Peter J. Lewis

Why The Pessimistic Induction Is A Fallacy

Putnam and Laudan separately argue that the falsity of past scientific theories gives us reason to doubt the truth of current theories. Their arguments have been highly influential, and have generated a significant literature over the past couple of decades. Most of this literature attempts to defend scientific realism by attacking the historical evidence on which the premises of the relevant argument are based. However, I argue that both Putnams and Laudans arguments are fallacious, and hence attacking their premises is unnecessary. The paper concludes with a discussion of the further historical evidence that would be required if the pessimistic induction is to present a serious threat to scientific realism.

Life in Configuration Space

This paper investigates the tenability of wavefunction realism, according to which the quantum mechanical wavefunction is not just a convenient predictive tool, but is a real entity figuring in physical explanations of our measurement results. An apparent difficulty with this position is that the wavefunction exists in a many-dimensional configuration space, whereas the world appears to us to be three-dimensional. I consider the arguments that have been given for and against the tenability of wavefunction realism, and note that both the proponents and the opponents assume that quantum mechanical configuration space is many-dimensional in exactly the same sense in which classical space is three-dimensional. I argue that this assumption is mistaken, and that configuration space can be taken as three-dimensional in a relevant sense. I conclude that wavefunction realism is far less problematic than it has been taken to be. 1. Introduction2. Non-separability3. The instantaneous solution4. The dynamical solution5. Invariance6. What is configuration space, anyway?7. Conclusion Introduction Non-separability The instantaneous solution The dynamical solution Invariance What is configuration space, anyway? Conclusion

Quantum Mechanics, Orthogonality, and Counting

In quantum mechanics it is usually assumed that mutually exclusives states of affairs must be represented by orthogonal vectors. Recent attempts to solve the measurement problem, most notably the GRW theory, require the relaxation of this assumption. It is shown that a consequence of relaxing this assumption is that arithmatic does not apply to ordinary macroscopic objects. It is argued that such a radical move is unwarranted given the current state of understanding of the foundations of quantum mechanics.

Conspiracy Theories of Quantum Mechanics

It has long been recognized that a local hidden variable theory of quantum mechanics can in principle be constructed, provided one is willing to countenance pre-measurement correlations between the properties of measured systems and measuring devices. However, this ‘conspiratorial’ approach is typically dismissed out of hand. In this article I examine the justification for dismissing conspiracy theories of quantum mechanics. I consider the existing arguments against such theories, and find them to be less than conclusive. I suggest a more powerful argument against the leading strategy for constructing a conspiracy theory. Finally, I outline two alternative strategies for constructing conspiracy theories, both of which are immune to these arguments, but require one to either modify or reject the common cause principle. 1. Introduction2. The incompleteness of quantum mechanics3. Hidden variables4. Hidden mechanism conspiracy theories5. Existing arguments against hidden mechanisms6. A new argument against hidden mechanisms7. Backwards-causal conspiracy theories8. Acausal conspiracy theories9. Conclusion Introduction The incompleteness of quantum mechanics Hidden variables Hidden mechanism conspiracy theories Existing arguments against hidden mechanisms A new argument against hidden mechanisms Backwards-causal conspiracy theories Acausal conspiracy theories Conclusion

Empty Waves in Bohmian Quantum Mechanics

There is a recurring line of argument in the literature to the effect that Bohms theory fails to solve the measurement problem. I show that this argument fails in all its variants. Hence Bohms theory, whatever its drawbacks, at least succeeds in solving the measurement problem. I briefly discuss a similar argument that has been raised against the GRW theory. 1. Introduction2. Three Theories3. The Basic Argument4. Branches and Worlds5. Theory and Interpretation6. Size Matters7. Conclusion Introduction Three Theories The Basic Argument Branches and Worlds Theory and Interpretation Size Matters Conclusion

How Bohm’s Theory Solves the Measurement Problem

I examine recent arguments based on functionalism that claim to show that Bohm’s theory fails to solve the measurement problem, or if it does so, it is only because it reduces to a form of the many‐worlds theory. While these arguments reveal some interesting features of Bohm’s theory, I contend that they do not undermine the distinctive Bohmian solution to the measurement problem.

Credence and self-location

All parties to the Sleeping Beauty debate agree that it shows that some cherished principle of rationality has to go. Thirders think that it is Conditionalization and Reflection that must be given up or modified; halfers think that it is the Principal Principle. I offer an analysis of the Sleeping Beauty puzzle that allows us to retain all three principles. In brief, I argue that Sleeping Beauty’s credence in the uncentered proposition that the coin came up heads should be 1/2, but her credence in the centered proposition that the coin came up heads and it is Monday should be 1/3. I trace the source of the earlier mistakes to an unquestioned assumption in the debate, namely that an uncentered proposition is just a special kind of centered proposition. I argue that the falsity of this assumption is the real lesson of the Sleeping Beauty case.

Quantum mechanics and ordinary language: The fuzzy link

It is widely acknowledged that the link between quantum language and ordinary language must be “fuzzier” than the traditional eigenstate‐eigenvalue link. In the context of spontaneous‐collapse theories, Albert and Loewer (1996) argue that the form of this fuzzy link is a matter of convention, and can be freely chosen to minimize anomalies for those theories. I defend the position that the form of the link is empirical, and could be such as to render collapse theories idle. This means that defenders of spontaneous‐collapse theories must gamble that the actual form of the link renders such theories tenable.

Four strategies for dealing with the counting anomaly in spontaneous collapse theories of quantum mechanics

A few years ago, I argued that according to spontaneous collapse theories of quantum mechanics, arithmetic applies to macroscopic objects only as an approximation. Several authors have written articles defending spontaneous collapse theories against this charge, including Bassi and Ghirardi, Clifton and Monton, and now Frigg. The arguments of these authors are all different and all ingenious, but in the end I think that none of them succeeds, for reasons I elaborate here. I suggest a fourth line of response, based on an analogy with epistemic paradoxes, which I think is the best way to defend spontaneous collapse theories, and which leaves my main thesis intact.

Probability, Self‐Location, and Quantum Branching

The main problem with the many‐worlds theory is that it is not clear how the notion of probability should be understood in a theory in which every possible outcome of a measurement actually occurs. In this paper, I argue for the following theses concerning the many‐worlds theory: (1) If probability can be applied at all to measurement outcomes, it must function as a measure of an agent’s self‐location uncertainty. (2) Such probabilities typically violate reflection. (3) Many‐worlds branching does not have sufficient structure to admit self‐location probabilities. (4) Decision‐theoretic arguments do not solve this problem.