# Quantum entanglement and FTL information transfer. **URL:** \ **Category:** Factual Questions\ **Created:** [September 19, 2019, 5:08pm UTC](https://boards.straightdope.com/t/quantum-entanglement-and-ftl-information-transfer/840509 "2019-09-19T17:08:42Z")\ **Posts on this page:** 5\ **Page:** 3
**Author:** ![KidCharlemagne](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)\ **Post date:** [September 21, 2019, 2:05pm UTC](https://boards.straightdope.com/t/quantum-entanglement-and-ftl-information-transfer/840509/41 "2019-09-21T14:05:41Z")
> [@Half\_Man\_Half\_Wit](#): > > I’m not saying anything about ‘conscious’ choice or the like. Think of it more in terms of options: before receiving any information, say you have four options— > [ol] > [li]The British attack by land, at night[/li][li]The British attack by land, during the day[/li][li]The British attack by sea, at night[/li][li]The British attack by sea, during the day[/li][/ol] > > You have four options—four choices. To single out one of them requires log[sub]2/sub = 2 bits of information. Hence, the choices you have determine the information content of the message. > > Before you receive any bit of information, you’re maximally uncertain about the message (your uncertainty is, in this sense, equal to two bits). If you receive the first bit of the message, your uncertainty is reduced—say, you know that the British attack by land, but not when. You still have a choice between two options, so still an uncertainty of one bit, so a message needs to carry one bit of information to eliminate any residual uncertainty. I get the concept of information entropy, and that, for example, a “z” in a telegraphed message in English reduces the entropy of the message by more than an “e.” My misunderstanding came from various vague articles (and some posts) that left me thinking that my scenario was not FTL information transfer because information wasn’t being transferred, rather than because it wasn’t being transfered FTL. Then when I see a term like “choice” rather than your more instructive and entropy- reducing term “uncertainty,” I started to conflate the notion of “choice” with “can’t be the result of a coin flip.” Thanks for your help. ---
**Author:** ![ASL\_v2.0](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asl_v2.0/32/3525_2.png) [@ASL\_v2.0](https://boards.straightdope.com/u/ASL_v2.0)\ **Post date:** [September 21, 2019, 6:29pm UTC](https://boards.straightdope.com/t/quantum-entanglement-and-ftl-information-transfer/840509/42 "2019-09-21T18:29:44Z")
> [@Half\_Man\_Half\_Wit](#): > > If that doesn’t help, I think it would be more effective if you opened up a new thread to discuss these issues. I understand. I have understood. The point of the analogy was not to give another example of things being “entangled,” but the other half of this thread, which is how a variety of scenarios can be concocted that give the illusion of FTL information transfer, but that it all comes down to just that. An illusion. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [September 22, 2019, 9:07am UTC](https://boards.straightdope.com/t/quantum-entanglement-and-ftl-information-transfer/840509/43 "2019-09-22T09:07:54Z")
> [@ASL\_v2.0](#): > > I understand. I have understood. The point of the analogy was not to give another example of things being “entangled,” but the other half of this thread, which is how a variety of scenarios can be concocted that give the illusion of FTL information transfer, but that it all comes down to just that. An illusion. I think most people, myself included, reacted to statements such as these: > [@ASL\_v2.0](#): > > Sorry, not buying it. There is (or can be) as much a concept of “now” between two individuals separated by arm’s width as two individuals separated by a mile, the diameter of the Earth, the distance from Earth to the moon, a light-year, and beyond. Being local has nothing to do with it. > > […] > > Two people can synchronize watches, move apart, and take whatever means necessary to be reasonably confident (as confident as they need to be, to within whatever margin of error they deem acceptable for the experiment) that their watches remain synchronized, and then be “reading” the clocks at the same time, coming up with the same time (each having access to the same information) but without being able to communicate. > [@ASL\_v2.0](#): > > I don’t think so. Take points A, B, and, C. Put B midway between A and C. Flip a light on at B. A and C both receive news that the light has turned on at B at the same time—or merely “about the same time” if you prefer. > [@ASL\_v2.0](#): > > A and C both act off a signal from B in a way that suggests communication between A and C, but does not actually involve transfer of information from A to C, only the illusion of it due to the pre-arranged plan (which did require communication between A and C at some point, but was not done faster than light). What they suggest, on a straightforward reading, is that you claim that there would be some absolute sense in which one could put an order to events arriving at A and C—i. e. that it looks like A sends a message ‘FTL’ to which C immediately reacts, sends a message back, thus getting a conversation between the two that happens at apparent light speed, by merely following a fixed script. But that’s just not the case—in some reference frames, C will seem to reply before A sends the first message, and hence, it will not ‘look like’ there is communication between the two. And neither reference frame is objectively the right one. But in the original problem, one could claim that a sort of information exchange has taken place, although it would not be clear in which direction—i. e. which general measured first, thus causing the entangled state to collapse. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [September 22, 2019, 3:33pm UTC](https://boards.straightdope.com/t/quantum-entanglement-and-ftl-information-transfer/840509/44 "2019-09-22T15:33:54Z")
> [@ASL\_v2.0](#): > > I understand. I have understood. The point of the analogy was not to give another example of things being “entangled,” but the other half of this thread, which is how a variety of scenarios can be concocted that give the illusion of FTL information transfer, but that it all comes down to just that. An illusion. In quantum mechanics though there is non-locality, so it is not an illusion in the sensse that there is, or can be, a explanation that is ‘classical-like’ (i.e. realist) and doesn’t involve FTL information transfer (i.e. is local) for what happens. A local realist explanation could explain the correlation between two entangled particles, but Bell’s inequalties shows it would fail in other situations. What I basically mean is that any explanation of how quantum non-locality doesn’t ‘break’ causality will defy a simple classical analogy. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [September 22, 2019, 4:19pm UTC](https://boards.straightdope.com/t/quantum-entanglement-and-ftl-information-transfer/840509/45 "2019-09-22T16:19:27Z")
> [@Asympotically\_fat](#): > > In quantum mechanics though there is non-locality Well, although it’s often glossed like that, I think one should point out that it’s far from a settled issue, even though some would claim otherwise. On most accounts, the Many Worlds interpretation is thoroughly local—even local realistic, getting around Bell’s theorem by violating the (implicit) assumption that only one outcome of a range of possibilities ever obtains. Even on other interpretations, Bell’s theorem doesn’t force you to give up locality; all that a Bell inequality really is, is just a necessary condition for a certain set of variables (the experimental outcomes) to have a joint probability distribution, so their violation just means that no such distribution exists. And after all, what would be the meaning of the probability for observing, say, some simultaneous spin values for orthogonal directions, when there is no possible way to actually make such an observation? [Previous page](https://boards.straightdope.com/t/quantum-entanglement-and-ftl-information-transfer/840509.md?page=2)