When someone says that life, or evolution, or complex systems, or
whatever, doesn't obey the
second
law of thermodynamics, it's a pretty safe bet that person has no
idea what the second law of thermodynamics is.
If someone
points out to you that your pet theory of the universe is in
disagreement with Maxwell's equations—then so much the worse
for Maxwell's equations. If it is found to be contradicted by
observation—well, these experimentalists do bungle things
sometimes. But if your theory is found to be against the second law
of thermodynamics I can give you no hope; there is nothing for it
but to collapse in deepest humiliation.
-- Sir
Arthur Stanley
Eddington,1928
For one thing, the second law applies only to isolated systems. If
you isolate a living organism from its open environment, it will
equilibrate to a state of maximum entropy (die, decompose, decay).
That life obeys the second law is clear to anyone with a knowledge of
physics; what this book does is take that further, and explain how
complex self-organising systems, including life, actually accelerate
the increase in entropy, by being efficient gradient reducing
dissipators. Far from life and the second law being incompatible, the
truth is that the study of life requires the study of thermodynamics.
p4.
life can be regarded as one of a class
of complex systems ruled by energy and its transformations. As the
science of energy flow and chemical kinetics, thermodynamics is
crucial to understanding life. Theoreticians who want to understand
energy flow and transformations in biology must look the science of
thermodynamics in the eye, as any theoretical claim is meaningless
unless it conforms to thermodynamic principles.
This book is specifically about non-equilibrium
thermodynamics (NET): open systems
existing away from equilibrium, self-organising to exploit some form
of gradient (a difference across a
distance). They can exploit the gradient to do work. This tends
to dissipate the gradient, but if it is maintained by some
environmental source (the most clearly obvious being solar energy),
they can exist in a steady state, stable but not static, "feeding
"off the gradient. In fact, they organise themselves to help
ensure this.
p18.
Free energy is the quantity of energy
available that organisms can put to work. … This … is
directly proportional to the gradients machines can tap into---or
organisms can use to maintain and reproduce themselves as specific
kinds of material organizations.
And open systems are qualitatively different from closed, isolated
systems.
pp70-71.
Open systems enjoy energy and material
influx and outflow across their boundaries. They are systems that,
instead of reaching a predetermined end of equilibrium and
disappearing, accelerate the reaching of equilibrium in the areas around
them. Whereas isolated systems predictably head toward ruin, such
systems are rare. Almost all real systems except those studied in the
classical period of thermodynamics are open.
The book gradually builds on ideas, with many examples, to reach its
conclusion. Summarising the final 4 page summary of the argument:
- In the linear near-equilibrium
[Onsager] region,
reciprocity relationships exist in which forces and fluxes are
coupled. ...
- In the Onsager linear regime the
total entropy production of a system due to material and energy
flows reaches a minimum at the nonequilibrium steady state. ...
- Power is conserved in the system.
...
- As systems are moved away from
the linear near-equilibrium by imposed gradients, they will use
all avenues available to counter and degrade the applied
gradients. ...
- As the applied gradients
increase, so does the system's ability to oppose further movement
from equilibrium. ...
- Systems moved away from
equilibrium by greater gradients will be accompanied by increasing
energy flows and higher entropy production rates. ...
- Open nonequilibrium systems
reside at some distance from equilibrium, produce entropy that is
exported out of the system, and maintain a low-entropy level
inside the system ...
- If a gradient is imposed on a
system, and kinetic conditions permit, autocatalytic or
self-reinforcing organizational processes and structures arise.
... it is the second law and the behavior of nonequilibrium
dissipative systems that is the main generative force for complex
dynamic organizations in nature, including those of autocatalysis.
...
- Biological systems optimally
capture energy and degrade available energy gradients as
completely as possible.
- Biological processes delay the
instantaneous dissipation of energy and give rise to energy and
material storage, cycling, and structure. ... The most successful
dissipative autocatalytic structures degrade available gradients
in such a way as to maintain their gradient-degrading
capabilities. ...
- Life and other complex systems
not only do not contradict the second law but exist because of it.
Moreover, life and other complex systems reduce preexisting
gradients more effectively than would be the case without them.
On the way to this summary we get an interesting argument, peppered
with little gems and insights such as:
p2.
tough species are not necessarily
representative of the health of their surrounding ecosystems. For
example, some of the hardiest organisms belong to pioneer species that
repopulate damaged ecosystems. Such organisms thus may signify not
health but ecosystem illness.
p203.
Cycling of material and energy within
the ecosystem changes during succession. In early succession the
cycles are short, open, and fast. In mature ecosystems the material
and energy cycles are just the opposite, with long complex cycles that
are closed in upon themselves.
But don't believe everything you read here.
p35.
