The laws of physics are invariable and universal relations among physical quantities occurring in Nature. One the characteristics of the laws of physics is that they are not isolated or unrelated, but they show coherence and compatibility. The coherence in the laws of physics is compatible with laws coming from a unitary substance. In a monist universe, the laws of physics are laws in the behaviour of a unitary space (and they are universal and invariable because space itself is a unitary and inalterable substance).

One of the ways this coherence is manifested, is on how all the diversity and multiplicity of laws can be reduced to three main principles: conservation laws, minimal variation and maximal dynamic stability.

. Conservation laws, like conservation mass, energy, momentum, charge, etc., are related to the invariability of physical quantities in closed systems.

. Principles of minimal variation are related to the laws of motion. The most important example is the action principle. The action principle is one of the most fundamental principles in physics. Most of the laws of physics, from classical mechanics, optics, wave mechanics, electrodynamics, gravitation to particle physics can be derived from it.

The action principle states that a system evolving from an initial to a final point, does so through paths that minimises the action (where the action is normally a function of position and velocity).

The origin of the action principle can probably be traced to Maupertuis’ principle of least action. Maupertui stated that the quantity of action (a function of mass, velocity and distance) necessary for motion is the least possible. Another early form of the action principle, came in Fermat’s principle of least time, stating that a ray of light travels from one point to another in such a way as to make the time taken a minimum. Eventually it was taken into the mathematical form dòds/v=0 (where the variational condition was represented as an extremum rather than a minimum). For practical solutions on classical physics, the most convenient representation comes in the form of Hamilton’s principle, which states that the path a particle takes from point to point is that one which extremises the action s=òL.dt=extremum ; where the action s is given in terms of the Lagrangian (L). The motion of a particle then, is determined by its Lagrangian; which is a function of its position and velocity. Lagrange defined this functions as generalisation of the laws of mechanics, with the property of being invariant under transformations from one coordinate system to another.

On its most general form, the action principle is given by a four dimensional integral over a Lagrangian density; which is a function of fields and their derivatives.

. Principles of maximal dynamic stability, like the second law of thermodynamics or Pauli exclusion principle, are related to the laws describing the evolution of systems. In Nature, systems tends to evolve towards states of maximal dynamic stability.

These principles are, in a way, telling us how physical space behaves. Given that they describe the behaviour of a single entity, we would expect them not to be independent, but mutually related. And this is exactly what we find:

. One manifestation of this mutual dependence is found for example, in the first laws of thermodynamics (DE = Q – W , where the energy of a system increases if energy is added as heat, and decreases if energy is lost as work done by the system), which combines the conservation of energy with the evolution of the system towards dynamic stability.

. Another -and more explicit- manifestation is found in Noether‘s theorem. Noether’s theorem is one of the most important theorems in physics; showing the relation between the conservation of physical quantities and the action principle. It states that any symmetry transformation that leaves the action of a system invariant, is related to the conservation of a physical quantity (where the physical quantity is also related to the generators of the transformation). So for example, the conservation of momentum is related with invariance under space translations, conservation of energy is related with invariance under time translations, conservation of angular momentum is related with invariance under rotations, etc. In brief, Noether’s theorem shows how in Nature, the laws governing the motion of systems are linked to the conservation of their physical quantities.

The physical world then, seems to be governed by a set of universal and invariable laws. But the laws of physics remains principles; and a principle, by definition, is something that is valid without explanation of why it is so. And here with science, we find a clear example of the difference between knowledge and understanding. We have a great deal of practical knowledge about the physical world: we know its laws, we can sometimes achieve extraordinary degrees of accuracy on our predictions, and we rule and dominate the physical world with technology with sometimes extraordinary degrees of precision and efficiency. Yet, despite all this knowledge, we have little understanding about the physical world. We might know the laws that governs it, but we have no idea of why the physical world behaves as it does.

Practical knowledge (e.g. science) is a study of particulars with a useful purpose (e.g. measurement, prediction, technological applications, etc.). Understanding on the other hand, involves contemplating particulars as part of a universal. In the present, our particulars are the laws of physics and the universal the world’s metaphysics. So far, the laws of physics remain principles without any explanation of why they are so. To understand were the laws of physics comes from, we would have to understand the world’s metaphysics. In the present we are proposing a metaphysics of a monist universe. And physical monism, not only explains why these laws of physics are universal and invariable, but it also allow us to interpret them from the properties of space. Metaphysics then, might not be necessarily practical, but it allows us to form a better idea of why the world behaves as it does.

To begin with, in a monist universe the principles of interest are not three, as in physics, but two: conservation laws and dynamic stability. Minimal variation can be left aside, since minimal variation is related with the motion things in a classical sense, and in a monist universe the classical concept of motion looses its meaning. In a monist universe, the concept of space as a container of object where object move from one place to another, ceases to be valid. Space and objects are one and the same thing. And motion, is not a translation of objects from one place to another, but it’s a displacement of asymmetries in the continuity of Space. The motion of particles then, is a particular case of the dynamics of Space. That is, principles of minimal variation (like action principle) can be reduced to principles of maximal dynamic stability.

In a monist universe, we can interpret conservation laws as a manifestation of the invariability of space. In a unitary space physical quantities cannot be created nor destroyed. They might change indeed form one state to another. But if they do, their change is not arbitrarily but subject to the invariability of space. So the conservation of physical quantities are related to space‘s unitary and invariable qualities as a substance.

Dynamic stability can be interpreted as the dynamics of space itself. Physical space has a geometric, asymmetric and dynamic nature. So we can think of principles of dynamic stability, as the tendency of space to close upon itself towards the states with the lowest geometric differences and variation; that is, towards states with the lowest asymmetry, tension and energy. As a result, systems in Nature tends to evolve towards the states of minimal variation and maximal dynamic stability.

In the classical conception of things, the motion of particles is related to principles of minimal variation (in particular to the action principle). From a monist point of view, minimal variation is related to the dynamics of space. So in a monist universe, the motion of particles is a consequence of the dynamics of space.

An important concept that the action principle introduces, is the notion that the path of a particle is related to the function that characterises it (i.e. Lagrangian). That is, it is impossible to dissociate the particle from space. With the introduction of fields, this concept is taken even further: particles cease to be finite elements in space; instead, we have to think of them in terms of fields in space. But in any case, classical physics still fells short of contemplating the unicity or non duality of particle-space.

In a monist universe, where particles are constituted by a unitary space, the action principle can be contemplated in the following way: the paths that extremises the action of a system can be thought as the paths of maximal dynamic stability. That is, among all the possible paths that the particle can follow, the particle will follow the ones where the asymmetries in space are minimal, and where there is minimal variation of tension and energy. In other words, the motion of particles is confined to path related with states of maximal dynamic stability.

And this would still remain valid in Quantum Mechanics, where there is uncertainty on the path that a particle follows, and where the probability of its path is calculated through a path integral, given by an integral on all its possible paths and weighted by their respective action.

While science is the study of the invariable and universal laws of Nature governing the physical world, physical monism is a theory on the metaphysics of the universe (which can explain why there is only one Nature and its laws are universal and invariable). The current scientific point of view of the universe is not a monist one. And one of the main difference between science and monism, is that while in science Nature seems to be external to elements, in physical monism Nature is immanent to them. For example, in physics, physical elements are normally modelled as passive objects whose behaviour is governed by laws external to them. In a monist universe, physical elements have a dynamic nature since they are constituted by a dynamic space. Their behaviour then, is not governed an external order, but it is immanent to them and given by the behaviour of space itself.