September 1, 2017 feature

# Entanglement is an inevitable feature of reality

(Phys.org)—Is entanglement really necessary for describing the physical world, or is it possible to have some post-quantum theory without entanglement?

In a new study, physicists have mathematically proved that any theory that has a classical limit—meaning that it can describe our observations of the classical world by recovering classical theory under certain conditions—must contain entanglement. So despite the fact that entanglement goes against classical intuition, entanglement must be an inevitable feature of not only quantum theory but also any non-classical theory, even those that are yet to be developed.

The physicists, Jonathan G. Richens at Imperial College London and University College London, John H. Selby at Imperial College London and the University of Oxford, and Sabri W. Al-Safi at Nottingham Trent University, have published a paper establishing entanglement as a necessary feature of any non-classical theory in a recent issue of *Physical Review Letters*.

"Quantum theory has many strange features compared to classical theory," Richens told *Phys.org*. "Traditionally we study how the classical world emerges from the quantum, but we set out to reverse this reasoning to see how the classical world shapes the quantum. In doing so we show that one of its strangest features, entanglement, is totally unsurprising. This hints that much of the apparent strangeness of quantum theory is an inevitable consequence of going beyond classical theory, or perhaps even a consequence of our inability to leave classical theory behind."

Although the full proof is very detailed, the main idea behind it is simply that any theory that describes reality must behave like classical theory in some limit. This requirement seems pretty obvious, but as the physicists show, it imparts strong constraints on the structure of any non-classical theory.

Quantum theory fulfills this requirement of having a classical limit through the process of decoherence. When a quantum system interacts with the outside environment, the system loses its quantum coherence and everything that makes it quantum. So the system becomes classical and behaves as expected by classical theory.

Here, the physicists show that any non-classical theory that recovers classical theory must contain entangled states. To prove this, they assume the opposite: that such a theory does not have entanglement. Then they show that, without entanglement, any theory that recovers classical theory must be classical theory itself—a contradiction of the original hypothesis that the theory in question is non-classical. This result implies that the assumption that such a theory does not have entanglement is false, which means that any theory of this kind must have entanglement.

This result may be just the beginning of many other related discoveries, since it opens up the possibility that other physical features of quantum theory can be reproduced simply by requiring that the theory has a classical limit. The physicists anticipate that features such as information causality, bit symmetry, and macroscopic locality may all be shown to arise from this single requirement. The results also provide a clearer idea of what any future non-classical, post-quantum theory must look like.

"My future goals would be to see if Bell non-locality can likewise be derived from the existence of a classical limit," Richens said. "It would be interesting if all theories superseding classical theory must violate local realism. I am also working to see if certain extensions of quantum theory (such as higher order interference) can be ruled out by the existence of a classical limit, or if this limit imparts useful constraints on these 'post-quantum theories.'"

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**More information:**Jonathan G. Richens, John H. Selby, and Sabri W. Al-Safi. "Entanglement is Necessary for Emergent Classicality in All Physical Theories."

*Physical Review Letters*. DOI: 10.1103/PhysRevLett.119.080503

© 2017 Phys.org

**Citation**: Entanglement is an inevitable feature of reality (2017, September 1) retrieved 16 October 2019 from https://phys.org/news/2017-09-entanglement-inevitable-feature-reality.html

## User comments

rogerdallasEyeNSteinWave/particle duality is effectively a particle entangled with itself. (from two slits to one point)

Until we can bin the Copenhagen interpretation and explain how a particle can be distributed and then instantly point-like; we cant lose the weird quantum consequences.

Until we can access the Planck scale where the dimensions and strings hang out we may be stuck with quantum statistics. Even if we had a better theory we couldn't test it except via statistics.

JongDanBohmian mechanics, and it doesn't get rid of any quantum consequences that you want to get rid of.

sirdumpalothttps://arxiv.org...9002.pdf and https://arxiv.org...4064.pdf

sirdumpalotGiven that the core ontology of the scientific method is observation/measurement, who or what observes or can ever observe the pilot wave of all of existence?