In 1714 Daniel Gabriel Fahrenheit
introduced the first scale to the mercury thermometer. The low mark on
this scale, the lowest he could obtain in the lab, was zero,
thirty-two degrees less than the freezing point of water---the
temperature of ice.
Fahrenheit didn't just introduce the temperature scale: he invented
the mercury thermometer itself. And the rather meaningless "temperature
of ice" should be "freezing point of a water-salt mixture"
(or something
even
more technical). And on p45 there is mention of a small
hand-held "Sterling engine
[sic]" (I suspect it is
this
one with a misspelled filename on wikipedia, although the
correct spelling is used in its description). The authors also appear
to misunderstand gravity:
p51.
gravity, producing gradients at a cosmic
scale, must challenge any claim that the second law is an inexorable,
omnipotent force
But even gravitational collapse (from a uniform gas cloud to clumpy
blobs) does, of course, increase entropy. As well as the clumpy final
state, there is entropy produced from radiation (the collapsing gas
heats up) and/or material being ejected away (evaporated) from the
central part. So although gravitational collapse might be considered
an example of a case where nature does not "abhor a gradient",
the second law itself is still "inexorable".
There is another, minor, misconception that needs correcting:
p175.
Sir Frederick Hoyle, the astronomer, and
his Sri Lankan colleague Chandra Wickramasinghe (1984) were so bowled
over by the improbability of cells "snapping together" on
Earth that they compared it to the assembly of a 747 jet from detritus
in a junkyard by a passing tornado. Their solution to the problem was
to increase the available arena for biogenesis by removing it from
Earth to space. … However, if one assumes random interactions of
the atomic or molecular components necessary to construct even a
single minimal bacterial cell, even the seemingly adequate expansion
in time from the 4.6-billion-year-old Earth to a 15-billion-year-old
cosmos does not prove adequate.
I've seen this criticism in other places, too. I must speak in
defence of Fred Hoyle here (even if he didn't understand evolution).
He was by no means suggesting, as implied here, that a measly factor
of three increase in timescale was sufficient. 15 billion years is the
time since the Big Bang, the beginning of the universe in our current
cosmological model. Hoyle, who himself coined that name, had his own
preferred, Steady
State, model of the universe. In that model, the universe has
existed forever. So the timescale increase Hoyle was proposing was
from 4.6 billion years to infinity: plenty long enough for a
tornado to assemble a 747, or anything else!
These kind of errors in areas one knows about lead to less
confidence in believing the statements in the areas one does not know
about. Additionally, in many places the text is inconsistent (on p221
the units are calories/cm2/minute, and in the accompanying
figure 15.2 they are W/m2, and calories/tree/day);
also the prose is repetitive, purple, and elliptical, making it harder
than necessary to follow the argument. (Note to authors: metaphors are
of little use if you don't make clear the mapping from one domain to
the other, but leave the reader to guess it, and are of even less use
if the reader doesn't understand the metaphorical domain either.)
But despite these content and style caveats, the book is still well
worth reading. It contains a wealth of detail, drawing ideas from a
great range of complexity scientists, thermodynamicists, ecologists,
systems biologists, and more. As just one example, we learn about the
more modern understanding thermodynamics: the irreversibility
formulation of
Constantin
Carathéodory, the network thermodynamics of
Don Mikulecky, the dissipative
systems of Ilya Prigogine. Whilst the
traditional formulation was useful for analysing steam engines (which
is, after all, essentially why it was invented), this new approach is
more applicable to non-equilibrium open systems.
p81.
Prigogine popularized the term dissipative
structures. These dissipative systems, a term first used by Lotka,
maintain their stable, low-entropy state by importing material and
energy across their system boundaries. Dissipative systems are
nonequilibrium, open, dynamic systems with gradients across them. They
degrade energy and exhibit material and energy cycling. Dissipative
structures grow more complex by exporting---dissipating---entropy into
their surroundings
The book starts off discussing non-living, but nevertheless complex,
systems (such as tornadoes). These clearly depend on a gradient, and
their complexity can be attributed to the existence of this
(contextual) gradient.
p85.
Most "self-organizing" systems
feed on free energy from the outside to maintain their organization:
they are organized by the gradients they reduce---often they are
better described not as self-organizing, but as gradient-organized
systems with self-referential attributes.
p116.
Bénard cells are a striking
reminder that complex systems do not come from nowhere, but from
pre-existing gradients. Their complexity does not arise from within
but from their context.
Life is another such complex system, but it has more capabilities
than tornadoes or Bénard cells. For one thing, it can "time
shift" the energy it needs:
p107.
Stored energy such as fat, starch, and
glycogen frees the organism from the imperative of immediate gradient
breakdown.
