Vincent Torley
is a philosopher who contributes posts to The Skeptical Zone. In the past
year, he wrote an article critiquing my writings on the origin of life in
which he presented several counterarguments based on a variety of popular and
academic articles. He erred in his description of thermodynamics and the state
of the literature, but his mistakes were completely understandable. He has not
extensively studied non-equilibrium thermodynamics, and the ideas can be quite
subtle. In addition, he took at face value claims from origins puff pieces that
greatly exaggerated experimental results. And he attempted to discuss concepts
such as complexity that are often poorly defined and not used consistently even
in technical articles. However, he has assembled a fairly complete sampling of
common mistakes related to the origins conversation, so his efforts were of
great value. Today, I will correct the mistakes related to thermodynamics.
The core
thermodynamic problem for the origin of life is that nature always tends to
move towards states of higher entropy or states of lower energy or
both. More specifically, the entropy and energy (or enthalpy at constant
pressure) is commonly combined into the measure of the free energy, and all
spontaneous processes without outside assistance move toward
lower free energy. As an analogy, imagine a library with some
portion of the books on book shelves and many on the floor. The higher shelves
correspond to higher energy states. Also imagine a small percentage of the
books have been arranged according to the Library of Congress Classification
(LCC) system, but most are distributed randomly. Books more randomly arranged
correspond to higher entropy. Any state of life would then correspond to the
majority of books on the top shelves (high energy) with a large percentage arranged
in LCC order (low entropy).
The driving
tendencies in nature on the early Earth would have been analogous to seismic
tremors rearranging the books in the library. During the tremors, some of the
books on the floor would jump to the shelves, and some of the books on the
shelves would jump to other shelves or onto the floor. The natural tendency
over time would be for books on the higher shelves to fall to lower shelves,
and the largest number would ultimately reside on the floor. In addition, books
that were to some extent sequenced in a specific order would tend to randomly
shuffle around. The books would never end up highly ordered on the top shelf.
In the same way, any arrangement of chemicals at nearly any stage of coalescing
into the first cell would move away from that target and towards simple
randomly arranged molecules. Adding more energy would not help, since any
natural energy source would act like a more intense earthquake impacting the
library. The system would move in the opposite direction of life even faster.
As a technical
digression, the library books analogy works best for those who are comfortable
with the formalism of configurational entropy. However, the
principle still holds true even for those who wish to think only in terms
of traditional thermodynamic entropy. The bottom line is
that life has higher energy and lower entropy by any definition than the molecules
from which it sprang. Therefore, nature would always resist its spontaneous
formation. The fact that the building blocks have to be arranged in a highly
specific order could simply be added
to the entropy as a configurational part. Alternatively, the
probability of them coming together properly could be thought of as a separate
probabilistic challenge in addition to the entropy challenge. Either way, the
entropy/configurational barrier is insurmountable.
In relation to
energy, a common belief is that adding energy strongly biases molecules toward
higher energy states. This assumption is completely wrong. Systems will tend to
configure into states with a probability that drops off exponentially with
increasing energy as crudely illustrated in the books analogy. In other words,
lower energy states are always more likely than higher energy states unless the
higher energy states are considerably more numerous. At equilibrium, any system
would move towards the Boltzmann Distribution. If
energy were added, the net effect would be to raise the temperature which would
cause the distribution of higher energy states to drop off more slowly. In
other words, adding energy does not cause a large percentage of the lower
energy states to jump to significantly higher energy. The lower energy states
still dominate, just less so than before.
In addition,
adding energy always causes the entropy to increase. As an example, imagine
some environment that contains many individual amino acids and some amino acid
chains of varying length. A challenge is for the amino acids to combine with
the chains to lengthen them since that reaction is thermodynamically
unfavorable. Adding energy would increase the rate at which amino acids combine
into longer chains since they would on average have more
kinetic energy to overcome reaction barriers. However, the added
energy would to a much greater extent cause the existing chains to break apart
since the breaking of a peptide bond only has to overcome the activation
energy barrier which is smaller. Similarly, dehydrating a pond
could help amino acids to combine into chains, but the process would more
likely destroy existing chains. The net effect would always be to move away
from large numbers of longer chains that would be essential for life.
The only
solution is for some engine to process an energy source and then redirect that
energy to perform useful work. Also, information would be required, so the work
could be directed properly to assemble and operate the cell. In life, the
processing of energy requires cellular structures coupled to chemical cycles
which use sunlight or the breakdown of fuel (e.g., glucose) to produce
high-energy molecules such as ATP. And information is embedded in the highly
specific sequences of chains of amino acids in proteins. The sequencing causes
the chains to fold into the correct structures (enzymes)
which drive the needed reactions to build the right cellular components and
maintain the metabolism. The enzymes also link the breakdown of
the high-energy molecules to reactions and other processes that
move energetically uphill, so the net change in free energy is negative. The
energy from the former reaction is used to drive the uphill ones, thus
overcoming the free energy barrier.
Torley writes
that the work of Jeremy England has overcome all of these challenges by
demonstrating that natural processes could move a system toward higher free
energy. This claim represents a complete misunderstanding of his research. England’s
simulations study how energy could be absorbed from some source and then
released (dissipated) into the environment. His models presuppose that energy
is readily available, and it can be directly accessed to drive specific
reactions of interest. In other words, if his models did relate to the origin
of life, he would have assumed that the central problem of processing and
redirecting an available energy source would have already been solved.
However, in none
of his technical papers does he directly relate any of his work to concrete
origin-of-life research. He simply states that his models might offer possible
analogies, and he identifies minimum heat dissipation in self-replication.
Popular-level articles have strongly made the connection to the origin of life
but without any justification. To the contrary, England’s work is based
on fluctuation theorems which demonstrate
that systems driven from equilibrium tend towards states of higher entropy and
greater energy dissipation — the opposite direction of what is needed for the
first cell. For perspective on the problem: combining basic molecules into a
bacterium requires energy being absorbed (opposite of dissipated) from the
environment in the amount of roughly 0.27 ev/atom. This value,
if scaled, would parallel a bathtub of room-temperature water absorbing enough
heat from the environment to start boiling. A clear impossibility.
Torley also
references a paper by David Ruelle which attempts
to explain how the free energy challenges to the origin of life could be
overcome based on statistical mechanics. The paper is quite technical and
abstract, so the underlying arguments are not easily accessible. In addition,
Ruelle primarily references other highly theoretical research, and he makes no
attempt to ground his arguments in physical reality. However, the key point is
fairly straightforward. He first fully acknowledges that physical processes
tend toward lower free energy. He then describes how a set of stable reactions
could form that draw free energy from outside “nutrients” which act as fuel. In
other words, Ruelle presupposes the existence of an engine which can process
fuel and mechanisms which then redirect the energy toward specific chemical
reactions.
All other papers
that propose solutions to the thermodynamic challenges use the same approach.
They ignore nearly all practical challenges and completely disassociate their
work from realistic experiments. And they assume the existence of an unlimited
source of energy, an efficient energy converter (engine), and information.
However, the converter and the required information must
already exist before the converter could be created. The only explanation for
the sudden appearance of such molecular machinery and the information is
intelligence.
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