---
slug: convergence-c07
title: FEEDBACK / CYBERNETICS / HOMEOSTASIS
canonical: https://miscsubjects.com/a/convergence-c07
---

## The Claim

The universe corrects itself.

Not because it wants to.
Because error feeds back into the system that made it.
Feedback is the engine of every stable thing you see.
[SOURCE:wiener-1948|type:theoretical]

## Definitions

**Feedback** — Output returns to input.
The system listens to itself.
[SOURCE:wiener-1948|type:theoretical]

**Negative feedback** — Error reduces itself.
The thermostat turns off when the room gets warm.
The body sweats when it overheats.
This is not rest.
This is war against drift.
[SOURCE:ashby-1956|type:empirical]

**Positive feedback** — Error amplifies itself.
Microphones screech.
Forests burn.
Tumors grow.
Ponzi schemes explode.
Nuclear chain reactions detonate.
Runaway systems carry the seeds of their own end.
[SOURCE:ashby-1956|type:theoretical]

**Cybernetics** — The study of control through information loops.
Wiener named it in 1948.
He gave the loop a name and a mathematics.
[SOURCE:wiener-1948|type:theoretical]

**Homeostasis** — Active maintenance of internal balance.
Cannon named it in 1926.
It is not rest.
It is continuous war against entropy.
[SOURCE:ashby-1956|type:empirical]

**Requisite variety** — A controller must match the complexity of what it controls.
Ashby proved this in 1956.
Too simple a controller fails.
Too complex wastes energy.
[SOURCE:ashby-1956|type:mathematical]

**Circular causality** — A causes B causes A.
Linear causality is a myth.
All living control is a loop.
[SOURCE:maturana-1980|type:theoretical]

**Organizational closure** — A system produces the components that produce it.
The cell makes the membrane that makes the cell.
This is feedback taken to its limit.
[SOURCE:maturana-1980|type:theoretical]

**Sensor** — The part that measures.
Without measurement, there is no control.

**Comparator** — The part that judges.
It asks: is this right or wrong?

**Actuator** — The part that acts.
It fixes what the sensor found.

**Set point** — The target the system defends.
Your body temperature is 37 degrees.
That is not an average.
That is a command.

**Gain** — How hard the loop pushes.
Too little gain: the system drifts.
Too much gain: the system oscillates.
Goldilocks gain: the system holds.

**Ultrastability** — A system that can change its own parameters.
When the environment shifts, the old rules fail.
Ultrastability finds new rules.
This is adaptation itself.
[SOURCE:ashby-1956|type:theoretical]

## The Logic

Look at your body.
You eat sugar.
Your pancreas senses the spike.
It releases insulin.
Glucose drops.
The pancreas stops.
Every step is a loop.
No loop means diabetes.
No loop means death.
[SOURCE:ashby-1956|type:empirical]

This is not rest.
This is war.
Your body fights entropy every second.
You do not feel the battle.
You feel the victory.

Claude Bernard saw it first in 1878.
He called it the milieu intérieur.
The body maintains its own sea inside.
Blood pressure holds.
Temperature holds.
pH holds.
Not because the world is kind.
Because feedback loops fight without pause.

Walter Cannon named it homeostasis in 1926.
He watched dogs bleed.
He watched their blood pressure drop.
He watched their hearts race.
He watched their vessels constrict.
The body pulled itself back from the edge.
Cannon called it the wisdom of the body.
He was right.
[SOURCE:ashby-1956|type:empirical]

James Clerk Maxwell studied governors in 1868.
He watched steam engines spin.
He saw the flyball governor.
Speed rises.
Balls fly outward.
They throttle steam.
Speed drops.
Balls fall.
Steam opens.
The engine holds steady.
The loop is mechanical.
The principle is universal.
Every autopilot traces back to Maxwell.
Every thermostat.
Every cruise control.