And it can evolve to exploit energy sources, such as other
organisms, or other organisms' waste products. Here the authors focus
on a fundamental difference between material (nutrients) and energy
(initially sunlight):
p85.
Far-from-equilibrium systems pay for
their reduced entropy by exporting a concomitant increase in entropy
into the surrounding environment. A most familiar, if troublesome,
example of such necessary external disorder is pollution. All
organisms, not just human technological ones, produce waste. ... There
are no recycling bins in nature; everything is elegantly used and
reused because organisms, however mindless, have evolved to make use
of relatively limited materials in an environment of relatively
unlimited energy.
p148.
In every instance considered natural
selection will so operate as to increase the total mass of the organic
system, to increase the rate of circulation of matter through the
system, and to increase the total energy flux through the system, so
long as it is presented an unutilized residue of matter and available
energy ... (Lotka 1922, 149)
We might be more appreciative of this matter/energy distinction if
we were plants:
p186.
The kind of energy required for
organisms to maintain their bodies, their metabolism, is strictly
limited. The list includes light (photoautotrophy), organic chemical
energy (heterotrophy), and a very limited number of inorganic
energy-yielding chemical reactions ... Organisms also need food, which
forms the stuff of their bodies. Energy gets used up; food is
transformed into matter and materials of the body. One of the reasons
we tend to be confused about these things is that we animals don't
distinguish food from energy in our metabolism. In animals the source
of energy and food is the same (sugars and other carbohydrates, amino
acids, and proteins). In plants, however, the sources of energy and
food are entirely different; sunlight is the energy source and carbon
dioxide, chemically converted to sugars and other materials, is the
source of food.
Because the material is relative scarce, it must be used
efficiently.
p203.
In the rain forest even moisture is
recycled. Early morning and noontime temperatures, clear skies, and
sunlight lead to afternoon showers, a rapid-response cycling system.
Early successional systems do not have the root systems, leaf biomass,
and organic material to make this recycling possible. A key attribute
of a mature ecosystem is that it does not leak a lot of its nutrients,
material, and water from the system as it recycles these materials.
Diversity enables efficiency.
p244.
The climax ecosystem is a system of
energy fixers, photosynthetic food makers, and energy-degrading
herbivores. Entropy production takes place both in the making of food
and its consumption. Energy is degraded during both photosynthesis and
transpiration.
[One thing all this discussion of maximising recycling and reuse of
material nutrients: are animals, and even carnivores, inevitable in a
mature ecosystem? So, would alien ecosystems necessarily have animals?
Are they necessary to maximise the recycling, or could it all be done
with bacteria and viruses?]
When the 2nd law is cast in terms of open systems with inputs and
outputs (rather than the original, isolated systems formulations),
some problems disappear, and we can see our "selves" in a
different way.
p92.
mathematical descriptions of ecological
and evolutionary trends are, we argue, likely to follow increases in
rates and flow of energy and materials, which cycle, increasingly and
expansively, in growing thermodynamic systems. ... there is no need
for a new fourth law when the
second, stated for open systems, suffices.
p112.
Selves are not closed or isolated but
arise as metastable open systems in a sea of energy and flows. ...
Thermodynamic selfhood comes from dissipative systems that establish
boundaries. Far from sealing themselves off from the outside world,
their boundaries allow them to continue their operations. Biological
self-hood on Earth depends on the semipermeable layer, the ubiquitous
lipid cell membrane ...
p311.
… organisms remain open systems.
This means that their selfhood is already always open to encroachment,
both from the outside where they enter into alliance with other
beings, and from the inside where renegade cells, as in cancer, can
spread without concern for the good of the genotype to which they
belong. More importantly, a gene by itself is not a self; it
replicates only as part of the reproduction of a thermodynamic system
sufficiently coherent to access energetic gradients. ... Without that
integral association, a gene is just a chemical, as indeed are the
inert crystals of viruses separated from the active teleonomy of
living cells. … organisms are nested hierarchies, composed of
units that were once selves in their own right.
How can we resolve the inexorable linear march of the universal 2nd
law with biological evolutionary contingency and parochialism? Well:
p152.
The situation is similar to that between
a Boltzmannian microstate and a thermal macrostate. The specific
pattern of the particles composing the biosphere is our own, as is
that of an individual's body and life. However, the tendencies of
which these particles partake show universality.
Because of the strong thermodynamic driver in the organisation of
living systems, we may be able to see traces of earlier processes in
current ones:
p94.
Building up complexity over time,
energy-driven cycles embody a natural memory and record of their past
states. … The chemical cycles of modern cells … may contain
traces not only of their bacterial ancestors but of the thermodynamic
cycles from which bacteria themselves evolved.
The complexity of living systems originated in the physical
embodiment (metabolism), and only later was the biological information
(for replication) exploited to make the gradient reducing process even
more efficient:
p169.
