Stochastic dynamics from maximum entropy in action space
Pith reviewed 2026-05-25 07:06 UTC · model grok-4.3
The pith
Maximizing entropy over joint action-endpoint distributions produces a Boltzmann-like distribution in action space.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Maximizing Shannon entropy over a joint distribution of actions and endpoints, subject to normalization and a constraint on the mean action, produces a Boltzmann-like distribution in action space. This framework reproduces the standard Brownian propagator in the nonrelativistic limit and naturally extends to relativistic regimes, where the Wiener construction fails to preserve Lorentz covariance. The density of states is derived as Gaussian using large deviation theory, and the Markov property holds via the Chapman-Kolmogorov equation from additivity of the minimal action.
What carries the argument
The maximum entropy principle applied to the joint distribution over total actions and endpoints under normalization and mean-action constraints, yielding the Boltzmann-like action distribution.
If this is right
- The resulting dynamics are governed by a competition between extremization of the action and entropic effects in the diffusive regime.
- The propagator satisfies the Chapman-Kolmogorov equation, confirming the Markovian property.
- The approach bypasses functional integration over paths and makes entropic degeneracy explicit through the action-space density of states.
- The framework provides a transparent connection between the principle of least action and statistical inference.
Where Pith is reading between the lines
- This construction could be extended to interacting systems by including interaction terms in the minimal action.
- The effective action free energy interpretation might connect to variational principles in nonequilibrium thermodynamics.
- Testing the relativistic extension could involve simulating particle diffusion at speeds close to light and comparing to covariant formulations.
Load-bearing premise
Large deviation theory independently supplies a Gaussian density of states centered on the minimal action that justifies the saddle-point approximation.
What would settle it
A direct calculation showing that the density of states for actions deviates from Gaussian form, or experimental violation of the derived propagator in relativistic stochastic processes.
Figures
read the original abstract
We develop an information-theoretic formulation of stochastic dynamics in which the fundamental stochastic variable is the total action connecting spacetime points, rather than individual paths. By maximizing Shannon entropy over a joint distribution of actions and endpoints, subject to normalization and a constraint on the mean action, we obtain a Boltzmann-like distribution in action space. This framework reproduces the standard Brownian propagator in the nonrelativistic limit and naturally extends to relativistic regimes, where the Wiener construction fails to preserve Lorentz covariance. The approach bypasses functional integration over paths, makes the role of entropic degeneracy explicit through an action-space density of states, and provides a transparent connection between the principle of least action and statistical inference. We derive the density of states explicitly using large deviation theory, showing that it takes a Gaussian form centered at the minimal action, and rigorously justify the saddle-point approximation in the diffusive regime. The Markovian property of the resulting propagator is verified to hold via the Chapman--Kolmogorov equation, following from the additivity of the minimal action for free-particle dynamics. In the diffusive regime, the resulting dynamics are governed by a competition between extremization of the action and entropic effects, which can be interpreted in terms of an effective action free energy. Our results establish an unified, covariant, and information-based foundation for classical and relativistic stochastic processes.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents an information-theoretic approach to stochastic dynamics by maximizing the Shannon entropy of a joint distribution over actions and endpoints, subject to a mean-action constraint. This yields a Boltzmann-like distribution in action space that is claimed to reproduce the standard Brownian propagator in the nonrelativistic limit, extend covariantly to relativistic regimes, and satisfy the Markov property via the Chapman-Kolmogorov equation. The paper asserts an explicit derivation of a Gaussian action-space density of states from large-deviation theory and a rigorous justification of the saddle-point approximation in the diffusive regime.
Significance. Should the central derivation of an independent Gaussian density of states hold without circularity in the mean-action constraint, the work would offer a novel, covariant foundation for stochastic processes that bypasses path integrals and explicitly incorporates entropic effects through an action free energy. This could unify classical and relativistic stochastic dynamics under a statistical-inference principle.
major comments (2)
- [large-deviation derivation of density of states] The section deriving the density of states via large-deviation theory asserts a Gaussian form centered on the minimal action that is independent of the target propagator, but provides no explicit demonstration that this form (and the numerical value of the mean-action constraint) is obtained externally rather than from the same minimal-action saddle; without this independence the construction risks circularity and the claimed reproduction of the Brownian kernel fails to follow.
