For centuries, science developed its methods for deriving abstract concepts by reducing the features of a real object to an abstract (idealized) one that cannot be reduced further, such as mass or charge. Ions are an exception when using the concepts of classical disciplinary physics: the ions are charge and mass simultaneously, without a further possibility of reduction. The consequences of this item are listed in Table 1 of paper [8] as the ”Electrical vs Mechanical” dichotomy. Science has derived laws for the forces acting on those abstract objects, such as Newton’s universal law of gravitation and Coulomb’s law of electricity. Then one could apply Newton’s laws of motion. Experience shows that the generated forces, regardless of their origin, can be summed, and one can apply the laws of motion using the resultant force (see below for a discussion of the resultant force and its application in biology). However, notice that those experiences are based on the Newtonian ’instant interaction’, i.e., that the interactions’ speeds are equal.
Paper [8], which, in the context of this section, tends to be the precursor of our paper, sheds light on some remarkable dichotomies, scrutinizing which can result in ”a sound basis for unification of the physics of nerve impulses”. By deeply agreeing with that they have a ”potential impact on our understanding of (the physical nature of) neuronal signaling”, we list and uncover more dichotomies; furthermore, we uncover their fundamental, partly philosophical reasons.
In the electrical abstraction, no mass is present, so one can use the equations assuming ’instant interaction’ (aka infinitely large interaction speed), which leads to non-physical explanations of the observations (such as ’delayed current’). In the mechanical abstraction, mass is to be moved, making the finite-speed interaction evident. The same physical phenomenon, the interaction (or movement) of ions is described using an ’infinite’ electrical speed and a million times less mass propagation speed, respectively and simultaneously, which leads to an unresolvable discrepancy, given that physics is not prepared to handle different speeds in the same interaction event [22]. This item is listed in Table 1 in [8] as the ”Electrical vs Mechanical” dichotomy.
To deliver a current, one needs moving charged particles that need exerting of some external (electric, magnetic, or chemical) force or a mixture of forces. We have speeds of EM interaction, thermal motion of the charge carriers, macroscopic current, drift speed, and their mixing, simultaneously, in the same phenomenon. In the theoretical description of processes, instant interaction (i.e., the abstraction of non-physical, infinitely large interaction speed) is used in most cases, which is a good approximation only if the charge carriers are electrons. In the cases when absolutely needed, the generic notion of ”speed” is used without specifying which one of the mentioned speeds it means.
The low speed of ions in electrolytes introduces further problems. Any change in the local value of the state variables will be seen by the farther parts of the cell with a delay, The material transport represents simultaneously mass and charge, so the transport itself changes the gradient. This process keeps the entire volume of the electrolyte in (more or less intensive) continuous change. Furthermore, the biological objects inside the cell can absorb ions and charge up. With their potentials, they change the local gradients, accelerating or decelerating the ions. Not to mention that biological objects can be active in the sense that (depending on the environmental conditions) they can let ions from one separated volume part into the other. The same physical phenomenon, the interaction (or movement) of ions is described using an ’infinite’ electrical speed and a million times less mass propagation speed, respectively, which leads to an unresolvable discrepancy, given that physics is not prepared to handle different speeds in the same interaction event [22].
Although science is aware that the apparently continuous matter in nature cannot be divided infinitely, even though it knows that the abstracted discrete ’material points’ (as A. Einstein coined) have well-defined discrete values, it occurs rarely that both views must be applied in describing a single phenomenon. The continuous and discrete approaches (also called macroscopic and microscopic views) seem to be independent of each other. Connecting those views was one of the tasks performed by thermodynamics for particles with no long-range interactions. However, there is no similar discipline for electricity, although the behavior of charge carriers is similar to that of neutral discrete particles. It is not evident for electrons, but it is significant for ions. This item is listed in Table 1 of paper [8] as the ”Macroscopic vs Microscopic” dichotomy.
The third dichotomy is ”Reversible vs Irreversible”. A reversible process can proceed in either direction in time. Cellular operation seems to be cyclic (i.e., mostly reversible) in the short run, while in the long run, spanning from birth to death, it is irreversible. Experience suggests that a mixture of reversible and irreversible processes describes neuronal operation. As reviewed in [8], in contrast with the electricity-centered disciplinary conception HH model [9], all other disciplinary models discussing phenomena suggest reversible operation.
Reversibility seems to be closely related to the dichotomy ”Electrical vs Mechanical” and to the nature of the exclusively used electrical HH theory. In the framework of that theory, Ohmic currents flow through resistors that irreversibly dissipate heat due to friction, no matter in which direction () the ion currents flow. By introducing the concept of ’delayed current’ and the hypothesis that some hidden power controls the operation of neurons by altering their conductance, physiology gave rise to the fallacy that science and life sciences are almost exclusive fields. Furthermore, their (unintended) model provokes questions (for a review see [68]) whether it is a model at all, and what controversies it delivers. As Hodgkin wrote [87]: ”Hill and his colleagues found [65] that an initial phase [of the action potential] was followed by one of heat absorption. […] a net cooling on open-circuit was totally unexpected and has so far received no satisfactory explanation.” Since that discovery, experimental evidence from the missing ”leakage current” [78] to the conversion between elastic and kinetic energies [95] to demonstrating the pressure-wave-like behavior of AP witnesses that at least part of the phenomenon is of thermodynamic origin; that is, it requires a cross-disciplinary explanation. For discovering the reciprocal relations in thermodynamics [96], also in electrolytes, Lars Onsager was awarded the 1968 Nobel Prize in Chemistry. Those relations, together with the theoretical understanding, manifesting in the cross-disciplinary Nernst-Planck relation, paved the way to a combined theory. However, no thermodynamic explanation has been given so far. Our discussion provides, in line with the experimental results, a complex unified electrical/thermodynamic description of neuronal operation.