Review of Fields of Color: The theory that escaped Einstein by Rodney Brooks.
Brooks examines various subjects in Chapters 1 through 8 including gravity and relativity. In Chapter 9 Brooks examines the QMP and provides the following interpretation to Schrödinger’s Cat paradox:
QFT supplies a simple answer for Schrödinger’s cat and Einstein’s bomb. The answer, again, is quantum collapse. Quantum collapse happens with or without an observer. In the cat scenario, when a quantum is emitted from the radioactive sample, it first interacts with all other quanta that it encounters, as described by the field equations. These interactions are deterministic and reversible. This phase ends when the quantum collapses and transfers its energy to an atom in the Geiger counter. This triggers a discharge that trips the relay that releases the poison gas that kills the cat. Until then the cat is alive; after that the cat is dead. There are no superpositions of states.
The author has a correct understanding that in order to resolve the QMP, that an irreversible process is required. Furthermore, that such a collapse is not described by the field equations. Given that a measurement is to be made, the field equations will give the correct probabilities for occurrence. Hence QFT, amended by adding a collapse postulate, does help to explain measurement, given that a particular process can be identified with a collapse (such as a detector). Hence QFT is a reasonable interpretation to consider for the solution to such an a posteriori problem given that some measurement occurred, which we refer to as the philosophers’ measurement problem in our book.
The author does not present any particular collapse mechanism that follows only from QFT. In a related paper, A Physics Tragedy/eprint arXiv:1710.10291 a cloud chamber experiment and a statement by Art Hobson is referenced:
“The tracks are made by successive individual interactions between a matter field and gas or water molecules. The matter quantum collapses… each time it interacts with a molecule, while spreading out as a matter field between impacts.”
This statement has not been scientifically established to our knowledge. That is, how does one know for sure that there is not an entangled state of many ionization tracks, each that are interrogated using a light source and give off photons that move toward an observer’s eye, existing in a superposition that still exists after the initial ionization interaction? There is no experimental evidence that we are aware of that has differentiated the superposition predictions of unitary evolution versus collapse (which we call in our book a unitary versus measurement discrimination test or UMDT), for such a cloud chamber experiment. At minimum for scientific consideration, a theoretical argument is needed that compares the cloud chamber track if 1) the interactions were unitary and only later measured by observing the photons given off from the track, versus 2) the case when the cloud chamber is a bonafide detector such that an entangled state of many tracks does not form. We have not seen such an argument presented. More generally, at least in many cases of photon-matter interaction, the numerous cavity QED experiments by Haroche (and many others) would at least suggest the contrary hypothesis: the interaction is often deterministic and evokes entanglement, and not collapse. Hence the precise process(es) that lead to collapse is (are) still not known at this time, and this is a large part of the real problem that we are faced with in the modern-day QMP. What constitutes a bonafide detector that causes collapse? Brook’s claims that QFT supplies a simple answer to the QMP indicates to us nothing more than a shallow and incomplete understanding of the details of the QMP that are demanded for proper analysis as to what constitutes a valid solution. His claim that the lack of recognition of QFT as a solution to the QMP is a Physics Tragedy is in our view unwarranted.
Suggestions for future work:
Analyze the theoretical predictions that compare the cloud chamber track if 1) the interactions were unitary and only later measured by observing the photons given off from the track, versus 2) the case when the cloud chamber is a bonafide detector such that an entangled state of many tracks does not form. What experimental differences exist and what type of experiments would be needed to form a UMDT that can distinguish these two predictions for a cloud chamber? A simplified analysis would be to consider ionization of a single atom. How can one experimentally distinguish the two cases of measurement versus unitary measurement? Is ionization a necessary and/or sufficient condition for measurement?