The notion that the interpretation of quantum mechanics requires a conscious observer is rooted, I believe, in a basic misunderstanding of the meaning of a) the quantum wavefunction ψ, and b) the quantum measurement process. This misunderstanding originated with the work of John von Neumann (1932) on the foundations of quantum mechanics, and afterwards it was spread by some prominent physicists like Eugene Wigner (1984); by now it has acquired a life of its own, giving rise to endless discussions on this subject, as shown by the articles in the Journal of Cosmology (see volumes 3 and 14).

Quantum mechanics is a statistical theory that determines the probabilities for the outcome of a physical process when its initial state has been determined. A fundamental quantity in this theory is the wavefunction ψ which is a complex function that depends on the variables of the system under consideration. The absolute square of this function, ψ², gives the probability to find the system in one of its possible quantum states. Early pioneers in the development of quantum mechanics like Niels Bohr (1958) assumed, however, that the measurement devices behave according to the laws of classical mechanics, but von Neumann pointed out, quite correctly, that such devices also must satisfy the principles of quantum mechanics. Hence, the wavefunction describing this device becomes entangled with the wavefunction of the object that is being measured, and the superposition of these entangled wavefunctions continues to evolve in accordance with the equations of quantum mechanics. This analysis leads to the notorious von Neumann chain, where the measuring devices are left forever in an indefinite superposition of quantum states. It is postulated that this chain can be broken, ultimately, only by the mind of a conscious observer.

Forty five years ago I wrote an article on this subject with John Bell who became, after von Neumann, the foremost contributor to the foundations of quantum mechanics, where we presented, tongue in cheek, the von Neumann paradox as a dilemma:

We added the remark that "we emphasize not only that our view is that of a minority, but also that current interest in such questions is small. The typical physicist feels that they have been long answered, and that he will fully understand just how, if ever he can spare twenty minutes to think about it." Now the situation has changed dramatically, and interest in a possible role of consciousness in quantum mechanics has become widespread. But Bell, who died in 1990 , believed in the second alternative to the von Neumann dilemma, remarking that :

Actually, by now it is understood by most physicists that von Neumann's dilemma arises because he had simplified the measuring device to a system with only a few degrees of freedom, e.g. a pointer with only two states (see Appendix). Instead, a measuring device must have an exponentially large number of degrees of freedom in order to record, more or less permanently, the outcome of a measurement. This recording takes place by a time irreversible process. The occurrence of such processes in Nature already mystified 19th century scientists, who argued that this feature implied a failure in the basic laws of classical physics, because these laws are time reversible. Ludwig Boltzmann resolved this paradox by taking into account the large number of degrees of freedom of a macroscopic system, which implied that to a very high degree of probability such a system evolved with a unique direction in time. Such an irreversibility property is also valid for quantum systems, and it constitutes the physical basis for the second law of thermodynamics, where the arrow of time is related to the increase of entropy of the system.

Another misconception is the assumption that the wavefunction ψ describing the state of a system in quantum mechanics behaves like a physical object. For example, the authors of a recent book discussing quantum mechanics and consciousness claim that

If the wavefunction ψ is a physical object like an atom, then the proponents of this flawed concept must require the existence of a mechanism that lies outside the principles governing the time evolution of the wavefunction ψ in order to account for the so-called "collapse" of the wavefunction after a measurement has been performed. But the wavefunction ψ is not a physical object like, for example, an atom which has an observable mass, charge and spin as well as internal degrees of freedom. Instead, ψ is an abstract mathematical function that contains all the statistical information that an observer can obtain from measurements of a given system. In this case there isn't any mystery that its mathematical form must change abruptly after a measurement has been performed. For further details on this subject, see (Nauenberg, 2007) and (van Kampen, 2008). The surprising fact that mathematical abstractions can explain and predict real physical phenomena has been emphazised by Wigner (Wigner 1960), who wrote:

I conclude with a few quotations, that are relevant to the topic addressed here, by some of the most prominent physicists in the second half of the 20th century.

Richard P. Feynman (Nobel Prize, 1965):

John S. Bell: From some popular presentations the general public could get the impression that the very existence of the cosmos depends on our being here to observe the observables. I do not know that this is wrong. I am inclined to hope that we are indeed that important. But I see no evidence that it is so in the success of contemporary quantum theory.

So I think that it is not right to tell the public that a central role for conscious mind is integrated into modern atomic physics. Or that `information' is the real stuff of physical theory. It seems to me irresponsible to suggest that technical features of contemporary theory were anticipated by the saints of ancient religions... by introspection.

The only 'observer' which is essential in orthodox practical quantum theory is the inanimate apparatus which amplifies the microscopic events to macroscopic consequences. Of course this apparatus, in laboratory experiments, is chosen and adjusted by the experiments. In this sense the outcomes of experiments are indeed dependent on the mental process of the experimenters! But once the apparatus is in place, and functioning untouched, it is a matter of complete indifference - according to ordinary quantum mechanics - whether the experimenters stay around to watch, or delegate such 'observing' to computers, (Bell, 1984).

Nico van Kampem:

Appendix. Schrodinger's Cat: This cat story is notorious. It requires one to accept the notion that a cat, which can be in innumerable different biological states, can be represented by a two component wavefunction ψ, a bit of nonsense that Erwin Schrodinger, one of the original inventors of quantum mechanics, himself originated. One of the two components represents a live cat, and the other a dead cat. The cat is enclosed in a box containing a bottle filled with cyanide that opens when a radioactive nucleus in the box decays. Thus, this fictitious cat is a measuring device that is supposed to determine whether the nucleus has decayed or not when the box is opened. But according to the principles of quantum mechanics formulated by von Neumann, such a cat ought to be in a superposition of life and dead cat states, yet nobody has ever observed such a cat. Instead, it is expected that a movie camera - a real measuring device - that is also installed in the box containing the cat, would record a cat that is alive until the unpredictable moment that the radioactive nucleus decays, opening the bottle containing the cyanide that kills the cat. For obvious reasons such a gruesome experiment has never been performed. It is claimed that Schrodinger never accepted the statistical significance of his celebrated wavefunction.