202110231515 Feedback loop

A feedback loop is a system which takes some input, produces some output and that output is then fed back into the system as the next input.

graph LR
  input --> controller
  controller --> process
  process --> output
  output --> |deviation|controller

In 202203210833 Systems thinking, this is defined as a process where a a change in a stock (202205021252 Stock and flow) affects the flows into or out of that same stock. More precisely,

A feedback loop is a closed chain of causal connections from a stock, through a set of decisions or rules or physical laws or actions that are dependent on the level of the stock and back again through a flow to change the stock.¹

Feedback loops can be stabilizing (or balancing) if they act to drive the stock back to a goal value, or destabilizing (or reinforcing/runaway/amplifying/self-multiplying/snowballing/spiraling) if they continue to drive a stock further in the same direction the more/less if it there is.

Note that doubling time is roughly $70 \div rate$ e.g. If you earn 7% interest it will take roughly 10 years to double the initial amount (i.e. $70 \div 7 = 10$).

Ask yourself,

If $A$ causes $B$, is it also possible that $B$ causes $A$?

In real systems, there are often many feedback loops of varying strength at play. The real world is complicated and 202401291554 All systems thinking is a simplification.