I understand your confusion, but here's why people often feel that quantum entanglement is rather strange. Let's first consider the following statement you make:

2 things have some properties set in correlation to each other at the point of entanglement, they are separated, measured, and found to have these properties

A classical (non-quantum) version of this statement would go something like this. Imagine that you take two marbles and paint one of them black, and one of them white. Then, you put each in its own opaque box and to send the white marble to Los Angeles, and the black marble to New York. Next, you arrange for person L in Los Angeles and person N in New York to open each box at precisely 5:00 PM and record the color of the ball in his box. If you tell each of person L and person N how you have prepared the marbles, then they will know that when they open their respective boxes, there will be a 50% chance of having a white marble, and a 50% chance of having a black marble, but they don't know which is in the box until they make the measurement. Moreover, once they see what color they have, they know instantaneously what the other person must have measured because of the way the system of marbles was initially prepared.

However, because you painted the marbles, you know with certainty that person L will have the white marble, and person N will have the black marble.

In the case of quantum entanglement, the state preparation procedure is analogous. Instead of marbles, we imagine having electrons which have two possible spin states which we will call "up" denoted $|1\rangle$ and "down" denoted $|0\rangle$. We imagine preparing a two-electron system in such a way that the state $|\psi\rangle$ of the composite system is in what's called a superposition of the states "up-down" and "down-up" by which I mean$$ |\psi\rangle = \frac{1}{\sqrt 2}|1\rangle|0\rangle + \frac{1}{\sqrt{2}}|0\rangle|1\rangle$$All this mathematical expression means is that if we were to make a measurement of the spin state of the composite system, then there is a 50% probability of finding electron A in the spin up state and electron B in the spin down state and a 50% probability of finding the reverse.

Now me imagine sending electron $A$ to Los Angeles and electron B to New York, and we tell people in Los Angeles and New York to measure and record the spin state of his electron at the same time and to record his measurement, just as in the case of the marbles. Then, just as in the case of the marbles, these observers will only know the probability (50%) of finding either a spin up or a spin down electron after the measurement. In addition, because of the state preparation procedure, the observers can be sure of what the other observer will record once he makes his own observation, but there is a crucial difference between this case and the marbles.

In electron case, even the person who prepared the state will not know what the outcome of the measurement will be. In fact, no one can know with certainty what the outcome will be; there is an inherent probabilistic nature to the outcome of the measurement that is built into the state of the system. It's not as though there is someone who can have some hidden knowledge, like in the case of the marbles, about what the spin states of the electrons "actually" are.

Given this fact, I think most people find it strange that once one observer makes his measurement, he knows with certainty what the other observer will measure. In the case of the marbles, there's no analogous strangeness because each marble was either white or black, and certainly no communication was necessary for each observed to know what the other would see upon measurement. But in the case of the electrons, there is a sort of intrinsic probability to the nature of the state of the electron. The electron truly has not "decided" on a state until right when the measurement happens, so how is it possible that the electrons always "choose" to be in opposite states given that they didn't make this "decision" right until the moment of measurement. How will they "know" what the other electron picked? Strangely enough, they do, in fact, somehow "know."

Addendum. Certainly, as Lubos points out in his comment, there is nothing actually physically paradoxical or contradictory in entanglement, and it is just a form of correlation, but I personally think it's fair to call it a "strange" or "unintuitive" form of correlation.

IMPORTANT DISCLAIMER I put a lot of things in quotes because I wanted to convey the intuition behind the strangeness of entanglement by using analogies; these descriptions are not meant to be scientifically precise. In particular, any anthropomorphisations of electrons should be taken with a large grain of conceptual salt.

Rather than repeat some very good standard answers, I want to discuss this issue from the perspective as to why classical systems should be viewed as strange.

If we accept quantum mechanics as being fundamental, then in some sense we shouldn't really find things like entanglement to be strange at all. As pointed out by the answer given by joshphysics, as well as the answer given by Lubos Motl in the similar question, entanglement is really just correlation. The strangeness enters because we are accustomed to the the idea of classical locality and separability of systems.

Locality is best understood as the concept prohibiting action-at-a-distance, and is closely tied to Newton's Third Law of Motion. Newton's third law is the statement,

Every action has an equal and opposite reaction

which basically tells us that forces on an object are the result of the interaction by another object. Action-at-a-distance is a situation where two objects separated in space share perfect correlation in their motion, implying that one object is directly responsible for the other objects activities. In Newtonian mechanics, there is no limit on velocity, so action-at-a-distance, while seemingly unbelievable, is not prohibited.

