In reply to Stephen A. Lawrence's message of Wed, 09 Jun 2010 14:21:12 -0400: Hi,
Maybe polarizers do more than measure? Perhaps they actually change the polarization angle? e.g. if the electric field is more vertical than horizontal, then it gets forced completely vertical, if more horizontal then completely horizontal. Since essentially all photons will fall in one category or the other..... > > >On 06/08/2010 11:08 PM, [email protected] wrote: >> The QM problem here is that a "wave function" is NOT a physical reality. It >> is a >> mathematical equation which we use to *describe* the state of a system *to >> the >> best of our knowledge at the time*. When we make a real observation of the >> real >> physical system, our *knowledge* about it changes , and hence we need to use >> a >> different equation. The wave function is said to "collapse" but all that >> collapse really tells us is that we now know more about the system than we >> did >> previously ... >> > >I don't think that's quite right. You've described the "hidden gears" >model of QM and my impression is a superposition of states is more than >just simple state which we don't happen to know at present. > >For a possibly overly simplistic example, consider a single photon in a >beam of non-polarized light. Let it encounter, and pass through, a >vertical linear polarizer. We have now measured a single parameter of >its state -- and, if it got through the polarizer, we have found that >its polarization is vertical (/exactly/ vertical). > >Before we sampled it, its polarization was described by a superposition >of states, with all polarization angles being *equally* *likely*. Yet, >since half the time a nonpolarized photon will get through the >polarizer, after we sample it we would conclude that there was actually >a 50% chance that it was vertically polarized. > >Next consider a beam of incoherent unpolarized light passing though a >polarizer. > >Note the before/after difference: Before the beam encounters the >polarizer, *all* polarization angles are equally likely for each photon >in the beam. > >Yet, after it passes through a polarizer, we find that HALF the photons >in the beam (the ones which passed through the filter) are -- and, >apparently, WERE -- *vertically* polarized. > >By the act of *measuring* the polarization, we seem to have >retroactively changed the beam from a collection of randomly polarized >photons to a 50/50 mix of vertically and horizontally polarized photons. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/Project.html
