Philosophy of Quantum Mechanics

Quantum mechanics has significant consequences for central philosophical problems.

This ineludible fact poses a challenge to philosophy programs: how can philosophy of quantum mechanics be taught so that philosophy students grasp enough quantum mechanics to be able to critically assess its philosophical applications, without getting bogged down in philosophically irrelevant technicalities? In short: how ought we quantize philosophy curricula?

In taking up this challenge I have:

Course notes:

Lecture one notes: The concept of superposition. / Instrumentalism.

Lecture two notes: The mathematical formalism PI. / Philosophy of mind and quantum causal closure.

Lecture three notes: The mathematical formalism PII. / The dimensionality of space.

Lecture four notes: Entanglement & nonlocality. / Atomism and intrinsicality.

Lecture five notes: The measurement problem. / Solutions.

Lecture six notes: The Everett Interpretation. / Decoherence and emergence.

Lecture seven notes: Probability in an emergent multiverse.

Lecture eight notes: Critics of many worlds.

Lecture nine notes: Dynamical collapse theories and the tails problem.

Lecture ten notes: Consciousness and the collapse of the wave-function.

Optional additions: Bohmian mechanics I; Bohmian mechanics II; Consciousness & collapse (advanced).

Course objective:

The student will:

  • Be able to clearly formulate and explain one of the deepest theoretical problems of the modern age (the measurement problem) and the major contemporary solutions to it.
  • Gain an appreciation of the aspects of quantum mechanics relevant to contemporary philosophical problems.
  • Gain competence with philosophically problematic concepts in quantum mechanics.
  • Gain an appreciation of the importance of science to philosophy, and philosophy to science.
  • Contribute to contemporary debates in the philosophy of quantum mechanics.

Course Content:

The course is based on one of the deepest and most philosophically engaging problems in modern science: the measurement problem in quantum mechanics.

The course assumes only high-school level mathematics and although it is aimed at philosophers, it is open to anyone interested in modern science and what it says about reality.

The measurement problem was originally put in its most vivid and provocative form by Erwin Schrödinger (1926), in his notorious “Schrödinger’s cat” thought experiment. Roughly: if the state of a macroscopic system (e.g. a cat’s state of living) is set up so that it depends in some way on the state of a quantum particle, then quantum mechanics entails absurd results.

Schrödinger imagined a set-up in which a boxed cat is gassed to death if a particle decays, left alone if the particle does not decay. But the particle is neither decaying nor not decaying, instead it is in a peculiar quantum state: a “superposition” of both decaying and not decaying. Consequently, the cat evolves into a superposition of being both dead and alive.

Orthodox textbook quantum mechanics merely evades this problem by stipulating that measurements cause these superpositions to “collapse” into familiar definite states. The measurement problem refers to the imprecision of this criterion (does the cat measure/collapse the system? or human observer? or something else?).

A large portion of the course analyses contemporary solutions to this problem, with emphasis on the two most prominent solutions. The first removes the collapse stipulation and allows the cat (and consequently, the cat’s environment) to “superpose”. This is the Many Worlds theory. The second tries to make the collapse process precise, stipulating that collapse is caused spontaneously (on one version) or is caused by conscious observation (on another). All these solutions quickly run into thickets of philosophical problems, which engage philosophy of mind, metaphysics, epistemology, probability theory, and decision theory.

Form of Tuition:

Classes will have a seminar-like format: a lecture, based on assigned readings, followed by discussion. Mid-way through the course a take-home exam will be distributed. The exam tests the student’s grasp of the basic quantum formalism, the measurement problem, and includes short answer questions and a short essay. At the finale of the course the student must hand in an essay broadly relating to one or more solutions to the measurement problem

Course Reading:

We begin studying a simplified mathematical formalism developed specifically for courses like this, in chapter two of:

Albert, D.Z. (1992). Quantum Mechanics and Experience. Harvard University Press.

We will also look at excerpts from:

Saunders, S., Barrett, J., Kent, A., & Wallace, D. (Eds.). (2010). Many Worlds? Everett, Quantum Theory, and Reality. Oxford University Press.

Wallace, D. (2012). The Emergent Multiverse: Quantum Theory According to the Everett Interpretation. Oxford University Press.

Albert, D.Z. (2015). After Physics. Harvard University Press.

McQueen, K.J. (2015). ‘Four Tails Problems for Dynamical Collapse Theories’, Studies in the History & Philosophy of Modern Physics 49: 10-18. (Published version, Preprint)

We will also analyse public debates between contemporary advocates of the different positions:

All literature will be made available to students.


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