This situation changed when it was realized that there is an ultimate speed limit to how fast two objects can communicate, or rather influence each other via the third law. This is the speed of light, as enshrined in the theories of special relativity and general relativity. This ultimate speed limit on the transfer of real information between two spatially separated regions is where our "classical intuition" fails (which is not a statement about human intuition, it is a statement about an apparent contradiction that arises in the logical statements one can make in the context of a particular theory).

So really the question isn't so much,

"Why is quantum mechanics weird?"

it's

"Why does our classical intuition fail?"

Much of this failure in our intuition is related to the separability of states which is an inherent feature of classical mechanics.

Separability of states is possible when one is able to describe composite states as direct products of subsystem state vectors.

To explain this a little better, there is a postulate of quantum mechanics that states

The Hilbert space of a composite system is the Hilbert space tensor product of the state spaces associated with the component systems

This is written mathematically as $$\mathcal{H}_{AB} = \mathcal{H}_{A} \otimes \mathcal{H}_{B}$$This can be imagined as just an abstract infinite dimensional space (just a really big space). The direct product $\otimes$ tells us to take every component of the each space times every component of the other space (e.g. if I can provide a basis for one space as $x$,$y$,$z$ and the basis for the second space as $a$,$b$,$c$; the direct product space would be $xa$,$xb$,$xc$,$ya$,$yb$,$yc$,$za$,$zb$,$zc$ )

As implied above, the component subspace can be given a basis that spans the space (span = provide a complete coordinate system that can describe every point):

$$\mathcal{H}_{A} \rightarrow \{ |a_i \rangle \}$$and$$\mathcal{H}_{B} \rightarrow \{ |b_j \rangle \}$$

with our basis chosen, the pure state of the composite system can be defined as:

$$|\psi\rangle = \sum_{i,j} c_{ij} |a_i\rangle \otimes |b_j \rangle $$

As discussed in the wikipedia article, if the state $$|\psi\rangle \in \mathcal{H}_{A} \otimes \mathcal{H}_{B}$$ can be written as $$|\psi_A\rangle \otimes |\psi_B\rangle$$ and $$|\psi_i\rangle$$ is a pure subsystem (e.g. also has an independent Hilbert space), then the system is described as separable. If it is not separable, it is entangled, and therefore:

$$|\psi\rangle = \sum_{i,j} c_{ij} |a_i\rangle \otimes |b_j \rangle \neq |\psi_A\rangle \otimes |\psi_B\rangle$$

(Update Example borrowed from Marcini and Severini: Let $|\psi_{A1}\rangle$, $|\psi_{A\perp}\rangle$ be orthogonal states in $\mathcal{H_A}$, and $|\psi_{B1}\rangle$, $|\psi_{B\perp}\rangle$ be orthogonal states in $\mathcal{H_B}$. Then $$|\psi_{A1}\rangle \otimes |\psi_{B1}\rangle \in \mathcal{H_A} \otimes \mathcal{H_B}$$ as well as $$a|\psi_{A1}\rangle \otimes |\psi_{B1}\rangle + b|\psi_{A\perp}\rangle \otimes |\psi_{B\perp}\rangle \in \mathcal{H_A} \otimes \mathcal{H_B}$$ with $a$,$b$ $\in \mathbb{C}$. The first can be factorized into states of the subsystems, the second cannot. The existence of this second state would result in the above inequality.)

In our classical intuition, systems are separable, and it is only through some direct classical mechanical coupling that they show any correlation. So in the marble examples, there is some mechanical process that is involved in mixing marbles together. The marbles are still separable systems, and the correlation of one person finding a white marble, and one finding a black marble is still rooted in classical statistical mechanics, simply by the fact that the marbles have a definite color associated with them before they are put in the box. This means that the state of color for either marble is known and is not correlated with the state of the other marble. It makes sense for one to talk about the marbles being in a black or white state in classical mechanics. This is not a typical state in quantum mechanics, and systems having a definite state prior to observation is the root cause for the failure of our classical intuition

We must understand that the full state space in the entangled system is much larger than the space of separable systems. There is a good analogy in understanding the different size of state spaces in the context of the Born Oppenheimer approximation (and Emilio Pisanty does a good job explaining the derivation in his answer to this SE question). The Born Oppenheimer approximation provides a justification for allowing for the separation of the nuclear and electronic states of a molecular system:

$$\Psi_{Total} = \psi_{electronic} \times \psi_{nuclear}$$

This is possible by showing that one can ignore "vibronic coupling" associated with transitions of particles which would be represented by off-diagonal terms in the complete Hamiltonian matrix.

