>Interesting, but my schedule makes it hard for me to analyse this just >now. Now, if you think you can argue for non-locality from Renninger >type of measurement, don't hesitate to show us. Here the point was >just that the violation of Bell's inequality does not lead to non- >local action, unless measurement leads to single realities. > >A long time ago, I convinced my self that Elizur Vaidman type of >measurement without interaction might be problematic with the MWI, but >that was not the case. Is Renninger measurement related to this?
Well Vaidman wrote something about that. "The word “measurement” in quantum theory have many very different meanings. The purpose of the Renninger and Dicke measurements is preparation of a quantum state. In contrast, the purpose of the EV [Elitzur-Vaidman] interaction-free measurement is to obtain information about the object. In Renninger and Dicke measurements the measuring device is undisturbed (these are negative result experiments) while in the EV measurement the observed object is, in some sense, undisturbed. In fact, in general EV IFM the quantum state of the observed object is disturbed: the wave function becomes localized at the vicinity of the lower arm of the interferometer (see Sec. 3 of the EV paper). The reasons for using the term “interaction-free measurements” are that the object does not explode (if it is a bomb), it does not absorb any photon (if it is an opaque object) and that we can claim that, in some sense, the photon does not reach the vicinity of the object." "I can see something in common between the Renninger–Dicke IFM and the EV IFM in the framework of the many-worlds interpretation. In both cases there is an ‘‘interaction’’: radiation of the scintillator in the Renninger experiment or explosion of the bomb in the EV experiment, but these interactions take place in the ‘‘other’’ branch, not in the branch we end up discussing the experiment. In an attempt to avoid adopting the many-worlds interpretation such interactions were considered as counterfactual." "Reasoning in the framework of the many-worlds interpretation (MWI ) leads to the statement that while we can find an object in the interaction-free manner, we cannot find out that a certain place is empty in the interaction-free way. Here, I mean ‘‘interaction-free’’ in the sense that no photons (or other particles) pass through the place in question. Getting information about some location in space without any particle being there is paradoxical because physical laws include only local interactions. In the case of finding the bomb, the MWI solves the paradox. Indeed, the laws apply to the whole physical Universe which includes all the worlds and, therefore, the reasoning must be true only when we consider all the worlds. Since there are worlds with the explosion we cannot say on the level of the physical Universe that no photons were at the location of the bomb. In contrast, when there is no bomb, there are no other worlds. The paradox in our world becomes the paradox for the whole Universe which is a real paradox. Thus, it is impossible to find a procedure which tests the presence of an object in a particular place such that no particles visit the place both in the case the object is there and in the case the object is not there. Quantitative analysis of the limitations due to this effect were recently performed by Reif who called the task ‘‘interaction-free sensing.’’. This effect also leads to limitations on the efficiency of ‘‘interaction-free computation’’ when all possible outcomes are considered." See, in example, this paper http://www.tau.ac.il/~vaidman/lvhp/m87.pdf > >Of course, with computationalism all this are open problem. Would the >physics extracted from computationalism leads to non-locality, I would >decide to be a gardiner ;) > >Bruno Well being a farmer, not a mathematician, I can make a mistake. So when Vaidman writes "Getting information about some location in space without any particle being there is paradoxical because physical laws include only local interactions" actually he is talking about *some* sort of non-locality. At least, this is my humble feeling. s. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
