Before starting with the theory concepts, it is recommended to know the paradigms to break before denial.
An interaction is just an action and a reaction. If you have read the paradigms to break before denial before starting, you will understand that all systems react to stimulus. Therefore, after each stimulus over a system –the action–, there is always a reaction. Reactions are non proportional –non-linearity– and delayed. It is difficult to delimit actions and reactions, meaning that it is very difficult to delimit an interaction, but that is the same problem of the delimitation of systems on the Systems Theory. The systems definition problem leads to questions like… Where does a cloud end? Where does a heart begin and end? Does it include the blood? What is a person? The problem of boundarization of interactions is just an extension of such issue. When does the interaction between an atom of H and an atom of O started? Where?
Actions and reactions are transferences of contents. It is essential to understand that contents may codify messages, like sperm contains DNA chains or air vibrations from the voice of a person can codify and transport a narrative phrase. As interaction approach multiple dimensions (see the paradigms to break), a conversation can be understood as an exchange of vibrations or ideas. But always there is a physical content that is transferred from one system to another, like energy is exchanged when two balls bounce.
The interaction definition is this: an interaction is just an exchange of contents between two systems. Newton’s laws are so right that they can be extended not only to all physical systems but also to conceptual systems. For example, E=mc2 represents an interaction, where one entity transfers E to the other and the other returns back mc2. In real nature, a lot of interactions are non-reversible, all cost some energy to the interactors, and most of them can occur only in one direction (cows cannot transform milk into pasture).
Systems interact in compound dimensional spaces. Two balls can bounce, and that may cause a kinetic energy exchange. But if one of the balls is hot and the other is cold, there will be an additional exchange of energy. The balls can have different electric charges. And so on. But the amount of photons that are exchanged can probably be very low.
The classic Systems Theory studies all the interactions of a set of systems in a limited dimensional set. The TOI promotes the study of one interaction between two systems in all its dimensional sets. Economists can describe an economical crisis where the product demand decreases. But the TOI approach focuses on one system and all its dimensions. Why does one person rejects buying a product? Of course, this approach is just a formalization of something that is normally done as part of the analysis. But the TOI may help understanding that people have reduced interactions with sellers due to these have become aggressively greedy with clients. This isolated behavior may not mean a lot. But formally mixing psychological, economical, social, relational dimensions on one interaction may contribute enormously to understand a crisis.
Interaction produce order. Two systems that interact in some dimension acquire order in some dimensional set and therefore form a molecule in that dimensional set. Constructive interaction -interaction that produces benefits on both systems- cause attraction. Attraction ends in a persistent disposition of the interactors in that dimension. For example, to talk with someone without walking, normally you direct your face to that person. That is the order that conversation creates.
Chaos is the lack of interaction. Following the previous example, when you end a conversation, both faces will point towards different directions. That is chaos, the lack of order in some dimensional set.
Order and chaos always coexist. You may be talking to someone, so directional order on the faces may raise, but one can point your eyes in other direction, that is a normal disposition to happen when someone wants to end the conversation. Another example: after start, a set of billiard balls over a table continue ordered on the z dimension (they share the same altitude from the earth). But they will probably be in a chaotic disposition regarding the X and Y axis. Then, there is order on the Z dimension (provided by the balls interaction with the earth) and chaos on the X and Y dimensions (lack of interactions when nobody hits the balls). Another dimension of order example: they share the same temperature (normal: they are exchanging heat energy with the air). Another example of chaos: They have different colors.