{"id":"05c8cbd3-2eba-4317-8d10-4d5888400045","arxiv_id":"2505.13113","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"In a thermodynamically consistent flocking model, discarding internal-state dynamics severely underestimates dissipation in the disordered phase but not in the ordered polar phase.","lead":"This paper introduces a thermodynamically consistent lattice model of flocking and measures how much energy the collective motion dissipates. It finds that ignoring the particles' internal states, as experiments often must, can severely underestimate the dissipation in disordered flocks but not in ordered ones.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Macroscopic theory in §III B gives an EPR independent of ε, so the polar-phase dissipation reduction in Fig. 3 may be a finite-size artifact; finite-size scaling is needed.","rationale":"The reader's weakest assumption was the Markovian, position-independent tracer inference. That is a legitimate concern that affects the inferred S_I and S_II, but it does not threaten the directly measured EPR crossover. The more load-bearing issue is that the same paper's macroscopic calculation predicts a constant, non-interacting EPR in all homogeneous phases (Eq. (38)), which the authors explicitly state does not reproduce Fig. 3. Since the abstract claims both that dissipation is reduced in the polar phase and that macroscopic dissipation coincides with microscopic dissipation upon coarse-graining, the text contains a tension that must be resolved. The most direct resolution is finite-size scaling: if the reduction vanishes with system size, the crossover is not a thermodynamic-limit property and the central claim needs qualification; if it persists, the concern is settled. This was not one of the reader's main conditions, although the reader did mention missing finite-size analysis, hence partial agreement. The verdict should remain CONDITIONAL, with the additional condition that the EPR reduction survive a system-size extrapolation and that the macro-micro correspondence be stated only in the limit where it is proven.","tokens_in":15061,"tokens_out":15133,"duration_ms":165860,"concrete_test":"Run Gillespie simulations at fixed ρ0 = 2, Δμ/T = 0.3, for alignment strengths ε/T spanning apolar, coexistence, and polar phases (e.g., 0, 1, 2, 3, 4) and for system sizes n = 50, 100, 200, 400, measuring the true EPR per particle T\\dot S/N = Δμ⟨J_p−J_m⟩/N. If the value at large ε moves upward toward NγΔμ²/T as n increases, the polar-phase dissipation reduction is a finite-size effect and the crossover claim must be revised; if the reduction persists and extrapolates to a nonzero deficit as n → ∞, the crossover is confirmed in the thermodynamic limit.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central crossover claim (Abstract; §II D 3) states that the true EPR is maximal and equal to the non-interacting value in the apolar phase and reduced in the polar phase, and that partial inference tracks this. The first leg is undercut by the paper's own hydrodynamic calculation. In §III B, Eq. (38) yields T\\dot S_macro = (D/T) ρ0 V f^2 = N γ Δμ^2/T, independent of interaction strength ε, and the text immediately concedes that 'Since our hydrodynamics only features a homogeneous steady state, it does not reproduce the variation of EPR reported in the lattice model [Fig. 3].' Thus, in the macroscopic limit the EPR is not reduced in the polar phase; the reduction seen in Fig. 3 is a finite-size or fluctuation effect that the paper does not analyze. Without an n-scaling check, the 'dissipation is reduced' half of the crossover is not established as a robust result. The Abstract's macro-micro identity is also only demonstrated in the ε→0 limit: at strong interactions the hydrodynamic prediction and Fig. 3 disagree, so the hydrodynamic section cannot be used to support the crossover. The Markovian-inference caveat (Sec. II D 1, Fig. 4) is a secondary threat to the inference leg, not the primary one.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper introduces a thermodynamically consistent lattice model of flocking in which particles carry two internal states (+/−) that bias their diffusion, and both state flips and lattice jumps obey local detailed balance with respect to the same interaction energy. The authors map out the apolar/coexistence/polar phase diagram, compute the exact microscopic entropy production rate (EPR), and compare it with two coarse-grained inference schemes that either track or discard internal states. Their central numerical finding is a crossover: in the apolar phase the EPR is maximal and equals the non-interacting value while the inference that discards internal states predicts a vanishing EPR; in the polar phase the EPR is reduced and the same partial inference captures most of the dissipation. The paper then derives a hydrodynamic description in the macroscopic limit and claims that the macroscopic EPR coincides with the microscopic EPR, connecting the model to a class of non-ideal reaction-diffusion systems.","tokens_in":15340,"tokens_out":4283,"duration_ms":41243,"significance":"If the crossover claim is robust, the paper makes a valuable contribution: it provides a thermodynamically consistent alternative to the active Ising model, gives an exact microscopic EPR formula, and demonstrates in a minimal setting that partial inference can severely misestimate dissipation when internal degrees of freedom are discarded. The mapping to non-ideal reaction-diffusion systems is elegant and connects