In the previous essay, we followed the photon from physical difference to detection.
A photon does not contain information in any mysterious sense. It is simply part of the electromagnetic processes through which physical differences can propagate and interact with matter. But when a physical system becomes capable of responding differently to different wavelengths, intensities, directions or temporal patterns, something new becomes possible.
A difference can be detected.
And once differences can be detected, they can be preserved, transformed and used.
We reached, therefore, the beginning of a sequence:
physical difference → detection → discrimination → information
But there is another step.
Information is not yet meaning.
A photoreceptor can respond to light without knowing what light is. A camera can record an image without seeing anything. A thermostat can register a temperature without having a concept of temperature.
So when does a physical difference become a sign?
When does something in the world come to stand for something else?
And can we trace any part of that transition back into physics itself?
The answer, I think, requires us to be both ambitious and careful.
Physics does not suddenly turn into semiotics.
But physical organisation can make semiotic organisation possible.
And that distinction may be one of the most interesting things we have discovered so far.
A sign is not just a signal
We need to begin with a distinction.
A signal is a physical event that affects a system in some organised way.
A sign is something more.
If a sudden sound causes an animal to turn its head, the sound is a signal.
If a particular sound has become associated with danger, and the animal responds to it as indicating danger, we are moving toward something recognisably semiotic.
The difference is subtle but important.
The signal participates directly in a causal process.
The sign participates in a process in which something can stand for something else.
A falling branch causes a noise.
But the noise can also indicate that something has happened nearby.
A red patch on a fruit is a physical difference.
But for an animal capable of exploiting the correlation, it can indicate ripeness.
A footprint is a physical impression in the ground.
But for a tracking animal, it can indicate the recent presence of another organism.
In each case, something present becomes significant because of its relation to something that is not immediately present.
The sign allows the system to respond to what the sign indicates, rather than merely to the sign itself.
That is a remarkable expansion of possibility.
The world acquires a past and a future
Consider the footprint.
Physically, it is simply a disturbance in the ground.
But it has an unusual property.
It is a present physical state that has been produced by a past event.
An animal capable of detecting the footprint can therefore respond to something that is no longer there.
The footprint becomes a bridge between present and past.
Likewise, smoke can indicate fire.
Clouds can indicate approaching rain.
A particular smell can indicate food.
The track of an animal can indicate where the animal has gone.
A particular movement can indicate what another organism is about to do.
Once a system can exploit such relationships, its effective environment becomes much larger.
It no longer responds only to what is physically happening now.
It can respond to traces of what happened before.
It can anticipate what may happen next.
Semiotic organisation therefore transforms the temporal structure of an organism's world.
The present becomes populated by signs of the absent.
And this is one reason why the emergence of sign-use is such a profound transformation of possibility.
The photon enters the story again
Now return to the photon.
Suppose light reflects from an object and enters an animal's eye.
At the physical level, we have a chain of electromagnetic interactions.
Photons are absorbed by molecules in photoreceptor cells.
Molecular configurations change.
Biochemical processes follow.
Electrical activity changes.
Neural signals propagate.
None of this, by itself, requires meaning.
But suppose the pattern of light reaching the eye reliably corresponds to an object in the environment.
The organism can now use that pattern to alter its behaviour.
The light does not merely cause a retinal response.
It provides a route through which the environment can become relevant to behaviour.
That is a more sophisticated relation.
The organism is not simply responding to photons.
It is responding to what particular patterns of photons indicate about its surroundings.
This distinction marks the beginning of semiotics.
The sign is a relationship
It is tempting to ask:
Where is the sign?
Is it the photon?
The retinal image?
The neural pattern?
The object?
But perhaps this is the wrong question.
A sign is not simply an object sitting somewhere in the world.
It is a relationship.
Something functions as a sign when it participates in an organised relation between:
- a physical occurrence,
- something that occurrence indicates,
- and a system capable of responding to the indication.
A footprint is not inherently a sign.
To a bacterium, it may be nothing of interest.
To a tracking animal, it may be extraordinarily significant.
The physical footprint is the same.
What changes is the organisation of the system encountering it.
This gives us another important principle:
Meaning does not reside entirely in the signal; it arises in the relation between a difference, what it indicates, and a system capable of exploiting that relation.
