Schrödinger's Kittens is the most recent book by John Gribbin about the interpretation of quantum mechanics. It is the sequel to In Search of Schrödinger's Cat, which was published in 1984. In his newer book, Gribbin claims to have "solved the quantum mysteries", and presents a relatively recent interpretation of quantum mechanics, the "transactional interpretation", which he argues is the best available interpretation. MIM disagrees with Gribbin. We prefer the interpretation known as Bohmian Mechanics (BM).

Science for the People

When reading books about science, it is important for revolutionaries to keep in mind the difference between the science of the bourgeoisie and that of the people. The bourgeoisie needs science that produces results, so it can produce sophisticated killing machines to use against the people, and luxuries for its amusement. The proletariat needs its science to agree with reality as well, but for different reasons. Proletarian science is used to serve the people, rather than to oppress and kill them.(1) Philosophically, the bourgeoisie needs its science to be presented in a way that obscures reality, because the future is not bright for the bourgeoisie: facing reality would be too depressing. The people, however, need not be reluctant to face the truth, because the future is ours.

Materialism or Idealism?

As Marxist-Leninist-Maoists, we at MIM are materialists. All this means is that we believe that we exist in the world and not that the world exists in us. Lenin put it this way in his Materialism and Empirio-Criticism:

"The sole "property" of matter with whose recognition philosophical materialism is bound up is the property of being an objective reality, of existing outside the mind."(2)

The nonrecognition of the property to which Lenin refers is called solipsism, or subjective idealism. When it comes to the interpretation of quantum mechanics, many physicists come very close to solipsism. Physicist John Wheeler, for example, believes that human beings created the universe by looking at it, and he supports this "theory" with arguments based on the prevailing interpretation of quantum mechanics. Gribbin is not nearly as bad as Wheeler.

In Ludwig Feuerbach, Engels said this about the difference between materialism and it's arch-nemesis, idealism:

"The answers which the philosophers gave to [the question of the relation of thinking to being, and which is primary] split them into two great camps. Those who asserted the primacy of spirit to nature--and, therefore, in the last instance, assumed world creation of some form or another... comprised the camp of idealism. The others, who regard nature as primary, belong to the various schools of materialism."(3)

Nearly all physicists advocate interpretations of quantum mechanics which implicitly side with the idealists according to this criterion of Engels. This is the camp Gribbin is in, and he is actually one of the less idealist physicists in this camp.

Isn't Science Objective?

We Maoists believe science is science, and anyone who wants to know what it means for something to be a science should read On Practice, by Mao Tse-Tung, or Lectures on Physics, by Nobel prize-winning physicist Richard Feynman (both great scientists).(4) By definition science applies the Marxist theory of knowledge that truth is determined by practice. Practice can take the form of class struggle in the case of Maoism (the science of revolution), or scientific experiment, in the case of physics. The issue dealt with in Gribbin's book is one of interpretation of current scientific knowledge, and so the controversy is really a result of the bourgeoisie paying people to legitimize bourgeois philosophy by calling it science. The entire field of psychology is also an example of this.(5) The interpretation of quantum mechanics that MIM advocates and the interpretation most physicists advocate are diametrically opposed philosophically, but make the same predictions about every conceivable experiment, so the science underlying them is the same: it's the philosophy that's different. The reason MIM thinks this matters, rather than just being idle speculation, is that the prevailing interpretation affects the way physics is taught, so that today when people learn quantum mechanics they are also learning to think of subjectivity as fundamental to the way the universe works; they are learning to be idealists. This disarms the masses ideologically, and clears the road for all sorts of unscientific mystical and religious ideas to take root.

Gribbin's Approach

Throughout the book Gribbin promises to offer his choice of the "Best Buy" for an interpretation of quantum mechanics. His approach in deciding on this best buy is an unscientific one, and he even explicitly says as much; the best interpretation for him means the one that gives the results he wants.(6) Philosophically, Gribbin, like most scientists, presents a muddled mixture of materialist and idealist arguments and positions. At his best, Gribbin presents a very good materialist exposition of the relation between absolute and relative truth in the context of scientific discovery.(7) More often, however, he comes across as a solipsist or, at best, a very muddled materialist. He confuses reality with theories about it, by saying the atom is a model!(8) He makes many analogous statements, all of which tend to blur the distinction between absolute and relative truth. Gribbin's point in saying that the atom is a model, and that humans invented quarks, is that the experiments that scientists perform and the way the results are interpreted are influenced by the theoretical models in the heads of the scientists. However, this goes both ways, and the results of experiments change the theoretical models. The model of an atom is a model, but the atom is an atom, and it's objective existence is proved by voluminous experimental data, irrespective of the likelihood that it will eventually turn out that the current theoretical model of the atom is less than 100% correct. Gribbin makes this point, and then immediately ignores it. This muddleheadedness leads him to call the final chapter of his book "A Myth for Our Times". Gribbin is looking for a myth about quantum mechanics because he doesn't think there can be any truth about quantum mechanics: for him theories are reality.

