# Interpretation of entanglement

Gold Member

## Main Question or Discussion Point

Once I heard a fellow-layman on QM say that he imagined two entangled particles never been separated in the conceptual sense, that is: the two particles are conceptually 'one', only they connect two parts of spacetime, and are so able to exhibit correlations over spacetime with respect to the entangled property. So I think you could say then that entanglement is a kind of spacetime bending.

Is such a view part of any existing interpretation, and if yes, which one?

Thanks.

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I would think what you're referring to is the ER = EPR conjecture proposed by Maldacena and Susskind. Briefly the idea is that a duality exists between entanglement and Einstein-Rosen bridges (wormholes).

Perhaps the Hidden Measurements Interpretation says something of that sort?

...we are forced to accept that microscopic quantum entities, like electrons, protons, etc., are not permanently present in space, and that only at the moment they are detected by a measuring apparatus, would a position for them be created. In other terms, the HMI indicates that when a quantum entity, like an electron, in a non-spatial (superposition) state is detected, it is literally “dragged” or “sucked up” into space by the detection system. And this means that our physical reality would not be contained in space, but the other way around[17]. To quote Aerts [21] :

Reality is not contained within space. Space is a momentaneous crystallization of a theatre for reality where the motions and interactions of the macroscopic material and energetic entities take place. But other entities – like quantum entities for example – “take place” outside space...

https://en.wikipedia.org/wiki/Hidden-measurements_interpretation

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It is true that two particles that are entangled are viewed as in one state rather that two things in separate states. Is that what you mean?

Nugatory
Mentor
Once I heard a fellow-layman on QM say that he imagined...
That's unlikely to be a good starting point... Not impossible, but unlikely.
two entangled particles never been separated in the conceptual sense, that is: the two particles are conceptually 'one'
That might be an attempt to wrap some words around the way that a quantum system, even a multi-particle one, is mathematically a single system described by a single quantum state. Statements like "I measured the spin of an electron at detector A and got spin-up" and "I measured the spin of an electron at detector B and got spin-down" are not statements about properties of electron A and electron B; they are descriptions of measurement results on a single multi-electron quantum system. That's just how the mathematical formalism works - it's part of the recipe for calculating the probability of getting various results from various measurements.
only they connect two parts of spacetime, and are so able to exhibit correlations over spacetime with respect to the entangled property. So I think you could say then that entanglement is a kind of spacetime bending.
There's no support whatsoever for that idea in the math, so...
Is such a view part of any existing interpretation?
no.

JK423
Gold Member
I think a rigorous way to define, and consequently interpret, entanglement is the following:

Given two separated and non-interacting quantum systems A and B, they are said to be entangled if and only if
we cannot assign a definite quantum state to each system ( $\sigma^k_A$ and $w^k_B$, respectively) independently of the state of the other system:
$\rho_{AB} \neq \sum_k p_k \sigma^k_A \otimes w^k_B.$
In other words, the statistics that you get out of measuring entangled systems A and B do not correspond to statistics that "independent systems" produce, since the probability distributions do not factorize. Therefore, an entangled state describes "separated" and "non-interacting" quantum systems that are nonetheless "not independent" from each other.
And this is the spooky/paradoxical/non-intuitive characteristic of entanglement!

But, in the discussed experiments, those "separated systems" have nothing actually separating them, except their observers trying to impose their own separatedness on what they observe...

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JK423
Gold Member
But, in the discussed experiments, those "separated systems" have nothing actually separating them, except their observers trying to impose their own separatedness on what they observe...
Indeed, sepatedness is not fundamental to entanglement per se. However we do use it in the argument in order to demonstrate clearly and beyond doubt how "paradoxical" entanglement is. If the systems are not separated, and therefore not independent from each other, it's not clear what's so special about entanglement. But, in any case, you are right and in the definition of entanglement that i gave above the word "separated" is not required.

vanhees71
Gold Member
2019 Award
If you have entanglement you have correlations between far-distantly measured observables. E.g., in the usual Aspect experiment setup you have polarization entangled biphotons whose polarization part is
$$|\Psi \rangle=\frac{\sqrt{2}}{2} (|HV \rangle-|VH \rangle).$$

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JK423
Gold Member
If you have entanglement you have correlations between far-distantly measured observables. E.g., in the usual Aspect experiment setup you have polarization entangled biphotons whose polarization part is
$$|\Psi \rangle=\frac{1}{2} (|HV \rangle-|VH \rangle).$$
But as AlexCaledin pointed out, the particles don't have to be separated to be described by an entangled quantum state.

