Talk:Superluminal communication

message: Because superluminal communication is a subtopic of faster than light, the FTL page seems to encompass almost all this information and much more in a more comprehensible way. If anything, I think superluminal communication should be a sub-topic within the FTL page. 
If there's no objection I'll merge within a few months. Kdmeaney (talk) 18:21, 7 April 2014 (UTC)
thread_title:  Merge to [[Faster-than-light]] page 

message: I'm probably missing something here, but it seems to me that you really could use qubits for superluminal communication. The article says: 
:"If Alice wishes to transmit a "0", she measures (...), collapsing Bob's state (...). To transmit "1", Alice does nothing to her qubit."
But I was thinking, instead of just measuring or not measuring, couldn't Alice measure one qubit to transmit a 0, and measure a different qubit to transmit a 1? It could go something like this: Alice and Bob create a state which is an entanglement of three qubits. Then, after it's created, Alice keeps the first and third qubit. Bob takes the second qubit and goes to some far-off distance. So now: 
*Alice has |\psi\rangle_{A} and |\psi\rangle_{C} 
*Bob has |\psi\rangle_{B}
Then, to transmit a zero, Alice performs a measurement on only |\psi\rangle_{A}, and leaves the other two qubits alone. To transmit a one, Alice performs a measurement on only |\psi\rangle_{C}. Then, after Alice performs her measurement, Bob measures |\psi\rangle_{B}. The three-qubit state could be initally set up so that:
*|\psi\rangle_{A} has a high probability (greater than .5) of being measured as |0\rangle
*If |\psi\rangle_{A} is measured as measured as |0\rangle, then, subsequently, |\psi\rangle_{B} has a high probability of being measured as |0\rangle
*|\psi\rangle_{C} has a high probability of being measured as |1\rangle
*If |\psi\rangle_{C} is measured as measured as |1\rangle, then, subsequently, |\psi\rangle_{B} has a high probability of being measured as |1\rangle
There would be a probability of error in the transmission, but this error would be less than .5. One could compensate for that error by using many sets of three qubits to transmit each bit. Or maybe one could compensate with classical error-correcting codes. 
Would all of that work? I'm guessing that I've missed something, since I'm not an expert on quantum mechanics. Most of what I know is from taking a one-semester class on quantum computing. --Navigatr85 03:10, 22 August 2007 (UTC)
thread_title:  Using qubits for superluminal communication 

message: The page for no-cloning theorem states "The no cloning theorem does not prevent superluminal communication via quantum entanglement, as cloning is a sufficient condition for such communication, but not a necessary one", yet this page says that it does. Who is correct?
J0lt C0la (talk) 22:42, 4 October 2009 (UTC)
thread_title: Contradiction with [[No-cloning theorem]]

message: A suggestion for a communication system using quantum entanglement:
A(lice) and B(ob) are measuring corresponding particles from pairs of quantum mechanically entangled photons - so-called Bell-couples. 
The distance between the transmitter and the source are suitably much shorter than between the source and the receiver, so with synchronized watches the transmitter will detect its twin particle before the other twin reaches the receiver. 
The transmitter can change its measuring setup by inserting a mirror or not – choice situation, T (1) or T (0).  It keeps its choice for an agreed period – for instance 1 / 300.000 sec. 
The receiver has a fixed preset setup. It should by measuring its part of the pairs with at least 99% probability, guess the Transmitters choice.
As the exchange between the entangled particles takes place instantaneous it will for a growing distance between A and B create superluminal communication. 
A suggestion for transmitter and receiver - gives problems UChr (talk) 18:55, 5 June 2011 (UTC)
thread_title: A thought experiment – using entanglement

message: I may be wrong, but is there any reason why a simple non elastic string stretched between point A and B couldn't transmit signals from A to B and back, faster than light? If an observer as A is to send a message to an observer at B it wold push the string, the movement   wold be seen immediately by the observer at B so we can assume a signal to propagate faster than light.  — Preceding unsigned comment added by 2.82.203.179 (talk) 12:57, 30 March 2012 (UTC)
replies: text: See this Physics Forum FAQ post for an explanation why this cannot lead to FTL communication. --FyzixFighter (talk) 07:20, 11 April 2012 (UTC)
thread_title:  FTL communication 

message: I'm no expert, but the following would seem to have some bearing on this subject.
(ISNS) -- Researchers working at the Clarendon Laboratory at the University of Oxford in England have managed to get one small diamond to communicate with another small diamond utilizing "quantum entanglement," one of the more mind-blowing features of quantum physics... BobbyBoykin (talk) 20:11, 26 April 2012 (UTC)
thread_title:  Possibly Relevant Experiment 