The Quantum World

In order to understand the problem addressed in this book, one first has to have some idea of the ways in which quantum physics differs from the so-called classical physics which describes the way the everyday world works. It is just a fact of nature, demonstrated by countless experiements, that small-scale physics is nothing like what can be extrapolated from what is known about the large-scale, and all interpretations of quantum mechanics agree about this. Two of the main ways in which quantum physics differs from classical physics are wave-particle duality and nonlocality.

The classic demonstration of wave-particle duality occurs in the two-slit experiment. If you take a piece of opaque material and cut two tiny slits in it very close together, put a detection apparatus on one side and then shoot at the material a succession of particles from the other side (any particles you want: electrons, protons, photons, muons, ...), you'll find that the detector detects a pattern called an "interference pattern" that is typical of wave behavior. If the particles all behaved classically, like baseballs, you would expect almost all the detections to occur in a small region behind each slit, mostly towards the center of the region, but instead experiments show that if everything is set up right, there are almost no detections at that location. This wavelike behavior lead physicists to posit that instead of evolving according to the old physics of Newton, particle behavior is actually described by a wave equation, the Schrödinger equation. This turned out to be a remarkably successful theory. Schrödinger himself consistently opposed the subsequent idealist direction quantum physics went in. The Schrödinger equation remains a fundamental part of most interpretations of quantum mechanics, including the interpretation we favour, BM.

Nonlocality is much more controversial than wave-particle duality. Many physicists still don't accept it, although it has been demonstrated conclusively in a series of experiments. Nonlocality refers to the instantaneous influence of macroscopically seperated entities on one another. The classic demonstration of nonlocality is the Aspect experiment, which wasn't performed until the early 1980's, and was based on a thought experiment, called the EPR (for Einstein-Podolsky-Rosen) paradox, which was developed in the 1930's. The EPR paradox was designed to make the prevailing interpretation of quantum mechanics look absurd, so to understand it one has to know something of that interpretation. The experiment, when performed, showed that something called Bell's inequality was violated. Bell's inequality is an equation worked out by physicist John Bell relating the probabilities of various measurement results given the assumption of locality.

Philosophically, we Maoists aren't just materialists, we're dialectical materialists. A major part of dialectics is expecting the unexpected: we expect the phenomenology of the world will always be far more rich than what is explained by our theories, and thus we expect that it will always be possible to find an experiment to perform whose results disagree with the prevailing theories, making possible and in fact necessitating the further development of science. Unlike the proletariat which has time on its side, the bourgeoisie is doomed, so it retreats into idealism to avoid having to face this reality. Part of this idealism is the metaphysics of theorizing a static, unchanging, undialectical universe. So the paid ideologists of the bourgeoisie in the physics community always expect their theories to be good for all time, no matter how often these expectations are shattered by reality, as in the double-slit and Aspect experiments. Physicists who know dialectics welcome unexpected experimental results, but most bourgeois physicists just try to cover them up, which explains why most physicists are still trying to cover up nonlocality after more than a decade of experiments proving it.

Quantum Orthodoxy

The orthodox interpretation of quantum mechanics is called the Copenhagen interpretation (CI), because it was created by Niels Bohr and his collaborators in Copenhagen. Recently it has been falling somewhat out of favour, so that today, of those physicists who have a position, not many more than half prefer CI. This is the interpretation underlying all the problem-solving formalism taught in most college courses on quantum mechanics, although the way these courses are taught, most students are probably barely aware that there is any way of interpreting quantum mechanics as anything other than a mathematical formalism.