KBK..that line comes back full force..and is possibly the only observation point that allows a 'person' (3d self labeled mass aggregate) to ponder realization outside of th given matrix it is ensconced within.

The reality and necessity of philosophy as the father of all the sciences comes back full force...due to objectivity and scientism/dogma finding it's head up it's ultimately twisted back on itself mobius ass. In engineering terms, scientism finds itself hoisted by it's own ass (tied to the origins of the word engineer, which were originally dark age urine stirring bomb makers who blew themselves up)

HyperfuzzyHyperfuzzyQM? Like playing with blocks, not reality!

HyperfuzzyEyeNSteinWhat is it about 'space' that can be manipulated or strained to form a single charge (mass attracts mass of General Relativity); two charges (+/- electric of QED); or three charges (RGB of QCD) but no known four charge force?

What is 'spin'? Why does it behave like some kind of Mobius strip (720 degree rotation) in space?

Why don't photons exhibit Fourier sidebands even when extremely compressed in time?

All these and other questions for a genius near you?

Da SchneibWith these new results from the paper discussed in this article in hand, it's my expectation that the researchers' investigations will indeed indicate that recovering classical mechanics from a non-classical quantum theory requires that the quantum theory violate the Bell Inequality. This will be interesting to watch.

DingboneDa SchneibDingboneDa SchneibI have a pet conjecture regarding interpretations of QM, strongly influenced by the FT: all interpretations of QM must necessarily violate our intuitive concepts in order to correctly describe quantum reality. This is bolstered by the current article and its underlying paper's conclusion that these counter-intuitive concepts are necessary to derive the intuitive ones we are used to. Feel free to argue either way. I'm sure it would be an interesting conversation.

DingboneDa SchneibThis is a deep question, and the answer appears to be, the dimensionality of our spacetime. We require 3+1 dimensions for gravity, another dimension for EM, two more for the weak force, and three for QCD. Are there more? Not that we see. Experiment seems to show that there are no more, so far. I wouldn't put them in the order you do; U(1) is EM, SU(2) is weak (and it's actually U(1) + SU(2) for electroweak in current formulations), SU(3) is color (AKA "strong"), and no one has found a group theory for the 3+1 of gravity (this would be a quantum gravity theory which we have not yet discovered).

[contd]

Da SchneibGiven that the SU(3) theory of the color force seems to be confined, it's possible that higher order group theories describe higher dimensions and more complex forces, and that these are even more confined than the color force, and possibly weaker than gravity, and therefore undetectable. But that's not even a conjecture; it's a rank speculation.

This is not such a good question. First of all, this is only the laws of spin and statistics for fermions; it's not true of bosons. Second, this is fully described and explained by those same laws of spin and statistics. You should make sure you understand them; the probability amplitude is the distinguishing factor here.

Because they are bosons. See laws of spin and statistics.

DingboneDa SchneibMaybe if you knew something more than the buzzwords I might pay more attention. Or if, after all your posturing as an expert, you actually turned out to know anything about what you're posting all those buzzwords about. But you keep posting stuff like this and it makes it obvious you're attempting to participate in a conversation you aren't qualified to say anything about.

So, how much do they pay you to post here? Just askin'.

DingboneSpaced out EngineerBulk-5 electrons, but which existence?

A lone ambiguous black hole's event horizon, (thus features are trivial)

Tachyon condensates

Weyl and toy universe models, but once again which existence.

Maybe we can read enough Maxwell Demon minds and put them together into a Laplace's one.

Machine learning for a Heisenberg Compensator and complementary properties of quantum clones.

If this is wrong, it is still happily existential.

Da Schneib"...but it doesn't invalidate string theory either." Your false claim: "...the observation of extradimensions has been excluded by collider research..." Nothing's been excluded. This is an outright lie about the contents of the very article you linked.

Welcome to reality, comrade.

Da SchneibWaiting's over, @Dingbat. You're a committee, comrade.

