|
| |
Entropy and Life
Over the last century, much writing and research has been devoted to the
relationship between the thermodynamic quantity entropy and the evolution of
life. The 1944 book What is Life? by Nobel-laureate physicist Erwin Schrödinger
served largely to stimulate this research. In this book, Schrödinger states that
that life feeds on negative entropy, or negentropy as it is sometimes called.
Recent writings have utilized the concept of Gibbs free energy to elaborate on
this issue.
Origin
In 1863, Rudolf Clausius published his noted memoir "On the Concentration of
Rays of Heat and Light, and on the Limits of its Action" wherein he outlined a
preliminary relationship, as based on his own work and that of William Thomson,
between his newly developed concept of entropy and life. Building on this, one
of the first to speculate on a possible thermodynamic perspective of evolution
was the Austrian physicist Ludwig Boltzmann. In 1875, building on the works of
Clausius and Kelvin, Boltzmann reasoned:
“ The general struggle for existence of animate beings is not a struggle for raw
materials – these, for organisms, are air, water and soil, all abundantly
available – nor for energy which exists in plenty in any body in the form of
heat, but a struggle for entropy, which becomes available through the transition
of energy from the hot sun to the cold earth. ”
The solar system from a thermodynamic systems perspective.
Early views
In 1876, American civil engineer Richard Sears McCulloch, in his Treatise on the
Mechanical Theory of Heat and its Application to the Steam-Engine, which was an
early thermodynamics textbook, states, after speaking about the laws of the
physical world, that "there are none that are established on a firmer basis than
the two general propositions of Joule and Carnot; which constitute the
fundamental laws of our subject." McCulloch then goes on to show that these two
laws may be combined in a single expression as follows:
“ When we reflect how generally physical phenomena are connected with thermal
changes and relations, it at once becomes obvious that there are few, if any,
branches of natural science which are not more or less dependent upon the great
truths under consideration. Nor should it, therefore, be a matter of surprise
that already, in the short space of time, not yet one generation, elapsed since
the mechanical theory of heat has been freely adopted, whole branches of
physical science have been revolutionized by it. ”
McCulloch then gives a few examples of what he calls the “more interesting
examples” of the application of these laws in extent and utility. The first
example he gives, is physiology wherein he states that “the body of an animal,
not less than a steamer, or a locomotive, is truly a heat engine, and the
consumption of food in the one is precisely analogous to the burning of fuel in
the other; in both, the chemical process is the same: that called combustion.”
He then incorporates a discussion of Lavoisier’s theory of respiration with
cycles of digestion and excretion, perspiration, but then contradicts Lavoisier
with recent findings, such as internal heat generated by friction, according to
the new theory of heat, which, according to McCullen, states that the “heat of
the body generally and uniformly is diffused instead of being concentrated in
the chest”. McCullen then gives an example of the second law, where he states
that friction, especially in the smaller blooded-vessels, must develop heat.
Without doubt, animal heat is thus in part produced.” He then asks: “but whence
the expenditure of energy causing that friction, and which must be itself
accounted for?
To answer this question he turns to the mechanical theory of heat and goes on to
loosely outline how the heart is what he calls a “force-pump”, which receives
blood and sends it to every part of the body, as discovered by William Harvey,
that “acts like the piston of an engine and is dependent upon and consequently
due to the cycle of nutrition and excretion which sustains physical or organic
life.” It is likely, here, that McCulloch was modeling parts of this argument on
that of the famous Carnot cycle. In conclusion, he summarizes his first and
second law argument as such:
“ Everything physical being subject to the law of conservation of energy, it
follows that no physiological action can take place except with expenditure of
energy derived from food; also, that an animal performing mechanical work must
from the same quantity of food generate less heat than one abstaining from
exertion, the difference being precisely the heat equivalent of that of work. ”
What is life?
Later, building on this premise, in the famous 1944 book What is Life?,
Nobel-laureate physicist Erwin Schrödinger theorizes that life, contrary to the
general tendency dictated by the Second law of thermodynamics, decreases or
maintains its entropy by feeding on negative entropy. In a note to What is
Life?, however, Schrödinger explains his usage of this term:
“ Let me say first, that if I had been catering for them [physicists] alone I
should have let the discussion turn on free energy instead. It is the more
familiar notion in this context. But this highly technical term seemed
linguistically too near to energy for making the average reader alive to the
contrast between the two things. ”
This is what is argued to differentiate life from other forms of matter
organization. In this direction, although life's dynamics may be argued to go
against the tendency of second law, which states that the entropy of an isolated
system tends to increase, it does not in any way conflict or invalidate this
law, because the principle that entropy can only increase or remain constant
applies only to a closed system which is adiabatically isolated, meaning no heat
can enter or leave. Whenever a system can exchange either heat or matter with
its environment, an entropy decrease of that system is entirely compatible with
the second law. The common justification for this argument, for example,
according to renowned chemical engineer Kenneth Denbigh, from his 1955 book The
Principles of Chemical Equilibrium, is that "living organisms are open to their
environment and can build up at the expense of foodstuffs which they take in and
degrade."