Norbert Wiener saw it everywhere.
He saw it in nerves.
He saw it in machines.
He saw it in society.
He wrote Cybernetics in 1948.
He gave the loop mathematics.
He showed that control is information.
Information is measurement.
Measurement is life.
[SOURCE:wiener-1948|type:theoretical]

W. Ross Ashby built the Homeostat in 1948.
Four needles.
Four electrical circuits.
He disturbed them.
They corrected themselves.
They found stability.
The machine learned to balance.
It was not conscious.
It was controlled.
[SOURCE:ashby-1956|type:empirical]

Ashby went further.
He proved the law of requisite variety.
Only variety can destroy variety.
A thermostat with one setting cannot regulate a house with ten rooms.
A government with one policy cannot regulate a nation of millions.
The controller must match the complexity of the controlled.
This is not advice.
This is a theorem.
[SOURCE:ashby-1956|type:mathematical]

William Powers pushed feedback into psychology.
He said behavior is the control of perception.
You do not act because you sense.
You act to make your senses match your goal.
A man walks to the door.
He is not moving his legs.
He is controlling his distance to the door.
The legs are the actuator.
The eyes are the sensor.
The brain is the comparator.
This inverts psychology.
The stimulus-response chain is false.
The loop is true.

Now look at Rome.
Rome grew on conquest.
Conquest brought slaves.
Slaves fed the empire.
The empire needed more conquest.
This was positive feedback.
Growth fed growth.
But conquest has limits.
Borders stretch.
Armies thin.
Cost rises.
The loop reversed.
The empire starved.

Injustice destroys itself.
Not because anyone stops it.
Because it runs out of fuel.

The American South built an economy on slavery.
Cotton flowed.
Wealth piled.
But the system calcified.
It stopped innovating.
It stopped adapting.
The North out-produced it.
The South clung to the loop that had made it rich.
The loop killed it.

Ponzi schemes work the same way.
New money pays old money.
The loop spins.
But the pool of new money shrinks.
The comparator never fires.
There is no sensor.
There is no brake.
The scheme collapses.

A forest fire starts small.
It feeds on dry fuel.
The fire grows.
It consumes more.
This is positive feedback.
But the fire burns its own fuel.
Eventually it hits a river.
It hits rain.
It hits bare rock.
The loop ends.

A tumor grows.
It hijacks blood supply.
It grows faster.
But it outruns its own nutrients.
It necroses at the center.
The loop chokes on itself.

Every runaway system carries the seeds of its own end.
The absence of feedback is not freedom.
It is doom.

Look at the immune system.
It senses invaders.
It mounts a response.
It kills the pathogen.
Then it stops.
This stopping is feedback.
Autoimmune disease is feedback failure.
The loop does not quit.
It attacks the body it was built to defend.
[SOURCE:darwin-1859|type:empirical]

Blood clotting is a feedback cascade.
A vessel tears.
Platelets aggregate.
Clotting factors activate.
The clot forms.
The bleeding stops.
But the clot must not grow forever.
Tissue plasminogen inhibitor dissolves it.
Two loops: one builds, one destroys.
Both are necessary.
Hemophilia is the first loop broken.
Thrombosis is the second loop broken.
[SOURCE:ashby-1956|type:empirical]

The kidney regulates water.
Blood volume drops.
Osmolarity rises.
ADH releases.
Water reabsorbs.
Blood volume restores.
You do not feel this.
It happens three hundred times a day.
Diabetes insipidus breaks the sensor.
The loop cannot close.
The patient dies of thirst in a sea of water.

Gene expression is feedback.
A gene produces a protein.
The protein inhibits the gene.
The level holds steady.
This is the lac operon.
This is the repressor and the promoter.
Every cell in your body runs on these loops.
Jacob and Monod won the Nobel for showing it in 1965.
[SOURCE:darwin-1859|type:empirical]

Predators eat prey.
Prey numbers drop.
Predators starve.
Predator numbers drop.
Prey recover.
The loop oscillates.
It does not settle.
It persists.
This is ecological feedback.
It is not peace.
It is dynamic balance.
[SOURCE:darwin-1859|type:empirical]

Markets correct.
Prices rise.
Demand drops.
Prices fall.
Supply shrinks.
Prices rise.
The loop is crude.
It is slow.
It is brutal.
But it is a loop.
Without it, there is no price.
There is no signal.
There is no coordination.
[SOURCE:ostrom-1990|type:empirical]

Elinor Ostrom proved that commons survive when feedback is structured.
Clear boundaries.
Monitored rules.
Graduated sanctions.
Without these loops, the tragedy of the commons wins.
With them, cooperation sustains.
[SOURCE:ostrom-1990|type:empirical]

Climate change is feedback running both ways.
CO2 rises.
Temperature rises.
Ice melts.
Dark water absorbs more heat.
Temperature rises faster.
This is positive feedback.
But clouds may reflect more light.
Vegetation may absorb more carbon.
These are negative feedbacks.
We do not know which wins.
The loop is too big.
The sensor is too slow.