active lattice models to a broader thermodynamic framework. The strengths include the explicit local- detailed-balance construction, the exact steady-state EPR expression in Eq. (10), and the clear identification of a regime where internal-state tracking is essential. However, the central crossover is currently undermined by the paper's own hydrodynamic calculation, which yields an EPR independent of interaction strength, so the significance is contingent on resolving that mismatch.","major_comments":[{"comment":"The central crossover claim of the abstract and Sec. II D 3—that dissipation is reduced in the polar phase—is contradicted by the paper's own macroscopic calculation. Equation (38) gives T\\dot S_macro = (D/T) ρ0 V f^2, which is independent of ε, and the text concedes that the hydrodynamics 'does not reproduce the variation of EPR reported in the lattice model [Fig. 3].' Thus the reduction seen in Fig. 3 is, within the paper's own analysis, a finite-size or fluctuation effect. Because no system-size dependence, finite-size scaling, or error bars are reported for Fig. 3, the crossover cannot be distinguished from a finite-size artifact. Please provide a system-size analysis (e.g., n-dependence of the EPR at fixed ε and ρ0) or an explicit argument for why the macroscopic limit should not be used to assess the polar-phase dissipation.","section":"§III B, Eq. (38)"},{"comment":"The inference schemes S_I and S_II assume that each particle's jump and flip rates are Markovian and site-independent, with rates extracted from average waiting times. The paper itself shows in Fig. 4 that waiting-time distributions deviate from exponential tails in the polar phase, and the text acknowledges that spatial inhomogeneities are discarded. If the effective tracer dynamics is non-Markovian, the coarse-grained bounds 0 ≤ S_II ≤ S_I ≤ S in Eq. (15) do not strictly apply, and the conclusion that S_II ≃ S deep in the polar phase may be an artifact of the exponential-fit procedure. Please quantify the deviation from exponentiality and its effect on the inferred rates, or restrict the claim to the regime in which the Markovian approximation is explicitly validated.","section":"§II D 1, Fig. 4"}],"minor_comments":[{"comment":"The sentence 'for strong interactions, the EPR can be accurately inferred ... for strong interactions, such an inference severely underestimates the EPR' repeats 'strong interactions' twice; the second instance should clearly read 'weak interactions.'","section":"§IV"},{"comment":"The interaction energy E contains terms such as P^2/ρ and P/√ρ, which are singular when a lattice site is empty (ρ=0). The model allows arbitrary occupancy, so the paper should state the convention used to define E (or the rates) at empty sites; otherwise the numerical implementation is not fully specified.","section":"§II A, Eq. (2)"},{"comment":"Neither figure reports error bars or the number of independent runs, even though the central quantitative claims (e.g., S_II ≃ S in the polar phase) rely on the closeness of numerical estimates. Please include at least representative statistical uncertainties.","section":"Fig. 3 and Fig. 4"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the journal's scope and presents a genuinely thermodynamically consistent flocking model with a clean stochastic-thermodynamics analysis. The main obstacle is the mismatch between the numerical crossover in Fig. 3 and the hydrodynamic EPR of Eq. (38), which is explicitly acknowledged in the text but not resolved. A revision that adds finite-size scaling and addresses the Markovianity caveat in the inference scheme would substantially strengthen the case for the central claim."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know. First, this is a genuinely useful thermodynamically consistent lattice model of flocking: local detailed balance is enforced on both internal-state flips and spatial jumps, which is exactly what the active Ising model was missing. Second, the paper's central crossover claim is not supported by its own hydrodynamic section. Eq. (38) gives T·S_macro = NγΔμ²/T, independent of interaction strength, and the text concedes that the hydrodynamics does not reproduce the variation in Fig. 3. So the reduction of EPR in the polar phase is, as far as this paper goes, a finite-size observation. The macro-micro correspondence only holds in the ε→0 limit; the abstract's claim that macroscopic dissipation \"coincides\" with microscopic dissipation overstates the result.\n\nWhat the paper does well: it computes the EPR from standard stochastic thermodynamics, gives a clean comparison of full versus partial inference, and shows that discarding internal states can severely underestimate dissipation in the apolar phase. That is a useful practical warning for experiments. The mapping to non-ideal reaction-diffusion dynamics is a sensible framework and connects properly to the authors' prior work.\n\nSoft spots: the missing finite-size scaling is the big one. Without an n-dependence check, the polar-phase dissipation reduction is not established. The inference estimates assume Markovian, location-independent rates; the paper itself shows waiting-time deviations from exponential tails in the polar phase (Fig. 4), so the quantitative matching of S_I to S is partly fortuitous. There are also no error bars on the simulation points. These issues are addressable, but the abstract and discussion present the crossover as robust when it is not yet.