DingboneDingboneParsecDingboneDa SchneibSorry, comrade, you blew it. Whatever you were here to make political posts about, that's blown too, comrade. Sorry, PLA 61398, you're done here.

RealityCheckAt least @Dingbone is being RELEVANT pointing out flaws/alternatives; while all YOU do is post PERSONAL insults to him.

@Dingbone's WATER (underwater/surface waves/solitonic features etc) DIMENSIONAL perspectives are VALID; as EINSTEIN HIMSELF used similar analogies! OK?

RealityCheckSo, DS, please stop insulting others while YOU are just as lost in confused speculations due to confused CONFLATION of "REALITY PHYSICAL DIMENSION" and "ABSTRACT ANALYTICAL DIMENSION" (especially CONFLATED BADLY in MATHS-based HYPOTHESES).

RealityCheckONLY THREE REAL DIMENSIONAL 'contexts' for real phenomena:

- 'passive' REAL SPACE in balance but always subject to CHAOS effects;

- 'active' ENERGY-space which arises from CHAOS phenomena imbalances in previously 'passive' space context; and

- 'emergent' VACUUM consisting of emergent RANGE of 'sub-quantum/higher aggregation' activity/entities manifesting observable physical effectiveness/interactions etc.

AL OTHER DIMENSIONS 'context' (as currently used/alluded to by MATHS 'theories' like String/QM/SR/GR etc) are ALL ANALYTICAL 'abstractions contructs' thus having NO DIRECT EFFECTIVENESS meaning in real DYNAMICAL phenomenological MOTIONS/DIRECTIONS in ALL THREE above REAL 'contexts'.

Your perspective comes closest, but not quite 'there' yet, @Dingbone. :)

PhonicsirdumpalotI'm not sure how the above examples relate. Those may be considered physically beyond observations (and hence still verifiable, with some level of tech), but a QM observer observing All QM system is a logical fallacy (unless reflexive observation makes sense, and 'X=X' - the tautology - has always been a 0 information observation). De-Broglie Bohm simply can't be extrapolated from observing (n-1) QM objects to observing n QM objects. Without the observation, you lose the science.

sirdumpalotJayaravaJayarava"It's not possible to specify the state of a system by listing the state of its subsystems individually. We have to look at the system as a whole, because different parts of the system can be entangled with one another." (2016: 100)

DingboneDingboneDingboneDingbonethingumbobesquireJ Doug"The physicists anticipate that features such as information causality, bit symmetry, and macroscopic locality may all be shown to arise from this single requirement. The results also provide a clearer idea of what any future non-classical, post-quantum theory must look like."

I had read this several years ago and while I sure don't fully understand the concept of why and how Quantum Entanglement matters, this paper and how it was reported did a better job that this current piece from Phys.org.

"Quantum Entanglement Links 2 Diamonds Usually a finicky phenomenon limited to tiny, ultracold objects, entanglement has now been achieved for macroscopic diamonds at room temperature" December 1, 2011

J Doughttps://www.scien...glement/

Since Phys.org. spends so much time trying to convince readers that CO₂ is an evil devil in the sky that must be feared and if possible eliminated from the earth due to all the imagined consequences of its very existence, such as hurricanes, hemorrhoids and heat waves. Because Phys.org has such a struggle trying to connect the dots regarding CO₂ where, since they can find no proof of what they are asking people to believe, they must approach this subject of Quantum Entanglement with the same approach that makes whatever they say that they believe to be basically beyond most folk's ability to comprehend.

OjorfMight higher dimensional objects not just be too heavy to exist, except under unbelievably extreme conditions?

I'm just speculating, but the largest conceivable particle accelerator might be many orders of magnitude away from reaching the energies to reveal a 2D or 3D "particle".

The universe as it is now might just not contain any?

TheGhostofOtto1923They can only stomp it into the ground and drop a large pile on it.

ShootistDyson made the maths work. Feynman had the vision.

