page russell

who said anything about instantaneous? yes, multiple measurements were required in the setup done by walburn et al, and most of those measurements required the detector to run for 400 seconds. But this isnt about instantaneous signals, but super luminal signals. obviously this set up i have proposed would have no practical implications for any distance we are now able to traverse. you couldnt do this on the surface of the earth, let alone a table top. but the theoretical possibility of signaling from distances in such a way that the information must travel outside of the light cone still seems possible. who cares if it takes an hour of measurements to send a very simple message if that message comes from a source a billion light years away? Merged post follows: Consecutive posts mergedlet me put it this way: what the walburn et al experiment is doing in general is using entanglement to infer which-way information. It turns out, experimentally, that the availability of this information destroys the interference pattern. All I am suggesting is it ought to be possible to use that general mechanism to communicate faster than light. various set ups are irrelevant; the thought experiment still stands.

I think I can add to the complexity of this discussion in two ways. first the experimental setup provided by bascule is unclear, and second by pointing out that delayed earasure is possible. First off, the setup. It ought to look like this: A laser beam entangles pairs of photons using spontaneous parametric down conversion (SPDC - dont ask me for a more complicated discussion of that, however, it is important to note that what we mean by "entangled photons" is that the two photons have and will always have corresponding polarizations.) and then that laser beam is then split. Call the resulting beams S and P. The S beam is sent off towards a Young double slit setup, and the P beam is sent towards a simple detector which will register the polarization of the P beam (and thus we can infer the polarization of the S beam). At this point, we have no way of determining any so called "which-way" information, and so running this experiment will produce an interference pattern as a result of the S beam traversing the double slit experiment. However, if we were to add quarter wave plates directly in front of the two slits, we could gain the possibility of infering which-way information. This is becuase the quarter wave plates change the polarization of the S beam, which results in a correlated change in the P beam's polarization. Thus we ought to be able to infer the which way information without disturbing the S beam in any way (it is important to note that tchanging the polarization has no effect on the interference pattern emerging or not, as will become doubly clear when I discuss delayed erasure in a moment). Alas, the interference pattern is destroyed and replaced by the additive pattern. That is pecular enough, but at this point we still do not have the possibility of superluminal signaling as bascule has in mind, because the two measurement stations must still communicate results to each other in a classical way. But consider the following; placing a polarizer in the path of the P beam will destroy the possibility of which-way information, and incredibly the interference pattern returns. This is the point at which bascule thinks we can communicate superluminally, and I agree with him. Now we have a scenario in which purposeful, systematic and deterministic action at one location will result in clear results in another, and the notion of locality seems to be violated (if you dont think so, ask and I will attempt to explain how and why bells theorem implies that either locality or determinism must be false, or at least irrelevant to quantum mechanics). Thus what bascule has in mind is this: Alice at the P beam can place and remove the polarizer, corresponding to a 0 and 1 repectively, and Bob at the S beam can observe either an interference or an additive pattern, correlating to a 0 or 1, respectively. Here is a nice graphic, which was obtained from the following site, which has a splendidly clear explanation of this setup: http://grad.physics.sunysb.edu/%7Eamarch/ Now, for those of you who dont yet beleive, consider delayed erasure. In this same experiement, the researchers went on to lengthen the P beam. This had the result that the S beam photons entered the double slit apparatus and did whatever they do there before the P beam photons either hit or did not hit a polarizer. The interference pattern still disappeared if there was a mere possibility of which-way information. Thus there appears to be some sort of backwards causality, which is only possible given superluminal speeds. So consider this all a comlex smoke signal. Alice sits there and puts the polarizer over the p beam for some time and then removes it, and then puts it back, and so on. Bob sits tehre and observes alternating interference patterns and additive patterns correlating perfectly to the action of alice. What could we say about this other than superluminal signaling, assuming alice and bob are outside of each others light cone?