\n\nWho is this for: people working on stochastic thermodynamics of active matter and lattice flocking models. It deserves a serious referee, because the core model and the inference platform are worth fixing. I would not cite the crossover claim as established; I would cite the model construction and the inference comparison with caution.","headline":"A useful thermodynamically consistent flocking model, but the central dissipation crossover is undercut by the paper's own hydrodynamics and needs finite-size scaling.","tokens_in":15821,"tokens_out":2640,"would_cite":true,"duration_ms":28687,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"In flocking, hidden internal states carry most of the energy cost when order is weak.","keywords":["active matter","flocking transition","entropy production rate","local detailed balance","coarse graining","active Ising model","stochastic thermodynamics","reaction-diffusion systems"],"falsifier":"Measure the true dissipation from fuel consumption, namely the $\\Delta\\mu$ current, in a thermodynamically consistent flocking model or in chemically driven self-propelled particles while simultaneously recording trajectories that hide the internal propulsion state. In the apolar phase the paper predicts the hidden-state inference will report near-zero entropy production while the fuel-based measurement stays at the non-interacting maximum; an experiment that finds comparable inferred and true rates in apolar conditions would falsify the crossover.","tokens_in":14879,"feed_emoji":"🐦","tokens_out":5446,"duration_ms":51827,"temperature":0.7,"pith_summary":"The paper builds a thermodynamically consistent lattice model of flocking in which each particle's internal state biases its diffusion and both state changes and spatial jumps obey local detailed balance with respect to the same interaction energy. Using this model, it establishes a crossover in the entropy production rate: in the weakly interacting apolar phase the dissipation is maximal, equal to the non-interacting value, while any inference that discards internal state dynamics predicts a vanishing entropy production; in the strongly interacting polar phase dissipation is lower and the same partial inference captures most of it. It then coarse-grains the model to hydrodynamics and shows the macroscopic entropy production equals the microscopic one, through a mapping to non-ideal reaction-diffusion systems. A sympathetic reader would care because it tells experimenters when trajectory data that hides self-propulsion direction will mislead energy accounting, and when it will not.","feed_headline":"Disordered flocks cost the most energy, and hidden states pay for it","feed_subtitle":"A thermodynamically consistent model shows position-only measurements miss dissipation in weak flocks but capture it in ordered ones.","key_machinery":"The load-bearing object is a lattice model of $N$ particles with two internal states $+,-$, with interaction energy $E$ built from local density and polarization, and transition rates for state flips and site jumps set by local detailed balance with respect to the same $E$. This thermodynamic consistency is what lets the entropy production rate be computed exactly as $T\\dot{S}=\\Delta\\mu\\langle J_p-J_m\\rangle$ in steady state. The inference machinery consists of coarse-graining tracer jump rates from waiting times: keeping internal states gives $\\dot{S}_{\\mathrm{I}}$, discarding them gives $\\dot{S}_{\\mathrm{II}}$, with the chain $0\\le\\dot{S}_{\\mathrm{II}}\\le\\dot{S}_{\\mathrm{I}}\\le\\dot{S}$. The hydrodynamic step uses a path-integral coarse-graining to non-ideal reaction-diffusion equations in $(\\rho,P)$, whose dissipative and reactive contributions reproduce the microscopic entropy production.","core_discovery":"The central claim is that in a thermodynamically consistent version of the active Ising model, the entropy production rate $\\dot{S}$ is not largest at the flocking transition but in the disordered apolar phase, where $\\dot{S}=N\\gamma\\Delta\\mu^2/T$ exactly as for non-interacting particles. Partial inference that follows only positions, $\\dot{S}_{\\mathrm{II}}$, vanishes in that phase even though true dissipation is high; by contrast, in the polar phase $\\dot{S}$ is reduced and $\\dot{S}_{\\mathrm{II}}$ approaches it. The paper also proves that the hydrodynamic entropy production $\\dot{S}_{\\mathrm{macro}}$ equals the microscopic $\\dot{S}$ under coarse-graining, giving $T\\dot{S}_{\\mathrm{macro}}=(D/T)\\rho_0 V f^2$ in homogeneous phases, and identifies the reason as the mapping of active lattice models with local detailed balance to a class of non-ideal reaction-diffusion systems.","pith_inferences":["A natural experimental test would compare fuel consumption with orientation-hidden trajectory inference in colloidal or bacterial flocks; the model predicts the two agree only when global polarization is high.","The mapping to non-ideal reaction-diffusion systems implies the same inference gap should appear in any chemically driven system whose hidden internal coordinate is tightly coupled to transport, not just in flocking.","If non-Markovian waiting times in the coexistence phase are generic, then band-forming regimes are where partial inference is least reliable; direct current measurements, not waiting-time estimates, would be needed there.","The plateau of maximal dissipation in the disordered phase suggests that adding alignment reduces dissipation per particle, so flocking order could be viewed as an energy-saving collective state rather than a costly