HeloMeneloHeloMeneloDinggnat, jdung and his riot of puppets got entagngled into another round of circle jerk, the night is still young and we're going to have some more fun :D

HyperfuzzyVery appropiate

HyperfuzzyReg MundyrogerdallasDa SchneibActually, it's not really an "extra dimension." It's an extension of physics from point particles to multidimensional particles. We now have mathematical theories, incorrectly called "string theory," which work with 2D and higher order "branes."

[contd]

BenniDa SchneibIt's important not to confuse this with the addition of realistic extra dimensions via Kaluza-Klein theory and the further extensions of it that also include the flavor and color forces. "Strings" are the generalization to multidimensional *particles* from the specific point particle theories of the SM in which all particles are considered to be 1D. The dimensionality of the particle representations is separate from the dimensionality of the spacetime in which they act. And I use the word "act" in its full physics meaning relating to the physics term "action."

It's not only 1D. See branes.

The rest of your arguments are based on this thesis which is shown incorrect. What do you think now?

Da SchneibWhen Regge theory emerged it was stonewalled by physics theorists for years. It was not until Gell-Mann and Nishijima developed the eightfold way that these academics began to accept it, and they have not admitted that string physics was essential to the development of the SM to date. Even physics theorists can be clannish and deny reality; the difference is, only so long, then they get caught.

Spaced out EngineerExactly, but you buy the relational theory. Who says it has identity as such? It is a problem of dicotomy. If EPR=ER and entanglement is both the early universe not decoupling from its white hole like nature, and the partitioning of spacetime fading as black holes decay, we might just find a twice over impossible empty, self referential as recombinatorial anthropic tables for electrons. A pressureless pressure that cools, from naught but self interaction more apt and compact. Timelike. If that doesn't would why not near missing highly improbable positive and negative pressure in an unapt configuration space over forever. Spacelike.

So space as a resource to cool a lack of hotness or time as a resource to configure space.

mrlewishI myself think that minimal orbit of Bohr's thingy is a bit off. Or at least a bit is missing, as to why. I think that the electron radial wave function is related to time as in the electron occupies all the volume for its given energy as a wave in a given length of time. I think it would be somehow related to planck time. What the relationship is, is beyond me.

Da SchneibParsecAmritSorliReg Mundy"Only so long" can be an awfully long time.......

DingbonesirdumpalotA relational ontology and epistemology fixes many things - no Zeno paradoxes because permanent entities are not evident. You don't have to get your head around an endless cause and effect, because with no concrete entities or properties, you don't have to ask 'what was the first cause', works well with a local flat spacetime, works well with conservation laws, works well with the fact that no 'thing' has ever been observed to last for ever (even protons and black holes). Anatta is a neat solution to most all philosophical problems, there is no longer any notion of determinism for any notion of a whole.

Newton had absolute Time, absolute Space, absolute Property and absolute Object. Relativity has worked for the first two, why not the last two?

sirdumpalotSo long as observer independence is allowed and observer independent inferences are followed, you will end up with problems and paradoxes. Maybe the choice is that observer independent theories provide more consistency but less completeness, whilst observer dependent theories offer something complete but inconsistent! In fact, is anyone still searching for something complete and consistent in the science world?

antialias_physorgNot really. Science is about getting knowledge and information.

Information is only existent in a state if there is an alternative to a state.

(E.g. if there was no "0" bit state then all bit states on your computer would be "1" and you could not store any information - because everything you store would look like everything else and you could never tell the difference)

If you just say "everything has property X" then you're not adding information.

(That's the main scientific problem religion has, BTW. They say "everything is god" - which by the above means that the concept of 'god' is utterly meaningless.)

sirdumpalotI do like that for further gedankenexperiments - just add more patches to fix the boat rather than getting a new one, but then verifiability escapes even further! :)

DingboneHyperfuzzyCCCCUBEDOf course, the creator would enable us to not only travel faster than light but also to communicate faster than light. These features were part of the intelligent design of this reality.

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