In 1964, James Lovelock was among a group of scientists who were requested by
NASA to make a theoretical life detection system to look for life on Mars during
the upcoming space mission. When thinking about this problem, Lovelock wondered
“how can we be sure that Martian life, if any, will reveal itself to tests based
on Earth’s lifestyle?” [3] To Lovelock, the basic question was “What is life,
and how should it be recognized?” When speaking about this puzzling issue with
some of his colleagues at the Jet Propulsion Laboratory, he was asked, well what
would you do to look for life on Mars? To this Lovelock replied:
“ I’d look for an entropy reduction, since this must be a general characteristic
of life. ”
Thus, according to Lovelock, to find signs of life, one must look for a
“reduction or a reversal of entropy.”
Gibbs free energy
In recent years, the thermodynamic interpretation of evolution in relation to
entropy has begun to utilize the concept of the Gibbs free energy, rather than
entropy. This is because biological processes on earth take place at roughly
constant temperature and pressure, a situation in which the Gibbs free energy is
an especially useful way to express the second law of thermodynamics. The Gibbs
free energy is given by:
The minimization of the Gibbs free energy is a form of the principle of minimum
energy, which follows from the entropy maximization principle for closed
systems. Moreover, the Gibbs free energy equation, in modified form, can be
utilized for open systems when chemical potential terms are included in the
energy balance equation. In the popular textbook 1982 textbook Principles of
Biochemistry by noted American biochemist Albert Lehninger, it is argued that
the order produced within cells as they grow and divide is more than compensated
for by the disorder they create in their surroundings in the course of growth
and division. In short, according to Lehninger, "living organisms preserve their
internal order by taking from their surroundings free energy, in the form of
nutrients or sunlight, and returning to their surroundings an equal amount of
energy as heat and entropy."
In 1998, noted Russian physical chemist Georgi Gladyshev, in his book
Thermodynamic Theory of the Evolution of Living Beings, argues that evolution of
living beings is governed by the tendency for quasi-equilibrium, semi-closed,
hierarchical living systems to evolve in the direction that tends to minimize
the Gibbs free energy of formation of each structure. Variations of the Gibbs
function of formation of a thermodynamic system at any stage of the evolution,
for instance ontogenesis and phylogenies, such as a social system, according to
Gladyshev, "can be calculated by means of thermodynamic methods." Gladyshev
calls this a form of sociological thermodynamics.
Similarly, according to the chemist John Avery, from his recent 2003 book
Information Theory and Evolution, we find a presentation in which the phenomenon
of life, including its origin and evolution, as well as human cultural
evolution, has its basis in the background of thermodynamics, statistical
mechanics, and information theory. The (apparent) paradox between the second law
of thermodynamics and the high degree of order and complexity produced by living
systems, according to Avery, has its resolution "in the information content of
the Gibbs free energy that enters the biosphere from outside sources."
Books
Schrödinger, Erwin (1944). What is Life - the Physical Aspect of the
Living Cell. Cambridge University Press. ISBN 0-521-42708-8.
a b
Lehninger, Albert (1993). Principles of Biochemistry, 2nd Ed.. Worth
Publishers. ISBN 0-87901-711-2.
Gladyshev, Georgi (1998). Thermodynamic Theory of the Evolution of Living
Beings. Nova Science Publishers. ISBN 1560724579.
Gladyshev G. P. (2006). "The Principle of Substance Stability is
Applicable to all Levels of Organization of Living Matter" [PDF], Int. J. Mol.
Sci., 7, 98-110 - International Journal of Molecular Sciences (IJMS) (ISSN:
1422-0067 Online; ISSN: 1424-6783 CD-ROM; CODEN: IJMCFK).
Avery, John (2003). Information Theory and Evolution. World Scientific.
ISBN 981-238-399-9.
Scientific Approaches To The Meaning
of Life Entropy and Life
What is Life?
Philosophical views on the meaning of life
Religion and Religious humanism
Spiritual and mystical views
Cosmogony
Abiogenesis
Emanationism
Eschatology
Back to
Spiritual Ideas
| |
|