Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B

It’s about Time!
Juan G. Roederer
GI/Physics, Director/Prof. Emeritus




The concept of time has been a subject of speculation by philosophers for millennia. Only since the late 1800s has it been the subject of serious investigation by physicists, mainly in the study of irreversible thermodynamic processes and the theory of relativity. My talk will be on the meaning of time in the quantum domain, based on the informational interpretation of quantum mechanics described in my last seminar. I argued then that pragmatic information—the one and only which our brains can handle—is a macroscopic, classical-world concept which does not operate in the quantum domain. I now posit that the very concept of time, too, cannot be defined in the quantum domain. The time variable in the Schrödinger equation or in any propagation operator should be interpreted as the macroscopic time, measured by a macroscopic clock, at which the quantum system in question would cause a certain macroscopic change (given by the equation’s solution) if it were to interact with the macroscopic environment (or a measurement instrument). We are used to the fact that for photons “time does not pass” (because their world-lines are ds2 = 0 lines in 4-D space-time). So it should not be too difficult getting used to the idea that, more generally, time does not exist in any quantum system! I will show how this would explain (i) why, given several unitarily interacting quantum systems, we must describe them by a single composite state vector (a trick that’s usually just taken as one of the QM postulates); (ii) why measurement results on different components will be correlated, even if they are far away from each other in macroscopic space and time (Einstein’s “spooky” correlation without causation). But what about the decay of an unstable nucleus or elementary particle—don’t they carry a teeny-weeny clock inside? No, they don’t, as I will show.


Friday, 25 March 2011

Note different location this week: GI Auditorium, Elvey Building

3:45 PM