ON SEPARABILITY IN THE NOBEL WINNING ENTANGLEMENT EXPERIMENTS
ON SEPARABILITY IN THE NOBEL WINNING ENTANGLEMENT EXPERIMENTS
AN OPEN LETTER TO THE 2022 NOBEL COMMITTEE
Abstract: We show that the seminal experiments by Aspect and Zeilinger did not have any causal isolation between source and detectors but only between detectors. We argue that the subsequent calls for the death of separability are premature. Finally, based on new experimental evidence [1], we advance that a standing wave interpretation of the entanglement experiments, as opposed to the classic Copenhagen interpretation transmutes the paradoxes of entanglement into visual tautologies.
PART I: 100 YEARS OF SEPARABILITY AND ENTANGLEMENT
I.1: On separability and quantum entanglement.
Einstein pointed out that quantum formalism seemed to imply that two physically distinct systems could not be separated, a feature Schr ̈odinger, would eventually call ”entanglement”. An instantaneous “spooky action at a distance”, no matter what the distance, seemed embedded in the predictions of quantum mechanics. This bothered Einstein because it violated Special Relativity and, in-fine, causality. The famous EPR (Einstein, Podolsky, Rosen) paper, mostly written by Podolsky, is the published account of this point of view [2].
I.2: On relativity and separability.
In private communications between Einstein and Schrodinger, Einstein lamented the ‘needlessly erudite’ presentation of Podolsky and preferred to couch the argument in terms of the speed of light of special relativity (SR) and what it implies for the separability of systems. Indeed, if there exists a maximum speed of propagation for signals, then one can isolate the causes and effects from one subsystem to another. One simply needs to put enough distance between the two subsystems so that they are causally isolated during the time the experiments take. The time it takes for light, and thus information, to travel from one system to the other should be larger than the time it takes to perform the experiments. This is a condition that can always be realized provided we put enough distance between the systems. In the parlance of SR the systems lay outside their respective cones of light. Causality, separability and the finite speed of light are all linked.
I.3: On non-separability and philosophical dragons.
Separability is a foundational pillar of physics as we know it for without it we cannot speak of systems in isolation. Physics becomes nonsensical without separability because everything depends on minute and distant influences. From Newton to Einstein, the notion of instantaneous propagation of effects was apocryphal. Today it is gospel. Professional physicists and the public court of opinion are ready to declare Nature non-local.
I.4: On Bell’s theorem and separability.
In the 60’s, while at CERN, John Bell turned the argument of separability into a mathematical theorem that could eventually be tested in the lab. Separability was expressed in the mathematical language of joint probabilities as P r(A ∧ B) = P r(A) ∗P r(B). This factoring of probabilities is the definition of statistical independence as joint probabilities can be factorized as the product of their single probabilities. This is simple statistics. This factorization leads without further ado to Bell’s theorem, where a certain measure called CHSH-S (named after Clauser, Horne, Shimony and Holt) cannot exceed the numerical value 2 (S < 2).
I.5: On experimental violations of the S < 2 limit.
This would eventually be tested years later by Clauser, Aspect and Zeilinger among others. Repeated violations of the S > 2 limit, also known as Bell Inequality Violations (BIV), are now routinely observed in the lab and in industry. Entanglement is central to quantum computing and quantum encryption.
I.6: On the rumored death of separability.
From a physics foundations standpoint, the increasingly loophole-free versions of the classic experiments have prodded professionals to seriously ponder abandoning the concept of separability in Nature. The general public loves this narrative because indeed, as every religion has ever claimed, everything is connected to everything.
I.7: On separability and time: a meditation.
One only needs to meditate on the James Webb pictures to realize this as a truism: everything is indeed connected to everything. All the galaxies and structures we see in these awe inspiring pictures are there because an electromagnetic signal from these distant objects is present at the location of the satellite at the moment of recording: the whole universe is thus indeed connected with that single point in space at that moment in time. This is also true of every other point in space, if you move positions you still see this same background, thus establishing that everything is connected to everything and everywhere. However, due to the finite speed of light, this connection between every point of the universe to every other point of the universe is not instantaneous: signals propagate locally and realistically, i.e. relativistically. It takes a long time for these signals from deep space to reach us. Indeed, everything is connected to everything but not instantaneously. What we test scientifically with entangled photons is the instantaneity of this connection. A finite speed of light guarantees separability, instantaneous communication precludes it.