Similarly in our "classical intuition" we can ignore many terms that describe the state of the system simply because their effects are too small to be considered. As systems become smaller, these effects are harder to ignore, and the notion of a quantum object being able to have a definite state (e.g. being a definitely black or white marble) prior to our observation is not possible. However, the correlation of the outcomes is not removable from the system, in this sense the correlation must be viewed as more fundamental then the definiteness of the state. This is a very different state of affairs than what we find in classical mechanics, where definiteness of state is viewed as more fundamental.

So hopefully this gives a little more clarity as to why we think quantum entanglement is a "big deal". It requires a fundamental change in our understanding and approach to physics.

Ecco la risposta che mi ha fatto capire qual è il problema. La descrizione seguente è fondamentalmente una versione ampliata di questo post del blog, che ho letto molto tempo fa.

Immagina che stiamo per giocare. È un gioco cooperativo, quindi vinceremo entrambi o perderemo entrambi. Se vinciamo, otteniamo molti soldi, ma se perdiamo moriamo entrambi, quindi dovremmo fare del nostro meglio per vincere.

Il gioco si svolge come segue: verrai portato su una navicella spaziale su Plutone , mentre io resterò qui sulla Terra. Quando arrivi a Plutone, qualcuno lancerà una moneta equa. A seconda del risultato, chiederanno una delle seguenti due domande:

1. Ti piacciono i cani?
2. Ti piacciono i gatti?

Dovrai quindi rispondere "sì" o "no". Nello stesso momento, qualcuno sulla Terra lancerà una moneta equa diversa e mi farà una delle stesse due domande in base al suo risultato.

Le regole del gioco sono leggermente strane. Sono i seguenti: vinciamo la partita se ognuno di noi fornisce una risposta diversa dall'altra, a meno che non ci chiedano entrambi dei gatti, nel qual caso dobbiamo dare la stessa risposta reciproca per evitare di perdere.

Dato che siamo a diverse ore luce di distanza, non possiamo comunicare tra di noi durante il gioco, ma noi possiamo dedicare tutto il tempo che ci piace a discutere di strategie prima di andare e ognuno di noi può portare con sé tutto ciò che vuole per aiutarci a rispondere alle domande.

Ora, con un po 'di riflessione dovresti riuscire a convincerti che in un mondo classico, il meglio che possiamo fare è avere una possibilità di $ 75 \% $ di vincere la partita. Per fare questo, siamo solo d'accordo che, indipendentemente dalla domanda che ci viene posta, dirai "sì" e io risponderò "no". Se lo facciamo, vinceremo a meno che non ci venga chiesto entrambi dei gatti e la probabilità che ciò accada è di 1 su 4. Non importa cosa portiamo con noi, purché si comporti secondo le regole familiari di meccanica classica, non può aiutarci a fare meglio di questa semplice strategia. In particolare, non fa alcuna differenza se ognuno di noi porta con sé un oggetto nascosto, che in seguito misuriamo in qualche modo.

Tuttavia, in un mondo quantistico le cose sono leggermente diverse: possiamo vincere il gioco $ 85,3 \% $ del tempo. Non entrerò nei dettagli di come esattamente lo otteniamo, ma implica la creazione di una coppia di particelle intrecciate, di cui tu prendi una e io prendo l'altra. A seconda che ti venga chiesto di cani o gatti, esegui una delle due misurazioni diverse sulla tua particella e io faccio qualcosa di simile. Funziona semplicemente secondo le regole della meccanica quantistica che se seguiamo correttamente questa procedura, vinceremo questa partita con una probabilità di $ \ cos ^ 2 (\ pi / 8) $, o $ 85,3 \% $. Sono stati eseguiti molti esperimenti equivalenti a questo gioco (si chiamano esperimenti di Bell test) e il gioco è stato effettivamente vinto $ 85 \% $ delle volte.

