Summer Workshop: Time-Asymmetry and Quantum Reality
Sydney :: Saturday 4 December 2004
Click on titles for abstracts.
Invariant Intrinsic Decoherence
Quantum decoherence can arise due to classical fluctuations in the parameters which define the dynamics of the system. In this case decoherence, and complementary noise, is manifest when data from repeated measurement trials are combined. Recently a number of authors have suggested that fluctuations in the space-time metric arising from quantum gravity effects would correspond to a source of intrinsic noise, which would necessarily be accompanied by intrinsic decoherence. This work extends a previous heuristic modification of Schrödinger dynamics based on discrete time intervals with an intrinsic uncertainty. The extension uses unital semigroup representations of space and time translations rather than the more usual unitary representation, and does the least violence to physically important invariance principles. Physical consequences include a modification of the uncertainty principle and a modification of field dispersion relations, in a way consistent with other modifications suggested by quantum gravity and string theory.
is the Difference between a Quantum Observer and a
Not much. But where there is a difference, there lies quantum theory's most direct statement about properties of the world by itself (i.e., the world without observers or weathermen). In this talk, I will try to shore up this idea by writing quantum mechanics in a way that references probability simplexes rather than Hilbert spaces. By doing so, the connection between quantum collapse and Bayes' rule in classical probability theory becomes evident: They are actually the same thing up to a linear transformation depending upon the details of the measurement method. Looking at quantum collapse this way turns the usual debate in quantum foundations on its head: Only LOCAL state changes look to be a mystery. State changes at a distance (as after a measurement on one half of an EPR pair) are completely innocentóthey simply correspond to applications of Bayes' rule by itself, without the extra transformation. That is, collapse-at-a-distance is nothing more than the usual (i.e., the weatherman's) method of updating one's information upon gathering data. Thus the idea develops that if a quantum reality is to be found in the quantum formalism, it will be found only in the formalism's DEVIATIONS from classical probability theory: Reality is in the difference. Time permitting at the end of the talk, I will try to sketch, without getting too lascivious, how such a reality may be best thought of in conjugal terms. Also, I will try to lay emphasis on some good, open research problems: Bring your students!
and Classical Electromagnetism
I examine the debate about how time-reversal should be definedóhow much of time-reversal symmetry is conventional and how much is an substantive, objective symmetry of nature. I draw a lesson from electromagnetism about how time and parity symmetries are related that has implications for how we think of quantum field theory as well as extensions of physics that involve additional dimensions attached to spacetime.
Towards DSM-I: A Diagnostic Template for Temporal Asymmetry
In both physics and metaphysics, practitioners are frequently
confronted with puzzling asymmetries between past and future. It would
be helpful to have clear diagnostic guidelines for attempting to
classify, understand, and explain these asymmetries. This talk
Nelson's Mechanics, Time Symmetry and Mach's Principle
Nelson attempts to derive the wave function and the Schrödinger equation from a time symmetric diffusion process for point particles. The resulting theory looks like de Broglie-Bohm theory with added noise, but the wave function is crucially a derived concept. I conjecture that quite generally in a stochastic theory a suitable requirement of time symmetry could give rise to something that plays the role of a "pilot wave". Nelson's derivation suffers from a notorious problem. He derives coupled equations for two quantities R and S (hydrodynamic or Madelung equations), but the equivalence with Schrödinger's equation depends crucially on the single- or multivaluedness assumptions for S. I sketch possible strategies for overcoming this problem. In particular, I suggest constructing a "Machian" version of Nelson's theory, arguing it would solve the problem.
Last updated: 25.11.04