The Conscious Observer in Quantum MeasurementCan We Have Quantum Measurement Without an Observer? Niels Bohr, Werner Heisenberg, John von Neumann, and Eugene Wigner
insisted that a measurement depends on the mind of a conscious observer. Pascual Jordan, David Bohm, John Bell, and textbook authors like Landau and Lifshitz, Albert Messiah, and Kurt Gottfried denied this. Hugh Everett invented automatic measuring equipment without a mind. John Bell asked whether the observer needs a Ph.D.? Without Recorded Information, an Observation Is Not Possible. Every interaction between quantum systems may lead to a collapse of the wave function. But most collapses are never recorded. When a change of quantum state is recorded as information in a macroscopic apparatus, it becomes available for observation at a later time. Most measurements in quantum physics are made by complex, computer-controlled apparatus, whose data may wait for days, weeks, or even months to be completely analyzed and thought about by physicists. Once Recorded, the Observer Can Then Look at the "Observable." When the new information is observed (recorded in a human mind), it becomes an observation. This last stage has no effect on the measurement (it's after the fact!),
but it does increase human knowledge. So When Does the Wave Function Collapse Without an Observer? At some random time and place, before which ψ evolution is unitary, time-reversible, and deterministic. For example, when a radioactive nucleus decays, when a spontaneous photon is emitted, when an electron jumps between eigenstates of an atom, or when a collision between atoms changes their internal states. If we could predict exactly when these events will happen, it would not be quantum mechanics.
The Heisenberg "Cut" or "Schnitt"Werner Heisenberg described the collapse of the wave function as requiring a "cut" (Schnitt in German) somewhere along the transition from the microscopic quantum system through the "classical" apparatus to the observer and the observer's "knowledge" about the quantum system. He asked, "Where is the cut to be between the description by the wave function and the classical description?" He said it did not matter where this cut was placed, because the mathematics would produce the same experimental results wherever it was placed. Like Niels Bohr, his goal was to describe quantum mechanical observations in the normal everyday language about a classically understandable measuring system. For Heisenberg, an observing system could be the human eye or a familiar photograph, because for the Bohr-Heisenberg "Copenhagen Interpretation" the final aim of physics is to describe experiments and their results like we describe the things and events in everyday life, i. e., by intuitive, common sense concepts of the space-time world and in the words we use for this classical space-time world. The "cut" is frequently conflated with the "quantum to classical transition, the point at which the "classical" laws of physics, for example Newton's laws of motion, emerge from the quantum world. There has been a lot of controversy and confusion about the location of this cut. Eugene Wigner placed it outside a room which includes the measuring apparatus and an observer A, and just before observer B makes a measurement of the physical state of the room, which is imagined to evolve deterministically according to John von Neumann's "process 2" according to the Schrödinger equation. The case of Schrödinger's Cat is thought to present a similar paradoxical problem. Is the cat simultaneously (in a "superposition" of) dead and alive just before the observer learns which is the case? The simple answer is that live and dead are "possibilities," with calculable probabilities. John von Neumann contributed a lot to this confusion in his discussion of subjective perceptions and "psycho-physical parallelism," which was encouraged by Neils Bohr. Bohr interpreted his "complementarity principle" as explaining the difference between subjectivity and objectivity (as well as several other dualisms). von Neumann wrote:
The difference between these two processes is a very fundamental one: aside from the different behaviors in regard to the principle of causality, they are also different in that the former is (thermodynamically) reversible, while the latter is not. Let us now compare these circumstances with those which actually exist in nature or in its observation. First, it is inherently entirely correct that the measurement or the related process of the subjective perception is a new entity relative to the physical environment and is not reducible to the latter. Indeed, subjective perception leads us into the intellectual inner life of the individual, which is extra-observational by its very nature (since it must be taken for granted by any conceivable observation or experiment). Nevertheless, it is a fundamental requirement of the scientific viewpoint -- the so-called principle of the psycho-physical parallelism -- that it must be possible so to describe the extra-physical process of the subjective perception as if it were in reality in the physical world -- i.e., to assign to its parts equivalent physical processes in the objective environment, in ordinary space. (Of course, in this correlating procedure there arises the frequent necessity of localizing