Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B


The Quantum Wars of 2011
Juan G. Roederer
GI/Physics, Director/Prof. Emeritus




Since the beginning, there has been a problem with the interpretation of fundamental concepts of quantum mechanics (QM). What is the physical meaning of the “state” (or wave function) of a quantum system (QS)? Does a QS already “possess” the value of an observable before it is measured? What is the mechanism responsible for the collapse of the superposed state of a QS during a measurement? How can a particle be in two places “at the same time”? How come a macroscopic system made up of many QS behaves “normally” (no Schrödinger cats)? Heisenberg declared that “a particle trajectory only arises thorough the process of observation”; Bohr made the observer an integral part of the measurement process; Einstein made his famous statements that “QM is incomplete” and “God does not play dice” and even von Neumann, who had given QM a solid linear operator-based framework, declared at one point “I don’t believe in Hilbert spaces anymore!”. For many decades physicists were told to “shut up and calculate—QM works, and that is what counts”! (I call this the “don’t ask, don’t tell” period of QM).

Then, in the eighties came the famous table-top experiments capable of manipulating individual, single QS (photons, electrons, etc.), and QM seemed to become spookier and spookier. The concepts of decoherence, delocalization and einselection were introduced and questions of interpretation became real and physical. Today, there are several schools of interpretation engaged in a fierce but very civil debate. Some start from information-theory postulates or linear-algebra axioms, others from Bayesian statistics; some start exclusively from experimental results, others include the observer’s consciousness as an integral part; some postulate multiple universes, others base their framework on quantum computing simulations. I have begun to interact with some of the principal players, trying to sell my own premise (explained in previous JC talks) that it is in principle impossible to dig “meaningfully” into a QS because (i) information and time cannot be defined in that domain and (ii) QM really only deals with the potential macroscopic (i.e., perceptible) effects that a QS may elicit in the environment. I will discuss my personal experience in this endeavor mainly from the “human” point of view, and compare the situation with that of the “skeptics” vs. “believers” in the global warming debate (sadly, no US political parties have taken sides in the quantum case—yet).


Friday, 14 Oct. 2011

Note this week: GI Auditorium, Elvey Building

3:45 PM