- [saddle-point approximation justification] The abstract claims a rigorous justification of the saddle-point approximation in the diffusive regime together with error estimates or checks against known limits, yet the supplied text contains no such explicit derivations or verifications; this justification is load-bearing for both the nonrelativistic reproduction and the relativistic extension.
Simulated Author's Rebuttal
We thank the referee for the careful reading and for identifying points where the derivations require greater explicitness. We agree that the manuscript would benefit from expanded sections addressing both concerns and will revise accordingly.
read point-by-point responses
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Referee: [large-deviation derivation of density of states] The section deriving the density of states via large-deviation theory asserts a Gaussian form centered on the minimal action that is independent of the target propagator, but provides no explicit demonstration that this form (and the numerical value of the mean-action constraint) is obtained externally rather than from the same minimal-action saddle; without this independence the construction risks circularity and the claimed reproduction of the Brownian kernel fails to follow.
Authors: We acknowledge that the current text does not supply a sufficiently detailed, self-contained derivation demonstrating independence. In the revised manuscript we will expand the large-deviation section with an explicit step-by-step calculation: starting from the rate function for action fluctuations around the classical path, deriving the quadratic expansion that yields the Gaussian form and its variance from the Hessian of the action, and showing that both the centering and the variance are fixed before the mean-action constraint is imposed. This will remove any appearance of circularity and allow the subsequent reproduction of the Brownian kernel to follow directly. revision: yes
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Referee: [saddle-point approximation justification] The abstract claims a rigorous justification of the saddle-point approximation in the diffusive regime together with error estimates or checks against known limits, yet the supplied text contains no such explicit derivations or verifications; this justification is load-bearing for both the nonrelativistic reproduction and the relativistic extension.
Authors: The referee is correct that the abstract asserts a rigorous justification with error estimates while the body of the paper does not contain the corresponding derivations or verifications. We will add a dedicated subsection that (i) derives the leading-order error term of the saddle-point approximation in the diffusive scaling limit, (ii) supplies explicit bounds on the remainder, and (iii) verifies the approximation against the exact non-relativistic Brownian propagator as well as consistency checks in the relativistic regime. These additions will make the claimed justification fully explicit. revision: yes
Circularity Check
No circularity: explicit large-deviation derivation of density of states supplies independent input
full rationale
The derivation maximizes entropy subject to normalization and a mean-action constraint to obtain the Boltzmann-like form, then separately invokes large-deviation theory to derive an explicit Gaussian density of states centered on the minimal action; this density is used to justify the saddle-point step. Because the density-of-states derivation is presented as an independent calculation (not obtained by fitting the target propagator or by self-reference), the mean-action constraint does not reduce to the output by construction. No self-citation chains, ansatz smuggling, or renaming of known results appear in the load-bearing steps. The reproduction of the Brownian propagator functions as a consistency check rather than a fitted prediction. The framework therefore remains self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
free parameters (1)
- mean action constraint value
axioms (2)
- domain assumption Additivity of the minimal action for free-particle dynamics
- domain assumption Large-deviation theory supplies a Gaussian density of states centered at the minimal action
Lean theorems connected to this paper
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IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
By maximizing Shannon entropy over a joint distribution of actions and endpoints, subject to normalization and a constraint on the mean action, we obtain a Boltzmann-like distribution in action space … We derive the density of states explicitly using large deviation theory, showing that it takes a Gaussian form centered at the minimal action
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
Works this paper leans on
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[1]
Micropath ensemble At the microscopic level, each pathγ:a→bhas actionA[γ] and probability P(γ|a) = e−ηA[γ] Z(η) ,Z(η) = ∑ γ:a→⋆ e−ηA[γ] .(63) The coarse-grained distribution,p(A,b|a) = g(A,b)e −ηA /Z(η), arises from marginalizing over paths with the same action value, whereg(A,b)counts the degeneracy
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[2]
forward” process with protocolλ F (t)and its “re- verse
Action-work definition To derive fluctuation theorems, we compare two path en- sembles: a “forward” process with protocolλ F (t)and its “re- verse”λ R(t) =λ F (τ−t). These define two action functionals, AF [γ] =A[γ;λ F ],A R[ ˜γ] =A[ ˜γ;λ R],(64) where ˜γdenotes the time-reversed path. Theaction-workis defined as the variation of action between forward an...