Ci sono altri giochi che possono essere costruiti, che sono leggermente più complicati da spiegare, dove usare l'entanglement ti permette di vincere $ 100 \% $ delle volte, anche se nel mondo classico non puoi evitare di perdere un po 'di tempo. Un documento che descrive un tale gioco (tra gli altri esempi di tali giochi quantistici) può essere trovato qui.

Questo è il motivo per cui l'entanglement è un grosso problema. Ci consente di correlare le cose in questo modo leggermente più di quanto possano essere correlate nel mondo classico. Ci permette di fare qualcosa che non sarebbe possibile se l'entanglement non esistesse.

Per inciso, c'è un altro motivo per cui l'entanglement è un po 'strano: nel gioco dei cani e dei gatti, perché l'entanglement è solo permetterci di vincere $ 85 \% $ delle volte e non $ 100 \% $? Si scopre che puoi inventare universi con "fisica alternativa" in cui questo gioco può essere vinto $ 100 \% $ delle volte, pur non lasciando che le informazioni vengano trasmesse più velocemente della luce, ma nel nostro universo, $ 85,3 \% $ è il punteggio massimo possibile. Il motivo per cui l'entanglement dovrebbe essere limitato in questo modo è una questione aperta nelle basi della meccanica quantistica.

What happened here? I am in complete shock that so many respondents are answering "yeah, no big deal, nothing really spooky going on, yeah it's just correlation..." What in the world is everyone talking about?

Peter Oakey, forget all the math for a minute. This will take a few minutes of detailed but entirely non-mathematical setup, but if you can bear with me I can explain to you in a very pointed way why entanglement is spooky and cannot be explained by classical correlations alone.

Hour Time is Your Time

First, we need something easily visualized with which to set up the situation. A clock with only one hand, an hour hand, works nicely.

Did I mention that the hands on these clocks are a bit weird? Well, actually... a lot weird.

Instead of being sharp pointy lines, the hands are painted onto a disk... badly. They are severely smeared, to the point that they are fully black only in the exact direction of the time they represent, e.g. 3 o'clock. From that direction they fade off into gray as you go around the disk on which the hand is painted. In fact, the disk remains pure white only on the exact opposite side from the pure black direction. So, if the pure black is pointing at 3 o'clock, the pure white is pointing the opposite direction at 9 o'clock. (I may add some simple graphics for this tomorrow, but it's too late tonight.)

Through a Slot Darkly

Um, did I mention that reading these clocks is also a bit weird? Well... a lot weird.

That's because you are only permitted to read them by looking through a single slot that you can dial into any position you want, such as 12 o'clock. Now, you might think that would make seeing the hand impossible most of the time, but don't forget: the hands on these clocks are so badly smeared out that in most cases when you look through the slot you will see some kind of gray, probably at least 50 different shades of it.

Occasionally, though, you will happen to see pure black or pure white. That means you got lucky and set your analyzer to one of the two positions from which you can read the clock with 100% certainty. Thus if you set the slot to 3 o'clock and see pure black, it means the clock was set to that same time, 3 o'clock. But notice that if you had instead set the slot to 9 o'clock, you would have seen the pure white that is always opposite to the pure black, and you again would have known with certainty that the time was 3 o'clock. Alas, if you had instead chosen any other setting for the slot, you would have seen only some shade of gray. Darker grays would have meant you were "closer" to the time on the clock, while lighter grays would have meant you are farther away from it. But for any of the gray shades you can only make a guess about the exact time.

Game, Reset, Match

Which leads to a final but very important oddity about these clocks: Every time you read one, the hand resets itself to match the orientation of your reading slot. Now that's really weird! How does this final twist work?

It's somewhat random, actually, but in a way that is strongly guided by how gray the disk is at the point where you read it. If you happened to read pure black or pure white, there is no problem: The hand simply stays exactly where it was, on black or white. If instead you happened to see the shade of gray that lies $90^{\circ}$ away from pure black or pure white, e.g. 12 or 6 for a hand pointing at 3, then the dial resets in a fully random fashion, with a 50/50 chance of moving either pure black or pure white into the reading slot position after. Everything in between becomes a probability that is more in favor of black or white. Thus a very dark shade of gray will almost always cause the clock dial to rotate pure black into the reading slot position... but not quite every time. As long as the disk has some white mixed in with the black, the pure white side of the dial disk will occasionally get rotated into the reading position.

