability is already puzzling in ordinary quantum mechanics, and even in classical physics. Cold water could boil spontaneously, but we never see this happen. Standard probability arguments suggest that what is possible but hugely improbable will not be experienced. Much suggests that probabilities in some form are inescapable in quantum theory simply because it explores mutually exclusive possibilities. Instants of time are natural candidates for the ultimate exclusive possibilities. If certain very specially structured instants do get hugely larger probabilities than others, and are the ones habitually experienced, that must, I feel, count as explanation. But as an indication of the depth of this problem, I add here in Box 16 an edited email exchange I had with Fay Dowker of Imperial College, London. I had especially asked her to read my first draft, since she is a very clear thinker but is sceptical about both many worlds and canonical quantization, the approach to quantum gravity that I favour.

CHAPTER 22: THE EMERGENCE OF TIME AND ITS ARROW