I.8: On Copenhagen decoherence by measures and the emergence of Paradoxes
The narrative that surrounds the Bell experiments is usually rooted in the Copenhagen interpretation. First, one talks of particles at Alice and Bob, the photons that travel in different direction, their entangled state, and their spatially and causally separated physical places. Secondly, the Copenhagen interpretation states that the act of measuring at the detectors triggers the “collapse of the wavefunction”. The wavefunction is a mysterious being which collapses in an abstract and mathematical Hilbert space, instantly and everywhere, aka “decoherence”. It is this very decoherence effect, caused by a distant measure, that leads to the paradoxes. When we consider this collapse to be a real physical phenomenon taking place in material space then the action seems to be non-local. The action propagates from Alice to Bob, a.k.a ”at a distance”, and acts at arbitrary distances and apparently instantaneously. This is what the Copenhagen interpretation of Bell violations indicates. Very spooky interpretation indeed.
I.9: On Magical thinking.
This interpretation is of a magical order. Could this “magical thinking” be a glamour that has contributed to the continuing appeal and visibility of the field? It was certainly the case for me, as a young graduate student when I first studied entanglement under the supervision and tutoring of Alain Aspect himself at the Polytechnique back in the early 90s in Paris for my Masters’ thesis!
I.10: On Physics vs Meta-Physics.
Metaphysics certainly states this magical fact of timeless oneness about the creation [3]. So do all religions and mystics, unanimously. Scripture further tells us that ‘the heavens shall not be measured’. Time and Space emerge from the monad, in the mind of ‘the one that comes from the zero’. But, surely, when it comes to physics and the measurable material world it describes, non-separability is apocryphal. Accepting that the material world is non-separable requires extraordinary physical proof for it is an extraordinary claim.
PART II: II. ON ISOLATION IN ASPECT AND ZEILINGER BETWEEN SOURCE AND DETECTORS
II.1: On the separability achieved in the Aspect and Zeilinger experiments.
We will now argue that, contrary to popular belief, the Aspect and Zeilinger types of experiments offer no such definitive proof: we will show that the source and the detectors were never separated in the classic experiments (and their modern photonic descendants), only the detectors between themselves are/were isolated.
II.2: On the role of the optical modulators.
This lack of separability between source and detectors is due to technicalities of the optical switches we will now review. In [1] we have shown that in all these geometries there exists a static line of sight between the source and the detectors through the optical modulators. See fig. 1
First let’s observe (figure 1) that in both the geometries of Aspect and Zeilinger, the 4 possible detectors are all static. The settings are all static. Only the choice of the detector is dynamic. In fact, “setting the measures during the flight of the photons”, as was originally prescribed by Bell, is technically and mechanically impossible, still to this day: we can not actuate real polarizers this fast.
This was detailed in the doctoral thesis of Prof Weihs, who implemented the experiments for Zeilinger [4]. Instead it is the choice of the detectors which is dynamic in both the Aspect [5] and Zeilinger [6] class of experiments. This selection of detectors is done by switching the optical path of the photons via Acoustic or Electronic Optical-Modulators (AE/OM) in Aspect and Zeilinger, respectively. These AE/OMs route the photons randomly to one of two preset and static analyzers. The key thing to observe here, with respect to the isolation claims of the experiments, is that these AE/OMs components are semi-transparent. Because of this the source is exposed to (“sees”) a very large residual signal from all 4 static detectors, at all times. This is a static background signal between all possible outcomes and the source of the photons. The source is never isolated from the detectors. The Aspect Acoustic Opto-Modulators have a 20% residual signal, this is still true of modern AOMs. Their Electro Optic-Modulator cousins, used to this day in the Zeilinger class of experiments, are fully transparent in amplitude for they only modulate the phases of the incoming photons. A static line of sight is hiding in plain sight. From the point of view of the source, these tests are mostly static bell tests. These tests are dynamic from the point of view of the choice of the detectors. There is no setting of the measure during the flight of the photons as prescribed by Bell. The settings are all static and there is no separation of the source to all the preset detectors. This geometry can exhibit BIV as motivated in [1].