Incidentally, in case you were wondering how to translate some weird shade of gray into a specific reading of the clock, this gray-based resetting feature provides the answer. What happens is that you final answer always is based on how your set your analyzing slot, specifically on the value that gets rotated into that position after you read the original value on the clock. So for example, if you set your analyzer to 12 o'clock, you will always get an answer of either 12 o'clock (pure black rotated into the 12 o'clock position) or 6 o'clock (pure white rotated into the 12 o'clock position). The original clock dial position no longer matters at that point, since the very act of reading the clock resets it and makes the new value into the only one that matters.

Strange Times

Strange times (and time pieces) indeed! But if you are wondering why I am putting in so many seemingly pointless restrictions, I assure you they are not as arbitrary as they seem. What I am doing it translating large chunks of quantum mechanics into a physical model that helps visualize certain types of quantum relationships. Because quantum mechanics deals with small systems that contain very little information, it is all about understanding these odd constraints that do not allow the huge freedoms to which we are so accustomed from the classical world.

I'll call these constructions fuzzy clocks due to all the probabilities going on in reading them.

Igor, Pull the Lever!

Next comes the experimental arrangement using these clocks, one that is the same for both classical correlation and quantum entanglement:

1. Set two fuzzy clocks to have exactly opposite but randomly selected times, e.g. 1-and-7 or 10-and-4. Keep these times secret from everyone in the universe.

2. Place the fuzzy clocks in two spaceships A and B and fly them to locations very far apart. For example, you could fly them so far away from each other that light takes an hour just to get from one spaceship to the other.

3. Have your observers in each spaceship read their clocks. There are multiple ways to do this, but in this case we'll prearrange for the observers to use identical orientations of their slot readers. For the rest of this discussion, we'll assume their slot readers are set to 3 o'clock.

Recall that when a slot reader is set to 3 o'clock, the final reading will always be either 3 o'clock (pure black) or 9 o'clock (pure white). That's because reading the clock causes it to reset (rotate) based on how much gray is seen through the slot. It is those new pure black or pure white values that become the final readings of the clocks.

Workin' 12 to 6, What A Way to Make a Livin'

Now let's focus on a particular subset of correlated fuzzy clocks, which is the ones that were set originally to either 12 or 6. What happens to these clocks when they are read by the 3 o'clock slot readers on both spaceships?

Recall that any clock value initially set to 12 or 6 will for a 3 o'clock slot reader show the shade of gray that results in a 50/50 toss-up. So, half of these clocks will end up with pure black at the slot position (3 o'clock), and the other half with pure white (9 o'clock).

Let's assume that ship A reads one of these 12-or-6 clocks and gets a value of pure black, meaning that it has been reset to 3 o'clock. What can the observer say then about what the other spaceship will see when looking at the correlated clock in the same way?

Losing It

Well... nothing, really. From the perspective of the observer, this worst-case scenario of 50/50 random reassignment has completely erased any information that would have been available about the time on the other fuzzy clock. So, all the observer on ship A can say for this group of clocks is "since this is the 12-or-6 clock group, ship B will have a 50/50 chance of reading black or white." Which is exactly correct: Ship B will get just as random a result in this case as ship A did. The correlation that potentially existed was in effectively erased by the nature of the reading procedure, so neither ship can say anything about what the other would have seen.

That's the classical case: No correlation -- no predictability -- is possible between ships for the 12-or-6 clock pairs analyzed using 3 o'clock slots.

Finding It

So, what if the clocks are quantum entangled instead of just sharing a correlated past?

Easy: When the observer on ship A sees pure black at 3 o'clock for a 12-or-6 clock pair, she knows that the observer on ship B will see pure white. Always. 100%.

Oops.

Um... how exactly did that happen?

Spooky Is as Spooky Does

Spooky action at a distance remains a pretty good name for it, because I guarantee you are not going to be able to construct a meaningful explanation for it in terms of actual experimentally accessible parameters. Nor is it a hypothetical effect. Real examples of this effect are always more complicated than the intentionally extreme version I've used here, but it doesn't get any less weird. John Bell was the fellow who first figured out that this effect was real and testable, decades after minds as great as Einstein and Bohr came very close to it but missed seeing the opportunity.

The fuzzy clocks provide a quite physical image of what has to happen. When one of the two spaceships A or B analyzes their clock, they cause it to reset (rotate) to the new time enforced by their slot position, e.g. from 12-or-6 to 3-or-9.

