The Measurement Problem
Is there a problem? There is. It concerns the relationship of the measurer to the measured, the scientist (or her measuring tools) to whatever-is-being-measured. Philosophers tend to view it as the relationship of subject to object, noting inherent problems in discussing such a thing using a language structured around exactly that relationship.
In contemporary physics, there is general agreement that the measuring apparatus used to measure sub-atomic phenomena cannot be held neatly separate from the phenomena themselves. Initially presenting two independent systems, the act of measuring produces another system that involves both, having changed both. The two become “entangled” with one another. The “problem,” generally, is that in order to know anything about a system, we have to measure it, and when we do that, we change “it”. At the “macro” level, where we usually live, measuring sugar in cups or distance in miles, the interaction is so small, relatively, that we’ve been able to completely ignore it for millennia without noticing any negative effects. But particle physicists DO notice whole complex systems “collapsing” when they are measured. And just because we haven’t noticed such collapses at the macro level definitely does not mean there haven’t been any.
So, if we can’t pin it down any better than that, is there any “reality” at all? If so, are we capable of seeing or hearing or feeling it? Assuming what we “know” of physical matter — that is, “classical” physics — is a representation of reality, a “mirror” or map, if you like, is it trustworthy? What if it isn’t? Niels Bohr, the man widely credited with having established the defining principles of quantum mechanics, insisted that whatever measurements we make must be reported in the “language” of so-called “classical” physics. That is, the description must use terms like momentum, position, speed, etc. to describe the existence and behaviour of particles. There is no consensus about the reasons for insisting, but I suspect it’s because this is the condition of our understanding them at all (my emphasis). Reports that use the terms of quantum physics, he thought, rely so completely on mathematical concepts that we can no longer grasp them as referring to “real” objects or events.
These are basic philosophical questions, and they are open. Even more remarkable, perhaps, they seem to resolve — at least in Bohr’s view — around a very particular and absolutely critical act of reporting, a kind of translation from mathematical abstraction into humanly perceptible space-time, that is, what we know as reality. No such translation can be perfect, in the sense of uniquely “right”. As for any translation, there are multiple possibilities. Any version perceptible to us will involve decisions — conscious or not — on the reporter’s part, decisions that are profoundly creative, decisions that make worlds.