That is why the same physical event can be meaningless in one context and highly meaningful in another.
The organism changes the question
This brings us back to the central theme of the series.
Physics asks what happens.
Biology can ask what something does for an organism.
Semiotics asks what something means within a system of interpretation.
These questions are not interchangeable.
But neither is disconnected from the others.
An electromagnetic interaction can produce a molecular change.
That molecular change can alter cellular behaviour.
Cellular behaviour can affect an organism.
The organism can use the resulting distinction to discriminate aspects of its environment.
The distinction can thereby acquire significance.
The sequence is not:
physics mysteriously becomes meaning.
It is:
physical capacity → organised interaction → detection → discrimination → functional significance → signification.
At each stage, the organisation becomes more elaborate.
Nothing supernatural is required.
But neither should we pretend that the later stages are simply synonyms for the earlier ones.
Meaning is not identical to causation.
It is something that causal organisation can make possible.
Why correlation matters
For a physical difference to function as a sign, there normally has to be some reliable relationship between the sign and what it indicates.
Smoke works as an indication of fire because smoke and fire are regularly related.
A particular smell can indicate food because chemical properties of the food generate molecules that can be detected by the organism.
A particular sound can indicate danger because the sound has become associated with situations in which danger is present.
The organism therefore exploits correlations in the world.
This is important because it prevents us from making meaning purely subjective.
The organism does not simply invent the world it perceives.
Its interpretations work because the world contains regularities that make them viable.
A predator really does generate particular patterns of movement.
A ripe fruit really does have particular chemical and optical properties.
A particular sound really can be produced by a particular event.
Semiotic systems therefore depend upon an underlying physical world whose regularities make signs possible.
Meaning is not arbitrary all the way down.
It is constrained by reality.
But correlation is not enough
Yet correlation by itself does not produce meaning.
Consider a thermometer.
The height of the liquid column correlates with temperature.
The column therefore carries information about temperature in a perfectly respectable physical sense.
But does the thermometer understand temperature?
No.
The correlation becomes meaningful only when incorporated into a system for which the distinction has a role.
Perhaps a person reads the thermometer.
Perhaps a control system uses it to regulate a furnace.
Perhaps an organism uses a temperature-sensitive mechanism to move toward a preferred environment.
The same physical correlation can therefore enter different organisations and acquire different functions.
This gives us a useful distinction:
Information can exist as a physical correlation; meaning arises when that correlation participates in an organised economy of consequences.
The phrase "economy of consequences" is worth lingering over.
A sign matters because what the system does in response to it matters.
The sign is embedded in a network of possibilities.
The organism lives in a world of affordances
This takes us naturally toward another concept that has been important throughout our work: affordance.
A branch affords grasping to a monkey.
A surface affords walking to an animal capable of walking.
A gap affords passage if it is large enough for the organism.
Food affords nourishment.
Shelter affords protection.
These are not merely properties of objects.
Nor are they purely projections of the organism.
They arise from a relation between the capacities of the organism and the structure of its environment.
Semiotics adds another layer.
A particular visual pattern may indicate that something is edible.
A sound may indicate that something dangerous is approaching.
A change in colour may indicate that a fruit has become ripe.
The organism is therefore not merely detecting the world.
It is detecting possibilities for action within the world.
This is where our series begins to return to its original question.
What becomes possible?
The photon allows an organism to detect a difference.
The visual system allows the difference to become information.
The organism's organisation allows the information to become significant.
And significance allows the organism to discover possibilities for action.
The world has become not merely a collection of physical states, but a field of things that can matter.
The first semiotic loop
We can now construct a loop.
Something happens in the environment.
It produces a physical difference.
The difference reaches the organism.
The organism detects it.
The detection alters the organism's internal state.
The internal state changes behaviour.
The behaviour changes the organism's relation to the environment.
The changed environment produces new differences.
Those differences are detected again.
So:
world → difference → detection → internal change → action → world
This is more than a causal chain.
It is a self-maintaining loop of sensitivity and response.
And once such loops become sufficiently elaborate, signs can acquire histories.
A system can learn that one event predicts another.
It can alter its behaviour accordingly.
It can become sensitive not merely to what is present, but to what the present indicates about what is absent, hidden or forthcoming.
The organism's environment has become temporally extended.
