Our universe and our understanding

The universe is a collection of entities. 
An entity is organised matter. 
Matter is made up of compounds and molecules. 
Molecules consist of atoms. 
Atoms are composed of elementary and composite particles. 
We do not know what particles are made of.

This is easy enough to understand. The biggest thing is the universe, the smallest things are elementary particles: “an elementary particle or fundamental particle is a particle whose substructure is unknown; thus, it is unknown whether it is composed of other particles.” In between are various things of differing sizes.

That’s reality, the external world. But what about the abstract world, the inner, idea-world of an individual person? What is the biggest thing? What is the smallest thing? And what’s in between? Here’s what I came up with:

Our understanding is the sum of our implicit and explicit knowledge.
Our knowledge is composed of narratives and models.
Our narratives and models are constructed out of concepts.
Our concepts are based on perception and imagination.
Our perception and imagination is shaped by our interpretation of reality.
Our interpretation of reality is determined by our understanding.