In our first essay, we asked what a particle does.
In the second, we asked what its properties make possible.
The distinction seemed modest at first. An electron has a negative electric charge. It participates in electromagnetic interactions. Its quantum properties constrain the ways in which it can behave.
But once we begin following those capacities through the world, something remarkable happens.
The electron turns out to have a very long journey.
It begins as a particle.
It becomes part of an atom.
Atoms become capable of forming molecules.
Molecules become capable of forming increasingly elaborate chemical structures.
Chemistry becomes capable of sustaining networks of reactions.
Some of those networks become part of living systems.
And living systems eventually become capable of using the physical world to build eyes, brains, languages and technologies.
The electron does not cause all these things in any simple sense.
Nor does it contain them.
What it does is more interesting.
Its physical capacities participate in a succession of organisations in which new possibilities become available.
So let us follow the journey.
The electron enters the atom
An electron on its own is already an extraordinarily rich physical object.
But place it in the presence of a positively charged atomic nucleus and something new becomes possible.
The electromagnetic interaction binds the electron to the nucleus.
Quantum mechanics then determines the allowed states of the resulting system.
The atom is not simply a nucleus with a particle orbiting around it like a tiny planet. Its structure is quantum mechanical, and the available states have particular energies and spatial distributions.
This matters because the atom now has a stability and a structure that neither component possesses in isolation.
The electron has not acquired a new fundamental property.
The nucleus has not acquired one either.
What has appeared is a new organisation.
And with that organisation comes a new set of possibilities.
An atom can absorb or emit radiation in characteristic ways. It can interact with other atoms. It can participate in chemical bonding. It can form part of a solid, a liquid or a gas.
The atom is therefore more than the sum of its ingredients in a very specific sense.
Not more in substance.
More in possibility.
The organisation of the components creates capacities that do not belong to the isolated components considered separately.
The strange generosity of the quantum rules
There is an especially important feature here.
Quantum mechanics does not simply tell us where the electron is.
It tells us about the states available to the electron within the atom.
And those restrictions are extraordinarily productive.
The electron cannot occupy just any state whatsoever. The atom has a structured set of possible states.
This is another example of the theme from the previous essay:
constraint can create possibility.
The quantum rules restrict the ways in which matter can be organised.
But precisely because they do so, atoms acquire stable and differentiated structures.
Different elements possess different electron configurations. These differences give rise to different chemical behaviours.
The periodic table is therefore, among other things, a map of possibilities generated by quantum structure.
It is difficult to overstate how strange this is.
The diversity of ordinary matter—the difference between hydrogen and oxygen, carbon and silicon, sodium and chlorine—depends in part upon different ways of organising electrons around nuclei.
The world of chemistry emerges from a highly constrained physical space.
What looks to us like an astonishing abundance of substances is made possible by a comparatively small set of underlying physical principles.
The universe does not need a separate fundamental law for every kind of molecule.
It needs rules capable of generating structured possibilities.
From atoms to bonds
Now the electron takes another step.
Atoms can interact with other atoms.
And when their electrons participate in the appropriate arrangements, atoms can form chemical bonds.
This is where the electron's journey becomes particularly interesting for our purposes.
A chemical bond is not merely an event in which two objects happen to come close together.
It is a new organisation of matter.
And that organisation has capacities of its own.
A molecule can have a particular geometry.
It can rotate around some bonds and not others.
It can absorb particular wavelengths of radiation.
It can react with some molecules and not others.
It can participate in chains of reactions.
It can become a building block for something larger.
None of these capacities belongs to an isolated electron.
Yet none of them would be possible without the electronic structure of matter.
This is the sense in which the electron has a "function" in chemistry.
Not a purpose.
Not an intention.
Simply a role in what the system can do.
The electron participates in the formation of structures that have chemical possibilities.
That is enough.
Chemistry is the art of making possibilities
Once chemical bonding exists, the number of possible structures expands enormously.
A few kinds of atoms can produce vast numbers of molecules.
Carbon is the spectacular example.
Its electronic structure permits it to form stable bonds in a remarkable variety of arrangements. Chains, rings, branches and complex three-dimensional structures become possible.
Hydrogen, oxygen, nitrogen, phosphorus, sulphur and other elements add further possibilities.
The result is not merely a larger collection of objects.
It is a new combinatorial space.
Chemistry takes a relatively limited repertoire of elements and generates an enormous variety of structures and transformations.
This is one of the places where the notion of possibility becomes especially useful.
The periodic table tells us what kinds of atoms exist.
Chemistry tells us what those atoms can do together.
And what they can do together is vastly richer than what any one atom can do alone.
