Monday, February 23, 2015

Why QM is the only possible theory of nature

Just stumbled across this absolutely gorgeous explanation of why quantum mechanics is the only possible theory of nature that both allows for complete knowledge and probabilities.  It's one of the best written pieces of science popularization I have ever read.  It takes you from zero to a pretty deep understanding in just a shade over 1000 words.  It's brilliant, almost a work of art.  If you're interested in QM, this is well worth the five minutes of your time it will take to read it.


Luke said...

I'd love to get your thoughts on Thomas Breuer's The Impossibility of Accurate State Self-Measurements (pdf).

Ron said...

The central claims sound incoherent to me:

1. it is impossible for an observer to distinguish all present states of a system in which he or she is contained

I don't know what could possibly be meant by "all present states of a system". A system at a single point in time can only be in one state (assuming one considers a superposition state to be a single state), so the phrase "all present states of a system" seems non-sensical to me. It should be "the present state of a system." But then I don't know what can possibly be meant by "distinguish". The only thing I can imagine it could possibly mean is that you can't simultaneously measure all observables, but that's not exactly earth-shattering news.

2. it is impossible for an observer to measure the EPR-correlations between himself or herself and and outside system

This indicates an ignorance of what measurement is (somewhat understandable in 1995). Measurement *is* entanglement. When you measure a system you necessarily entangle yourself with the system you are "measuring", so it is impossible *not* to measure EPR correlations between yourself and an outside system.

I don't have time at the moment to dig deeply into this to see if I can wring any sense out of the body of the paper. If you think you understand it and want to clarify what these claims are actually saying I'll take another look.