message: This article seems to imply that quantum nonlocality is not feasible for FTL communication since the spin state of the first entangled particle is unpredictable and therefore cannot be used to meaningfully transfer data in the form of spin state to the second particle, even though this interaction has been observed to occur faster than light could travel between the particles. But isn't the fact that the first particle was observed information in and of itself? 
Couldn't a system of binary communication be theoretically accomplished by using observed/unobserved as the binary states instead of spin direction? —Manicjedi (talk) (contribs) (templates) 17:03, 16 January 2013 (UTC)
replies: text: Except how does one know, with just access to the second particle, if the first particle was observed or not? For example, if one measures the spin direction of the second particle as down (or up) how does that indicate whether the other person has observed the first particle or not? The closest thing to what you suggest might be a type of Quantum eraser experiment (see refs 4-6) where the placement of one detector effects whether or not the other detector sees an interference pattern. But that also is supposed to require a classical, subluminal channel for correlation detection. --FyzixFighter (talk) 18:13, 16 January 2013 (UTC)
replies: text: Okay that makes sense, thanks for the explanation. -—Manicjedi (talk) (contribs) (templates) 20:56, 16 January 2013 (UTC)
thread_title:  Observed/Unobserved considered Information? 

message: Hi all!
Here is a discussion about Dopfer's experiment. Please, if you are able, improve the paragraph. 84.114.197.3 (talk) 17:23, 16 February 2014 (UTC)
thread_title:  Birgit Dopfer's Experiment 

message: I reverted the removal of the diagram.  Could we please bring in at least one other editor?  I will post a request at Wikipedia talk:WikiProject Physics?--Guy vandegrift (talk) 08:03, 18 May 2016 (UTC)
replies: text: Per wp:unsourced, wp:NOR, wp:BURDEN and wp:BRD, reverted again, and formally warned on your user talk page. - DVdm (talk) 08:29, 18 May 2016 (UTC)
thread_title:  Use of the space-time diagram in "proof" 

message: It seems to me that the scope of this article is a bit muddled. It does not seem to always make a distinction between superluminal phenomena and superluminal communication. For example, superluminal group velocity is a well known and accepted fact, but I can't find any reliable source that has suggested it as a means of superluminal communication. On the other hand, I can find reliable sources that have suggested using quantum entanglement as a superluminal communication - not saying it is feasible, just that notable (not crackpot) scientists have proposed it. Certain proposals in fact directly led to the no cloning theorem. Likewise I'm sure there are sources for wormholes (perhaps a Thorne reference). But tachyons on group velocity - do we have a source that shows a notable proposal of these as means for superluminal communication? Thoughts? --FyzixFighter (talk) 14:49, 5 June 2016 (UTC)
replies: text: Agreed - the distinction between the two could certainly be clarified.  Regarding group velocity > c, at least in the context of tachyonic fields there was definitely confusion early on - people believed in the past (and some not so well educated may still think) that tachyonic fields propagate FTL. A good reference for that is the paper that coined the term "tachyon", by Feinberg.  Waleswatcher (talk) 19:29, 5 June 2016 (UTC)
thread_title:  Phenomenon vs. communication 

message: The work of Remi Cornwall seems to have dispelled the No-communication theorem. He shows that an interferometer which can work out mixed state (measurement) and pure (no-measurement) can lead to the system being factorisedhttps://www.academia.edu/29296558/The_misuse_of_the_No-communication_Theorem and is able to do this with a one (path entanglement)https://www.academia.edu/12881929/Superluminal_Signalling_by_Path_Entanglement and two photon setup (HV entanglement). He also approaches the problem from a Decoherence Theory viewpointhttps://www.academia.edu/12881902/Disproof_of_the_No-communication_Theorem_by_Decoherence_Theory.TheCampaignForRealPhysics (talk) 11:50, 21 May 2017 (UTC)
replies: text: I'm not seeing any of those references as being published in a reliable source so WP:SPS applies. Nor am I seeing any indication that Remi Cornwall is a noted source in the field. On the other hand, John Cramer and Nick Herbert are well-known in the field. In a paper they've submitted (An Inquiry into the Possibility of Nonlocal Quantum Communication), they argue that find that a scheme based on Dopfer's interferometer experiment cannot result in FTL communication. The Cramer/Herbert source isn't published (which is why I'm hesitant to insert it) but may be acceptable since the two authors are established experts whose works in the relevant field have been published by reliable third-party publications. --FyzixFighter (talk) 13:55, 21 May 2017 (UTC)
replies: text: As you say but it's obvious that the material is quality and a very good argument. I imagine Cornwallhttp://webspace.qmul.ac.uk/rocornwall will be peer reviewed at some point and was just listed here to show what is coming on the horizon. I think the comparison to Dopfer's setup is probably misdirection as Cornwall's setup is different (and more direct in exposition) and not related to a Heisenberg microscope. Ultimately people have to make their own minds up and an argument using standard analysis ought to worry the community. The single photon path entanglementhttp://webspace.qmul.ac.uk/rocornwall/Flyer_QSE1.gif version he lists is QM101 really, hard to argue against. Perhaps you could supply a direct counter proof to Cornwall's arguments, FyzixFighter or find someone who can?TheCampaignForRealPhysics (talk) 15:23, 21 May 2017 (UTC)
replies: text:  But "quality or very good argument" is not what Wikipedia is after. Wikipedia needs reliable secondary sources. As soon as these become available, Cornwall can (and probably should) be mentioned here. - DVdm (talk) 16:27, 21 May 2017 (UTC)
replies: text:  Agreed but I'm sure good people will pick up on Cornwall's work as it has the falsifiability criterion of true science (Karl Popper) and appeals to experiment.TheCampaignForRealPhysics (talk) 07:15, 23 May 2017 (UTC)