The important transition is therefore:
elements → combinations → structures → chemical possibilities.
The electron is present throughout the story.
But increasingly, it disappears from view.
This is a recurring feature of emergence.
The lower-level mechanism becomes so deeply incorporated into a higher-level organisation that we stop talking about it.
We speak of "chemistry" rather than "electrons."
And that is perfectly legitimate.
The existence of a higher level does not make the lower level unreal.
It means that new explanatory patterns have become available.
The molecule becomes an actor
Consider a molecule of water.
We can describe it in terms of atoms and electrons.
But we can also describe what water does.
It dissolves substances.
It participates in chemical reactions.
It has characteristic thermal properties.
It forms hydrogen-bond networks.
It interacts with biological molecules.
At the molecular level, we can speak naturally about structure, behaviour and role without constantly reducing everything back to particle physics.
The molecule has become a meaningful unit of organisation.
This is important because it suggests that emergence is not merely a matter of our descriptions.
Something physically new has happened.
The molecule has capacities that arise from its organisation.
It can do things that the isolated atoms cannot do.
The hydrogen and oxygen atoms do not individually possess "the function of dissolving salt."
Water does.
The property belongs to the organised system.
This gives us a useful formulation:
New organisation creates new capacities.
And when those capacities become available, they create new possibilities for still further organisation.
The ladder becomes a network
It would be tempting to represent the story as a simple ladder:
electron → atom → molecule → organism
But that image is too neat.
Reality is much messier.
Molecules interact with other molecules.
Chemical reactions form networks.
Networks influence their environments.
Environments feed back into the networks.
Structures persist, break apart and recombine.
Some reactions enable others.
Some products become catalysts for further reactions.
The electron is therefore not travelling upward through a single chain.
It is participating in an increasingly elaborate network of possibilities.
This is why "journey" should not be taken literally.
The electron is not climbing a ladder toward life.
Rather, the structures in which electrons participate become increasingly capable of sustaining further structures.
The journey belongs to the organisation, not to the particle.
That distinction will become increasingly important as we move toward biology.
When chemistry begins to organise itself
At some point in the history of the universe, chemistry becomes sufficiently complex for another possibility to emerge.
Chemical networks can become coupled.
Some reactions can help sustain the conditions for other reactions.
Molecules can participate in cycles.
Compartments can separate chemical processes from their surroundings.
Systems can use energy flowing through them to maintain organisation.
Eventually, under conditions that remain the subject of active scientific investigation, life emerges.
We should be careful here.
We do not know that there was one simple moment at which "chemistry became life."
The origin of life was almost certainly a complicated historical process involving many stages.
But the conceptual point does not depend on knowing the exact pathway.
What matters is that chemical organisation opened possibilities that were not available to isolated molecules.
Once self-maintaining, reproducing and evolving systems became possible, the character of the story changed.
Chemistry acquired history.
Evolution changes the meaning of possibility
Evolution introduces something new.
Before biological evolution, a structure can exist or fail to exist according to physical and chemical processes.
With evolution, structures can be retained because of what they enable organisms to do.
This does not introduce purpose from outside nature.
Variation produces differences.
Some differences affect survival and reproduction.
Those differences can become more common.
Over many generations, biological organisation can therefore accumulate functional structures.
Now we can legitimately talk about the function of an eye, a wing, a digestive enzyme or a photoreceptor.
Not because nature has suddenly acquired a cosmic intention.
But because biological organisation has acquired a mechanism through which capacities can be preserved and elaborated according to their consequences for the organism.
This gives us a crucial distinction.
The electron has a role in molecular organisation.
The molecule can have a role in a chemical network.
A biological structure can have a selected function.
These are not identical concepts.
But they are connected by a history of increasing organisation.
The electron reaches the eye
We can now return to the photon.
The eye is an extraordinarily elaborate structure.
Yet its operation ultimately depends upon interactions between electromagnetic radiation and matter.
Photons interact with molecules in the retina.
Those molecular changes initiate biochemical processes.
Those processes alter cellular activity.
Signals propagate through neural networks.
The organism constructs a representation of aspects of its environment.
And the organism can act upon what it detects.
The electron has not become an eye.
The photon has not become information.
But the physical capacities of electrons and photons participate in the organisations that make these things possible.
This is why the long journey is worth following.
The causal chain is not a simple chain of billiard-ball impacts.
It is a succession of organisational transformations.
At every stage, physical processes are rearranged into structures capable of doing something new.
The emergence of a new kind of possibility
Consider the difference between a rock and an eye.
Both are physical.
Both are composed of matter governed by the same fundamental laws.
Yet the eye can detect electromagnetic radiation.
It can distinguish patterns.
