Review of S. Adler, Connecting the Dots: Mott for emulsions, collapse models, colored noise, frame dependence of measurements, evasion of the “Free Will Theorem” , Foundations of Physics, 48, 1557-1567, (2018)
Latent image formation occurs whereby an image is created in a chemical emulsion which can be developed at any time in the future to yield the image. This paper examines the possibility that latent image formation is a bona fide measurement.
The paper initially examines the creation of tracks in Mott’s analysis of cloud chambers which he applies also to an alpha emitter that is embedded in a photographic emulsion material. Adler distinguishes latent image formation from the cloud chamber in that the emulsion can be developed at any time in the future to yield the image.
In Section II, Adler examines latent image formation in relation to continuous spontaneous localization (CSL) models. In CSL models in addition to Schrödinger’s equation, there is an additional noise term that couples in a non-linear manner. Adler has performed computations that lead to the conclusion that for latent image formation to constitute a measurement, and for consistency with the observed inter-galactic medium heating over the age of the universe, the CSL noise must be a factor of times larger than the estimates from the pointer model of measurement, corresponding to a CSL noise coupling strength of .
In Section III it is found that the noise in a CSL model must be colored and therefore frame dependent. This means the CSL theory is not Lorentz invariant. In Section IV Adler claims that the non-relativistic CSL model evades the Conway-Kochen “Free Will Theorem” for which an implication is that no relativistic theory can provide a mechanism for reduction. The model is nonlocal, and because the noise that drives state vector reduction is frame dependent, the model is expressly not Lorentz covariant. The model does not satisfy the relativistic invariance of measurement assumptions in the Free Will Theorem. Hence Adler states, “only a nonrelativistic objective reduction model can be compatible with experiment.”
Additionally Adler refers to a tentative noise signal that has been identified in a cantilever experiment for which the residual noise coupling was . This is consistent with a CSL noise bound coming from the LISA pathfinder mission. That would certainly be remarkable if verified.
The author is one of the few that thoroughly understands the measurement problem and is addressing the physical reasons and the conditions that measurement occurs. This as opposed to addressing the philosophers’ measurement problem  of proposing interpretations of the current incomplete von Neumann postulates that presuppose measurement has occurred, but do not tell us the reasons nor the conditions that measurement occurs.
Adler explains clearly why the noise is non-white and hence frame dependent. This in turn is used to explain how the CSL model evades the Free Will Theorem. Additionally, the new tentative estimates of the noise coupling in the CSL model could be significant, if this is continued to be found in other experiments.
The identification of emulsion as a sufficient condition to be a bona fide measurement device is justified partly by the inherent stability of the emulsion latent image which Adler states:
… for collapse to occur only on development would require that a spherically symmetric infinity of virtual tracks be present up to the exposure of the emulsion plate to a developer. This makes no sense both in terms of the molecular mechanism of latent image formation, and in terms of energetics.
We think it is a very good hypothesis that latent image formation is a bona fide measurement and would be very surprised if the molecular mechanism of latent image formation is not a measurement. The formation of a latent image in an emulsion as Adler notes allows for an arbitrary time between development, indicating that the image is stable and consistent with measurement. Still, for future work it would be desirable if additional theoretical or experimental work could justify that the unitarily predicted image would be less stable than under measurement, when subject to decoherence for example.
Granted, it may make no sense both in terms of the molecular mechanism of latent image formation, and in terms of energetics that latent image formation could be unitary. However, as we recently found in reviewing the paper , there appear to be cases where ionization occurs in superposition, hence in such cases is not necessarily a bona fide measurement. As such ionization events are related to the energetics of physics of Mott’s cloud chamber, we would regard latent image formation as a hypothesis for bona fide measurement, but one for which more evidence is needed to rigorously establish that latent image formation has been scientifically established to be a bona fide measurement.
