By Adam Frank
So yesterday I had the pleasure of attending a seminar on The Measurement Problem in Quantum Mechanics at the University of Rochester. After an hour and half of delightful discussions on all the ways to interpret the weirdness of quantum physics I get in my car to drive home and WHAM, there is NPR's Joe Palca telling me all about ... quantum mechanics. It seems there was no way of getting away from the most important issue in foundational science (if you ask me) that day.
At the core of the problem with interpreting quantum physics (or at least one core) is what people call the measurement problem. Since it's Saturday and I really should deal the mess I call a yard, I won't bend your ear much on this today. Suffice it to say here is one simple way to put the measurement problem...
Left to their own devices the dynamical equations of quantum mechanics predict things we would not understand if they happened right infront of our face. Quantum mechanics is famous for allowing objects (sub-atomic particles) to be in two places at the same time or to have two "logically" opposite properties at the same time (hence the famous analogy of Schrodinger's' cat being simultaneously dead and not dead). This is what the equations lead us to but, of course, this is not what we ever see. We can't even imagine what it would mean to see what the equations, on their own, predict. What does a dead/live cat look like? How does a particle appear when it both is, and isn't, in a box? To get from the otherwise super accurate quantum equations to what we actually see when we run an experiment, there has to something "added" to the mathematics when a measurement is made.
This really bums us all out.
You have these beautiful equations. You should be able to let them run along and describe the world just fine. But if you want to look at what they describe - make a measurement- then all that beautiful mathematics has to be suspended. The situation is neither elegant nor clear. What is a measurement? How long does it take? Does it matter what makes the measurement? There are all kinds of issues that are beguiling and profound and still unresolved after a century.
So for today I just thought I would pass along a nice reference in honor of NPR 's story. David Albert is a well-regarded philosopher of science at Columbia. His book Quantum Mechanics and Experience is worthwhile for those who want both a clear explanation of the overall problem and some deep philosophical reflection on it. It is at a higher level than "popular" books on the subject but Albert is a good writer and the book is worth exploring if you are interested.