II.3: On detector isolation.
Strictly speaking there is no separability between source and detectors in the modern experiments, only isolation between detectors. The accepted separability narrative to the contrary, e.g that the experiments achieve loophole-free separation, is true only of the detectors. It is the measuring stations at Alice and Bob, and the acts of measuring that are causally isolated in increasingly impressive and strict fashion. The act of emitting photons at the source is however statically connected to all the detectors.
This misdirection of our focus, focusing only on the detectors and not the source, is largely due to the Copenhagen interpretation: we talk of collapse of the wave function at Alice and Bob during measures while the measures are isolated from each other. The interpretation focuses on the detectors as triggering the collapse, this leads to the paradoxes. But the emitting atoms, which in retrospect play a more central role in the birth of the photons, are exposed to all the detectors: they are not isolated.
II.4: On the logical structure of the Bell theorem.
Let us consider the logical structure of the Bell theorem for a moment, it reads:
Bell’s Theorem
IF (separability) THEN (no BIV).
The logical reverse gives us the following corollary :
NoBell's Theorem
IF (BIV) THEN (no separability).
This is basic logic: (P =⇒ Q) =⇒ (¬Q =⇒ ¬P).
Therefore, when it comes to the experiments of Aspect and Zeilinger, the observation of BIV implies (by the NoBell Theorem) that the sub-systems are not separated (for if they were we wouldn’t).
III. ISOLATION BETWEEN SOURCE AND DETECTORS WITH A FOUCAULT MIRROR
III.1: On stricter source to detector isolation with a Foucault mirror: an experiment.
Having convinced ourselves that this was so, we proceeded to design and perform a Bell measure in a geometry where we would achieve a stricter separation of source and detectors. We have used a state of the art multi-faceted rotating mirror, known as a “Foucault mirror”, to create a physical gate and causally isolate the source from the detectors. We have performed a Bell CHSH-S measure in a simple and static 2 channel experiment as detailed in [1].
The rotating mirror creates a 10−7s gate. 400m of single fiber between the source and the detectors guarantees causal separation. A photon birthed at the crystal and informed by the detectors (even instantly) does not have the time to propagate back to the detectors: the mirror has moved by the time the photon exits the fibers and they do not point to the detectors anymore. This achieves a close to true 0% transmission when the mirror gate is switched off as opposed to 20-100% for the acoustic and electrical switches described above. See fig.2
III.2: On the observation of Bell violations S > 2 in the Foucault geometry.
With the residual signals gone, even if intermittently, we were expecting (hoping for) a loss of Bell violations. We have performed the experiment and have instead observed S > 2, as reported. By the same logic detailed above (NoBell Theorem: IF (S > 2) THEN (non-separated)), we can immediately conclude that we are still not separated, even with the Foucault mirror.
IV. ON STANDING WAVE ONTOLOGIES
IV.1: On standing waves mediating the Bell effect
We concluded, after analysis of the stricter isolation achieved, that no traveling optical wave could be involved. This included super-luminal, and instantaneous optical signals from the detectors to the source. Our experiment invalidated the class of all super-luminal signals carried by the fibers.
We further argued and hypothesized, in discussion, that standing waves are one candidate to mediate the Bell effect. The emphasis here is on the standing nature of the waves as opposed to propagating waves. One can visualize a vibrating piano string or a drum surface, both examples of standing waves, as opposed to a propagating surf wave. Mathematically this reads as cos (wt − kx) for propagating waves (where the spatial and temporal components are mixed) versus the factorized cos (wt) cos (kx) for standing waves. See fig.3
IV. 2: On wave ontologies vs particle ontologies and categorical paradoxes.
Part of our paradoxes on entanglement may derive from the ontologies and the language we use, i.e our interpretation. We talk of particles, of measures on said particles at distant detectors, and a mysterious “collapse of the wave function”, aka ‘the Copenhagen’. In the particle ontology, entanglement at the detectors implies instantaneous action at a distance between the detectors, because the detectors are indeed causally separated in the Aspect and Zeilinger class of experiments.
