Talk:No-communication theorem
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Added conflict of interest label, clear dispute by the author(s)on the subject, weasel words and general disagreement. Certainly not an expert in the subject; suggest weaving opposing viewpoints into single article that presents both ideas before removing label. —Preceding unsigned comment added by 130.215.232.181 (talk) 03:24, 5 December 2009 (UTC)
It's going to be hard to find anyone competent to write on such a specialised topic who is not close to it. And because it is technical, what can usefully be said without the mathematics? Mike --Netteville (talk) 11:08, 30 December 2009 (UTC)
Not sure if it's relevant but there was a semi-recent experiment that pretty much destroys this theorem. http://news.softpedia.com/news/Entangled-Light-Stored-in-Cooled-Atoms-80659.shtml --Mike reddog418
means that Alice's measurement apparatus does not interact with Bob's subsystem
But this is what communication with Bell-pair is about: That Alice’s measuring apparatus interact spontaneous with Bob’s receiver system. The theorem only holds for the situation, where no successful connection is created between Alice’s system and Bob’s system. UChr (talk) 20:36, 6 January 2011 (UTC)
This proof only proves that it can't be done instantly since it assumes no time passes. This doesn't really seem to say anything about whether we can communicate faster than the speed of light, just that we can't do it in zero time flat. I keep hearing that the no communication theorem disproves superluminal communication completely- does this mean that there is a more complex proof somewhere that handles extremely brief time evolution? Particularly, the time frame that would be needed to surpass the speed of light? Even if it's too elaborate for the article, it should be described if the result exists. AllUltima (talk) 19:13, 27 March 2010 (UTC)
Not true. The no-communication and superluminal theories imply that the speed of light is a cosmological constant, and that with absolute certainty, cannot be violated. However, this assumes that particles have well-defined individual properties [hidden variables]; they do not. This was also the assumed hypothesis of the EPR experiment performed by John Bell-- if there was no communication going on that violates the speed of light, then John Bell's experiment would have resulted in locality, solidifying the cosmological constant of light, and proving that Einstein's objections of assumed realism were correct all along. It did not; information transmission between particles is instantaneous. Both this and the superluminal article approach quantum physics from the world-view of EPR, and not quantum physics in itself. Here's an article by Alain Aspect from a 1999 issue of Nature magazine that explains everything and cites further repeated experiments. — Preceding unsigned comment added by 209.105.184.93 (talk)
- According to Special Relativity, for any two events which are connected by a super-luminal signal (which therefore are the endpoints of some space-like vector) there is a frame in which an observer would see the events as exactly simultaneous. In other words, for any space-like vector, there is a Lorentz transformation which makes the extremes to have the same time coordinate t (and vice-versa). Therefore, proving the theorem (in a Special Relativistic setup) for all simultaneous events means having proved it for any super-luminal speed (unless I'm missing something which goes beyond Special Relativity) 89.202.228.211 (talk) 14:06, 26 July 2010 (UTC)
Regarding erasers experiments. Do I understand correctly that the only reason they do not show FTL communication is because of the filtering? Is the filtering really needed? What if the source of the entangled particles already provides a well defined state - say, with a given polarization? If that is the situation, it would be better to return to the version were no final conclusion is made. Srjmas (talk) 10:28, 14 October 2010 (UTC)
- The coincidence counters are what prevents FTL communication. Those counters are needed because a quantum eraser will actually produce two sets of interference patterns phase shifted from each other. So if you superimpose those interference patterns, you get essentially the same result as you would without an interference pattern. 184.100.111.110 (talk) 17:59, 15 November 2010 (UTC)
I think it is a no – proof – theorem. The proof is circular. It postulates: no connection / independency between Alice and Bob and uses this for later to show: no connection / independency between Alice and Bob. UChr (talk) 11:11, 15 January 2011 (UTC)
Opposing Viewpoint
The following is misleading in suggesting super luminal communication because it does not state all the conditions of the experiment.
"it is possible to cause or prohibit an ensemble of photons into making an interference pattern on a screen, by remotely manipulating their entangled twins"
There is no interference pattern without also the use of "Coincidence Logic" as shown in fig 3 of of the Zeilinger reference (Dopfer 1998 experiment). This coincidence logic requires a sub luminal communication from the non slit half before the interference pattern can be shown. Therefore there is no suggestion of super luminal communication and this section of the Opposing Viewpoint should be rewritten or removed. —Preceding unsigned comment added by 83.59.122.251 (talk) 00:23, 16 February 2011 (UTC)
Of course – the best way to argue against the theorem is to prove the opposite – here as a gedanken- experiment.
Idea: To take advantage of quantum entanglement to create superluminal communication.
Something likes the following:
Alice and Bob are measuring corresponding particles from pairs of quantum mechanically entangled photons - so-called Bell-couples – here called A and B.
The distance between Alice and the source are shorter than between Bob and the source, so with coordinated watches Alice will measure A before B reach Bob.
Alice can choose between inserting a mirror or not. She keeps her choice for an agreed period – for instance 1/100.000 sec. In that time perhaps 1000 pairs are sent to Alice and Bob, respectively.
By measuring his part of the 1000 pairs Bob should, with at least 99% probability, guess what Alice has chosen? Can he do so there is a practical basis for communication? As the exchange between Alice's particle and Bob's particles takes place immediately it will for a growing distance between Alice and Bob create superluminal communication.
Alice 0 = No mirror: A is meeting a polarizing beam splitter = PBS (0 / 90) who transmits horizontal polarized light and reflects vertical polarized. Photo detectors ensure that A has chosen one of the two options and not just remain in a superposition of both.
The detectors for 0 degree and 90 degrees should measuring approximately 50% - 50%.
Alice 1 = with a mirror: A is first meeting a PBS (+45 / -45). The light following the ‘+ 45’ degrees route are next meeting a PBS (0 / 90). Photo detectors should detect ‘-45’ – 0 – 90 approximately in 50% - 25% - 25% of the coincidence.
BOB's RECEIVER: Bob's receiver is an interferometer of the type ‘Mach and Zender’. The polarizing Beam splitter at the start is always set for transmitting horizontal polarized light and reflecting vertical.
The theory says that B will behave as polarized opposite to A - i.e. perpendicular to the direction A was measured.
Alice 0: Perpendicular to the vertical is horizontal and perpendicular to the horizontal is vertical. B will therefore behave as polarized either vertically or horizontally. When B reaches Bobs polarizing beam splitter (vertical / horizontal), B will choose the road corresponding to its polarization. B will follow exactly one of the ways and be detected – so the detectors D1 – D2 will detect approximately 50% - 50%.
Alice (1): Perpendicular to ‘-45’ – 0 – 90 are ‘+45’ – 90 – 0. The 25 % - 25% vertical / horizontal light will be detected by D1 – D2 as 25 % - 25 %. The ‘+45’ photons have a dilemma. With probability 0.5 to 0.5 they must split up in a horizontal part and a vertical part. Here we have interference / a superposition and we tuned the interferometer so they all will go to D1. So now D1 – D2 will detect approximately 75% - 25%. UChr (talk) 02:25, 27 February 2011 (UTC)