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[3]
Crooks-like relation The path measures for forward and reverse processes are PF [γ] = e−ηAF [γ] ZF (η) ,P R[ ˜γ] = e−ηAR[ ˜γ] ZR(η) .(66) Taking the ratio: PF [γ] PR[ ˜γ] =exp −η[A F [γ]−A R[ ˜γ] · ZR ZF =exp −ηW A[γ] · ZR ZF .(67) 12 TABLE II. Formal structural analogy between equilibrium thermodynamics and the action-space formulation of stochastic dyna...
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[4]
Jarzynski-like equality Summing over all paths weighted by the forward measure, ⟨e−ηWA⟩F = ∑ γ PF [γ]e −η(AF [γ]−AR[ ˜γ]) = 1 ZF ∑ γ e−ηAR[ ˜γ] = ZR ZF .(70) This yields theJarzynski equality in action space, ⟨e−ηWA ⟩F = ZR(η) ZF (η) =e −η∆F .(71)
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[5]
Second law in action space By Jensen’s inequality,⟨e−ηWA ⟩ ≥e −η⟨WA⟩. Combined with Eq. (71), ⟨WA⟩ ≥∆F.(72) This is the second law of thermodynamics in action space – the average action-work required to change the control pa- rameter is at least as large as the free action difference, with equality for reversible (quasi-static) processes. The dissipated a...
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[6]
Terminology We emphasize thatW A is anaction-work, not mechanical work in the conventional sense. The term reflects the struc- tural analogy with thermodynamics: just asβWis dimen- sionless in standard fluctuation theorems (withβ=1/(k BT) andWin energy units), hereηW A is dimensionless (withηin inverse-action units andW A in action units). The standard en...
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[7]
Interpretation for free particles For the free Brownian particle studied in this work, where no external protocolλ(t)is applied, the fluctuation theorems take a simplified form. In the absence of time-dependent driving, the forward and reverse processes are statistically equivalent:A F (γ) =A R( ˜γ)for corresponding paths, implying WA =0 and∆F=0. The Jarz...
work page 2024
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[8]
Microscopic derivation from random collisions We deriveg(A,b)from first principles by modeling Brow- nian motion as a sequence of random collisions between the diffusing particle and molecules of the surrounding thermal bath, without assuming the Langevin equation. a. Collision model.Consider a free particle of massm initially at positionx a at timet a. D...
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[9]
Verification via large deviation theory and Langevin dynamics As a complementary approach and consistency check, we now rederiveg(A,b)using the continuum Langevin descrip- tion and large deviation theory. This confirms that the micro- scopic collision model yields the same result as the standard stochastic differential equation framework. f. Definition an...
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[10]
Consistency of microscopic and continuum approaches Both derivations—microscopic collision model (Section 1) and continuum Langevin dynamics (Section 2)—yield the same Gaussian form forg(A,b)with identical scalingσ 2 A ∼ mkBT D∆t∼m 2D2 ∆t/τrelax. This consistency confirms that the action-space MaxEnt formulation correctly captures the statistics of Browni...
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[11]
Generalization to Higher Dimensions The action-space MaxEnt formulation extends naturally to d-dimensional free Brownian motion. For a particle moving inR d, the Lagrangian is L= m 2 ∥ ˙⃗x∥2 = m 2 d ∑ i=1 ˙x2 i ,(B24) and the total action decomposes into a sum over independent components: A= d ∑ i=1 Ai,A i = Z tb ta m 2 ˙x2 i dt.(B25) For isotropic diffus...
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[12]
(28) is justified in the diffu- sive regime
Justification of the slowly-varying approximation We now verify that the approximationg(A,b)≈ g(Amin(b),b)used in Eq. (28) is justified in the diffu- sive regime. The characteristic scale of variation ofg(A,b)with respect toAis determined by its logarithmic derivative: dlng(A,b) dA = |A−A min(b)| σ 2 A .(B31) Evaluated atA=A min, this vanishes. ForAwithin...