After all, one does not discuss the double slit experiment with particle trajectories, for that is absurd, one instead uses the language of electromagnetic fields and waves. The classic double slit experiment which contains ‘the only mystery of Quantum’, as Feynman would have it, does not yield to the ballistic interpretation of particles. Ballistic trajectories cannot account for the interference patterns for you have two separate blobs. The particle ontology is absurd with regards to the double slit, it is an ontological miscategory. We simply and automatically think of the double slit in terms of fields and waves. Then, when waves superimpose, the interference pattern is a visual tautology.
But for entanglement, we persist in using the particle ontology and vocabulary, and in our opinion this is what leads to the apparent paradoxes. The paradoxes may be linguistic / categorical in nature. The key point here is that in the ontology of standing waves there may not be entanglement paradoxes. One can visualize a piano string, in 1 dimension (as in fig3), or a drum surface, in 2 dimensions, and readily observe that the movements of distant points in space are correlated. There is no magic here and entanglement is then a visual tautology: observe that indeed many distant points of a standing wave vibrate in phase across vast distances, i.e. are correlated, by definition of standing waves.
IV.3: On Bohr Complementarity.
The above analysis uses the hypothesis that a field is mediating the Bell correlation effect (Einstein realism). For the sake of completeness it should be pointed out that Bohr argued that observers and the observed are never separated but inter-connected, an argument known as ‘Bohr Complementarity’. We will simply mention that Bohr Complementarity still finds enthusiastic exponents as mentioned in[1] and does not make the assumption of a background field. Our experimental evidence supports this interpretation as much as the standing waves one.
V. ON THE IMPACT OF THE NOBEL AWARD ON INTERPRETATIONS
V.1: On deploying standing waves experimentally.
The trick to entanglement experiments, then, is to deploy these standing waves across said vast distances. Not to take away from the experiments: it takes real experimental savoir-faire to maintain phase coherence across increasingly impressive chasms: kilometers in the lab, underground through land [7], through submarine fibers [8], and more recently orbital stations [9]. After all most of the experimental protocols center on phase correction for proper polarization as measured in correlation counts at the end of the transport: it’s all about maintaining polarization and phase coherence. I personally know firsthand the blood sweat and literal tears that went into maintaining polarization synchronization across 400 meters of single-mode fiber in my own lab-based entanglement experiments. As a result, I appreciate the mastery and tour-de-force of doing so across kilometers of land, sea and space.
V.2: On the Nobel prestige and the Wizards of OZ.
Heisenberg, Pauli and Schr ̈odinger felt compelled to write letters answering Einstein because they feared ‘the harm that might otherwise be done among physics students in the US who could be led astray by Einstein’s prestige’.
Oh, the rich irony of it! For 100 years the Schr ̈odinger cat has confused every generation of physics student. The orthodox semi-instantaneous (and global) collapse of the wave function has become dogma we accept as is. And the mantra of ‘shut up and calculate’ is the Modus Operandi harming students psyche in the whole world.
The Copenhagen interpretation scars every inquisitive young mind, and a cult-like acceptance of spooky action at a distance prevails. Resistance is futile and in fact slightly dangerous. We similarly felt ‘otherwise compelled to write this letter because we fear the harm done to physics student in the whole wide world who could be led astray by the Nobel prestige’.
The point of this letter, again, is not to criticize the choice of the Nobel committee in awarding the prize to the courageous pioneers of experimental entanglement. It is more than deserved and overdue, in our opinion. We simply want to warn against closing the book too prematurely on interpretations and separability by appeal to Nobel authority.
V.3: On magic vs realism in Physics.
We have instead pointed out that the magical narrative of non-separability that as a result of these experiments is being pushed everyday, may be spurious. On the surface of it, the Nobel prize seems to further validate and rubber stamp this magical interpretation. And this is what we object to: the magical thinking. We persist and insist: that If we observe S > 2, by the No-Bell Theorem, one should humbly strive to identify the ways in which the subsystems are, actually, physically, statically and realistically not separated. Instead everyone delights in ‘proving Einstein wrong’.
V.4: On the premature death of separability.
We have shown such a trivial connection hiding in plain sight between source and detectors in the Nobel winning experiments. There is a static optical line of sight between source and detectors and Bell’s theorem does not apply.
