Entanglement

[Pugdaddy]

I have a question about entanglement. Is it assumed that the entangled particle are entangled with each other? Is that what leads to the conclusion that "spooky action" is either a result of instantaneous transfer of information or a hidden variable.

It is pretty much accepted that violations of the speed of light information transfer is not possible and Bell pretty much disproved the hidden variable with A not B + B not C is equal or greater that A not C.

Is that it or is there another option? Is it possible that the particles are entangled with spacetime and every point in spacetime is instantaneously sensitive to changes in every other point in spacetime. I am not an expert, so if I am way off base here I apologize.

[ydoaPs]

Is it assumed that the entangled particle are entangled with each other?

 

They are deliberately entangled in experiment, so it's not exactly an assumption.

[swansont]

Superluminal information transfer is not permitted outside of the system, but the effect is nonlocal — internal workings are not subject to the same constraint.

[Pugdaddy]

Superluminal information transfer is not permitted outside of the system, but the effect is nonlocal — internal workings are not subject to the same constraint.

 

So if spacetime is part of the system, the effect could be considered local? Or am I missing the point?

[juanrga]

I have a question about entanglement. Is it assumed that the entangled particle are entangled with each other? Is that what leads to the conclusion that "spooky action" is either a result of instantaneous transfer of information or a hidden variable.

It is pretty much accepted that violations of the speed of light information transfer is not possible and Bell pretty much disproved the hidden variable with A not B + B not C is equal or greater that A not C.

Is that it or is there another option? Is it possible that the particles are entangled with spacetime and every point in spacetime is instantaneously sensitive to changes in every other point in spacetime. I am not an expert, so if I am way off base here I apologize.

 

Yes the entangled particles are entangled with each other.

 

Entanglement is neither a result of instantaneous transfer of information nor requires a hidden variable theory. Entanglement is a quantum correlation, therefore the entangled particles are not independent and no "spooky action" needs to be invented to correlate both.

 

Spacetime has nothing to do with entanglement, because entanglement is possible in more fundamental theories where spacetime does not exist (spacetime is recovered as an approximation).

[Pugdaddy]

If two electrons are put in close proximity they will in a given time become entangled with each other. One will be spin up and the other will be spin down, but which one is spin up and which one is spin down is not known. If they are separated by any distance when the spin of one of the electrons is measured and found to be spin up or spin down the other entangled electron will always be measured with the opposite spin. How does the one electron communicate the information to the other electron to spin opposite?

[swansont]

If two electrons are put in close proximity they will in a given time become entangled with each other. One will be spin up and the other will be spin down, but which one is spin up and which one is spin down is not known. If they are separated by any distance when the spin of one of the electrons is measured and found to be spin up or spin down the other entangled electron will always be measured with the opposite spin. How does the one electron communicate the information to the other electron to spin opposite?

It's not known how it happens, just that it does.

[juanrga]

If two electrons are put in close proximity they will in a given time become entangled with each other. One will be spin up and the other will be spin down, but which one is spin up and which one is spin down is not known. If they are separated by any distance when the spin of one of the electrons is measured and found to be spin up or spin down the other entangled electron will always be measured with the opposite spin. How does the one electron communicate the information to the other electron to spin opposite?

 

As stated just above entangled electrons are not independent electrons that need to send/receive information from the other. The information is contained in the correlation for the pair. Spin is a purely quantum property and difficult to visualize but velocity is much more simple to do.

 

Consider two electrons with known velocities [math]v_1[/math] and [math]v_2[/math] that enter in a chamber, collide and abandon the chamber moving in opposite ways. You do not know the final velocities. After a time someone measures the velocity of particle 1 when the particle is 2 km away the chamber. Automatically you know the velocity of the other particle (by the law of conservation of momentum). No signal has been sent between particles 1 and 2. Both particles got correlated when collide in the chamber so what the velocity of one (independently of its value) was correlated with the velocity of the other particle.

 

The situation with spin is somehow similar, but the whole analysis is more complex. Entanglement implies correlation, not sending of 'signals' between independent particles.

