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Europhysics Letters (EPL)

Stochastic model related to the Klein-Gordon equation revisited

Arbab I. Arbab

Published Sep 27, 2011• 2 citations
Publisher

Abstract

Recently, Plyukhin and Schofield have shown that there is a close analogy between collective oscillation of a system composed of an assembly of interacting particles and the propagation of a free quantum particle in one dimension. They could not have interpreted some of the equations involved in this analogy. We show here that the arbitrary field, they have introduced, satisfies the Klein-Gordon equation, too. Moreover, the arbitrary field is proportional to the local electric field. This local electric filed may induce a transition between the two-particle states; one moving to the left and the other to the right with the speed of light.

DOI
10.1209/0295-5075/96/20002

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Recently, Plyukhin and Schofield have shown that there is a close analogy between collective oscillation of a system composed of an assembly of interacting particles and the propagation of a free quantum particle in one dimension. They could not have interpreted some of the equations involved in this analogy. We show here that the arbitrary field, they have introduced, satisfies the Klein-Gordon equation, too. Moreover, the arbitrary field is proportional to the local electric field. This local electric filed may induce a transition between the two-particle states; one moving to the left and the other to the right with the speed of light.
In this note, a one-dimensional system composed of an assembly of interacting particles, is considered. Each particle in the assembly moves in a well-defined trajectory on a line with a velocity of fixed magnitude, which randomly reverses direction. The intrinsic forces in the system are assumed to induce stochastic transitions between velocity states in such a way that the average dynamics of the assembly is Newtonian. It is shown that there is a close analogy between collective oscillations in the model system and the propagation of a free quantum particle in one dimension.
The Klein-Gordon equation is often created by taking the deterministic relativistic invariant EE = pp+ momo (c=1), replacing E with E-V(x), E=id/dt partial and p with -id/dx partial and having the derivatives act on a function W(x,t). This seems to suggest that the starting point is deterministic classical mechanics (special relativistic form) E,p equation with stochasticity somehow introduced by having average E and p follow from the action of the operators id/dt partial and -id/dx partial on a stochastic function W(x,t). It also makes it somewhat difficult to understand, from first principles, why one would create a linear equation in E,p (compatible with EE=pp+momo), i.e. the Dirac equation. We suggest that the entire approach to Klein-Gordon equation is stochastic, with the EE=pp+momo equation appearing as an invariant expression of average values which describes motion as seen from different frames moving with constant average velocity v. In such a case, one is not limited to the form EE=pp+momo and there is nothing unusual about trying to create an equation linear in E and p. In particular, we argue that the free particle form exp(-iEt) exp(ipx) follows from two separate maximizations of Shannon’s entropy subject to complex constraints (for periodicity). As a result, free motion with a constant E and p is already stochastic as seen from a photon moving in a region with an index of refraction n or a particle moving in a region with constant potential. Changing to a potential V(x) leads to the notion of an average kinetic energy because a constant p is associated with a distribution in x i.e. exp(ipx). One may think in terms of these average values in order to consider frames moving with constant v. This leads to both -Et+px -EE+pp=momo being invariants. If a V(x) is present, one may replace E with E-V(x), but then needs a statistical average Sum over p a(p)exp(ipx) to describe pp.. The time portion may still be exp(-iEt) if one has a bound system characterized by a single average energy. This yields the Klein-Gordon equation.There is, however, no particular reason why one could not use an equation linear in E and p (consistent with -EE+pp=momo), because the latter follows form the an average v (deterministic view) of the stochastic exp(-iEt+ipx) two-dimensional probability.