The brain itself is a feedback machine.
Neurons fire.
Inhibitory circuits dampen them.
Excitatory circuits amplify them.
The brain hovers at the edge of seizure.
Too much excitation: epilepsy.
Too much inhibition: coma.
Consciousness lives in the loop.
[SOURCE:kauffman-1993|type:theoretical]

Stuart Kauffman argued life began at the edge of chaos.
Too ordered: dead crystal.
Too chaotic: noise.
Life lives in the seam.
Feedback holds it there.
[SOURCE:kauffman-1993|type:theoretical]

Per Bak showed that sandpiles self-organize to criticality.
Grain by grain, the pile builds.
Avalanches of all sizes occur.
The system tunes itself.
No external hand sets the parameter.
Feedback is the tuner.
[SOURCE:bak-1987|type:empirical]

Maturana and Varela took feedback into biology.
They called it autopoiesis.
A cell produces the membrane that produces the cell.
The loop is not a mechanism bolted onto life.
The loop is what life is.
[SOURCE:maturana-1980|type:theoretical]

Shannon showed that information is the reduction of uncertainty.
Wiener showed that control is the movement of information.
Landauer showed that erasing information costs energy.
The three are one loop.
Information flows.
Control acts.
Entropy pays the bill.
[SOURCE:shannon-1948|type:mathematical]
[SOURCE:landauer-1961|type:theoretical]

Gödel proved that a system rich enough to describe itself cannot be both complete and consistent.
Turing proved that a machine rich enough to compute anything cannot predict whether it will halt.
Von Neumann proved that a machine can contain its own blueprint.
These are feedback theorems.
Self-reference is the strangest loop of all.
[SOURCE:godel-1931|type:mathematical]
[SOURCE:turing-1936|type:mathematical]
[SOURCE:von-neumann-1966|type:theoretical]

Heraclitus saw it in fire.
Fire lives by consuming itself.
It is never the same fire.
It is always fire.
This is the oldest feedback intuition.
The road up and the road down are one.
[SOURCE:heraclitus-500|type:philosophical]

Spinoza saw it in God or Nature.
Nature is not commanded from outside.
It commands itself.
Each mode is cause and effect of every other mode.
The loop is total.
[SOURCE:spinoza-1677|type:philosophical]

Lao Tzu saw it in wu wei.
Do not force.
Align with the grain.
The sage does nothing.
And nothing is left undone.
This is feedback as ethics.
[SOURCE:lao-tzu-c6th-bce|type:philosophical]

Whitehead saw it in process.
Reality is not being.
Reality is becoming.
Each event prehends the past.
The past feeds back into the present.
The loop is temporal.
[SOURCE:whitehead-1929|type:philosophical]

## The Mathematics

A feedback loop is three functions in a circle.

Sensor: measures the output.
Comparator: subtracts the measurement from the target.
Actuator: drives the difference toward zero.

In the language of control theory:

G(s) = forward path transfer function
H(s) = feedback path transfer function
Closed-loop gain = G / (1 + GH)

If GH is positive and large, the system amplifies.
This is positive feedback.
If GH is negative, the system damps.
This is negative feedback.
The sign determines the fate.

Nyquist proved the stability criterion in 1932.
Plot GH in the complex plane.
If the curve encircles the point (-1, 0), the system is unstable.
This is not metaphor.
This is a theorem.
Every airplane, every amplifier, every market obeys it.

The time constant matters.
A loop that responds too fast oscillates.
A loop that responds too slow drifts.
The engineer tunes the gain and the lag.
Nature tunes them through selection.
Both solve the same equation.

Ashby formalized ultrastability.
A system that cannot correct its parameters will die when the environment changes.
A system that can change its own gain survives.
The Homeostat did this.
It changed its own wiring to find stability.
This is feedback on feedback.
[SOURCE:ashby-1956|type:mathematical]

## The Evidence

James Clerk Maxwell published "On Governors" in 1868.
He proved that feedback systems can stabilize or destabilize.
He gave engineers the mathematics of control.
Every autopilot, every thermostat, every cruise control traces back to Maxwell.

Claude Bernard published *Leçons sur les phénomènes de la vie* in 1878.
He established the concept of the milieu intérieur.
The internal environment must remain constant despite external change.
This was the seed of all homeostasis theory.

