by Peter Byrne
4 Albert, a proponent of Bohm’s hidden variables theory, is the author of a widely read and accessible text on quantum mechanics, Quantum Mechanics and Experience (1992). In 2004, he was deceived by the makers of a New Age film called What the Bleep? into talking about physics on camera. His comments were then edited out of context to make it appear as if he supported anti-realist, thoroughly ridiculous and inaccurate notions linking quantum mechanics to religion. He disavowed the scientifically dishonest film.
5 See Barrett (1999) for an explication of the Albert-Loewer theory and other many minds models that claim Everett as a source of inspiration.
6 Everett to Raub, 4/7/80.
7 Everett to American Institute of Physics, 6/1/57.
8 Bohm, D. and Hiley, B. J. (1993). 296.
9 Ibid. 301.
10 Ibid. 315.
11 Ibid. 303.
12 Chalmers, D. J. (1996). 346–357.
13 Deutsch, D. (1985).
14 Deutsch told science journalist Julian Brown that he first thought about quantum parallelism as a way to test the existence of the Everett worlds. Brown, J. (2000). 22.
15 Deutsch interview, 2006.
16 Deutsch, D. (1985A).
17 Deutsch, private communication, July 2009. In his 1984 paper Deutsch made the important observation: “Unlike the C.I.[Copenhagen interpretation], the Everett interpretation can therefore be applied at all instants, not just after measurements. It gives a picture of a world (i.e. everything that exists) consisting of many coexisting universes (i.e. maximal sets [of] observables with values) evolving approximately independently on large scales, but in intimate interaction, through interference effects, on small scales.” Deutsch, D. (1985A). 19.
18 Lockwood, M. (1996). 173. Lockwood’s argument is interesting, but too complex to fully describe here.
19 Deutsch, D. (1996).
20 Ibid.
21 Deutsch, D. (1999).
22 Deutsch interview, 2006.
23 Deutsch, D. (1999).
24 Wallace, D. (2003). Wallace subsequently switched his profession to philosopher of science, a discipline he now teaches at Oxford. He is writing a book on Everettian quantum mechanics for Oxford University Press.
25 Wallace, D. (2007). 11.
26 Wallace, D. (2002). 3.
27 Savage, L. J. (1954). Savage was a game theorist and a Bayesian (as was Everett).
28 Ibid. 60.
29 Ibid. 154. Italics added.
30 Greaves, H. (2004); Greaves, H. and Myrvold, W. (2007). Greaves appeals to Bayesian updating and the evidential nature of “confirmation theory” to arrive at the Born rule.
31 Wallace, D. (2007).
32 Wallace, D. (2002). 62. For Saunders, “branching should be understood as objective probability, and Deutsch-Wallace should be taken as showing that subjective probability should track those objective probabilities.” Saunders, private communication, July 2009; see also Saunders, S. (2005). Everett, himself, tended to view probability as a purely subjective phenomenon for the single observer, even though he laid the foundation for Saunder’s view that there is an objective probability (from the bird’s eye perspective). Unfortunately, the definition of “single” observer gets increasingly hazy the more you think about it in these terms.
33 It is worth noting that a half century ago, a RAND researcher named Daniel Ellsberg (later of Pentagon Papers fame) wrote a critique of the rationality of using the Savage axioms to make risky decisions. In the face of ambiguous information, Ellsberg explained, in technical language, it is not irrational for decision-makers to not use “their best estimates of probability,” i.e. people who do not use the Savage axioms are not necessarily irrational. Ellsberg, D. (1957).
34 Philosopher Jeffrey Barrett (University of California, Irvine), an Everett expert who has substantial disagreements with Oxford Everettians, notes: “If every consequence is in fact realized, then there cannot possibly be constraints on rational action since action must be determined as rational or not by differing consequences contingent on the action, but all rewards and punishments are typically in fact fully realized regardless of what action an agent performs.” Barrett, private communication, 2009.
35 Another way of looking at the situation, from a bird’s eye view, is that the possible consequences of one action are correlated with the possible consequences of the many other actions with which it is entangled as described by the universal wave function. Therefore, a particular outcome occurs with relative frequency across the set of all post-event branches that include all possible outcomes of that action in their subsequent history. That is, from the bird’s eye view, outcome A is recorded in 20 percent of the branch histories, B in 30 percent, C in 50 percent. And in a single branch, a frog-observer records a sequence of squared amplitudes: A at 0.2, B at 0.3, C at 0.5.
36 Wallace’s work is more sophisticated than this summary. The point is that modern Everettians are addressing the probability problem by expanding the terms of the debate and, like Everett, questioning probability (as we think we know it).
37 See: Dennett, D. C. (1991).
38 Wallace, D. (2003A). 6.
39 Ibid. 12–17.
40 Wallace, D. (2001). 23.
41 Ibid. 23–24.
42 Deutsch, D. (2002).
43 Quoted in Saunders, S. et al. (2010).
44 Ibid.
45 Ibid.
46 In military game theory, probability measures were inextricably linked to maximizing utility values placed upon a limited range of supposedly rational choices. As Anatol Rapoport pointed out in his critique of game theory: “For the most part, decisions depend on the ethical orientations of the decision-makers themselves. The rationales of choices so determined may be obvious to those with similar ethical orientations but may appear to be only rationalizations to others. Therefore, in most contexts, decisions cannot be defended on purely rational grounds. A normative theory of decision which claims to be ‘realistic,’ i.e. purports to derive its prescripts exclusively from ‘objective reality,’ is likely to lead to delusion.” Rapoport, A. (1964). 75. But in quantum mechanics, nature itself selects the menu of choice, and assigns probability weights, and the Born rule discovers the weights. It is rational to use the Born rule to construct a mini-max solution, (even if, as Everett said, probability is, ultimately, an illusion).
47 Saunders, S. et al. (2010).
48 Ibid. See also Kent, A. (2009). In which physicist Adrian Kent dissects the Oxford Everettian arguments.
1 Op-ed The New York Times, 7/7/2005, A23.
2 Bernard Carr’s Universe or Multiverse? (2007) is a collection of 28 articles by top physicists ruminating on how to test for the existence of a variety of multiverses. Many of the essays discuss Everett’s considerable influence on cosmology.
3 The biannual meeting of the Foundational Questions Institute, www.fqxi.org
4 For example, Chown, M., (2007). Geftner, A. (2009). Bignami, L. (2008).
5 Wheeler, J. A. (1973). 245.
6 Susskind, L. (2005).
7 There are several sorts of multiverse—including an incredibly tedious one. If we consider the universe to be infinite in size, it should, according to the laws of probability, reproduce an infinite number of recurrences of everyone and everything in the vastness beyond our cosmic horizon: an infinitely repetitive Groundhog Day (à la the Bill Murray movie). It would include the Everettian splits.
8 Susskind, L. (2005). 317–323.
9 Private communication, Maldacena, July 2009.
10 Chang, S., M. Kleban, et al. (2008); Kleban interview, August 2009.
11 Mersini-Houghton, L. and R. Holman. (2009).
12 Kobakhidze, A. and L. Mersini-Houghton (2006). See also: Aguirre, A., et al. (2007). On the other hand, researchers at the University of Michigan assert that the Cold Spot may be a statistical anomaly. See: Zhang, R. and Huterer, D. (2009); Merali, Z. (2009). Regardless of media-driven bubbles of excitement, there is a distinct prospect of finding evidence o
f other universes in the CMB. See Kashlinsky et al. (2009).
13 Maldacena interview, 2006.
14 Newton, I. (1730). 379–380.
15 Donne, J. (circa 1621). “The Good Morrow.” 3.