CI is usually formulated as a collection of postulates. One postulate is quantization, which gives a purely formal way of taking a classical analysis of a physical system and generating a quantum one. Part of this says that a quantum system is described by a "state vector" which generates a probability distribution for the possible configurations of the system. Another postulate is that the state vector evolves according to the Schrödinger equation. And finally, there is the postulate of the "collapse of the state vector" which says that a measurement of the state of a quantum system has the effect of changing the state to accord with the result of the measurement. It is from this last postulate that much of the difficulty with the interpretation of quantum mechanics arises.

For example, consider the Schrödinger's cat thought experiment: take a cat and put it in a box. Also put in the box some amount of radioactive material which you know has a 50% chance of emitting radiation within the next hour, and a radiation detector which is wired to indicate the presence of radiation by cracking open a vial of cyanide. An hour later there are two possibilities: either radiation was emitted, and the cat is dead, or not, and it is alive. CI says that until someone opens the box and looks inside, collapsing the state vector, the quantum system in the box is actually in a combination of the two states (cat dead and cat alive).

This thought experiment highlights some of the difficulties with CI: it is formulated in terms which aren't given any precise meaning. What is a measurement? Can the cat perform a measurement on itself to determine whether it's dead? Gribbin describes other thought experiments in which it seems as though a measurement cannot be said to have been made unless an observer is present who knows how to perform computations in quantum mechanics!(9) This makes it easy to understand how such an extremely prominent physicist as John Wheeler can argue that "it is only the presence of conscious observers, in the form of ourselves, that has collapsed the wave function and made the universe exist."(10) This is the ultimate in solipsism.

It should be pointed out that not all physicists who advocate CI agree with Wheeler. In fact, it is misleading to refer to CI as an interpretation at all; the CI formalism still has to be interpreted. Gribbin presents some of the less idealist ways of interpreting it, among which are the "transactional interpretation" that he advocates, and the ensemble interpretation, which says that CI formalism is just a calculational tool for predicting the distributions of results of large numbers of measurements of similar systems.(11)

However, MIM does not just have a problem with the extremely solipsistic interpretations of CI a la Wheeler. MIM, along with the advocates of the interpretation which we favour, BM, believe that all versions of CI are implicitly idealist. We agree with the criticisms of CI given by advocates of BM, so we will reproduce them here: CI is a theory of epistemology. It doesn't talk about what actually happens in a quantum system, just about what can be known about it. So there is a state vector which tells the possible outcomes of measurements we might make, and their probabilities, and a state space representing the conceivable states of the system, and observables which act on the state space representing things we might measure, and then the state vector collapse which expresses the change in the information we have about the system after measuring an observable. All of these elements of the CI formalism have to do with our knowledge of the system. This built-in subjectivity is the reason why so many of the terms are ill-defined and so much of the resulting physics is observer-dependent, and leads to all the solipsism.

Alternatives

There are an extremely large number of alternative interpretations of quantum mechanics. Gribbin deals with most of the more popular ones, without doing any of them justice in the small amount of space he devotes to them. Most of the alternative interpretations Gribbin deals with retain part of the CI formalism, altering other parts.

The most popular alternative to CI is the Many Worlds interpretation (MW). As with CI, this is not really one interpretation but a collection of interpretations built on a common mathematical formalism. Most versions of MW would interpret the Schrödinger's cat puzzle by saying that rather than the cat existing in a combination of states (dead and alive) there were rather two universes, one where the cat died and one where it lived, that the one universe split into at the beginning of the experiment. Performing the experiment just amounts to deciding which universe you're in. Gribbin reports that materialist physicist John Bell developed an interpretation of MW that didn't involve any actual universe splitting, but went on to criticize MW as extreme solipsism: one of the fundamental elements of the theory is the description of "observers" by "quantum memory states", which are required to describe "coherent histories".(12) These sort of ideas are also the basis of the Decohering Histories interpretations (DH).

Gribbin correctly ridicules the Many Minds interpretation (MM), which says, for example, that the mind of the observer in the Schrödinger's cat experiment splits into two minds, one perceiving a dead cat, the other a live one.(13)

The best of the interpretations which retain parts of CI are the "corrections" interpretations. In these interpretations the Schrödinger equation is modified in such a way as to make the problem of state vector collapse disappear. Most such approaches propose that this happens via some mechanism, such as heat or the gravitational field. Gribbin's favoured interpretation, the "transactional" interpretation, is similar to these in that it gets around the problem of state vector collapse via a trick that allows it to view the state vector as always collapsed, leaving the rest of the CI formalism unaltered.

