The medium in which light propagates is space. This space can curve. The curvature is not static. So, this space moves. Its behavior can be analyzed by a kind of fluid dynamics. Let us call this method quantum fluid dynamics. It differs from conventional fluid dynamics in the medium that is treated. In conventional fluid dynamics this is a gas or a fluid. Fluid dynamics concerns density distributions and currents. In quantum fluid dynamics these are space density distributions and space current density distributions. They can be combined in quaternionic distributions, where the real part is the space density distribution and the imaginary part is the space current density distribution.
Quantum state functions are probability amplitude distributions. They can be specified as complex functions or as quaternionic functions. In the last case they fit the purpose of quantum fluid dynamics. With other words quantum state functions describe the flow of space. Light is nothing else than oscillating space. It is constituted from the same stuff as the quantum state function. Thus light is an oscillation probability amplitude distribution. Quantum state functions characterize the state of tiny particles.
In the quaternionic format of the Dirac equation the quantum state function ψ acts as a drain. This drain is coupled to a source. The source is a second probability amplitude distribution φ. The coupling factor m takes the role of mass characteristic.
In quaternionic format the Dirac equation is a quaternionic continuity equation. (See Wiki)
The drain compresses the local space. As a consequence in the neighborhood of the coupling the space gets curved. The Dirac equation describes what happens for the electron. Every elementary particle type has its own coupling equation. Free probability amplitude distributions must oscillate. They are photons or gluons.
The coupling is characterized by four properties: coupling factor, electric charge, spin and color charge. Color charge relates to the direction of anisotropy. Apart from color these properties act as sources of fields. These are known as physical fields. Their charges are located at the position of the particle and they are preserved. These rather static fields have a fundamentally different nature than the primary probability amplitude distributions.
In quantum fluid dynamics the quaternionic probability amplitude distributions act on their own parameter space. The shared parameter space of all quaternionic probability amplitude distributions comprises the whole universe. It is the arena where everything occurs.