Walter Cannon published his homeostasis paper in 1926.
He expanded it in *The Wisdom of the Body* in 1932.
He showed that living systems maintain temperature, glucose, pH, and blood pressure through active feedback.
He worked at Harvard.
He worked with dogs and cats.
He measured blood pressure.
He measured shock.
He proved that life is not passive.
Life is control.
[SOURCE:ashby-1956|type:empirical]

Norbert Wiener published *Cybernetics* in 1948.
He worked at MIT.
He was a mathematician.
He was a philosopher.
He saw that messages and machines obey the same laws.
He gave the field its name.
The word cybernetics comes from the Greek for steersman.
Wiener showed that a steersman, a thermostat, and a neuron are the same thing.
They all measure.
They all compare.
They all act.
[SOURCE:wiener-1948|type:theoretical]

W. Ross Ashby published *An Introduction to Cybernetics* in 1956.
He built the Homeostat.
He ran it at the Burden Neurological Institute in Bristol.
He showed that a machine could adapt to disturbance.
He showed that stability is a property of the system, not the parts.
His *Design for a Brain* appeared in 1960.
He was a psychiatrist.
He was looking for the mechanism of mind.
He found the mechanism of control.
[SOURCE:ashby-1956|type:empirical]

William Powers published *Behavior: The Control of Perception* in 1973.
He inverted the stimulus-response model.
He showed that organisms control their perceptions, not their outputs.
The implication is vast.
Psychology must be rebuilt around the feedback loop.

Humberto Maturana and Francisco Varela published *Autopoiesis and Cognition* in 1972.
They showed that living systems are organizationally closed.
The cell makes itself.
The loop is not a feature.
The loop is the identity.
[SOURCE:maturana-1980|type:theoretical]

The 2008 financial crisis was a feedback failure.
Banks lent.
Borrowers borrowed.
Risk models said the system was safe.
But the models did not sense the real risk.
They fed on past data.
They amplified confidence.
The loop ran positive.
Then it crashed.
The sensor was broken.
The comparator was blind.
The actuator was a money printer.

The Gaia hypothesis extends feedback to the planet.
James Lovelock proposed it in the 1970s.
He argued that Earth regulates its own temperature and chemistry.
Life modifies the atmosphere.
The atmosphere modifies life.
The loop is planetary.
But this is contested.
Doolittle demolished strong Gaia in *Science* in 2019.
He showed that planetary homeostasis is not proven.
It may be passive equilibrium.
It may be a metaphor.
The jury is out.

Neural avalanches show power-law statistics.
Beggs and Plenz recorded them in cortical slices in 2003.
The brain operates near criticality.
It is not frozen.
It is not random.
It is controlled chaos.
Feedback keeps it there.
[SOURCE:bak-1987|type:empirical]

Schrödinger asked what life is in 1944.
He said it feeds on negative entropy.
It exports entropy to stay ordered.
This is the thermodynamics of feedback.
The cell is a dissipative structure.
It maintains itself by flowing energy through.
[SOURCE:schrodinger-1944|type:theoretical]

Prigogine won the Nobel Prize for proving this in 1977.
Far-from-equilibrium systems can maintain order by exporting entropy.
The steady state is not equilibrium.
It is a war.
[SOURCE:prigogine-1977|type:theoretical]

England pushed further in 2013.
He showed that dissipation drives self-replication.
A system that dumps heat into its surroundings tends to copy itself.
Feedback is not an accident of life.
It is a thermodynamic tendency.
[SOURCE:england-2013|type:theoretical]

## The Falsifier

Find a stable system that maintains its variables without any feedback.
No sensor.
No comparator.
No actuator.
Just pure stability from nothing.
If you find it, this whole node collapses.
So far, nobody has.

## The Honest Limits

Feedback is not the only pattern.
It is one convergence among many.
It does not explain structure at rest.
A crystal has no feedback loop.
It is stable by symmetry, not by control.
[SOURCE:noether-1918|type:mathematical]

Feedback does not explain where complexity comes from.
It explains how complexity maintains itself.
The origin of order is another convergence: dissipation, selection, criticality.
[SOURCE:prigogine-1977|type:theoretical]
[SOURCE:england-2013|type:theoretical]
[SOURCE:darwin-1859|type:empirical]

The rival frame is strong.
Feedback is a model, not a mechanism.
Markets are not thermostats.
People are not sensors.
The mathematics of control does not capture the mess of human systems.
Sociologists say feedback is a metaphor stretched too thin.
They may be right.

