Quantum entanglement poses a particular challenge to our conception of space and time, and to our conception of the relation between physical objects. It does so in a very interesting way because it revolutionizes an already revolutionary conception at the root of Einstein’s theory of relativity.
Einstein’s relativity theory postulates that nothing can travel faster than the speed of light in vacuum. As such, this postulate revolutionized our understanding of space and time. Spatial lengths, and the duration and simultaneity of events, were found to depend on one’s frame of reference and not be absolute things. Matter and energy were found to be the same thing in different forms. These ideas perfected and deepened older Newtonian conceptions of space and time, matter and energy, previously considered to be absolute, unrelated, and mechanical. They showed that Newton’s theories only approximate reality, but in a way that described objects traveling much more slowly than the speed of light. Our understanding of reality had to be updated.
This didn’t mean that Newtonian mechanics did not give correct physical predictions. It did and it still does, except in cases that could not have even been conceived, nor tested, at the time of Newton, particularly, objects moving at speeds near the speed of light. Newton’s theory deviates from physical reality in such instances.
The advent of quantum theory, in turn, challenged one of the fundamental conceptions of Einsteinian physics. This conception says that the factual situation of any entity is independent of what is done on another entity that is spatially separated from it. In other words, it challenged the idea that events involving two things that cannot communicate or reach each other, either directly or by intermediate material means, cannot affect each other’s state of being. This is called Einstein’s locality principle. It is also called local realism. It postulates that cause and effect must be locally related. Most importantly, this principle implies that cause and effect have to be close enough to relate to each other within the bounds of the speed of light.
Quantum theory predicts that it is possible to violate local realism through quantum entanglement. Two or more particles, such as electrons or photons (particles of light), can be assembled into physical states in a way that their individual physical properties lose their reality but the relation between them does not. Their relation to each other exists before their separate material existence. Crudely speaking, one is up and the other is down, or one spins clockwise and the other spins counter-clockwise, are examples of relations. For entangled particles, the relation between them exists and is real before they materialize as separate entities. Their individual separate physical states do not have physical reality. They lose their individuality. Particle 1 is not spinning in any particular fashion, and neither is particle 2. But the entangled object does have material reality and its spin angular momentum is zero. Both component particles spin in opposite senses if, and once, observed. This is explored further in the following section.
The reality of such entangled states was challenged by Einstein, Podolsky, and Rosen in 1935 on the basis that it violated local realism.1 A measurement of the physical properties of one of a pair of entangled particles (say, that one is found to be spinning clockwise) immediately determines the state of the spatially separated second entangled particle (it is immediately put in a counter-clockwise spin state). This is called the EPR paradox. Subsequent experimental tests since then have definitely confirmed that quantum entanglement is real and that these predictions of quantum theory are true.
The 2022 Nobel prize in Physics was awarded to Alain Aspect, John Clauser and Anton Zeilinger, precisely for experimentally establishing the reality of quantum entanglement. The award was described to acknowledge “experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science”. Bell inequalities refer to mathematical inequalities that must be obeyed if local realism should hold.
The reality of quantum entanglement should not be understood as the overcoming of relativistic physics. Rather, it should be understood in a dialectical way, as the deepening of our understanding of material reality. It should not even be understood as a violation of the limitation of signaling faster than the speed of light.
In fact, there is a no-go theorem in quantum information theory, called the no-communication theorem or no-signaling principle, which states that through the measurement of entangled particles it is not possible to communicate information from one observer to another. The theorem states that, given some initial entangled state prepared in some way, there is no action that a person making a measurement of the state of one of the entangled particles can take that would be detectable by another person measuring the state of the other entangled component.
So, what does quantum entanglement say about physical reality? First of all, it says that a quantum entangled object constitutes a single entity with certain physical properties of its own. But these physical properties are not determined by the individual properties of its components, only by their mutual relation. In fact, the physical properties of the individual components have no reality until a measurement is performed. So, it is possible for particles, previously comprehended as separate entities, to lose their individuality.
Secondly, quantum entanglement calls into question the nature of the space-time in which entangled particles exist. John Clauser2 says that entangled particles cannot be described by placing them separately in our standard three-dimensional space but that their physical description requires a higher dimensional space than joins together the individual spatial and spin components of each constituent particle. If the spatial and spin components of particle 1 are x1, y1, z1, S1 and those of particle 2 are x2, y2, z2, S2, the space in which they exist must be described by eight interrelated components x1, y1, z1, x2, y2, z2, S1, S2, called configuration space. This is another way of saying that these entities do not have separate existence, and that the speed of light communication limitation between them does not apply. In other words, the relation between the two particles must be considered as a totality.
