BTW, I appear to contradict myself when I said "measuring cannot increase the energy of the particle" vs I agree with the claim that measuring can concentrate energy in a system. In the former, I mean I don't accept the idea that measuring can somehow increase the energy the particle without the transfer of energy from somewhere else.
Harry On Sat, Aug 18, 2012 at 7:31 PM, Harry Veeder <hveeder...@gmail.com> wrote: > Hi LP, > > I haven't read the paper, but I don't disagree with claim. In fact it > should not be unexpected. > > Even in a macroscopic system a concentration energy can come about as > a result of energy being transferred from the measuring system to the > system being measured. Of course, such a measuring system would be > considered defective because it provides a distorted picture of the > energy content of system being measured. However, classical mechanics > says a measuring system can be designed in theory to have an > arbitrarily small distorting effect, whereas quantum mechanics says > this is not possible in theory. > > Harry > > On Sat, Aug 18, 2012 at 2:44 PM, <pagnu...@htdconnect.com> wrote: >> Hello Harry, >> >> To be really precise, though, an energy measurement of a particle in a >> superposition of energy eigenstates might find it in one of the states >> higher than the weighted average energy of its wavefunction. So, you >> might say that the measurement increased its energy, but over many such >> measurements would just produce the mean energy of the wavefunction. >> >> While I am not convinced they are correct, the authors of the paper I >> referenced end with the conclusion - >> >> "From a general perspective a phenomenon like the energy concentration in >> a composite quantum system can indeed be motivated physically. There exist >> processes, where there is a redistribution of energy among different >> system degrees of freedom making possible some amounts of system >> self-organization. In particular, one could examine the possibility of >> concentrating the total energy of the system into a subset of degrees of >> freedom producing a decrease of its entropy, which in order to avoid a >> violation of the second law of thermodynamics, would compel the release of >> energy to the environment, thus keeping the free energy constant. This is >> possible only if the system is open..." >> >> "Concentrating Energy by Measurement" >> http://arxiv.org/abs/1012.5868 >> >> Interesting theory. >> >> -- LP >> >> Harry Veeder wrote: >>> Actually, I tend agree with Robin that measuring cannot increase the >>> energy of the particle. My question reflects my own attempt to >>> understand why it is so. Now that I have thought about it, it is >>> because one doesn't measure energy per se. Most measurements are >>> really the result of calculations based on measurements of length and >>> time plugged into a formula. BTW, the same is true of measurements of >>> momentum. The modern physicists habit of refering to energy and >>> momentum as "observables" is a perscription for phenomenological >>> confusion. The resulting measures of length and time are only >>> consistent with the supposed law-like properties of energy and >>> momemtum on a statiscal level. >>> >>> Harry >>> >>> >>> >>> On Fri, Aug 17, 2012 at 11:31 PM, <pagnu...@htdconnect.com> wrote: >>>> Hello Harry, >>>> >>>> You asked -- >>>> "So, the measuring instrument itself will produce energy, if it is used >>>> to precisely measure the energy of a particle?" >>>> >>>> Probably not. >>>> But maybe there are subtleties that obey the 2nd Law of Thermodynamics, >>>> but allow for some counterintuitive effects. For example, refer to -- >>>> >>>> "Concentrating Energy by Measurement" >>>> http://arxiv.org/abs/1012.5868 >>>> >>>> -- LP >>>> >>>> Harry Veeder wrote: >>>>> On Fri, Aug 17, 2012 at 8:57 PM, <mix...@bigpond.com> wrote: >>>>>> In reply to pagnu...@htdconnect.com's message of Fri, 17 Aug 2012 >>>>>> 13:11:31 >>>>>> -0400 (EDT): >>>>>> Hi, >>>>>> [snip] >>>>>>>Pardon for this very late postscript, time is hard to find. >>>>>>> >>>>>>>I believe you assume a wave function totally confined in all >>>>>>> 3-dimensions. >>>>>>> This is probably not what was intended. It is easy to find papers >>>>>>>describing crystal/lattice channel conduction of much higher energy >>>>>>>particles (electrons, protons, ...). These are extended states - only >>>>>>>confined in one or two dimensions. High energy particles do not >>>>>>>necessarily break the lattice structure. >>>>>>> >>>>>>>-- LP >>>>>> >>>>>> What I meant to do was calculate the momentum (assuming a kinetic >>>>>> energy >>>>>> of >>>>>> 0.782 MeV for the proton), and divide it into h-bar/2. However it >>>>>> appears I got >>>>>> something slightly wrong the first time around. The value I get now is >>>>>> 2.57 fm >>>>>> for a proton, and 0.93 fm for the deuteron. >>>>>> >>>>>> However I don't really stand behind the entire concept. I don't think >>>>>> the energy >>>>>> of particles magically increases when they are confined. I do think >>>>>> the >>>>>> measurement uncertainty increases, but that's not the same thing as >>>>>> their actual >>>>>> energy. Instead, I see it as a limitation on our ability to measure, >>>>>> not >>>>>> a >>>>>> change in the actual properties of the particle itself. >>>>>> IOW the restriction applies to us, not to the particles. >>>>>> Regards, >>>>>> >>>>>> Robin van Spaandonk >>>>>> >>>>>> http://rvanspaa.freehostia.com/project.html >>>>>> >>>>> >>>>> So, the measuring instrument itself will produce energy, if it is used >>>>> to precisely measure the energy of a particle? >>>>> >>>>> >>>>> Harry >>>>> >>>>> >>>>> >>>> >>>> >>> >>> >>> >> >>
