Quantum Entanglement

Custom Student Mr. Teacher ENG 1001-04 8 September 2016

Quantum Entanglement

When two objects separated in space instantly interact with each other without the agency of a medium (or a known medium), it is called action at a distance. Although such a notion controverts the very rationale of science and harks back to primitive magicalism, it had to be propounded in classical physics for the lack of a better alternative in explaining the fundamental modus operandi of the force of gravity. Newton surmised that gravitation acted instantly across the universe, regardless of distance.

This was a very spooky notion indeed, but since classical physicists did not have a clue about how to crack the enigma of action-at-a-distance, its spookiness was downplayed and it was simply considered as one of the several unexplained phenomena in science. However, this unexplained phenomenon was not at the fringes but at the very core of classical physics. Till Einstein, no one could face the problem head on. Einstein postulated his path-breaking special theory of relativity in 1905.

Einstein’s theory, however, required that nothing in the universe moved faster than the speed of the light. The phenomenon of action-at-a-distance apparently violated Einstein’s theory. In order to resolve this conflict, Einstein worked for 10 years more and came up with his general theory of relativity which shattered the entire Newtonian framework of space and time in one stroke. In the general theory, space is visualized not just as an empty container but as an elastic fabric which warps in accordance with the mass of the objects embedded in it.

Gravity is simply an effect of the curvature in space-time continuum. A massive object such as a planetary body would affect the fabric of space in the same way as a heavy iron ball placed on a thin stretched-out rubber sheet would warp it. The heavier the mass of an object the greater is its gravity simply because it creates a larger depression in the fabric of space-time. The shape of deformation in space around a massive object dictates the behavior of objects in its vicinity.

Between sun and earth, for example, there is no mysterious or mystical action-at-a-distance, it is only that the fabric of space is indented in such a way that the earth moves in a groove created by the presence of sun. This radical explanation offered by the general theory for the effects of gravity apparently did away with the action-at-a-distance effect and the problem was solved forever… or so it was thought. In 1913-15, even as the theory of general relativity was shaping up, Niels Bohr formulated the solar system model of the atom and began the quantum revolution.

Bohr hypothesized that the negatively charged electrons inside an atom moved in orbits around the positively charged central nucleus. However, to prevent the orbit of the electron from rapidly deteriorating and the electron falling into the nucleus, which was supposed to happen according to Maxwell’s laws, Bohr proposed that the electrons moved in discrete orbits around the nucleus and emitted electromagnetic radiation in tiny discrete bundles called quanta.

Bohr’s model was a tremendous leap of imagination because it implied that the electron can move from one orbit and appear in another orbit without ever being in between for howsoever a little span of time. Bohr’s notion of quantum leap was just as “spooky” or even more so than Newton’s action at a distance, but it was resorted to for the lack of a better solution. And moreover it directly explained a crucial empirical observation, the discrete lines in the hydrogen spectrum. With Bohr’s mysteriously quantum-jumping electrons, spookiness once again came and settled at the core of a newly emerging science.

Once again, it was simply taken for granted. But quantum mechanics was very different from Newtonian mechanics because not only one of its central postulates but most of them and the entire science built upon them turned out to be spooky and weird. In fact, Einstein’s relativity itself is just as weird for all intents and purposes, but despite all its extreme weirdness it still conforms to the traditional paradigm of scientific thinking, whereas quantum theory goes a little beyond and changes the paradigm.

Though Einstein himself was one of the pioneers of quantum mechanics and Bohr took his inspiration from the previous work of Einstein and Planck in coming up with the strange notion of quanta, Einstein stood vigorously opposed to the rapidly developing science of quantum mechanics. Despite the fact that Einstein’s theories toppled the edifice of classical physics, Einstein himself was regarded as a classical physicist, the last of the breed. Many of the basic concepts of quantum mechanics went against Einstein’s deeply cherished assumptions regarding the nature of the universe.

Einstein was especially troubled by the random, probabilistic nature of quantum mechanics (Gibbins, 1987). Quantum mechanics (the Copenhagen interpretation) says that there is no ‘objective reality’ independent of measurement and observation. However, Einstein was an ardent believer in objective reality and thought that quantum mechanics was only an incomplete theory of the atomic world; that probabilities and the central emphasis on the act of observation entered into it only because of our limited knowledge and not because the intrinsic nature of reality was that way.