I. a. What is Quantum Entanglement
Quantum mechanics allows the creation of individual particles, such as photons or electrons, that can be simultaneously paired up with other particles in physical states incompatible with each other. For example, Fig. 1 shows a photon represented by a red circle, with spin angular momentum pointing up, and another photon, represented by a purple circle, with spin angular momentum pointing down. In this image, the photons may represent light of the same or of different colors. The spin of a particle may be thought of as the particle rotating clockwise or counter-clockwise around its axis, although, technically speaking, photons cannot be thought of as little rotating balls. However, they can transfer their spin angular momentum to other particles, such as electrons.
Entanglement means that in Fig. 1, the red photon simultaneously has spin up AND spin down at the same time. BUT, for the case when the red photon has spin up, the purple photon has spin down, and vice versa. This is hard to imagine because in our human experience we never encounter physical entities that can be two different things at once. If we imagine the Earth rotating from East to West and from West to East at the same time, it is hard to make sense. But this type of thing is actually true for entangled quantum particles.
Let’s say |↑⟩A represents particle A with spin angular momentum pointing up, and |↓⟩B represents particle B with spin angular momentum pointing down. Then, physical states can be created where particle A has both spin up AND spin down, and where particle B has spin down if A has spin up, and vice versa. These physical states are represented as
and are unprecedented in previous physical theories. This is an actual mathematical expression in quantum theory. The expression contains contradictory states within one entangled material object. Measurements resolve the contradiction into one of the options.
There is a technical reason for the minus sign having to do with mathematically writing things down in a way that the state is not changed if one looks at it from a rotated reference frame. These states are called entangled states and were considered by Einstein to lead to what he called “spooky action at a distance.”
Why “spooky action at a distance”? If one goes to the lab and measures the spin of A to be up, |↑⟩A, the spin of B is immediately transformed into a state of spin down, |↓⟩B, And the state of the system is transformed into |↑⟩A|↓⟩B. The contradiction is resolved and the two material particles now exist separately. However, it turns out that this does NOT mean that one may be able to transmit information faster than the speed of light. So, there is actually no “spooky action at a distance” going on.
The point is NOT that A was previously already in state |↑⟩A and you just didn’t know it. A was in both spin up and spin down states. But the fact that you looked and found it to be in one of the two, immediately transformed B into the opposite state. No matter how far B was from A. Maybe in a lab in another continent.
I. b. Experimental Generation of Entangled Particles
There are different ways to produce entangled particles. Early work made use of “cascade” optical transitions in calcium atoms.3,4 The atoms were optically pumped (illuminated) to bring ground state electrons (4s2 1S0) into an excited atomic state. These electrons decay back into the ground electronic state in stages by emitting two photons, one after the other. Conservation of angular momentum imposes the condition that their polarizations, although different, be correlated with each other, producing an entangled state. Their polarizations have to add up to that of the excited state (4p2 1S0) they originate from.
An alternative, and more efficient way, of producing entangled photons is to split a single photon into two by a process called parametric downconversion,5, 6 as described in Fig. 2. In this process laser light is shone into a special type of crystal, called a nonlinear crystal, that converts single photons into entangled pairs.
I. c. Experimental Verification of Entanglement
How does one make sure that entanglement is real? This can be checked by coincidence measurements. For example, two entangled photons with undetermined but orthogonal polarizations relative to each other, say, vertical and horizontal, are sent to different detectors. Then if one detector measures vertical polarization for one of the photons, the other detector will measure horizontal polarization for the other photon. By detecting both photons at the same time, one rules out the possibility that there has been any communication limited by the speed of light.
II. Einstein-Podolsky-Rosen (EPR) Paradox
The quantum mechanical prediction that entangled particles may exist, led Einstein, Podolsky and Rosen to conclude in 1935 that the description of reality given by quantum mechanics was incomplete1 and that it violated clear cause and effect correlations. They argued that quantum mechanics makes it possible to determine the state of particle B based on measurements of the state of a spatially separated particle A, without there having been any interaction with particle B, and conclude that this cannot happen.
The argument raised in the EPR paper has at its crux the following assertion by Einstein, called Einstein’s locality principle:7
But on one supposition we should, in my opinion, absolutely hold fast: The real factual situation of the system S2 is independent of what is done with system S1, which is spatially separated from the former.