Abstract This work presents an alternative approach to obtain the quantum field equations in curved spacetime, considering that sufficiently small particles follow stochastic trajectories around geodesic. Our proposal is based on a stochastic differential equation in which the noise term experienced by the quantum particles is a consequence of the stochastic background in spacetime. This fact allows the particles to describe erratic movements and locally the universe exhibits characteristics akin to a lake with gentle ripples rather than a flat unyielding surface. Building upon this foundational understanding, we investigate the influence of this background on quantum-scale particles without considering the metric to be stochastic, rather we let test particles move randomly around the geodesic of macroscopic particles. Their behavior aligns with solutions to the Klein-Gordon (KG) equation specific to this curved spacetime. As the KG equation, in its non-relativistic limit within a flat spacetime, reduces to the Schrödinger equation, consequently, we propose a compelling connection: the Schrödinger equation may emerge directly from a spacetime lacking local smoothness.
A new Quantum Theory is herein obtained by imposing a classical stochastic proce.ss on the kinematics of Relativity, A fundamental consequence is that the Quantum mechanism is subject t•oi i I ~~e examine some implications attending classical interpretG.tion.the view that.a mathematical model, representing a perfectly defined material particle in an exa.ctly duplicable deterministic potential field, cannot be an adequate approximation to a realistic~ physical process but must lead to untenable predict ions at atomic dimensions.\'le first assume a nonvanishing fluctuating background interaction .due to "distant stars" that results in rand.om, I scattering along the 'dorld line of the particle.He then 1ntroduce. ! an ensemble of particles• and explore most probable motions in the associated 3-apace projection as given by a pair of coupled nonlinear equations, The most probable motions are in turn found to satisfy the Klein-Gordon equation, viii '
The Klein–Gordon equation, written down in 1926 by Oskar Klein and Walter Gordon (and earlier in unpublished form by Schrödinger himself), is the natural relativistic extension of quantum mechanics for spin‑zero particles: (□ + m²c²/ℏ²) Ψ = 0 where □ = (1/c²) ∂ₜ² − ∇². The equation is second‑order in both time and space, treats them symmetrically, and reduces to the free‑particle Schrödinger equation in the non‑relativistic limit. Its plane‑wave solutions satisfy the relativistic mass‑shell condition E² = p²c² + m²c⁴. Why is a relativistic version needed at all? The Schrödinger equation describes how quantum systems evolve when they’re moving slowly compared to the speed of light — fine for atoms, molecules, and everyday chemistry, where electrons move at less than 1% of c. But the Schrödinger equation is first‑order in time and second‑order in space, treating the two on different footings. Special relativity says space and time are unified into a single four‑dimensional structure where Lorentz transformations mix them, and any equation that privileges time over space breaks Lorentz invariance. A truly fundamental quantum equation must respect this symmetry. Klein–Gordon is the minimal scalar‑field equation that does. The standard derivation runs by analogy: start with the relativistic energy–momentum relation E² = p²c² + m²c⁴, replace E by iℏ∂ₜ and p by −iℏ∇, apply both sides to a wavefunction. This produces the right equation but it’s not really a derivation — it’s a guess motivated by the Schrödinger operator‑substitution procedure. This walkthrough shows how the Event Density framework derives the Klein–Gordon equation from substrate primitives — the same primitives that gave the Born rule, the Schrödinger equation, and the Bell–Tsirelson bound — plus the commitment to Lorentz covariance. The participation measure becomes Lorentz‑covariant. The unique second‑order Lorentz‑scalar differential operator on a scalar field is the d’Alembertian; the minimum‑order Lorentz‑scalar linear equation is therefore (□ + M²) Ψ = 0. Dimensional analysis fixes M² = m²c²/ℏ². Local U(1) gauge invariance forces the covariant derivative and the conserved four‑current. The non‑relativistic limit, via rest‑energy factorization, recovers the free‑particle Schrödinger equation exactly. The structural payoff: the Klein–Gordon equation is what you get when the substrate ontology is pushed through a Lorentz‑covariant reformulation. No new primitives are required. Relativistic and non‑relativistic quantum mechanics are not two theories glued together by analogy; they are the same substrate ontology applied at different velocity regimes. The walkthrough is honest about the known caveats — negative‑energy solutions and the non‑positive‑definite j₀ current — both of which resolve at the Dirac level and at QFT.