text: Please sign all your talk page messages with four tildes (~~~~) — See Help:Using talk pages. Thanks. - DVdm (talk) 09:55, 29 August 2021 (UTC)
thread_title:  Remi Cornwall's disproofs 

message: There is a summary of ficticious superluminal devices at Ansible#Other fictional FTL communication devices. Does it belong as a new section here or would it be better moved to a standalone article? — Cheers, Steelpillow (Talk) 11:56, 30 May 2017 (UTC)
replies: text: OK, I moved that section here and edited it a fair bit. — Cheers, Steelpillow (Talk) 16:55, 2 June 2017 (UTC)
thread_title:  Fictitious devices 

message: I am no expert in physics, but I find the "Proposed Mechanism" section extremely difficult to read to a layperson. Could somebody add one paragraph at the end of each subsection that, although crude, would be understood by a broader audience? Specifically, what is "group velocity" and what is "signal velocity"? Cristiklein (talk) 23:06, 6 June 2017 (UTC)
thread_title:  Layperson explanation 

message: This page was recently moved from Superluminal communication to Faster-than-light communication. I don't think I agree with the move based on WP:COMMONNAME. Doing a Google Ngram search here shows that the previous name occurs at least twice as much as other variants. I would like to propose we move it back to Superluminal communication and update articles that link to faster-than-light communication to match. --FyzixFighter (talk) 03:29, 10 June 2017 (UTC)
thread_title:  Recent page move 

message: For reasons that are not entirely clear, any mention of "Faster than light" or quantum entanglement based instant communication seems to be a topic that is targeted for attack by quantum creationists.  It is nearly impossible to sort out the origin of such attacks unless it is traced to one of hundreds of quantum creationist disinformation websites on the internet.  I have only been able to verify this in a small number of cases.  They are at least as pervasive as scientology, and appear to be well funded.
For the record, there is no particular reason instant quantum entanglement commmunication must be considered to be faster than light.  An inertialess quantum field for which the instant of now is universal would mean that communication between points already connected by means of entangled photons (limited by the speed of light) actually may be occurring both instantly and SLOWER than light propagates, because entanglement spin flips occur with respect to the relativistic invariant non-inertial rest frame of the quantum field itself.
Faster, slower (than light) are also with respect to relative states of motion, particularly for entangled photons.  Even the invariant speed of light must be measured with respect to some other inertial reference frame that is invariant. While not really an original idea, this is a valid counterpoint to the FTL explanation of the same effect somewhat more palatable to quantum relativists and QFT.Danshawen (talk) 22:09, 3 July 2017 (UTC)
thread_title:  FTL communication under attack by quantum creationists 

message: It's impossible because when we think about it we attain a paradox? 
: That's a paradox in itself. Kortoso  (talk) 23:11, 8 November 2017 (UTC)
thread_title:  Paradox? 

message: There is no mention of other (science) fictional settings where communication is instant (or nearly so). In the Star Wars universe, for example, interstellar communication appears to be instantaneous (as portrayed in Attack of the Clones), but movement of matter across such distances requires traveling through hyperspace. — Loadmaster (talk) 19:52, 10 August 2018 (UTC)
thread_title:  Star Wars universe 

message: I don’t believe the ansible was “stolen” from the “Buggers”.  They have an inborn ability to communicate instantly.  Once Humans realized this, the ansible was developed. 2600:1700:D2B1:1490:D0B2:7411:B48B:38D6 (talk) 06:23, 1 March 2023 (UTC)
thread_title:  Ansible in Ender’s Game