III. Bell’s Inequality
In 1964, physicist J.S. Bell proposed a way to check whether Einstein's locality principle holds for entangled quantum particles.8 By assuming local causality, Bell came up with probabilistic predictions about the results of spatially separated experiments. These predictions took the form of inequalities in the results of measurements performed by such experiments. This was particularly important because it allowed one to test experimentally whether or not the predictions of quantum mechanics violated local causality.
Such experiments have been done to check this, and it was found that Einstein's locality principle can be violated. It does not always hold. Modern versions of Bell’s Theorem,8 show that if measurements are performed independently on two separated particles of an entangled pair, then the assumption that the outcomes depend on Einstein locality principle implies a mathematical constraint on the outcomes on these measurements. Bell’s and subsequent works8 showed that quantum physics predicts correlations that violate the predictions based on Einstein’s locality principle. Experimental tests prove unequivocally that entangled particle systems violate the locality principle.
IV. Pre-Marxian Materialism and Dialectical Materialism
Local Realism is the foundation of Einstein’s conception of reality. Spatially separated phenomena or events are independent of each other, i.e., may not affect each other. In other words, local realism postulates that there is no cause/effect relation between them, unless they are “locally” connected. That means that they locally interact with each other through some means, such as through electromagnetic signals, e.g., sending out photons that connect both phenomena. Physically that means, for example, that photons are emitted by one or both of the spatially separated entities participating in the events, and received (absorbed by or scattered from) the other entity. In this setting the materiality of the objects precedes any materiality of relation.
There are two operative assumptions that underlie this conception, as follows:
Einstein’s relativity postulate: No physical entity can move faster than the speed of light in a vacuum. This also implies that only massless particles (such as photons) can travel at the speed of light. This postulate implies that if two spatially separated physical entities participating in an event or phenomenon cannot be mutually linked through signals at or below the speed of light, then there is no cause-effect relation between them. They are completely independent from each other. They do not depend on one another.
Individual physical entities (objects, particles) always maintain their separate physical identities, their individualities.
Quantum entanglement overturns these two assumptions, in the following sense. Entangled “particles” no longer act as separate particles but as a single entity (a totality). They do not exist separately in three-dimensional physical state. If one conceives of them as separate physical objects, then human activity upon them (making a measurement) has the effect of violating Einstein’s speed of light limit. The point is not that the speed-of-light signaling limitation is violated—it is not—But, the conception of the entangled particles as separate self-enclosed physical entities is wrong.
One should be careful not to use the seeming strangeness of quantum phenomena to argue in support of dialectical materialism under false pretenses. One such instance is the case of quantum interference where electrons exhibit wave-like behavior, or the case of electron clouds in hydrogen atoms.9 One Trotskyist analysis contends that individual (not-entangled) particles follow well-defined spatial paths to argue in favor of a supposedly Marxist interpretation of quantum mechanics.9 There is no such physical evidence. He writes:
But does the path exist? Yes, providing that motion is understood dialectically. The path is the trajectory along which the particle moves. When the particle is in motion, it is not at any one position; it is in the process of moving from position to position. It moves along a definite trajectory.
This is not materialist dialectics. It is sophistry. It is a throwback to local causality. Dialectical materialism does not mean to assume the unwarranted assertion that electron paths exist, and then to assert that motion must be “understood dialectically.” That “when the particle is in motion, it is not at any one position.” It is typical of Trotskyists to take a phenomenon as it is understood within hegemony, tack on the word “dialectical,” and claim to have made some profound discovery.
Dialectical materialism means that states of matter, such as entangled particles, exist. That the individual physical states of spatially distant entangled particles do not exist, but that this physical condition can be resolved into a physical reality. This is the dialectics of nature.
There have been attempts to argue that additional hidden variables must be added to quantum theory to explain such phenomena. But hidden-variable theories have been definitely and experimentally shown to be unnecessary, and in the case of quantum entanglement, local causality has been shown to be false. However, the alternative to local causality and hidden variables is not a rejection of materialism. The alternative is that material reality works differently from how it is conceived by hegemony.
Marx criticized such hegemonic materialism in his critique of Feuerbach10:
The chief defect of all hitherto existing materialism is that the thing, reality, sensuousness, is conceived only in the form of the object or of contemplation, but not as sensuous human activity, practice, not subjectively. Hence, in contradistinction to materialism, the active side was developed abstractly by idealism — which, of course, does not know real, sensuous activity as such.