Adler states that CSL is the unique theory via the assumptions of state vector normalization and absence of faster-than-light signaling. We do not agree. There is also an added assumption of continuity needed, see Gisin  where he states: “However, assuming that the evolution is Markovian and the solution continuous in time, then … Essentially there is only one [solution].” However, when discontinuous quantum jumps are at the heart of the issue that separates unitary evolution from measurement, such a continuity assumption is a valid hypothesis but is not a valid assumption in a deductive investigation of the problem. Fundamental assumptions that we agree are valid within the deductive approach are no-signaling, gauge-invariance of measurement results, etc. [1, p. 405], however time continuity is not one of these. Hence, we believe this invalidates CSL as having being established as the unique collapse theory at this time, within a deductive framework. Note that it is also known that CSL type theories generally violates energy conservation , although one can hypothesize that another source exists that provides this extra energy. Aside from these criticisms, CSL is still a major contender within the theories proposed so far.
The paper is well written, the author thoroughly understands the need for a solution to the physical measurement problem [1, p. 92-98] and is furthering the theory in CSL and attempting verification via experiment. We expect that latent image formation is a measurement, but this is still a hypothesis at this stage. CSL, while being a good candidate amongst the few physical collapse theories that exist, is not unique as it requires that assumption of continuity which is a hypothesis at this time, if one agrees that the measurement problem is best addressed by a deductive investigation.
 M. J. Steiner, R. W. Rendell, The Quantum Measurement Problem, Inspire Institute (2018).
 F. Lindner, M. G. Schatzel, H. Walther, A. Baltuska, E. Goulielmakis, F. Krausz, D. B. Milosevic, D. Bauer, W. Becker, and G. G. Paulus. Attosecond Double-Slit Experiment, PRL 95, 040401 (2005).
 N. Gisin, Collapse of the Wave Function, Edited by Shan Gao, Cambridge University Press 2018 pp. 207-224.
 A. Bassi, E. Ippoliti, and B. Vacchini, On the energy increase in space-collapse models, J. Phys. A. Math. Gen., vol. 38, p. 8017, 2005.
Implications on Sufficient Conditions for Measurement
Although not part of the review, as the issue of consciousness is not mentioned in Adler’s paper, we thought it useful to provide some related viewpoints in some final afterthoughts. The identification of particular configurations of matter that constitute a bona fide measurement device is at the heart of the physical measurement problem which is defined in . The only somewhat detailed measurement configurations of matter that we currently know of are those that provoke a conscious tinge within the measurement device; such tinge was known to Bohr and others to be a sufficient condition for measurement. However, the science of consciousness is only in its infancy, in fact it is quite remarkable about how little is known of the physics of consciousness; it is not a trivial matter. Whether or not there exist other non-conscious configurations of matter that measure is not known at this time.
Suppose that it is confirmed, as Adler expects, that emulsion absorption is a bona fide sufficient condition for measurement. One might conclude that such a result would imply that consciousness is ruled out as a necessary condition for measurement. Still, even in such an event, one has to be careful to conclude prematurely that latent image formation is not related to consciousness. If there were a tinge that occurs within the grains of the emulsion when a measurement occurred, it could amount to the presence of a primordial process related to consciousness. One might at first dismiss this as silly or ridiculous. But prior to the understanding of gravitation, one would most likely dismiss the notion that a piano will fall at the same rate as a feather in a gravitational field. Or that mass can be converted to a tremendous amount of energy prior to relativity theory. And the list goes on and on with such issues nearly always arising when a deductive investigation is called for to resolve a major scientific problem. And there exist sensing structures within cells that are on the same order of size as the grains that are formed in an emulsion under measurement. And often the sensing structures that are involved in consciousness involve amplification similar to the little understood catalytic effects that occur in photographic emulsions. Hence from a purely logical perspective, any current argument that latent image formation does not involve consciousness would be specious: the science of consciousness is currently unknown. We simply do not know at this time either what is necessary to constitute a conscious system nor do we know what is necessary to constitute a measurement device. This doesn’t imply that the two are related, this remains to be determined by future work.
For example, if in future work, a science of consciousness was to be developed, and the molecular mechanism of latent image formation found not to generate tinge or be related to consciousness, then if latent image formation constitutes a measurement, that would certainly imply from a scientific perspective that the generation of tinge is not a necessary condition for measurement.