John Larkin wrote: : On Mon, 23 May 2011 20:16:08 -0700, Jamie wrote: : >For a radio transmitter that is transmitting a 1MHz sine wave at 1kW : >power into free space, and then a 1MHz receiver is turned on 1 km away, : >which draws 1uW? of power from the transmitted wave, will the : >transmitting power supply increase by 1uW at the time that the receiver : >is turned on or at a later time proportional to the distance to the : >receiver?
: It may not change at all. If the antenna+receiver reflects no power : back towards the transmitter, the transmitter doesn't know they are : there. Power that is absorbed isn't reflected.
With an ordinary transmitter configuration the case is like John described: each transmitted photon either gets absorbed in the far-away receiving antenna or travels to infinity. No information gets carried back to the transmitter about which way the photon went.
It is a different story if each photon gets created by a special process, which guarantees that the photons are created in pairs in such a way that a conservation law guarantees one of the photons being 'up' while other photon being 'down'. (Ordinary rf transmitters do not create photons in that way.) You can then somehow store the one photon locally for future reference while transmitting the other photon away. Now, if an observer in the far-away receiving station catches the photon (sort-of-absorbs it, but the 'dumb' unobserved absorption is not enough to cause interesting effects) and measures its spin to be 'up', the sender can be sure to have his stored photon to be 'down'. (note that the transmit rate must be slow enough so that the sender and receiver can be sure that the photons belong to the same pair).
This still is not enough for anything interesting. It is equivalent of splitting a coin in the darkness of your pocket, without looking, and giving one half to your friend, still without looking. Your friend then travels oversees and there looks at his half. If it is tails, you can be sure (without looking) that your half is heads. However, it would be silly to say that your coin half magically transformed into heads in your pocket because of 'superluminal quantum correlations'. There is nothing quantum in this effect yet.
The strange part comes about only when you and your far-away friend are given the freedom to measure whether the photon spin is left/right instead of up/down. Such a measurement accesses quantum superpositions. Even then you and your friend must come together and compare your results in order to notice that something weird has happened. So, even by utilizing quantum correlations, there is no way to detect at the transmitting station, superluminally, whether someone has absorbed a photon which you have transmitted. But many *other* counterintuitive quantum effects demonstrably do exist.
Note that I did not go into details of what happens when one *does* measure in the left/right basis - the reason is that two-photon correlations that the OP was groping for give rise to just statistical correlations and hence sound vague and uncomfortable to a layman (at least at the "Bertelmann's socks" level). With three photons (the GHZ experiment) it is possible to get more assuring bang-bang kind of results.
Unfortunately there is no way to measure the split coin in other than the heads/tails -basis, to make an analogy which would convince a layman...
Regards, Mikko