Marx gives significance to “ human activity,” or labor because these constitute relations between individuals. Entanglement shows that material objects are not self-enclosed things. The materiality of the entangled entity involves the relation between its individual components BEFORE those components acquire separate individual existence. The two photons of an entangled pair are not separate entities. But their having opposite spins after measurement, and their realization as separate entities after measurement, exists materially before their separate individual existence. Thus, the totality of the relationship takes primary form, over the fact that the objects are in relation with each other.
V. Conclusion
Throughout history, significant scientific discoveries have forced materialist ontology to update itself. In many cases, it has been philosophers who have made insights into the world, which then, experiments of natural scientists later verified. One such case is that of Kant. In “Dialectics of Nature,” Engels argued that Kant, in his “Universal Natural History and Theory of the Heavens,” was the first to offer a philosophical break from the idea that the universe appeared out of chaos in the state that is in today. He argued, rather, the universe came into being over the course of time. This has great implications because if the universe developed over time, then surely the Earth itself and all life on it have histories, a radical concept during Kant’s time. Species as they exist, did not always exist. The scientific discoveries of Lyell (in geology) and Darwin (in biology) gave evidence in favor of the musings of a philosopher before them.
Marx himself was a philosopher, though more than someone who simply thinks for the sake of thinking. The dialectical materialist philosophy introduced by Marx is difficult to let go. While world revolutions in the relations of production already force Marx into relevancy, discoveries in the natural sciences continue to force thinking beyond the limits of Anglo-empiricist hegemony of thought. The same laws that Marx used to discover the development of human history, Darwin used to discover the development of organic nature, both of which forced revolutions in the ontology of materialism. Today, the specifics of Marx’s thinking, such as the primacy of relations between objects over objects themselves—considering thetotality—is necessary for the natural sciences as much as it is for political activity. The division of labor within science, chiefly the hyper specialization into specific sub-fields, have caused scientists to lose the bigger picture of reality, and thus the ability to generalize their discoveries into a wider view of the world. In the best of cases, they are materialists in the sphere of nature and idealists in the sphere of human history. This fundamental disconnect will even affect their reflections on nature. This is the importance of Marx and Engels. By taking the kernel of Hegel’s system, and bringing it into material reality, they have offered a complete philosophy. Science will either catch up to this truth through a long process of continued investigation into material reality, or it can engage with dialectical philosophy today.
References
Einstein, B. Podolsky, N. Rosen, “Can Quantum-Mechanical Description of Reality Be Considered Complete?” Phys. Rev. 47, 777-780 (1935). https://cds.cern.ch/record/405662/files/PhysRev.47.777.pdf
John Clauser, “Experimental proof that nonlocal quantum entanglement is real”
S. J. Freedman and John Clauser, “Experimental Test of Local Hidden-Variable Theories,” Phys. Rev. Lett. 28 (14), 938-941 (1972).
Alain Aspect, Philippe Grangier, and Gerard Roger, “Experimental Tests of Realistic Local Theories via Bell's Theorem,” Phys. Rev. Lett. 47 (7), 460-463 (1981).
David C. Burnham and Donald L. Weinberg, “Observation of Simultaneity in Parametric Production of Optical Photon Pairs,” Phys. Rev. Lett. 25, 84-87 (1970).
Paul G. Kwiat, Klaus Mattle, Harald Weinfurter, Anton Zeilinger, Alexander V. Sergienko and Yanhua Shih, “New High-Intensity Source of Polarization-Entangled Photon Pairs,” Phys. Rev. Lett. 75, 4337-4341 (1995).
J.J. Sakurai and J. Napolitano, Modern Quantum Mechanics, Einstein’s Locality Principle and Bell’s Inequality, Second Edition, p.241
Harry Nielsen, “Against the Copenhagen interpretation of quantum mechanics – in defence of Marxism,” In Defence of Marxism (2005) https://www.marxist.com/quantum-mechanics-copenhagen130705.htm
Karl Marx, Theses On Feuerbach (1888) https://www.marxists.org/archive/marx/works/1845/theses/theses.htm
Miguel Levy is a Professor of Physics at the Michigan Technological University. His research activities presently center on photonics, with an emphasis on nonreciprocal phenomena, magneto-photonics, and nanophotonics.
Hassan Ali received his doctorate in Biomedical Sciences from Cornell University. He is currently involved in the development of artificial intelligence to improve cancer outcomes.
Good read.
I think it is also worth looking into the relationship between blackholes, dialectics, and the universe as a whole.
The laws of the universe are dialectical, a constant antagonism of opposites.
I think this article is also worth a read.
https://www.universetoday.com/161877/if-black-holes-evaporate-everything-evaporates/
-Rev