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[13]
Brownian paths fluctuate randomly around the classical trajectory (which minimizes the action)
Physical interpretation and regime of validity The Gaussian form (B23) of the density of states has a clear physical interpretation. Brownian paths fluctuate randomly around the classical trajectory (which minimizes the action). 18 The action along a fluctuating path differs fromA min by an amount determined by the accumulated velocity fluctuations over t...
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[14]
Breakdown of the slowly-varying approximation The slowly-varying approximationg(A,b)≈g(A min(b),b) derived above is valid in the diffusive regime∆t≫τ relax for free Brownian particles, whereg(A,b)is Gaussian-distributed aroundA min with varianceσ 2 A. However, this approximation can fail in systems whereg(A,b)exhibits sharp features, mul- tiple peaks, or ...
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[15]
There, g(A,b)has support only at two values:A min (withg=1) andA ∗ =A min +∆A(withg=N ∗ ≫1)
Entropic compensation (toy model):The discrete toy model in Appendix C provides an extreme example. There, g(A,b)has support only at two values:A min (withg=1) andA ∗ =A min +∆A(withg=N ∗ ≫1). The slowly-varying approximation would predictp(b|a)∝exp(−ηA min), entirely missing the entropic contribution from fluctuating paths atA∗. ForT info >T crit =∆A/lnN...
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[16]
Instantons and activated processes:In systems with tunneling or rare-event transitions (e.g., nucleation, barrier crossing), the action distribution may have a dominant con- tribution from instanton trajectories withA≫A min. If these paths have large degeneracyg(A)due to temporal freedom in the barrier-crossing event, they can dominate the propaga- tor de...
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[17]
Relativistic causality constraints:Near the light cone (∆x≈c∆t), the action approachesA→0 (null trajectories). The density of states may have enhanced phase-space volume near this boundary due to proliferation of near-lightlike paths. Ifg(A,b)grows rapidly asA→0, the slowly-varying approx- imation aroundA min (which corresponds to subluminal mo- tion with...
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[18]
with degeneracyg ∗ =N ∗, whereN ∗ ≫1 represents many nearly-degenerate fluctuating trajectories. The density of states is: g(A,b) = 1,A=A min N∗,A=A ∗ 0,otherwise (C1) Probability Distribution From the MaxEnt distribution Eq. (10): p(Amin|a,b) = gmine−ηAmin Z = e−ηAmin Z ,(C2) p(A∗|a,b) = g∗e−ηA ∗ Z = N∗e−η(Amin+∆A) Z ,(C3) where the partition fun...
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[19]
Change of variables Introduce the dimensionless variable u= xb −x a c∆t ,−1≤u≤1,dx b =c∆t du, and the shorthand α=ηm 0c∆t. Then the normalization condition (D1) becomes c∆t N Z 1 −1 eα √ 1−u2 −1 du=1.(D2) Hence N=c∆t I(α)−2 ,I(α) = Z 1 −1 eα √ 1−u2 du.(D3)
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[20]
Evaluation ofI(α) To computeI(α), we use the substitutionu=sinθ, with −π/2≤θ≤π/2. Then p 1−u 2 =cosθ,du=cosθdθ. Therefore I(α) = Z π/2 −π/2 eαcosθ cosθdθ(D4) =2 Z π/2 0 eαcosθ cosθdθ(D5) =π I1(α) +L −1(α) ,(D6) which is a classical integral representation of modified Bessel functionsI 1(α), and Struve functionsL −1(α). Substituting (D6) into (D3) gives th...
-
[21]
C. E. Shannon, Bell System Technical Journal27, 379 (1948), https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.1538- 7305.1948.tb01338.x
-
[22]
C. E. Shannon and W. Weaver,The mathematical theory of com- munication(University of Illinois Press, Urbana, 1949) publi- cation Title: Urbana
work page 1949
-
[23]
E. T. Jaynes, Physical Review106, 620 (1957)
work page 1957
-
[24]
Q. A. Wang, arXiv:cond-mat/0407515 [cond-mat.stat-mech] (2004)
work page internal anchor Pith review Pith/arXiv arXiv 2004
-
[25]
Q. A. Wang, Chaos, Solitons & Fractals23, 1253 (2005)
work page 2005
-
[26]
Q. A. Wang, Astrophysics and Space Science305, 273 (2006)
work page 2006
- [27]
-
[28]
Q. A. Wang, Chaos, Solitons & Fractals26, 1045 (2005)
work page 2005
- [29]
-
[30]
M. I. Freidlin and A. D. Wentzell,Random Perturbations of Dynamical Systems, 2nd ed., Grundlehren der mathematischen Wissenschaften, V ol. 260 (Springer, 1998)
work page 1998
-
[31]
At this point it is important to emphasize that these path-level approaches differ fundamentally from the one that shall be de- veloped in the present work, which formulates the variational principle directly inaction space, marginalizing over trajecto- 21 ries to obtain probability distributions over total action values rather than assigning probabilitie...
