Knowing the “what” and the “how” of the universe gives us enough information to begin building the model. We know that the model should capture cause and effect. So we want to model to describe what happens when something happens. Let’s call something happening an “Action”, and what happens an “Effect”. Our model should somehow connect Actions to their Effects, so there will be some sort of equation between them. We also feel like superposition is fundamental, so that means we feel like there is mixing. What are we mixing? It appears that we are mixing Actions and Effects. So we want to make a model that describes the relationship between our actions and their effects in a way that allows actions and effects to be mixed or combined. 

Linear systems of equations (matrices) fit this requirement perfectly. Superposition is a native property of linear systems. We will create a matrix of actions and their effects to define the “what” and “how” of the universe. If we focus on the “what” and “how” of a person, we can localize the model to that person. We will call this the person’s “Action Matrix”.

Superposition is big in quantum mechanics. And actually, it’s bigger than quantum mechanics. It’s the mechanism for creating stuff out of energy. If you mix waves of different energies, you can create a thing that acts like a particle. All of our particles are built this way. Particle-ness emerges from mixing waves in the correct quantum field, of the correct energies, in the correct amounts. Since this energy is quantized, we call them energy “states”. Superposition gives us the rules about how individual states combine to form new states. While causality is the “what”, superposition is the “how”.

So every bit of stuff is built with superposition. And it isn’t just quantum mechanics, all linear systems support superposition. Any system with multiple inputs and outputs where a single input may affect multiple outputs (and/or multiple inputs may affect a single output), follows these rules. Superposition is a fundamental property of all linear systems.

Every model has a foundation. Something everyone can accept as true. The more fundamental the foundation, the more general the model. It doesn’t get much more fundamental than physics, and causality is the most fundamental law physics has to offer. Even the ubiquitous “speed of light” takes the letter (c) from its true name: the speed of causality.  

The universe is basically a bunch of stuff (energy technically) that is constantly changing. In all of this, there has never once been an observation of an effect with no cause or a cause with no effect. Causality is always in effect. We can view the universe as a “causality engine”: a system that generates cause and effect at each instant. All the universe needs to “do” is to calculate the “next” positions and properties of each bit of stuff in the universe based on the “current” positions and properties of each bit of stuff in the universe. Then repeat this for tens of billions of years. Stuff happens. Can’t argue with that.