some of these processes at points which lie within the portion of space occupied by our own bodies. But this does not alter the fact of their belonging to the "world about us," the objective environment referred to above.) In a simple example, these concepts might be applied about as follows: We wish to measure a temperature. If we want, we can pursue this process numerically until we have the temperature of the environment of the mercury container of the thermometer, and then say: this temperature is measured by the thermometer. But we can carry the calculation further, and from the properties of the mercury, which can be explained in kinetic and molecular terms, we can calculate its heating, expansion, and the resultant length of the mercury column, and then say: this length is seen by the observer. Going still further, and taking the light source into consideration, we could find out the reflection of the light quanta on the opaque mercury column, and the path of the remaining light quanta into the eye of the observer, their refraction in the eye lens, and the formation of an image on the retina, and then we would say: this image is registered by the retina of the observer. And were our physiological knowledge more precise than it is today, we could go still further, tracing the chemical reactions which produce the impression of this image on the retina, in the optic nerve tract and in the brain, and then in the end say: these chemical changes of his brain cells are perceived by the observer. But in any case, no matter how far we calculate -- to the mercury vessel, to the scale of the thermometer, to the retina, or into the brain, at some time we must say: and this is perceived by the observer. That is, we must always divide the world into two parts, the one being the observed system, the other the observer. In the former, we can follow up all physical processes (in principle at least) arbitrarily precisely. In the latter, this is meaningless.The boundary between the two is arbitrary to a very large extent. In particular we saw in the four different possibilities in the example above, that the observer in this sense needs not to become identified with the body of the actual observer: In one instance in the above example, we included even the thermometer in it, while in another instance, even the eyes and optic nerve tract were not included. That this boundary can be pushed arbitrarily deeply into the interior of the body of the actual observer is the content of the principle of the psycho-physical parallelism -- but this does not change the fact that in each method of description the boundary must be put somewhere, if the method is not to proceed vacuously, i.e., if a comparison with experiment is to be possible. Indeed experience only makes statements of this type: an observer has made a certain (subjective) observation; and never any like this: a physical quantity has a certain value. Now quantum mechanics describes the events which occur in the observed portions of the world, so long as they do not interact with the observing portion, with the aid of the process 2, but as soon as such an interaction occurs, i.e., a measurement, it requires the application of process 1. The dual form is therefore justified.* However, the danger lies in the fact that the principle of the psycho-physical parallelism is violated, so long as it is not shown that the boundary between the observed system and the observer can be displaced arbitrarily in the sense given above. (The Mathematical Foundations of Quantum Mechanics, pp.418-21) Information physics places the cut or boundary at the place and time of information creation. It is only after information is created that an observer could make an observation. Beforehand, there is no information to be observed. Information creation occurs as a result of the interaction between the microscopic system and the measuring apparatus. It was a severe case of anthropomorphism to think it required the consciousness of an observer for the wave function to collapse. The collapse of a wave function and information creation has been going on in the universe for billions of years before human consciousness emerged. Fifty years after Heisenberg and von Neumann, John Bell drew a diagram of possible locations for the "cut" which he called his "shifty split." The Bell diagram identifies the correct moment when irreversible information enters the universe.
In the information physics solution to the problem of measurement, the timing and location of Bell's "shifty split" (the "cut" or "Schnitt" of Heisenberg and von Neumann) are identified with the interaction between quantum system and classical apparatus that leaves the apparatus in an irreversible stable state providing information to the observer. As Bell may have seen, it is therefore not a "measurement" by a conscious observer that is needed to "collapse" wave functions. It is the irreversible interaction of the quantum system with another system, whether quantum or approximately classical. The interaction must be one that changes the information about the system. And that means a local entropy decrease (the recorded information) and overall entropy increase to make the information stable enough to be observed by an experimenter and therefore be a measurement. Normal | Teacher | Scholar