In 1935, Einstein, along with Podolsky and Rosen, undertook a thought experiment — called the EPR Paradox — which intended to show the deficiencies of quantum theory (Davies, 2003). Though the EPR paradox was conceived as a challenge to the Uncertainty Principle of quantum mechanics, it also brought out a weird new aspect of quantum theory, the ‘spooky’ action-at-a-distance effect. Quantum mechanics seemed to possibly imply instantaneous influence, i. e. , faster-than-light interaction, between two particles separated in space.

In certain situations, known as ‘entangled states’, spatially separated elements of a quantum system would appear to inform each other without any time lag, irrespective of the distance between them. In one of its simplified versions the EPR paradox goes like this: A pair of polarization-correlated (i. e. , entangled) photons are emitted by a source. These two photons then move in opposite directions. We set up two detectors at two distant points to measure the polarization of photons.

Quantum theory asserts that the polarization of a particle is undefined until we observe it. This implies that both the photons are of random polarization when they leave the source and continue to have a non-definite polarization until we measure one of them. It is not possible to predict the polarization of either before the measurement actually takes place. But as soon as we measure the polarization of one photon, we know that the polarization of its twin particle is the same and can verify it too.

The two detectors could be as far away as possible, say, hundreds of light years away, but the experiment would still work (Farwell, 1999). There are two possible explanations for this thought experiment which was later on actually performed and verified on several occasions. One is that the photons carried a specific polarization all along, but in an encoded form. There are ‘hidden variables’ yet undiscovered by quantum mechanics. This is what Einstein intended to demonstrate.

But there is another possible explanation that the polarizations of both the electrons actually remained indefinite all along, as indeed they were supposed to be, but as soon as one of them assumed a definite value after the process of measurement, this value was somehow communicated — instantaneously — to the other photon. The first explanation — championed by Einstein — implies that a definite polarization is present in some form even prior to the act of observation; this would violate the Uncertainty Principle and would show that quantum mechanics still did not get the basics correct.

The second explanation implies either that a message traveled instantaneously from one photon to another, i. e. , action at distance, or that — the explanation preferred by Bohr — there is no such thing as distance in reality, a notion which violates something called locality assumption. The locality assumption — a cornerstone of all physics before the advent of quantum mechanics — simply says that different locations in the universe are separated from each other and have to be dealt with separately.

If this assumption does not hold true, it would mean that everything in the universe is potentially connected with everything else, and the local chains of cause and effect may often appear violated because local phenomena may be constantly influenced by distant phenomena in complex and mysterious ways. For thirty years after postulating the EPR paradox, not much headway was made in definitively resolving it one way or the other. Then in 1965, a physicist at CERN, John Bell, devised a way in which the locality assumption could be proven experimentally right or wrong.

Several tests were conducted in the laboratory to test the validity of ‘Bell’s inequality’. The final decisive test was conducted by Alain Aspect and his team in 1982. It conclusively proved that the locality assumption did not conform to reality, and therefore Einstein’s criticism of the Copenhagen interpretation of quantum mechanics was wrong. Even after the experimental rejection of Bell’s hypothesis which took the locality assumption for granted, it is still possible that there is an action-at-a-distance effect involved in Einstein’s thought experiment.

However, generally the most favored conclusion of a number of scientists — from Niels Bohr to David Bohm and others — is that there is no propagation of any signal, it is simply that two different areas in the universe are not in reality separated as we assume them to be. ‘Non-separability’ has become a widely accepted notion in modern physics. Everything is connected to everything else, and only this kind of holistic view of the universe can explain the synchronistic behaviors of two apparently separated particles which are nonetheless connected at a deeper level (Gilder 2009).

There is no action-at-a-distance here, but there is simply no distance to begin with. While action-at-a-distance could be seen a spooky phenomenon, as indeed Einstein saw it, the concept of ‘non-separability’ can present a highly gratifying holistic view of the universe which does not let science degenerate into magicalism but elevates it into some kind of lofty spirituality. References Davies, E. B. (2003). Science in the Looking Glass: What Do Scientists Really Know?

New York : Oxford University Press Gibbins, Peter. (1987). Particles and Paradoxes: The Limits of Quantum Logic. New York : Cambridge University Press Gilder, L. (2009). The Age of Entanglement: When Quantum Physics Was Reborn. New York : Vintage Farwell, L. (1999). How Consciousness Commands Matter: The New Scientific Revolution and the Evidence that Anything is Possible. Fairfield, IO : Sunstar Publishing Hey, T. & Walters, P. (2003). The New Quantum Universe. New York : Cambridge University Press.


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  • University/College: University of Chicago

  • Type of paper: Thesis/Dissertation Chapter

  • Date: 8 September 2016

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