Information
Flip a light switch.
The room is dark. Then it is bright. Two distinct configurations, separated by a simple action. Nothing material about the switch changes in any interesting way. The plastic remains plastic. The metal remains metal. And yet the situation of the system has clearly changed.
Something different is now the case.
The switch defines a set of possibilities. The room can be lit or unlit. These are not physical substances. They are states the system can occupy.
What matters here is what the system can become.
The same idea appears in more complex systems.
A thermostat can be set to different temperatures. A traffic light cycles through a fixed sequence of colours. A chess board admits certain legal positions and forbids others. A genetic code allows some protein structures and excludes countless alternatives. A computer program moves through a vast space of internal configurations as it runs.
In each case, the system is best described by the set of states it can occupy and the transitions between them.
Description shifts from substance to possibility.
A system becomes a landscape of configurations. Movement becomes a path through that landscape. Change becomes a transition from one state to another.
At this level, information reveals its real meaning.
Information is the structure of the space of possibilities available to a system. To specify information is to specify which states are accessible and how transitions between them are constrained.
Laws now appear in a new form.
They define what can happen. They shape the geometry of possibility. They carve out the paths that are available to the system as it evolves.
A system with no constraints would have no information. Everything would be possible, and nothing would be distinguishable.
Information links what exists with what can occur.
It becomes the link between structure and change. It connects what exists with what can occur. It encodes the rules that govern how reality unfolds through time.
Once matter is understood as stable pattern within interaction, and time as irreversible process, information appears as the space of potential transformations that those patterns can undergo.
The universe begins to resemble a vast network of states connected by allowed transitions. Every physical system traces a path through this network, moving from one configuration to another under the constraints imposed by its structure.
Reality is a structured space of possibilities, continuously explored by irreversible processes.
To describe the world, then, is to describe its possible states and the transitions between them.
And once reality is seen in this way, another concept becomes unavoidable.
Not what can happen. But how likely each possibility is.