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Is quantum mechanics materialist?
Quantum: Einstein, Bohr and the great debate about the nature of reality
By Manjit Kumar
Published by Icon Books, 2008, £20
WHAT DOES quantum mechanics, the study of atoms and subatomic phenomena, tell us about the world? In the 1920s and 1930s, the founders of quantum mechanics fell out among themselves over how to interpret the strange discoveries of this new science.
Take quantum leaps, a concept which Albert Einstein helped define in 1905. An electron can appear to be in one place in an atom and then, "as if by magic, reappear in another without ever being anywhere in between". It was like a tree disappearing in London and suddenly reappearing in Paris or New York.
Accessible to the non-scientist, Manjit Kumar’s Quantum draws a detailed study of Einstein’s objections to the orthodox interpretation of quantum mechanics, termed the ‘Copenhagen interpretation’. Kumar argues that, in 1927, the leading exponents of quantum mechanics, primarily Niels Bohr and Werner Heisenberg, abandoned realism, which holds that the world exists independently of us, a basic premise of materialism.
In 1958, Heisenberg wrote that the Copenhagen interpretation had "led physicists far away from the simplistic materialist views that prevailed in the natural sciences of the 19th century". Einstein, he said, wished to return to "the idea of an objective, real world", where subatomic particles "exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them". (Physics and Philosophy, pp82-83)
But the discovery of quantum leaps challenged previous, simplistic views of the world. A more sophisticated model of reality is emerging. Kumar tends to blur rather than clarify Heisenberg’s distinction between the certain existence of stones or trees and the strange world of the quantum where things are not so clear cut.
The contradictions in the subatomic world forced Bohr and Heisenberg to break through the old materialist preconceptions of solid particles with definite positions and orbits. For this work, Heisenberg won a Nobel prize. Kumar complains that Heisenberg’s method, "vitiated all attempts to unearth regular patterns in nature or any causal connection", and "marked the end of a golden age in physics". But the method was a means to an end. Kumar’s objections reflect the influence of an ossified trend of Marxism, which argues that modern science is riven with ‘subjective idealism’.
Quantum mechanics has provided descriptions of many previously unexplained phenomena while unearthing new paradoxes. In Physics and Philosophy, Heisenberg is specific: it was the ‘simplistic’ materialist views of the 19th century which could not account for 20th century observations. For Marxists, there is no immutable materialist ontology, that is, what comprises existence (such as matter, energy or motion). Old, simplistic materialist concepts have to be abandoned in the light of new discoveries. Friedrich Engels attacked the "shallow, vulgarised form" of materialism which persisted in the mid 19th century, explaining that with each epoch-making discovery materialism has to change its form.
Quantum mechanics was, and remains, epoch-making. It discovered phenomena which led scientists to construct a new theory or interpretation of the physical world which stepped outside of the philosophical constructs of all previously existing human society. It created the possibility of a new materialism. Technically, it led to lasers, transistors and computers which have transformed society.
However, in the 1920s and 1930s, Einstein looked for ways in which quantum mechanics might make predictions that were inconsistent with reality as he defined it. Kumar strongly supports Einstein’s views, but steps beyond them into idealism. Attacking Bohr, he states: "For Bohr the theory came first, then the philosophical position, the interpretation constructed to make sense of what the theory says about reality. Einstein knew that it was dangerous to build a philosophical world-view on the foundations of any scientific theory".
Kumar criticises Bohr for putting concepts arising from physical observations before philosophical speculation, and he attributes this criticism to Einstein. But there is a difference between attempting to defend a set of principles scientifically, as Einstein did, and relying primarily on a philosophical world-view while rejecting scientific theory if it violates it, which Kumar tends towards. Einstein clearly states: "The elements of physical reality cannot be determined by a priori philosophical considerations, but must be found by an appeal to the results of experiments and measurements". (Can Quantum-Mechanical Description of Physical Reality Be Considered Complete? Einstein, Podolsky and Rosen, Physical Review, 15 May 1935) There is sometimes a blurring of the line between fact and comment in Quantum.
Kumar identifies three ‘elements of reality’ which Einstein attempted to defend. One is causality. Kumar compares the random radioactive decay of atoms to an apple falling. Once the apple is let go, Kumar writes, it falls to the ground, caused by gravity. However, in the quantum world, Kumar asserts, there is no causality, and the apple would hover for an unknown period of time in the air before falling.
But this is misleading. In an apple orchard, the apples fall in autumn and we know the cause. Similarly, quantum mechanics has revealed the causes of atomic decay. Yet we do not know, precisely, when each apple will fall, just as we do not know, precisely, when each atom will decay. The wind blowing the apples down is chaotic and cannot be predicted precisely, nor can the atrophy of the cells in the stems of individual apples. It is not at all clear that there is a difference between causality as we commonly experience it and causality at the atomic or subatomic level as understood by quantum mechanics.
Furthermore, this atrophy cannot be studied without interfering with the apple and causing a change in its time of falling. Scientists cannot carry out experiments without interfering with nature at the atomic level, and this appears to have a degree of general validity. This illustrates the discovery that the separation of experimenter and subject, another element of reality which Einstein defended, appears to be an idealised concept.
The third element was locality, the belief that things in separate localities cannot be in instantaneous touch with each other in the way quantum mechanics appeared to suggest. Einstein derided this "spooky action at a distance" of quantum mechanics, yet it has since been proved experimentally. Isaac Newton’s gravity also had appeared to be this kind of spooky action. Ironically, to truly explain gravity, Einstein abandoned the concept of absolute time and space, which his contemporaries had thought was an element of reality. Consequently, Einstein’s relativity was considered a denial of materialism and objective reality by philosophers and some prominent scientists at the time.
Experiments in the 1980s demonstrated that if two photons are simultaneously emitted from an atom they are ‘entangled’ or in instantaneous touch with each other. Even though they travel away from each other at the speed of light, they are somehow still part of the same entity. Experiments performed on one photon appear to instantly affect the other. Just like the quantum leap of electrons, which appear to defy our concepts of space and time by disappearing from one place and reappearing in another without passing in between, these entangled objects appear to disregard space and time. They act as if they do not acknowledge the existence of separate localities. In scientific terms, they are non-local. Kumar downplays the great significance of this discovery.
In general terms, Einstein was the loser in the great debate about the nature of physical reality. What troubled Einstein, Kumar concludes, is the "renunciation of the representation of a reality thought of as independent of observation". It is at this point that one realises that Kumar’s study largely passes over some vital experimental results. The physicist Richard Feynman stated that the results from Young’s ‘two-slit’ experiments (which demonstrate the inseparability of the wave and particle characteristics of light and other quantum particles) are "absolutely impossible to explain" using the concept of reality Kumar wishes to preserve at the subatomic level. The omission of a discussion of these experiments makes it very difficult for the reader unfamiliar with them to judge Kumar’s conclusions objectively.
One day, a new theory will reveal the deeper reality behind subatomic particles, in the same way as the discovery of electromagnetic radiation helped us understand the transient nature of rainbows. But this reality will be non-local. As US physicist Nick Herbert pointed out, insisting that subatomic particles have an independent existence is like insisting that rainbows are solid objects and have some definite place in space irrespective of the observer. We know that rainbows appear to be in different places depending on the position of the observer. Kumar will never find that pot of gold at the end of the rainbow. Quantum is a fine book in many ways, but not an objective account.