DrChinese
Gold Member
But, in the discussed experiments, those "separated systems" have nothing actually separating them, except their observers trying to impose their own separatedness on what they observe...
And entangled photons can be "separated" in time as well. Photons that have never co-existed can be entangled.

bhobba
Mentor
But, in the discussed experiments, those "separated systems" have nothing actually separating them, except their observers trying to impose their own separatedness on what they observe...
Separated is not a property of entangled systems until observed to have it. You cant say nothing separates them any more than you can say the opposite. QM is silent on whats going on when not observed. That is one of the key things about QM that separates it from classical systems. Classical systems have properties independent of observation.

Thanks
Bill

...QM is silent on whats going on when not observed...
So, the Unitary Evolution is not going on?

bhobba
Mentor
So, the Unitary Evolution is not going on?
Yes. But like most things statements gain their meaning from context - here the context is observable properties.

Thanks
Bill

But we know Bohr's words,
“There is no quantum world. There is only an abstract quantum description.”

- perhaps separateness and entanglement may belong to that abstract description rather than observed reality? For example, if the measured particles can be described by something like Feynman diagram connecting them with coherent lines, then they are entangled.

bhobba
Mentor
But we know Bohr's words,
“There is no quantum world. There is only an abstract quantum description.”
As I have mentioned many times be very careful of what the early pioneers said.

In fact, without going into it, Bohr's view was deeply flawed:
http://scitation.aip.org/content/aip/magazine/physicstoday/article/58/11/10.1063/1.2155755 [Broken]

To be specific QM is silent on if there is a quantum world or not - we have interpretations with all sorts of takes on that.

Thanks
Bill

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http://scitation.aip.org/content/aip/magazine/physicstoday/article/58/11/10.1063/1.2155755 [Broken]

"Physicists and their apparatus must be governed by the same quantum mechanical rules that govern everything else in the universe. But these rules are expressed in terms of a wavefunction (or, more precisely, a state vector) that evolves in a perfectly deterministic way."

Well, if I got it right reading H. Stapp and others, such deterministic worldview must be wrong because it leaves no place for consciousness.

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bhobba
Mentor
Well, if I got it right reading H. Stapp and others, such deterministic worldview is wrong because it leaves no place for consciousness.
You got it wrong.

Again QM is silent on if consciousness is involved or not - we have interpretations that use it - most don't.

Stapp holds views quite a bit outside the mainstream.

Thanks
Bill

Well, what Stapp actually holds, it's Heisenberg's onthology. He is showing that it's strongly supported by the new brain research.

Nugatory
Mentor
QM is silent on whats going on when not observed.
So, the Unitary Evolution is not going on?
That phrase "going on" suggests some sort of ongoing process, that there's some physical thing that is evolving with time. That might be, but there's nothing in the math of unitary evolution that says that it has to be. We have an abstract mathematical object that we can subject to certain mathematical manipulations to find the probabilities of getting various measurement results at some place and time. We also have another mathematical manipulation, called "unitary evolution", which when applied to our original abstract mathematical object, will produce another abstract mathematical object that can be manipulated to find the probabilities of getting various measurement results at a given place at some later time. If you find it helpful to think of this unitary evolution as "something is going on" between the two times, you are free to do so - it's a very natural intuition. But there's nothing in the math to either confirm or deny that intuition.

perhaps separateness and entanglement may belong to that abstract description rather than observed reality?
"Separateness" has a clear meaning - it's a property of points in spacetime. Quantum mechanics tells us the probabilities of getting various measurements results at these points. "Entanglement" is a mathematical property of the abstract mathematical objects that I described above, one that leads to sometimes surprising predictions for the probabilities of some measurements made at different points in spacetime. (@JK423 provided a good definition of this mathematical property above).

bhobba
Mentor
Well, what Stapp actually holds, it's Heisenberg's onthology. He is showing that it's strongly supported by the new brain research.
I have read Stapp. To be blunt he is way outside mainstream.

There is zero need for consciousness in QM - end of story. Anyone that says different is telling porkies.

May I suggest instead of these 'fringe' views and quotes from early pioneers you study a modern book eg:
https://www.amazon.com/dp/0465062903/?tag=pfamazon01-20

Thanks
Bill

That's an honest good book! It shows the inconsistency of that mainstream most clearly.

Of course, the mainstream is all "FAPP-consistent".

It's just my personal problem, I can't help being interested in a consistent worldview...

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bhobba
Mentor
That's an honest good book! It shows the inconsistency of that mainstream most clearly.
There is no inconsistency in mainstream interpretations.

If you believe so start a new thread - this is way off topic.

Thanks
Bill

If you have entanglement you have correlations between far-distantly measured observables. E.g., in the usual Aspect experiment setup you have polarization entangled biphotons whose polarization part is
$$|\Psi \rangle=\frac{1}{2} (|HV \rangle-|VH \rangle).$$
How about √½( |HV⟩ - |VH⟩).

vanhees71