We have also argued for the role of standing waves as the conclusion of our own experimental work. Concluding that Nature is non-separable based on these experiments and our (paradox ridden) interpretations is spurious. It is most certainly premature, even after a hundred years of controversy.
VI. AN ADVOCACY OF EINSTEIN/DEBROGLIE REALISM
VI.1: On standing wave AND particle ontologies: the deBroglie vision.
This dual standing wave/particle ontology was after all the ontology espoused by Louis deBroglie, another one of the founding fathers of QM and 1929 Nobel recipient. It involved the couple of a particle and a standing wave guiding it. This class of models is called ‘pilot wave models’. Louis deBroglie took his award winning wave/particle duality at face value [10].
For a modern visual illustration of the standing wave and particle ontology we refer the reader to the hydrodynamic Walkers of Prof Couder [11]. There, a bouncing droplet particle is guided by a standing wake it itself creates as it bounces on a soapy bath parametrically driven at the Faraday threshold. Each bounce then creates a standing wave resulting in a dynamic wake (the sum of all the standing waves) as the particle moves along its path. This gives rise to behavior reminiscent of Quantum Mechanics [12]. This memory of the path leads to non-linear and chaotic dynamics (of the class: deterministic chaos) [13]. Deterministic chaos was one of the ingredients identified as a possible component to explain entanglement by Bell himself in [14]. See review [15]. See [16] for a very recent static violation of Bell inequalities in hydrodynamic walkers.
VI.2: On 1927 Solvay conference.
Ironically it was the Copenhagen interpretation that was to win the day and eclipse the deBroglie’s approach at the famous Solvay 1927 conference, despite the lone but enthusiastic support of Einstein. Bohr, Schr ̈odinger and Pauli were to claim victory over the realist but premature efforts of Louis deBroglie. The reason was simple: the Copenhagen formalism was operational. One could simply calculate predictions and see them at work in the lab. It was a practical tool for the working physicists and engineers. The ‘shut up and calculate’ mantra was justified by its fruits, which included the atom bomb, atomic power, lasers, the internet, the standard model and underpins most of our modern world.
By way of contrast the musings of Einstein and deBroglie were mostly philosophical and barren of new predictions. Foundations of physics was a backwater field for a long time and a career dead end. Bell famously asked Aspect if he had tenure, when the latter approached him about doing the risky experiments. The Nobel is more than deserved given the circumstances the pioneers faced.
VI.3: On the epistemology of QM.
From a foundations standpoint, given that our quantum formulas give us such fruitful predictions, one should strive to understand where these axiomatic formulas come from. Indeed, and in a reverse kind of way, the ‘shut up and calculate’ is a clear indictment of the Copenhagen interpretation.
If the Copenhagen interpretation leads to absurd paradoxes, then logically speaking, isn’t that a form of proof by the absurd against it? Isn’t it time we moved beyond these paradoxical interpretations? In fine we stake the following claims that 1/ the Copenhagen is a ontological mis-category, and 2/ that the paradoxes of BIV are as many proofs by the absurd of this. The Copenhagen is not an interpretation, it’s a formalism. Nobel notwithstanding, the modern record in fact does not favor the Copenhagen interpretation, precisely because of the paradoxes it raises. And yet, the magic is what makes this narrative popular. It is group psychology to a degree: big lies always attract a crowd and there is a psychological element to embracing them and defending them. As physicists, we have been facing a difficult group psychology for the past 50 years. Already so many threads on social media make appeals to authority mentioning the Nobel when discussing the finer points of interpretations.
VI.4: ‘Don’t Shut up (but still calculate)’.
To finish on a positive note, for we are passionate about these issues, we actually hope that the visibility of the Nobel prize, will spur others to look more deeply at the issues of foundations of physics. Again, because of it’s great successes, we should elucidate the foundations of quantum. The standing wave interpretation is one such approach.
VI.5: On redoing the classics with Foucault isolation.
Again, it should be noted that our experiment is a simple static 2-channel CHSH-S measure, not the more advanced dynamic choice 4-channel experiments of Aspect and Zeilinger. As argued in the paper, we would advise redoing the 4-channel experiments with the Foucault mirror isolation. This would strengthen both our own and the classic results. The author stands ready to openly collaborate for such an effort.
In the spirit of science, open collaboration and truth: onwards.
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