[Pugdaddy]

Thank you all for your replies. I do not think you can compare momentum and spin in this case. The initial condition of when the electrons were created dictates or correlates the momentum. EPR believed that this was the case for spin as well. They did not like the quantum mechanical approach that the electrons were in a superposition(a mix of all possible spin states) of spin states and thought that the initial condition imparted a kind of DNA in each particle that predetermined what they would do once they are separated. Like a pair of gloves where the LH glove is put in one box and the RH glove is put in the other box. One box is sent somewhere and when the box is opened and found to be LH you know the other box contained the RH glove.

In momentum the initial conditions sets the velocity. Spin is not set in the initial condition. The expectation value for each electron is 0. There is no unique eigenvalue = 1 for either. But once one is measured, there is an eigenvector with eigenvalue = 1 for the other electron. Since the act of measuring the one electron instantaneously gives the the other electron an eigenvector for which it's eigenvalue = 1, they must be in communication with each other.

John Bell proved that the DNA explanation could not be correct and it would seem the GR prohibits instantaneous information transfer. So that leaves???

I was trying to think outside the box and ask what else could link the two electrons. The only thing I could come up with is that they both exist in spacetime and if space time is a "thing" then it might provide the mechanism for this. We know that the expansion of space does not obey the speed of light. I was just thinking out loud.

I am not an expert. Just an old retired guy with too much time on my hands.

[swansont]

In the entanglement of e.g. spin, you can show that the particles were not in that state until they were measured. I don't know if that's been shown for a momentum state.

[Pugdaddy]

 

I am not an expert. Just an old retired guy with too much time on my hands.

 

I should also add with a wild imagination.

[michel123456]

(...)So that leaves???

(...)

 

That they are one and only one entity.

 

In the macrocosm, to be one and only one entity, it should be at the same place at the same time. As it seems, for quantum particles, it is not necessarily the case: a single entity can be at 2 different places (we knew that) at the same time (that is bizarre*).

 

So in the end it could be that it has more to do with our understanding of time than with our understanding of particles.

 

* I guess that point has been controlled experimentally.

[juanrga]

Thank you all for your replies. I do not think you can compare momentum and spin in this case. The initial condition of when the electrons were created dictates or correlates the momentum. EPR believed that this was the case for spin as well. They did not like the quantum mechanical approach that the electrons were in a superposition(a mix of all possible spin states) of spin states and thought that the initial condition imparted a kind of DNA in each particle that predetermined what they would do once they are separated. Like a pair of gloves where the LH glove is put in one box and the RH glove is put in the other box. One box is sent somewhere and when the box is opened and found to be LH you know the other box contained the RH glove.

In momentum the initial conditions sets the velocity. Spin is not set in the initial condition. The expectation value for each electron is 0. There is no unique eigenvalue = 1 for either. But once one is measured, there is an eigenvector with eigenvalue = 1 for the other electron. Since the act of measuring the one electron instantaneously gives the the other electron an eigenvector for which it's eigenvalue = 1, they must be in communication with each other.

John Bell proved that the DNA explanation could not be correct and it would seem the GR prohibits instantaneous information transfer. So that leaves???

I was trying to think outside the box and ask what else could link the two electrons. The only thing I could come up with is that they both exist in spacetime and if space time is a "thing" then it might provide the mechanism for this. We know that the expansion of space does not obey the speed of light. I was just thinking out loud.

I am not an expert. Just an old retired guy with too much time on my hands.

 

Both the momentum and spin cases were compared in the sense that none of them involves faster than light signals. This was emphasized. In fact absolutely no signal is sent between the particles. Spin has a more natural framework in a relativistic quantum theory, which in agreement with relativity prohibits sending any signal faster than light.

 

The modern interpretation of quantum mechanics (exposed in Ballentine textbook and with more detail in this Rev Mod Phys) states that the spin superposition state associated to the Schrödinger equation does not describe the pair of electrons, but a virtual ensemble of pairs of electrons each one with a given probability of being in a spin eigenstate. If the value of the spin for each electron is set or is not in the initial condition is today debated (hidden-variable people say "yes" others say "no"). Unlike the old Copenhagen interpretation, the modern interpretation is rather agnostic about this.

 

You are right on that the expansion of space does not obey the speed of light limit, but this is so because this speed is not an ordinary speed. Those faster-than-light speeds are not the speeds of travelling objects, but the speed of expansion of space. Moreover, this expansion speed does not apply to bound states. It does not apply to our galaxy but only to the space between galaxies.