The hardware by itself can exist,
metabolism can continue as long as there is energy flow, but software
cannot exist by itself; it is a virus, an "obligatory parasite."
... In life the hardware consists of the body, the software of the
genes. The thermodynamic cells and replicating nucleotides we find
together today are logically, and historically, separable. Just as one
can imagine a computer without software, so one can picture early
thermodynamic life without any genes. First came the apparatus,
functioning and physiological, then came the operating systems, user
manuals, and codes for making new, improved metabolic machines.
p251.
Variation offers new possibilities, and
natural selection whittles them down to potent systems adapted to the
current environment. But the original impetus---to make do with
available materials to dissipate high-energy systems as efficiently as
possible---is that of the second law. Even before natural selection,
the second law "selects" from the kinetic, thermodynamic,
and chemical options available, those systems best able to reduce
gradients under given constraints.
More mature ecosystems are more complex, and have a greater energy
flux, and greater entropy production (that is, life accelerates the
2nd law effect). Stressing them sends them into a less complex state,
with a lower energy flux.
p198.
One of the most obvious features of
ecosystem change during succession is the increase in biomass over
time. ... The biomass of an ecosystem increases, stabilizes, and
levels off. .... It grows. The more energy captured and flowing
through a system, the greater will be the number of entropy production
processes such as transpiration, photosynthesis, and metabolic
reactions, which all degrade in-coming energy. In ecosystems, biomass,
total system throughput, and entropy production go up with succession
and maturation.
p208.
In both living and nonliving systems the
reversion to earlier modes is triggered by reduced energy flows.
Stress sends the gradient-reducing system back to earlier modes able
to make do on less energy.
This increasing complexity producing ever more efficient energy
degradation defines a direction for evolution.
p236.
There is no essential mystery to these
heightened activities or to the thermodynamically based progressive
arrow to evolution. As organisms, tapping into the solar gradient,
expand their activities through reproduction, which is the offshoot of
thermodynamic metabolism, they bestow greater complexity upon the
environment---even as they export molecular chaos and heat to the
wider realm. Maintaining themselves in a low-entropy state, and
growing, they expand the reign both of complexity, locally, and of
disorder, pushing heat out into space. Ultimately the thermodynamic
system reaches the limits of its growth, and the energy formerly used
in expansion is redirected internally, showing up as diversity,
differentiation, and increased cycling.
p239.
Evolution's direction is that of the
equilibrium-seeking organizations of open system thermodynamics.
p316.
complexity accrues not only from the "bottom
up" via natural selection of replicating variants but
thermodynamically from the "top down" via gradient breakdown
The final part of the book focuses on economic systems and how they
might fit into the model.
p276.
Economic flows also have their entropy
production surrogates, such as transaction fees, taxes, and legal
fees. These overheads often add little value to the product or number
of energy units transferred but tend to smooth transactions. ...
Money, tradable for energy, work, and products, behaves like energy
changing forms as it organizes flows through nonhuman natural systems.
p277.
… markets and economies are not
themselves closed systems ... Markets, like organisms, depend upon
external sources for their complexity-maintaining gradient-reduction
activities. Economies, like ecosystems, expand via the natural wealth
of the gradients around them, and prosper relative to their ability to
develop conscious or unconscious mechanisms to degrade those
gradients. ... Economies and markets, like organisms and ecosystems,
are metastable, nonequilibrium systems.
p279.
the destruction of a gradient to release
its energy requires energy … thus it is that making money
requires money, and finding food requires catabolic burning of
metabolic fuel.
p284.
the economy is a system organized by
energy flows. A true NET economics would
recognize that economies, insofar as they are stable, are stabilized
away from equilibrium by material and energy flux. Such an economics
might require a modified accounting system that included urban flow
requirements. As Dyke (1988, 365) suggests, "... We never,
except in the most superficial ways, examine the relationships between
our patterns of social organization and the rate of material flow
needed to sustain them."
This rounds off the discussion that covers physical, biological, and
social complex self-organising systems (reminding me in places of
De Landa's aproach). There's a
good bibliography, for when you want to dig deeper. And it's an
extensive bibliography, because to fully understand life, we need to
consider (at least) biology, chemistry, and thermodynamics:
p303.
Evolutionary theory links organisms in
time. Ecology links organisms in space. Chemistry links them in
structure. NET links them in process.
![[stable on a gradient]](../_misc/gradient.jpg "[stable on a gradient]")
So, life (and any other complex self-organised system) is a
non-equilibrium thermodynamic system and process, living off a
gradient. I'm left with an image of forever walking up a down
escalator -- it takes effort to stay in place, but flowing down the
escalator is all energy and material needed to support this effort.