In classical physics, that's the end of it. Each disk rotates into its new position locally and without any connection to the other disk.

In entangled physics, the act of resetting the disk in A or B disturbs a very unforgiving conservation law, in this case the conservation of angular momentum (but other laws can also be used). It turns out that the universe is so unforgiving for such absolute conservation rules that issues such as the speed of light become secondary to ensuring that the quantity is absolutely conserved. So, spooky-style, the universe as a whole does not allow you to reset just one of the entangled disks, which would cause a slight non-conservation of angular momentum. Instead, when you must reset both.

So, when A analyzes her 12-or-6 clock with a 3 o'clock slot analyzer, she ends up resetting both disks to the new 9-or-3 orientation. All of this happens "instantly," even across light-years, whatever "instantly" means in such cases. (It doesn't really mean much when entanglement is involved, which is why I usually avoid such terminology.)

The Bottom (Entangled) Line

There are many ways to get lost in the weeds in all of this. However, entanglement in terms of a "something" that instantly resets the options available to distant events, even while prohibiting the conveyance of conventional information (a point I've skipped over), is both quite real experimentally and quite weird conceptually. It's one of those little mysteries of the universe that is still worth contemplating from time to time.

Il "grosso problema" sembra essere che, a causa del teorema di Bell * e della meccanica quantistica "data", possiamo scegliere solo tra non località ("azione inquietante a distanza") è vera e / o viene violata la definizione controfattuale (che potrebbe non implicare alcun "libero arbitrio", qualunque cosa significhi), se vogliamo scegli tutto . Il primo è "non intuitivo" e (la possibile implicazione di) il secondo è, beh, un "grosso problema" per molte persone (inclusi almeno alcuni scienziati che sostengono che implicitamente la scienza si basa sul "libero arbitrio ").

*" Non puoi discutere con un teorema. "

Mi piace usare le seguenti analogie quando penso all'entanglement quantistico. Se il mondo ha funzionato come @joshphysics descrive nella prima parte della sua risposta in cui due biglie di colore diverso sono collocate in due scatole separate e poi separate, quindi aprendo una delle scatole, la persona che guarda saprà con certezza di che colore si trova l'altra perché il colore delle biglie in ciascuna scatola è stato determinato durante il "processo di entanglement", ma non c'è nulla di "strano" in modo intuitivo in questo. Ma, come ha mostrato @joshphysics, questo non è equivalente all'entanglement quantistico.

L'entanglement è più simile a questo: immagina di mettere insieme due monete in modo tale che diventino 'entanglement' (forse lanci un qualche tipo di incantesimo o qualcosa del genere). Una persona porta una moneta sulla luna e un'altra persona porta l'altra moneta su Marte. Dal punto di vista di ogni persona, la probabilità che ottenga testa o croce dopo aver lanciato la moneta è del 50%. Ciò che implica l'entanglement quantistico è che una volta che una delle persone lancia la sua moneta e scopre che esce, diciamo, testa, allora non importa cosa (supponendo che le monete rimangano impigliate), quando l'altra moneta viene successivamente lanciata (può essere capovolto in qualsiasi momento dopo il primo), dovrà alzare la coda. Dal punto di vista del secondo flipper, scoprirà comunque di avere una probabilità del 50% di ottenere testa o croce, ma una volta che la prima moneta è stata girata e ha girato testa, la seconda moneta avrà una probabilità del 100% di essere croce, non importa quando è effettivamente capovolto dopo il primo. È strano.

Ci sono due cose che rendono sorprendente la versione quantistica di "metti una palla bianca in una scatola, una palla nera in un'altra, mescola le scatole, poi apri una scatola e impara cosa contiene l'altra".

Parte di ciò che rende il secondo punto particolarmente confuso è che l'accordo extra ancora non consentire la comunicazione. Esperimenti isolati possono ottenere alcune corrispondenze dopo il fatto, ma non possono segnalarsi a vicenda di cambiare la procedura che stavano già per seguire.