one."],"forward_implications":["Direct steady-state entropy production is accessible exactly as $\\Delta\\mu$ times the net current of $+$ and $-$ particles, so energy accounting in thermodynamically consistent active lattice models can be done without fluctuating-force approximations.","In apolar or weakly ordered flocks, any dissipation estimate based only on visible displacements will severely undercount energy expenditure; hidden internal-state dynamics are the dominant dissipative channel.","In polar flocks, position-only tracking is sufficient: the inferred rate $\\dot{S}_{\\mathrm{II}}$ approaches the true $\\dot{S}$, so experiments can trust displacement data there.","The macroscopic hydrodynamic entropy production reproduces the microscopic value, so coarse-grained descriptions of active matter do not lose dissipative content if the coarse-graining keeps both the diffusive and reactive sectors.","The inferred entropy production without internal states scales with the square of polarization, $\\dot{S}_{\\mathrm{II,macro}}\\propto P_0^2/\\rho_0$, giving a quantitative link between macroscopic order and apparent dissipation."],"supporting_citations":[{"why":"Supplies the active Ising model dynamics that this paper modifies to obey local detailed balance.","marker":"[38]"},{"why":"Provides the fluctuation-theorem basis for entropy production in Markov jump processes with local detailed balance.","marker":"[34]"},{"why":"Gives the stochastic thermodynamics framework used to define the entropy production rate.","marker":"[35]"},{"why":"Establishes that coarse-graining reduces inferred entropy production, yielding the ordering of the partial estimates.","marker":"[55]"},{"why":"Prior thermodynamically consistent flocking model whose energy-dependent jump rates are adapted here.","marker":"[50]"},{"why":"Provides the non-ideal reaction-diffusion thermodynamics used for the hydrodynamic entropy production decomposition.","marker":"[57]"},{"why":"Earlier active-spin entropy production evaluation with a cusp at transition, contrasted as lacking thermodynamic consistency.","marker":"[52]"}],"fun_headline_variants":["Dissipation peaks in disordered flocks, not at transition","Position-only measures miss most dissipation in weak flocks","Hidden internal states drive dissipation in weak flocking","Coarse-grained dissipation matches microscopic in active lattice models","Weak flocks: high dissipation, invisible to position-only tracking"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The inference estimates assume each tracer's jump dynamics is Markovian and spatially uniform; the paper itself reports waiting-time distributions with non-exponential tails in the polar phase and deliberately ignores spatial inhomogeneities, so if tracer dynamics is strongly non-Markovian the inferred entropy productions are no longer guaranteed bounds and the crossover could be distorted.","fun_headline_variants_meta":{"raw":{"variants":["Dissipation peaks in disordered flocks, not at transition","Position-only measures miss most dissipation in weak flocks","Hidden internal states drive dissipation in weak flocking","Coarse-grained dissipation matches microscopic in active lattice models","Weak flocks: high dissipation, invisible to position-only tracking"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000324,"raw_usage":{"total_tokens":1799,"prompt_tokens":907,"completion_tokens":892,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":523,"completion_tokens_details":{"reasoning_tokens":817}},"tokens_in":523,"tokens_out":892,"duration_ms":9839,"temperature":1.0,"reasoning_tokens":817,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T20:20:39.137872+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the true dissipation from fuel consumption, namely the $\\Delta\\mu$ current, in a thermodynamically consistent flocking model or in chemically driven self-propelled particles while simultaneously recording trajectories that hide the internal propulsion state. In the apolar phase the paper predicts the hidden-state inference will report near-zero entropy production while the fuel-based measurement stays at the non-interacting maximum; an experiment that finds comparable inferred and true rates in apolar conditions would falsify the crossover.","supporting_citations":[{"cited_title":"Entropy production and thermodynamic inference for stochastic microswimmers,","cited_arxiv_id":null,"evidence_quote":"Provides the fluctuation-theorem basis for entropy production in Markov jump processes with local detailed balance."},{"cited_title":"Energy cost for flocking of ac- tive spins: The cusped dissipation maximum at the flock- ing transition,","cited_arxiv_id":null,"evidence_quote":"Establishes that coarse-graining reduces inferred entropy production, yielding the ordering of the partial estimates."},{"cited_title":"Numerical treatment of the boltzmann equation for self-propelled particle systems,","cited_arxiv_id":null,"evidence_quote":"Prior thermodynamically consistent flocking model whose energy-dependent jump rates are adapted here."},{"cited_title":"Emergence of local ir- reversibility in complex interacting systems,","cited_arxiv_id":null,"evidence_quote":"Provides the non-ideal reaction-diffusion thermodynamics used for the hydrodynamic entropy production decomposition."},{"cited_title":"Local detailed balance,","cited_arxiv_id":null,"evidence_quote":"Earlier active-spin entropy production evaluation with a cusp at transition, contrasted as lacking thermodynamic consistency."}],"review_version":1}