-
[32]
Wiener, Journal of Mathematics and Physics2, 131 (1923)
N. Wiener, Journal of Mathematics and Physics2, 131 (1923)
work page 1923
-
[33]
Kac, Transactions of the American Mathematical Society 65, 1 (1949)
M. Kac, Transactions of the American Mathematical Society 65, 1 (1949)
work page 1949
-
[34]
R. H. Cameron and W. T. Martin, Annals of Mathematics45, 386 (1944)
work page 1944
-
[35]
R. M. Dudley, Arkiv för Matematik6, 241 (1966)
work page 1966
- [36]
- [37]
-
[38]
The maximum relative entropy principle
J. Banavar and A. Maritan, The maximum relative entropy prin- ciple (2007), arXiv:cond-mat/0703622 [cond-mat.stat-mech]
work page internal anchor Pith review Pith/arXiv arXiv 2007
-
[39]
Despite the nomenclature “informational temperature,” the quantityT info =1/ηhas dimensions of action[ML 2T −1]rather than energy[ML 2T −2], and depends on system-specific param- eters through the relationη=γ/(2k BT), whereγis the fric- tion coefficient. The term emphasizes a formal structural anal- ogy with the inverse temperatureβ=1/(k BT)in equilibrium...
-
[40]
A. I. Va˘ınshte˘ın, V . I. Zakharov, V . A. Novikov, and M. A. Shif- man, Soviet Physics Uspekhi25, 195 (1982)
work page 1982
-
[41]
S. Vandoren and P. van Nieuwenhuizen, Lectures on instantons (2008), arXiv:0802.1862 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv 2008
- [42]
-
[43]
R. Schilling, L. Partzsch, and B. Böttcher,Brownian Motion: An Introduction to Stochastic Processes, De Gruyter Textbook (De Gruyter, 2014)
work page 2014
-
[44]
This scaling can be derived microscopically from random colli- sions with thermal bath molecules, without assuming a specific stochastic equation. For a free Brownian particle, uncorrelated velocity kicks from Maxwell-Boltzmann distributed collisions yieldσ 2 A ∼mk BT D∆tvia the central limit theorem in the dif- fusive regime∆t≫τ relax (see Appendix B, Se...
-
[45]
Zwanzig,Nonequilibrium Statistical Mechanics(Oxford University Press, 2001)
R. Zwanzig,Nonequilibrium Statistical Mechanics(Oxford University Press, 2001)
work page 2001
-
[46]
C. M. Bender and S. A. Orszag,Advanced Mathematical Meth- ods for Scientists and Engineers(McGraw–Hill, 1978)
work page 1978
-
[47]
Risken, inThe Fokker-Planck equation: methods of solution and applications(Springer, 1989) pp
H. Risken, inThe Fokker-Planck equation: methods of solution and applications(Springer, 1989) pp. 63–95
work page 1989
- [48]
-
[49]
Debbasch, Journal of mathematical physics45, 2744 (2004)
F. Debbasch, Journal of mathematical physics45, 2744 (2004)
work page 2004
- [50]
-
[51]
We adopt the conventionA=−m 0c R ds(negative action for timelike paths) so thatA min <0 for subluminal motion and Amax =0 at the light cone. This choice ensures that the ac- tion is bounded above by zero, with the causal boundary (light- like trajectories) serving as a natural upper limit. The negative sign convention is consistent with the structureA∈[A ...
- [52]
-
[53]
G. E. Crooks, Phys. Rev. E60, 2721 (1999)
work page 1999
-
[54]
G. T. Landi and M. Paternostro, Reviews of Modern Physics93, 035008 (2021)
work page 2021
- [55]
- [56]
discussion (0)
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