Newton's second law may be used to obtain a wave equation, which reduces to Schrodinger's equation in the nonrelativistic limit and for a conservative force.
In (1), it is argued that the Schrodinger (nonrelativistic) quantum equation may be developed from steady state type classical equations linked to the continuity equation and Newton’s second law. Given the nonrelativistic treatment of (1), F=dp/dt = d/dt (mv) = m dv/dt partial + mv dv/dx. In (1) an equation (III.2) for many particles is obtained from the equation for a single particle: Md (dv/dt partial + v dot grad v) = dF + hbarhbar/4m grad dot (grad grad d - 1/d (grad d) (grad d) ). In (1), it is further assumed that v = grad (phi) for conservative forces, where phi is a function of x,t. One may then see that for d=1 case, for a single particle, that phi= -Et+px and that one may write a Schrodinger equation which is essentially a conservation of energy equation. Here, we consider starting with dp/dt=Force and using a special relativistic treatment. We note that for a conservative force, F = -grad V and suggest trying to write the LHS in terms of a gradient for a free particle so the gradient may be “pulled out” from both sides of dp/dt=F. From a physical point of view, F is a pull or push, but we argue that V (potential) is also physical and that given that p is almost like a force, that there should be meaning to p= grad phi(x,t). This is the basis premise. In the case, F=0, we show that one may obtain -EE + p dot p = constant via this approach which involves writing p = d/dx (-Et+px) (one dimension). We note that associating dp/dt = F with a Lorentz invariant -Et+px shows the close association of Newton’s second law with special relativity because dp/dt=Force is relativistic as long as p=mov/sqrt(1-vv/cc). We suggest that this approach associates operators id/dt partial and -i grad partial (hbar=1) with E and p and allows one to write a free particle equation (Klein-Gordon) in terms of exp(-iEt+ipx), which is a quantum form. We suggest that one way in which to see free particle quantum mechanics emerge (albeit in the simplest case-that of a free relativistic particle) is to try to consider dp/dt in terms of a gradient suggesting that there may be x, t features even for E,p constant. In Newtonian mechanics, a constant E and p immediately implies that derivatives are 0. This need not be the case if one considers p = d/dx (-Et+px). The legitimacy of considering p (which is closely linked to a force) is linked to the legitimacy of considering F = -grad V. In other words, V is a potential which is another way of considering the features of a force and p = d/dx (-Et+px) may mean that -Et+px (and exp(-iEt+ipx) may be another way of considering p,E at a deeper level than simply stating that one has a constant E,p for a free particle. We argue that one does not need to consider a continuity equation as done in (1) and that the full approach follows from analysis of a single free particle (constant E,p) in the special relativistic case, which then yields also the nonrelativistic one.
In (1) we argued that one may derive Newton’s second law (which is equivalent to an energy conservation equation) by using information arguments. We argued that V(x), a potential, is a fixed piece of spatial information linked to the x axis being divided into equal dx units. The variable spatial information is dt(x) i.e. the time spent in each dx or v(x) =dx/dt (to put this in the same form as the time displacement generator). One may not simply compare v(x) directly with V(x) because they change differently. v(x) changes in a weighted way i.e. v(x)d/dx or d/dt while V(x) changes as d/dx V(x). Thus we suggest d/dt v(x) = C V(x) which ultimately leads to Newton’s second law. Using d/dt → v(x)d/dx and integrating yields conservation of energy: p(x)p(x)/2m + V(x) = E. A similar argument was used in (2) to deal with the special relativistic case. There one cannot use d/dt → v(x)d/dx to obtain a conservation of energy equation. The point we wish to make is that for both the nonrelativistic and relativistic classical equations there are two types of “information” equations. The first is a “force” i.e. -dV/dx equation which is based on how V(x) changes with x. The LHS of this equation is linked to d/dt p(x). The second is a corresponding energy conservation equation. The quantum case is quite different, we argue, because a free particle is described by exp(-iEt+ipx). There is still the notion of p=mo dx/dt(x) as in the nonrelativistic case because p must be defined, but exp(ipx) is additional imposed piece of spatial information. -id/dx exp(ipx) = p exp(ipx) and -d/dx d/dx exp(ipx) = pp exp(ipx). This begs the question: How does one reconcile the two? For the nonrelativistic Newtonian and relativistic cases it is possible to have two equations (one with Force the other with energy) using one x dependent variable p(x). In the quantum case one may take an average to define a kind of complex = Sum over p a(p) p exp(ipx)/ Sum over p a(p)exp(ipx, but this is complex, not real. Furthermore both +/- is included in so there seems to be a problem linking it with changes in V(x) in one direction. Thus it seems that one is forced to consider the second kind of information equation from classical mechanics and define a <pp> = Sum over p a(p) pp exp(ipx)/ {Sum over p a(p)exp(ipx)}. In the nonrelativsitic case this may be multiplied by 1/2mo and then added to V(x) to obtain a constant E. If one only looks at <pp>/2mo as a spatial function then this is identical to KE(x) i.e. kinetic energy(x) for a classical system. Thus in the nonrelativstic case, Newtonian energy conservation is always embedded in the quantum system regardless of the energy. In other words the quantum bound equation i.e. the time independent Schrodinger is not obtained independently from the classical one in terms of information.One may ask: How does information related to exp(ipx) affect the quantum system? Two immediate ways are as follows. First <pp>/2mo = -1/2mo d/dx dW/dx / W where W= Sum over p a(p)exp(ipx). This leads to a differential equation which has discrete En values verified by experiment. Secondly W is linked to spatial density W*(x)W(x) which exhibits crests and near zero regions. Using <pp> suggests that p(x) in the classical case is linked to prms(x) quantum. Thus building quantum mechanics using “informational” ideas seems to involve embedding classical conservation of energy into the quantum equation a priori. This holds both nonrelativstically or relativistically (Klein-Gordon equation). This immediately raises the question: If classical mechanics (in the form of energy conservation) is embedded in quantum mechanics for any energy, why do people seek to take some kind of limit (3) to obtain classical mechanics from quantum? We argue that quantum mechanics has more spatial information than classical, but retains classical conservation of energy so there is no limit to take. One may simply ignore ideas related to the wavelength to obtain classical mechanics, we argue.
The Schrodinger equation for a single spinless particle is formally obtained via a classical phonon model, namely the Frenkel-Kontorova model. Starting from a one-dimensional lattice of coupled harmonic oscillators, we show that the continuous limit of the corresponding Newtonian equation of motion yields the Klein-Gordon equation for a real-valued field. By introducing a complex-valued change of variables mixing the real-valued displacement and velocity fields, and by separating fast and slow time scales, the Klein-Gordon equation is written as the Schrodinger equation within the non-relativistic limit. This complex change of variable also allows to rewrite classical global observables of the phonon field, such as the total energy or momentum, as the corresponding quantum observables. Additionally, we show that when a friction force is incorporated into the classical model, the corresponding Klein-Gordon equation can be rewritten as a Schrodinger equation with a non-Hermitian Hamiltonian. While the global approach is limited here to the non-relativistic regime and does not address the measurement problem, quantization or relativistic effects, it nonetheless illustrates how quantum algebra and complex-valued wave functions can be exactly reproduced using classical dynamics. The relativistic regime for a spinless particle and the link between commutators and Poisson brackets is addressed in the second part of this series.