On the Direction of Time: From Reichenbach to Prigogine and Penrose
Round 1
Reviewer 1 Report
I commend the author on their changes to the manuscript. I'm now happy to recommend it for publication.
Reviewer 2 Report
My concerns have been met in the revised version to an extent that allows for publication in the present form.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The paper offers a presentation of Reichenbach’s, Prigogine’s and Penrose’s views on the arrow of time. While the paper was interesting and at times inspiring to read, the analysis is often vague and sometimes questionable, and the philosophical core claims are not convincing.
The discussion of Prigogine and Penrose seems overall adequate and instructive and shows a high degree of immersion in those ideas. The discussion of Reichenbach, however, is rather confusing and misleading. Reichenbach’s main point, on the best of my understanding, is to propose a view on the arrow of time that is entirely based on the arrow of entropy increase. Therefore, he accounts for the possibility that individual subsystems, if decoupled for their embedding system, could lose their time direction if entropy does not increase for a significant period of time. While this point reaches out beyond Boltzmann’s considerations, it is fully based on Boltzmannian thinking (which, as the authors actually state, was emphasized by Reichenbach himself). The authors exaggerate and somewhat mystify the radicality of Reichenbach’s analysis and its distance from Boltzmannian thinking.
The paper’s own contribution consists in asserting connections between the three discussed authors. These connections, however, remain vague and less than convincing in the discussion. I cannot discern any substantial connection between Reichenbach and Prigogine. Prigogine does introduce a new element of thinking that goes beyond canonical statistical mechanics, while Reichenbach does not. The authors fail to make clear in which way Prigogine’s novel ideas are based on, related to, or inspired by Reichenbach’s thinking.
The authors claim that Penrose was influenced by Reichenbach’s causal net theories. The explanation of this point is contained in one paragraph at the end of 7.1 and is far too vague and unspecific to amount to an interesting philosophical claim.
The parallel between Prigogine and Penrose (who, as the authors concede, differ very substantially from each other in many respects), that is discussed on p19, is more specific and comprehensible: Penrose needs the idea of baryon decay and Prigogine, on their reading, provides a mechanism for that. It does not become clear in their discussion, however, in which way Prigogine’s approach leads to baryon decay. The way the authors present Prigogine’s analysis, it plays out at the level of simple quantum mechanics. The degrees of freedom for particle decay, however, only open up in quantum field theory. The text does not explain how Prigogine makes that step, nor does it offer a reference to Prigogine’s discussion of this point. In the absence of this discussion, however, the author’s core claim remains unsubstantiated. I t may be added that, even if their point holds, it would merely show a possible point of mutual support between Penrose’s and Prigogine’s hypotheses but would not amount to demonstrating a philosophically interesting conceptual similarity between their approaches.
More specific points:
P10:
“With Prigogine, something original – almost revolutionary – begins to take place: irreversibility is no longer a “bug” that has to be removed from the system using probability arguments, the approach inaugurated by Boltzmann [47,135] following some earlier leads from Clausius [46,50] and Maxwell [51–53].”
I don’t see how Maxwell, Clausius or Boltzmann can be construed as saying that irreversibility was a bug that had to be removed from the system. What they do say is (as the authors themselves note later on) that irreversibility is a matter of initial conditions rather than the fundamental laws.
“…all processes of dissipation and losses should be interpreted as emergent macroscopic phenomena induced by a large number of particles colliding with each other in a pattern that appears to us more probabilistic than deterministic due to the intractability of the computational demands of the model. This view, which more or less continues to dominate mainstream thinking in science in general, including theoretical physics…”
The stated position amounts to a classical mechanics perspective on statistical mechanics. Quite clearly it is not “the dominant view” in theoretical physics, not even an admissible view after QM.
P14: When discussion Prigogine’s view on solving the measurement problem by reformulating “the laws of quantum physics [..] in such a way that the distinction between pure and mixed states disappears“, it would be essential to mention the modern view on decoherence, which does imply that “a pure state will naturally evolve irreversibly into a mixed state”, while there is general consensus today that this does not, in itself, solve the measurement problem.
P15: Reichenbach did call the entropy of the present universe “low” but this is not at variance with Penrose. Obviously, Reichenbach would agree with Penrose that the entropy at an earlier stage of the universe was lower.
Author Response
Please see the attached PDF file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This is an interesting and generally well-written article, articulating the points of similarity and difference between Reichenbach, Prigogine and Penrose on entropy increase and the direction of time. I learned much from reading it, and regard it as being a valuable contribution to the literature. Thus, I recommend minor revisions.
This being said, I do think the manuscript could be improved in some respects. First: some passages are terse, and might be unclear to readers without the necessary background. I have tried to indicate these in yellow highlights on the attached marked up pdf. If the author(s) could expand these areas, that would certainly be helpful. Second: there are some small presentational issues. One is that the author(s) makes excessive use of italics: the paper’s presentation would be improved by removing many of these. Another is that the paper switches between the first singular and first person plural (the latter is more prevalent, so I’d suggest changing everything to the plural). These presentational issues have been highlighted in blue on the attached marked up pdf.
Comments for author File: Comments.pdf
Author Response
Please see the attached PDF file.
Author Response File: Author Response.pdf
Reviewer 3 Report
This article concerns the direction of time, especially in relation to the second law of thermodynamics. It focuses on relevant and important thinkers on the matter. The introductory section states the aims and the scope of the article very clearly.
I think the author’s treatment of the central issues is too dense. In its current form, the presentation is not compelling. The scope of the paper is way too extensive for an individual article. One could write a book on this topic. Instead of 27 pages, the author would need more like 270 pages to properly analyze and assess all the relevant aspects. I think journal article is not the best forum for such a research. If the author proceeds with their idea, I recommend they write a full-fledged monograph. I believe that would be a very important contribution.
Smaller points
- 4
lines 140–142. It is usually thought that kaon decay has a preferred direction of time.
lines 156–158. I do not recommend grouping together that many philosophers in a single sentence. One should write an entire book to show that they agree on irreversibility.
lines 160–165. Here the author mentions some concepts that elucidate irreversibility. This is better, although still contentious.
line 181. casual nets -> causal nets
p.6
line 247. ionion -> opinion
p.8
line 372. Here’s again an example of too dense way of writing. The author mentions Liouville’s rules. What are they? They should be properly introduced and analyzed before their relevance is clear to the reader.
p.9
section 4, first paragraph. The contrast between Boltzmann’s Darwinism and Poincare’s Kantianism sounds interesting, but again the author should extend their analysis on this matter considerably. Now the reader remains unconvinced by the use of these doctrinal labels.
- 12.
In the second paragraph of 5.2 the author mentions Prigogine’s book but does not elaborate on it.
p.12, line 552.
The contrast between the two spaces is unclear to me. They should be properly introduced. The same goes for the rest of central concepts.
Concerning the rest of the article:
What the author writes on Penrose and the relation of his ideas to Reichenbach and Prigogine might be correct, but the presentation is, like the article in general, too dense.
Author Response
Please see the attached PDF file.
Author Response File: Author Response.pdf