It can contribute to behaviour.
It can participate in an organism's relationship with its environment.
Where did this new possibility come from?
Not from a new fundamental force.
Not from a new kind of matter.
Not from something added to physics from outside.
It came from organisation.
The physical components were arranged into a system in which their capacities could be coordinated toward a new kind of activity.
This does not mean that the eye is "nothing but" its components.
Nor does it mean that the eye violates physics.
It means that physics permits organisations in which entirely new capacities arise.
That may be one of the most important things we can say about emergence.
Emergence is not the appearance of something without a physical basis. It is the appearance of new possibilities through physical organisation.
The electron disappears—and that is the point
There is a curious feature of the journey we have been following.
At the beginning, the electron was the protagonist.
By the time we reach biology, we barely mention it.
We speak about molecules, membranes, cells, enzymes, genes, nervous systems and organisms.
This might seem like a retreat from physics.
It is not.
It is evidence that the physical world can support multiple levels of organisation, each with its own useful units, regularities and possibilities.
If we insisted on describing everything only in terms of electrons, we would lose chemistry.
If we insisted on describing chemistry only in terms of chemistry, we would lose biology.
The lower level remains indispensable as a condition of possibility.
But the higher level acquires its own organisation and therefore its own explanatory vocabulary.
This suggests that reduction and emergence are not necessarily enemies.
We can acknowledge that molecules depend upon quantum physics while also recognising that molecular organisation has chemical capacities that are worth describing in their own terms.
The same applies to life.
And perhaps the same will eventually apply to information and meaning.
What has actually travelled?
We began with an electron.
We followed it into an atom, from atoms into molecules, from molecules into chemistry and from chemistry toward life.
But the electron itself has not travelled through these levels in any meaningful sense.
What has travelled is a possibility.
Or rather, a family of possibilities.
The electron's properties participate in physical interactions.
Those interactions contribute to stable structures.
Those structures open new chemical possibilities.
Chemical possibilities allow new forms of organisation.
Some of those organisations eventually make biological evolution possible.
Evolution generates still further forms of organisation.
The journey is therefore not:
electron → life
It is:
electron → capacities → organisation → new capacities → new possibilities → further organisation.
The electron is not secretly a molecule.
The molecule is not secretly an organism.
The organism is not secretly a mind.
Each is genuinely new.
But each becomes possible because earlier physical organisation has opened a space in which it can arise.
The remarkable thing is not that everything is made of particles
We often hear that everything is ultimately made of particles.
That is true in a certain sense, but it is not particularly illuminating.
The more interesting fact is that particles can participate in organisations that make worlds of new possibilities.
A few kinds of fundamental constituents, governed by a relatively small set of interactions, can give rise to an astonishing hierarchy of structures.
Atoms.
Molecules.
Crystals.
Stars.
Planets.
Cells.
Organisms.
Brains.
Cultures.
Technologies.
The striking question is not merely how these things are constructed.
It is how the physical universe can possess the generative capacity to make such radically different forms of organisation possible.
The electron is one small part of that story.
But it is a useful part because its journey lets us see the principle in miniature.
A universe that can become more than it is
Perhaps this is the point at which our title begins to acquire its full meaning.
The Physics of What Becomes Possible is not an attempt to replace physics with poetic language.
It is an attempt to ask what physics looks like when we pay attention not only to what exists, but to what existing things enable.
The electron does not know what it makes possible.
It does not need to.
Its properties are enough.
Given the right relations and constraints, those properties can participate in atoms.
Atoms can participate in molecules.
Molecules can participate in chemical networks.
Chemical networks can participate in living systems.
Living systems can participate in evolution.
And evolution can open possibilities that no physicist could have inferred simply by looking at an isolated electron.
This is not because physics has failed.
It is because possibility is relational and organisational.
The electron's possibilities are not exhausted by the electron considered alone.
They unfold through the structures in which it can participate.
And that may give us a first glimpse of a profound feature of the physical world:
The future possibilities of a system can depend not only upon what its components are, but upon how those components become organised.
The next question
We have now followed the electron from particle to atom, from atom to molecule, and from molecule toward the extraordinary possibilities of chemistry and life.
But one element of our story has been waiting in the wings.
The photon.
For the electron, the great story was the emergence of structure.
For the photon, the story will be rather different.
Because photons do not merely participate in causal interactions.
They can allow one system to become sensitive to the state of another.
They can carry differences across space.
And eventually, within organisms, those differences can become something much more remarkable.
They can become information.
The next stage of our journey will therefore ask a stranger question than "What does a particle do?"
It will ask:
When does a physical difference become a difference that matters?
No comments:
Post a Comment