The last two theories are recent developments and in line with our Causal Category Theory of Everything capable to generalize and complete new candidates for a unified physical theory, as causal sets program and the theory of causal fermion systems, considering general relativity and quantum field theory as limiting cases. In the causal sets program, the founding principles are that space-time is fundamentally discrete and that space-time events are related by a partial order, having the physical meaning of the causality relations between space-time events.

Ultimately, the ToE would unify all the fundamental interactions of nature, gravity, strong interaction, weak interaction, and electromagnetism, as well as shedding light on a postulated inflationary force, dark energy and dark matter.

As such, it is makes the Theory of All Forces in the Universe, ordered by the subordination and inclusion relationships (Abdoullaev A., Reality, Universal Ontology and Knowledge Systems: Toward the Intelligent World, IGI Global, USA, 2008):

Prime Force (ToE)::

Quantum Gravity (Space Curvature, Standard Model of Cosmology; Electronuclear Force (GUT, Standard Model of Particle Physics)::

Strong Interaction (SU (3); Electroweak Interaction (SU(2) x U(1))::

Weak Interaction, Electromagnetism U(1_>em)::

Magnetism and Electricity::

Non-Fundamental Forces (contact forces, elasticity, viscosity, friction, and pressure, etc.).

The non-fundamental forces are classified as

normal force,

friction,

tension,

elastic forces,

continuum mechanics forces of pressure,

drag and stress,

fictitious forces coming from non-inertial reference frames, as the centrifugal force and the Coriolis force,

general relativity gravity.

The pressure gradients and differentials is said to cause the buoyant force for fluids in gravitational fields, the aerodynamic forces of lifting in flight, winds in atmospheric science, like trade winds and anti-trade winds in the tropics.

Besides, forces are also classified as conservative or not conservative, where conservative forces are equivalent to the gradient of a potential energy field while not conservative forces are not. The former includes gravity, the electromagnetic force, and the spring force, while the latter friction, contact forces, tension, compression, and drag.

By their very nature, natural forces are natural causes and effects, all of the same kind of natural entities: events, actions, processes, or changes of states of some physical system, like the motive force is a rate of change of momentum. They are the mutual and reciprocal actions of one physical system or body to another to produce effects, or interactive relationships, the force-interrelationship.

Forces are not only what causing efficient changes of physical properties, but also what opposing any agency and efficiency. Both the active processes producing changes and the reactive processes opposing changes, as the inertial force and motive force, change of momentum-motion, acting power and operating energy, force-fields. And the actions of forces are always in both directions, progressive and retrogressive, direct and inverse, inductive and resistive, attractive and repulsive, forward and backward, while defining the symmetry operations and conserving critical physical quantities as mass, momentum and energy, parity and baryon number.

So forces are not only active agencies, but also passive agencies. Inertial forces, opposing any agency and efficiency, are the universal and inherent power of physical entities and systems to resist physical changes, mechanical, thermal, magnetic, or electric. Such resistive forces are opposing changes in the initial state of equilibrium, in motion, in electrical current, in magnetic fields, in electrical fields, in electromagnetic fields, etc. There are then mechanical inertia measured by mass, electrical inertia measured by conductivity and resistance, magnetic inertia by inductance and magnetic resistance, electromagnetic inertia by induction and permeability, etc.