Cercherò di illustrare con un gioco. Questo è un gioco in cui le strategie classiche non possono garantire una vittoria il 100% delle volte, ma le strategie quantistiche in cui condividi alcune cose intrecciate prima del tempo possono . Ecco le regole:

• Tu e un partner siete isolati gli uni dagli altri.
• Ottieni due gettoni.
• Un arbitro sceglierà una riga da un tabellone 3x3 a caso, e te lo dico.
• Non puoi usare i tuoi gettoni o usarli per coprire due celle della riga. Non è consentito coprire solo una singola cella. Solo 0 o 2.
• Il tuo amico segue un processo simile, ma gioca su una colonna anziché su una riga.
• Dopo aver scelto entrambi come giocare, ottieni torna insieme e confronta i risultati.
• Se la singola cella che si trova sia nella tua riga che nella colonna del tuo amico è coperta da esattamente un token, allora hai vinto. Altrimenti perdi.

Ecco un'immagine che illustra alcuni risultati di alcune persone che vincono, perdono e non rispettano le regole:

Puoi vedere che questa è una sorta di gioco di coordinazione. Tu e il tuo amico dovete cooperare in modo che uno di voi copra la cella comune, ma non l'altro. È difficile perché durante il gioco non sapete esattamente quale cella sia e non potete comunicare.

Cerca di trovare dei modi per vincere la partita. Scommetto che non puoi fare di meglio che aspettarti di vincere 8/9 delle volte. Puoi anche provare a inserire biglie colorate in scatole. Non importa. Il meglio che puoi fare è 8/9.

Un esempio di una strategia così ottimale è: giochi sempre nella cella sinistra e centrale della tua riga, mentre il tuo amico gioca solo se ottiene la destra- la maggior parte delle colonne. Perdi solo se viene selezionata la colonna più a destra e il tuo amico è sfortunato, il che accade 1/9 delle volte.

Ma, come ho detto, c'è una strategia quantistica che vince il 100% delle volte . Massaggia la corrispondenza dopo il fatto in una cooperazione per coprire la cella comune esattamente una volta, nonostante l'isolamento.

Sarebbe un po 'prolisso spiegare la strategia qui, ma è per questo che ho scritto questo post del blog pratico ma leggermente tecnico. Ecco un'immagine che mostra i circuiti quantistici utilizzati per vincere il gioco. È carino, ma non troppo informativo fuori contesto:

C'è anche un articolo di wikipedia, sebbene utilizzi una leggera variante del gioco Ho descritto.

(Aggiungendo solo un'altra risposta a quelle chiare fornite sopra) La "stranezza" dell'entanglement di due particelle di spin 1/2 è la seguente: se hai due osservatori Alice e Bob, separati da una qualsiasi distanza, e dì loro per misurare gli spin della coppia entangled, in modo tale che gli analizzatori vengano ruotati casualmente in modo che quando viene effettuata una misurazione su una particella della coppia non sia in contatto causale con l'altra particella. Cioè, l'evento "Alice che misura lo spin di una particella della coppia" non è nel passato cono di luce di "Bob misura l'altro spin della coppia" e viceversa. Anche così gli spin sono correlati. Questo è, in sostanza, l'esperimento di Alain Aspect e lo spirito della correlazione EPR.

Il tuo errore nell'interpretare l'entanglement come mera correlazione è molto comune. In effetti, l'intero argomento di Einstein contro la meccanica quantistica in EPR era di ripristinare la causalità alla meccanica quantistica interpretando l'entanglement come nient'altro che una correlazione preesistente. Tuttavia, Bell ha dimostrato che questo fallisce. Sfortunatamente, molte persone, Lubos Motl per esempio, non sono riuscite a comprendere questa intuizione mezzo secolo dopo la scoperta di Bell. Le particelle intrappolate devono ottenere le loro istruzioni su come comportarsi in qualche modo, e questo deve avvenire istantaneamente.

Vedi http://www.youtube.com/watch?v=lt6PFPKJqZg

there is no big deal. Usually people who don't uderstand it will tell you that it is a big deal...

Let's say,you have 2 objects and observable with only two eigenvalues.One object is in state "+1" and the other "-1".The world that these objects live in has a rule that the sum of all these values is constant (zero in this case).Let's imagine that these object collide (interact in a manner that this observable can be changed).

Now, the best guess (if you don't know any details) is just to assume that the system is in state "+1"×"-1" or "-1"×"+1". And that's it.

If you look at the one object and determine the state, then you immediatelly know the state of the other, because of the conservation rule.

What is kind of a big deal (but I'd rather say that it's just 'cool' and not a big deal), that there are states that preserve corelations for multiple observables ("+-"-"-+" spin state if measured along any axis will always produce correlated results).