It can act on the basis of traces of the past and anticipations of the future.
Learning changes the sign
This is where biology begins to take us beyond the simple detector.
An innate response can connect a physical difference directly to a behaviour.
But learning allows the organism to alter which differences matter.
A young animal may initially respond to a sound in a relatively unspecific way.
Through experience, particular sounds can become associated with particular outcomes.
A neutral stimulus can acquire significance.
The organism has not merely become better at detecting differences.
It has become better at discovering which differences matter.
This is an enormous increase in possibility.
The world contains indefinitely many physical distinctions.
No organism can respond to all of them.
Life therefore requires selective sensitivity.
Evolution can build the initial architecture.
Learning can refine it.
And nervous systems can transform it into increasingly sophisticated forms of discrimination.
The organism becomes, in effect, an active participant in constructing its own meaningful environment.
Meaning is not added to matter from outside
This is perhaps the point at which a familiar philosophical temptation appears.
We might say:
Matter is meaningless.
Then life appears.
Then minds arrive and add meaning to the meaningless physical world.
But that picture now seems too crude.
There is certainly a distinction between physical description and semantic interpretation.
But the capacity for meaning does not have to be imported from somewhere outside nature.
Physical systems can become organised in ways that support detection.
Detecting systems can become organised in ways that support information processing.
Organisms can become organised in ways that make some information relevant to their survival and reproduction.
Nervous systems can become organised in ways that allow learning, anticipation and flexible action.
Social organisms can become organised in ways that allow communication.
And communication can eventually become symbolic.
Meaning can therefore be understood not as an alien substance added to matter, but as a new relational possibility opened by particular forms of organisation.
This is precisely the sort of emergence we have been looking for.
But meaning is not reducible to causation
We should immediately add the other half of the argument.
If we say that meaning emerges from physical organisation, we must not conclude that meaning is therefore nothing but physical causation.
A book is made of paper, ink and physical marks.
But the meaning of the sentence printed on the page is not exhausted by listing the wavelengths reflected from the ink.
The physical substrate is indispensable.
It is not sufficient as an explanation of the semantic organisation.
Likewise, a spoken word consists physically of vibrations in air.
Yet its meaning depends upon a linguistic system shared by speakers.
The fact that meaning depends upon physical organisation does not make meaning identical to the physical organisation.
This is exactly analogous to our earlier treatment of molecules.
Water depends upon electrons and nuclei.
But "water dissolves salt" is not usefully explained by replacing every mention of water with a catalogue of quantum states.
Higher-level organisation creates new regularities and new possibilities.
Semiotics is one such level.
From signs to symbols
There is another extraordinary transition waiting ahead.
A natural sign depends upon a physical or causal relationship.
Smoke indicates fire.
A footprint indicates an animal.
A particular colour may indicate ripeness.
But human language contains signs whose relationship to what they signify is far more flexible.
The word "tree" does not resemble a tree.
The sound does not naturally cause the tree.
Its significance arises within a shared symbolic system.
Here we encounter a new possibility:
a sign can acquire significance through its relation to other signs.
Language is therefore not merely a more elaborate collection of signals.
It is a new organisational level.
Words can be combined.
Sentences can be constructed.
Questions can be asked.
Descriptions can be negated.
Hypotheses can be formed.
Imaginary worlds can be described.
A system of signs can begin to refer not only to the immediate environment but to things that are absent, possible, hypothetical or entirely fictional.
The semiotic world becomes extraordinarily generative.
And yet its physical preconditions remain.
Sound waves.
Light.
Ink.
Neural activity.
Memory.
Bodies.
Social interaction.
The symbolic world does not float free of physics.
It is physically instantiated organisation.
The possibility of being wrong
There is another feature of semiotics that deserves attention.
Once a system can interpret signs, it can also misinterpret them.
Smoke can indicate fire—but fog may look like smoke.
A footprint can indicate an animal—but the trail may be old.
A visual pattern may indicate food—but the organism may have learned the wrong association.
This seems like a small point.
It is not.
Causal systems do not, in themselves, have beliefs that can be true or false.
But representational or semiotic systems can.
The distinction between what is indicated and what actually obtains creates the possibility of error.
And error is enormously important.
It means that the organism's internal organisation can become decoupled from the immediate state of the world while remaining systematically related to it.
