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Open, Closed and Isolated systems


At a high level, systems are classified as Open or Closed.

Closed Systems (also known as isolated systems in thermodynamics – see further below)

  • No interaction outside of the system
  • No interaction with the systems environment
  • Receive no inputs from, or provide no outputs to, the environment

Closed systems with outputs are knowable only through its outputs.

Closed systems with no outputs are knowable only internally.

In classic mechanics, closed systems are physical systems which do not exchange matter with its environment and is not subject to any external forces.

In thermodynamics:

  • closed systems can exchange energy (heat or work) with its environment
  • isolated systems cannot exchange any heat, work or matter with its environment
  • open systems can exchange energy and matter with its environment

Open Systems

Every living organism is an open system maintaining itself in a continuous inflow and outflow, a building up and breaking down of components. As long as it is alive, it is never in a state of chemical and thermodynamic equilibrium but is maintained in a steady-state.

Open systems interact with their environment taking inputs from and providing outputs to their environment. They are dynamic due to their interaction and they also persist in time.

Expansion of physics in recent years (circa 1968) now includes open systems.

Principe of equifinality in open systems – when the same final state can be achieved with different initial conditions in different ways. In a closed system, the final state is unequivocally determined by the initial conditions.

Entropy (thermodynamics in physical nature) – transition to a state of maximum disorder and levelling down of differences.

Evolution (in living world) – transition towards higher order, heterogeneity and organisation.

In open system theory, contradiction between entropy and evolution disappear. In all irreversible processes entropy must increase.

  • Closed system – change of entropy is always positive – order is continually destroyed.
  • Open system – also has an import of entropy (in addition to that produced by irreversible processes) which can be negative. e.g. living organism imports complex molecules high in free energy thus maintaining a steady state and avoiding increase in entropy, possibly even developing state of increased organisation and order.

Examples from thermodynamics

Closed system: pan with a lid.

Exchanges only energy not matter with its environment.

With the lid on, no matter can be transferred into or out of the pan.

Pan put on stove and heated. Transfer of heat (energy) is allowed and so contents heat up.

Outside of pan becomes hot and transfers heat to anything next to it.

Isolated system: a “perfect” Thermos flask.

Perfect flask does not allow the contents to heat or cool – no energy transfer.

The closed lid also prevents matter transfer.

No known truly isolated systems.


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