Much of the success of modern science has come from
breaking things down to their pieces and parts.
We all know that if you want to be a good car mechanic you have to not only know
what an engine is, but how to take one apart and put it back together again.
As scientists have learned to break down organisms into cells,
cells into molecules, molecules into atoms, and all the way down to
fundamental particles or fields, we seem to get closer to achieving what
some scientists and philosophers have believed to be the goal of science, to explain everything in
terms of the smallest pieces and parts of nature, and the small collection of laws that govern them.
It seems like this complete Reduction of nature to fundamental physics, this Reductionism,
would refute the Thomistic notion of substances and substantial form,
since everything would ​really​ just be a complex collection of particles or fields or strings.
But, the belief that complete reductionism is actually possible
has never been more than that -- a belief, a hope, a promise, that we’ll figure it out eventually.
Scientists were able to make much more detailed and precise predictions in
biology once they understood that all living things are made up of cells, and even more so
when they started to understand the molecules that make up the cells and how they function.
Chemistry has been able to make more and more detailed predictions once we understood the atomic
structure that goes into various molecules and the physical forces involved in chemical reactions.
Physics has been on an ever increasing quest to find more and more fundamental constituents
of the physical world, first discovering the atom, then the electrons, protons and neutrons that make
up atoms, and then the quarks that make up the protons and neutrons, and perhaps even further.
There is real and very well established power in breaking a thing down into its constituent parts
and seeing how they work together. This has spurred the half-joking / half-serious claims
(particularly popular among physicists) that biology is just applied chemistry,
and chemistry is just applied physics; everything ultimately is just physics.
From the earliest days of modern science some have pushed towards a philosophical
and ontological reductionism, claiming that ​everything​ about physical things
can ​completely​ be said by finding the smallest pieces and the laws that govern them.
Nevertheless, many contemporary scientists and philosophers of science have
started to look more closely at the details of what biology and chemistry and physics
are actually telling us and the methods used in the various disciplines
and arguing that complete reductionism is simply not possible.
This is perhaps most strongly felt in biology, even though molecular biology has revolutionized
our understanding of organisms. We can not only talk about the organs of a cat,
its bones and heart and liver, but the cells that make up those organs and all
the different molecules that function in those cells. We can sequence the genome of the cat,
the complete set of genetic instructions that are used to build up all of these pieces and parts.
Nevertheless, many biologists who study the details of how these
molecules work together in a cell and how cells work together in an organism
are convinced that the complex systems of interactions that go into a cat cannot
be simply reduced to its molecules and their basic functions, or simply read off of the DNA.
Digging deeper,
the common belief that Chemistry can really be completely reduced to physics has issues as well.
It is commonly claimed that we know that temperature is ​just​ the average
kinetic energy of the molecules in some collection, and this is mostly correct.
But if you have a hot cup of coffee and a cool pitcher of milk, the moment you pour some
milk into the cup, the cup of coffee does not, properly speaking, have a temperature. In theory
we could average over the motion of the coffee molecules and milk molecules and get a number,
but no part of the liquid would actually have that temperature yet.
It is only once we let the coffee and milk mix and settle into thermodynamic equilibrium
that we can properly define the Temperature of the liquid, or part of the liquid, in the cup,
but the only way we have to rigorously define this equilibrium at the molecular level
already uses the idea of temperature.
There doesn’t seem to be a way to completely reduce the idea of
temperature into microscopic terms that aren't at least in some way circular.
Things get even more complicated when we look at other familiar chemical phenomena like
the transition from solid to liquid to gas, the ways chemicals dissolve,
and the rates at which chemical reactions take place.
All of these are better understood because of our knowledge of fundamental physics,
but many chemists and philosophers of chemistry are convinced
that they cannot be completely reduced to physics alone.
Even in a field like quantum chemistry, where chemists try to use the details
of quantum mechanics to describe the shapes and interactions between complex molecules,
only certain highly idealized examples can be completely “built up” from the electrons,
protons, and neutrons along with the basic rules of quantum mechanics, alone. Even here chemists
and philosophers argue that other experimentally derived data is needed to complete the picture,
and chemistry has not been simply reduced to “applied physics.”
It is important to reiterate that the method of reduction in science is a hugely important tool,
but so far, the dream of complete reductionism is still
just a dream. Moreover there is more and more evidence and
new and convincing arguments that there are important features about the molecular, chemical,
cellular, and biological worlds that cannot be reduced to particle physics, even in principle.
While there are a whole range of philosophical arguments that have been proposed to support these
complex features of the natural world, many thinkers have looked to Aristotelian concepts like
substance and substantial form to try and ground this
fascinating diversity of structure that we can’t seem to eliminate from nature.
While the physical world is clearly made up of particles like electrons and quarks and photons,
it is also made up -- in real ways that cannot simply be reduced -- of water and of salt and
sugar, of blood cells and skin cells and muscle cells, of dogs and cats and trees,
of you and me. Who would have thunk it?
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