Social systems are the open question.
Does feedback apply to governments?
To culture?
To history?
Economists say yes.
Sociologists say maybe.
The data is thin.
The models are thick.

We know feedback works in machines.
We know it works in bodies.
We know it works in ecosystems.
Beyond that, we extrapolate.
We model.
We hope.
The pattern is real.
Its boundaries are not.

Feedback also has a dark side.
The same loop that stabilizes can ossify.
A system with too much negative feedback stops adapting.
It defends the wrong set point.
The Soviet economy was a feedback system.
It sensed production quotas.
It compared them to plans.
It acted to close the gap.
The loop worked.
It produced the wrong things in the wrong amounts for decades.
The sensor was fine.
The set point was broken.

Racism is a feedback loop.
A neighborhood is redlined.
Property values fall.
Schools lose funding.
Crime rises.
The neighborhood is declared blighted.
More redlining follows.
The loop is tight.
The sensor is accurate.
The comparator is evil.

Not all feedback is good.
Not all loops are virtuous.
The pattern is neutral.
The set point is where morality lives.

## Related Sources

- [wiener-1948](/a/wiener-1948) — Cybernetics: control and communication in animals and machines.
- [ashby-1956](/a/ashby-1956) — Requisite variety, the Homeostat, and adaptive stability.
- [maturana-1980](/a/maturana-1980) — Autopoiesis: organizational closure and circular causality.
- [shannon-1948](/a/shannon-1948) — Information theory: entropy as the currency of control.
- [landauer-1961](/a/landauer-1961) — The thermodynamic cost of erasing information.
- [godel-1931](/a/godel-1931) — Self-reference and the limits of formal systems.
- [turing-1936](/a/turing-1936) — Computability and the universal machine.
- [von-neumann-1966](/a/von-neumann-1966) — Self-reproducing automata and strange loops.
- [prigogine-1977](/a/prigogine-1977) — Dissipative structures and far-from-equilibrium order.
- [schrodinger-1944](/a/schrodinger-1944) — Negative entropy and the physical basis of life.
- [england-2013](/a/england-2013) — Dissipation-driven adaptation and self-replication.
- [bak-1987](/a/bak-1987) — Self-organized criticality: sandpiles and avalanches.
- [kauffman-1993](/a/kauffman-1993) — The edge of chaos and the origins of order.
- [darwin-1859](/a/darwin-1859) — Natural selection as feedback between organism and environment.
- [noether-1918](/a/noether-1918) — Symmetry and conservation: the mathematics of stable form.
- [spinoza-1677](/a/spinoza-1677) — God or Nature: immanent order without external control.
- [whitehead-1929](/a/whitehead-1929) — Process philosophy: reality as becoming, not being.
- [heraclitus-500](/a/heraclitus-500) — Flux and opposition: the fire that sustains itself.
- [lao-tzu-c6th-bce](/a/lao-tzu-c6th-bce) — Wu wei: action through alignment, not force.
- [ostrom-1990](/a/ostrom-1990) — Commons governance: institutional feedback loops that work.
- [wilson-1971](/a/wilson-1971) — Renormalization group: scale and universality.
- [watts-1998](/a/watts-1998) — Small-world networks: clustering and short paths.
- [barabasi-1999](/a/barabasi-1999) — Scale-free networks: preferential attachment and hub structure.
- [mandelbrot-1967](/a/mandelbrot-1967) — Fractals: scale invariance in nature.
- [wallace-1858](/a/wallace-1858) — Natural selection: the co-discoverer with Darwin.

## Related Convergences

- [convergence-c01](/a/convergence-c01) — Gradient dissipation: feedback needs energy to flow.
- [convergence-c03](/a/convergence-c03) — Symmetry and conservation: stable form without control.
- [convergence-c04](/a/convergence-c04) — Symmetry-breaking: when feedback crosses a threshold.
- [convergence-c05](/a/convergence-c05) — Criticality: feedback tuned to the edge of chaos.
- [convergence-c06](/a/convergence-c06) — Information and entropy: the currency of control.
- [convergence-c08](/a/convergence-c08) — Recursion and self-reference: feedback eating its own tail.
- [convergence-c09](/a/convergence-c09) — Selection: feedback between organism and environment.
- [convergence-c10](/a/convergence-c10) — Scale invariance: feedback loops at every magnitude.
- [convergence-c11](/a/convergence-c11) — Networks: feedback topology of connection.
- [convergence-c12](/a/convergence-c12) — Autopoiesis: feedback as the definition of life.