Gribbin also mentions an interpretation called Quantum Logic (QL). This sounds like it might completely do away with the CI formalism, but Gribbin says so little about it, and MIM is so unfamiliar with it, that we can't say for sure.

An interesting thing about all these interpretations is that many of them make actual testable predictions that differ from CI predictions, via which it may be possible to test them. This means that there are experiments where they predict results different from what CI predicts. Thus it may be possible to definitively prove that some versions of these interpretations are wrong, or that CI is wrong (by doing the experiments and seeing whose predictions are wrong). Gribbin mentions only a few such tests, for versions of MW and MM, but MIM knows of such experimental tests that have been proposed for other versions of MW, several versions of "corrections", versions of DH, and a version of BM that incorporates Einstein's special theory of relativity.

The criticisms of CI given above apply to all the alternatives discussed here as well, with the possible exception of QL. Is there a way of getting around the subjectivity implicit in all these interpretations? The answer is yes.

The "Best Buy"

MIM disagrees with Gribbin about which interpretation of quantum mechanics is the "Best Buy". We prefer the Causal interpretation, or Bohmian Mechanics (BM), which is also called a "hidden variables" or "pilot-wave" interpretation. Bohmian mechanics is an interpretation of quantum mechanics from which the entire CI formalism can be derived in the context of describing the physics of specific experiments, but where state vector collapse in such situations is automatic because in BM all particles have completely well-defined positions at all times. It is completely deterministic and observer-independent.(14) And it is extremely simple to develop: there are two postulates in BM. The first postulate is: all particles have well-defined positions at all times, and the description of the state of any system consists of the positions of the particles in that system together with a wave function that evolves according to Schrödinger's equation. Second: the velocities are determined by a function which depends on the wave function. This function is determined by being the simplest function that satisfies certain natural symmetry properties. From these two postulates follow an interpretation of quantum mechanics which explains all the phenomenology that CI explains, most of it much more naturally than CI, and which doesn't require us to scrap materialism. This is why MIM recommends BM as the quantum "best buy". MIM will be publishing more information on BM in the future, in the form of a review of books by it's inventor, David Bohm.

Unfortunately, MIM cannot recommend this book as a first book to read about quantum mechanics, because all the experiments described in the book are described from the point of view of CI. This is unfortunately the way quantum mechanics is actually taught, but MIM recommends learning materialist quantum mechanics first and then reading this book to compare it to the idealist formulations.(15) It is important when reading the descriptions of experiments in this book to keep in mind that there is a perfectly good interpretation of quantum mechanics in which all particles follow perfectly well-defined paths. There are also a few chapters on the history of science that it could be useful for people to read, which describe how European scientists discovered the scientific method, or equivalently, the dialectical materialist theory of knowledge, and which describe some of the advances made through application of this method.

Notes:
1. To learn more about how science can be used to serve the people, read Science for the People, available from MIM for $5, or Away With All Pests, available from MIM for $7.
2. Materialism and Empirio-Criticism, Lenin, Foreign Languages Press, Peking, 1976, pg. 311.
3. Ludwig Feuerbach and the Outcome of Classical German Philosophy, Friedrich Engels, International Publishers, New York, 1996, pgs. 20-21.
4. "On Practice" is available from MIM as part of the Four Articles on Philosophy, available from MIM for $4. Lectures on Physics (all 3 volumes) are available from the MIM Supporters Group online bookstore at http://www.geocities.com/CapitolHill/Senate/8411/books/.
5. See MIM Theory 9: Psychology and Imperialism, available from MIM for $5.
6. Schrödinger's Kittens and the Search for Reality, John Gribbin, (New York: Little, Brown and Co., 1995), pg. 219.
7. Ibid. some of 184-6.
8. Ibid pg. 185.
9. Ibid. pgs. 143-4.
10. Ibid., pg. 16.
11. Ibid. 172-3. Also see ibid. pg. 148 for some not so idealist speculation as to the meaning of CI by CI advocates.
12. Ibid. pgs. 173-4.
13. Ibid. pg. 171.
14. It can actually be made indeterministic by adding randomness (Stochastic BM), but it isn't fundamentally so.
15. Sheldon Goldstein, a mathematical physicist at Rutgers, has written some very good introductory papers on BM. A good place to go to start learning materialist quantum mechanics would be his home page at http://math.rutgers.edu/~oldstein/

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