Information and Measurement
A Measurement Requires an Interaction that Creates Irreversible Information
In the absence of interactions, an isolated quantum system evolves according to the unitary Schrödinger equation of motion. Nothing ever "happens."
When there is any interaction with another system (e.g., the measurement apparatus), the two systems become entangled and there may be a change of state in either or both systems.
This change of state may create new information.
New Information Must Be Stable to be Observed.
If the new information is instantly destroyed, as in most interactions, it may never be observed.
If, on the other hand, the information is stabilized for some length of time, it may be seen by an observer and considered a "measurement."
To Be Stable, Positive Entropy Must Be Transferred Away from the New Information.
To satisfy the second law of thermodynamics, positive entropy must be transferred away from the negative entropy of the new information structure.