The organism can respond to what it takes to be the case.
That creates the possibility of anticipation, imagination, deception and planning.
A new dimension of possibility has opened.
The sign creates distance
This may be one of the deepest consequences of semiotic organisation.
A simple physical system responds to what physically affects it.
A semiotic system can respond to what something indicates.
The distinction creates distance between stimulus and response.
A predator is not immediately present, but its tracks are.
Rain has not yet arrived, but clouds are visible.
Food is hidden, but its smell is detectable.
A friend is not present, but a written message can convey what they have said.
The sign allows an organism to operate on a world that is not fully present to it.
It can act on traces.
It can anticipate.
It can remember.
It can communicate.
It can imagine.
In other words:
Semiotics expands the effective world of an organism beyond what is immediately given.
And that is another transformation of possibility.
The photon and the semiotic universe
We can now see why our original curiosity about photons was not misplaced.
A photon is not meaningful.
But photons participate in a physical universe in which organisms can detect electromagnetic differences.
Those differences can become signals.
Signals can become information.
Information can become significant within an organism.
Significant information can participate in learned associations.
Associations can become signs.
Signs can become symbols.
And symbols can become systems capable of describing worlds that do not currently exist.
The path is astonishing.
But we must not collapse it.
There is no single moment at which "physics becomes semiotics."
There is instead a succession of organisational thresholds.
At each threshold, existing physical capacities become incorporated into a system capable of doing something new.
This is the pattern we have been following from the beginning.
A new kind of function
We can now return to our original use of the word function.
The photon has a physical function in the sense that its behaviour participates in electromagnetic processes.
A photoreceptor has a biological function because its organisation contributes to an organism's capacity to detect particular physical differences.
A visual signal has an informational function because it can alter internal states in a way systematically related to environmental conditions.
A sign has a semiotic function because it can stand for something within an organised system of interpretation.
These are not four versions of exactly the same thing.
But they form a historical and organisational sequence.
At each stage, a capacity becomes incorporated into a larger system and acquires a new role within it.
Perhaps, then, function is not one thing.
Perhaps it is a family of relations between what a component can do and what an organisation can do because it does it.
That would allow us to speak naturally about the functions of particles without pretending that particles have intentions.
It would also allow us to understand how new forms of function can emerge.
The world becomes expressive
We have travelled a long way from the photon.
At the beginning, the universe contained physical differences.
Then some physical systems acquired the capacity to detect them.
Then organisms evolved systems that could exploit them.
The environment could now influence behaviour through patterns of difference.
And eventually some organisms acquired the capacity to interpret signs.
At that point, something extraordinary had happened.
The world had become expressive.
Not because the world itself had developed a voice.
Not because photons acquired meanings.
But because there now existed organisms for whom features of the world could function as signs.
A cloud could mean rain.
A track could mean predator.
A face could mean friend.
A word could mean an absent object.
A sentence could mean something that has never happened.
The physical world had acquired, through organisation, the capacity to enter into relations of significance.
That is not a small addition to physics.
It is one of the most remarkable things that physics makes possible.
The next question
We began this essay with a question:
When does a physical difference become a sign?
The answer now seems less like a moment than a trajectory.
A physical difference can be detected.
Detection can preserve a distinction.
A preserved distinction can become information.
Information can acquire significance within an organism.
Significance can become part of a system of signs.
And signs can become symbols capable of referring beyond the immediately present.
So our sequence has grown:
property → capacity → interaction → difference → detection → information → significance → sign → symbol
But one crucial question remains.
Why should some information matter to an organism at all?
Why does the organism care about one difference and ignore another?
Why should a particular pattern of photons become food, predator, mate or shelter?
The answer cannot lie in the photon alone.
It lies in the organisation of the organism itself—its needs, vulnerabilities, capacities and history.
And that brings us to a deeper idea.
Perhaps information becomes meaningful not simply when it is interpreted, but when it becomes relevant to a system's possibilities for continuing to exist and act.
The photon has brought us to the threshold of that idea.
The next essay will therefore ask what happens when a physical system no longer merely detects differences, but lives by them.
And there, perhaps, we will begin to see how function, information, meaning and life are connected by something deeper than metaphor:
an ecology of possibility.
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