The great founders of Western science stressed the universality and the eternal character of natural laws. They set out to formulate general schemes that would coincide with the very ideal of rationality.
As Roger Hausheer says in his fine introduction to Isaiah Berlin's Against the Current, "They sought all-embracing schemas, universal unifying frameworks, within which everything that exists could be shown to be systematically-i.e., logically or causally-interconnected, vast structures in which there should be no gaps left open for spontaneous, unattended developments, where everything that occurs should be, at least in principle, wholly explicable in terms of immutable general laws."[1]
Great progress has indeed been realized in the unification of some of the basic forces found in nature. Still, the fundamental level remains elusive. Wherever we look we find evolution, diversification, and instabilities.
Curiously, the unexpected complexity that has been discovered in nature has not led to a slowdown in the progress of science, but on the contrary to the emergence of new conceptual structures that now appear as essential to our understanding of the physical world—the world that includes us.
In classical science the emphasis was on time-independent laws. As we shall see, once the particular state of a system has been measured, the reversible laws of classical science are supposed to determine its future, just as they had determined its past. It is natural that this quest for an eternal truth behind changing phenomena aroused enthusiasm. But it also came as a shock that nature described in this way was in fact debased: by the very success of science, nature was shown to be an automaton, a robot.
The urge to reduce the diversity of nature to a web of illusions has been present in Western thought since the time of Greek atomists. Lucretius, following his masters Democritus and Epicurus, writes that the world is "just" atoms and void and urges us to look for the hidden behind the obvious".[2]
Yet it is well known that the driving force behind the work of the Greek atomists was not to debase nature but to free men from fear, the fear of any supernatural being, of any order that would transcend that of men and nature. What I refer to as an athiest agenda.
Modern science transmuted this fundamentally ethical stance into what seemed to be an established truth; and this truth, the reduction of nature to atoms and void, in turn gave rise to what Lenoble[3] has called the "anxiety of modern men." How can we recognize ourselves in the random world of the atoms? Must science be defined in terms of rupture between man and nature? "All bodies, the firmament, the stars, the earth and its kingdoms are not equal to the lowest mind; for mind knows all this in itself and these bodies nothing."[4]
This "Pensee" by Pascal expresses the same feeling of alienation we find among contemporary scientists such as Jacques Monod:
Man must at last finally awake from his millenary dream ; and in doing so, awake to his total solitude, his fundamental isolation. Now does he at last realize that, like a gypsy, he lives on the boundary of an alien world. A world that is deaf to his music. just as indifferent to his hopes as it is to his suffering or his crimes.[5]
In the past, strong distinctions were frequently made between man's world and the supposedly alien natural world. A famous passage by Vico in The New Science describes this most vividly:
... in the night of thick darkness enveloping the earliest antiquity, so remote from ourselves, there shines the eternal and never failing light of a truth beyond all question: that the world of civil society has certainly been made by men, and that its principles are therefore to be found within the modifications of our own human mind. Whoever reflects on this cannot but marvel that the philosophers should have bent all their energies to the study of the world of nature, which, since God made it, He alone knows; and that they should have neglected the study of the world of nations, or civil world, which, since men had made it, men could come to know.[6]
2
In the past, the questioning of nature has taken the most diverse forms. Sumer discovered writing; the Sumerian priests speculated that the future might be written in some hidden way in the events taking place around us in the present. They even systematized this belief, mixing magical and rational elements.[7]
Alexandre Koyres has defined the innovation brought about by modern science in terms of "experimentation."[8] That is, on the conviction that nature responds to experimental interrogation. Experimentation does not mean merely the faithful observation of facts as they occur, nor the mere search for empirical connections
between phenomena, but presupposes a systematic interaction between theoretical concepts and observation.
Nature cannot be forced to say anything we want it to. Scientific investigation is not a monologue. As Karl Popper concluded, rational science owes its existence to its success; the scientific
method is applicable only by virtue of the astonishing points of agreement between preconceived models and experimental results.[9]
The success of Western science is an historical fact, unpredictable a priori , but which cannot be ignored. The surprising success of modern science has led to an irreversible transformation of our relations with nature.
Science initiated a successful dialogue with nature. On the other hand, the first outcome of this dialogue was the discovery of a silent world. This is the paradox of classical science. It revealed to men a dead, passive nature, a nature that behaves as an automaton which, once programmed, continues to follow the rules inscribed in the program. In this sense the dialogue with nature isolated man from nature instead of bringing him closer to it. A triumph of human reason turned into a sad truth. It seemed that science debased everything it touched.
Modern science horrified both its opponents, for whom it appeared as a deadly danger, and some of its supporters, who saw in man's solitude as "discovered" by science the price we had to pay for this new rationality.
The cultural tension associated with classical science can be held at least partly responsible for the unstable position of science within society; it led to an heroic assumption of the harsh implications of rationality, but it led also to violent rejection.
Let us take an earlier example-the irrationalist movement in
Germany in the 1920s that formed the cultural background to
quantum mechanics.[10] In opposition to science, which was
identified with a set of concepts such as causality, determnism, reductionism, and rationality, there was a violent upsurge of ideas denied by science but seen as the embodiment of the fundamental irrationality of nature. Life, destiny, freedom, and spontaneity thus became manifestations of a shadowy underworld impenetrable to reason. We can state that this rejection illustrates the risks associated with classical science. By admitting only a subjective meaning for a set of experiences men believe to be significant, science runs the risk of transferring these into the realm of the irrational, bestowing upon them a formidable power.
As Joseph Needham has emphasized, Western thought has always oscillated between the world as an automaton and a theology in which God governs the universe. This is what Needham calls the "characteristic European schizophrenia."[11] In fact, these visions are connected. An automaton needs an external god.
Do we really have to make this tragic choice? Must we choose between a science that leads to alienation and an anti-scientific metaphysical view of nature? We think such a choice is no longer necessary. Modern science originated in the specific context of the European seventeenth century. We are now approaching the end of the twentieth century, and it seems that some more universal message is carried by science, a message that concerns the interaction of man and nature {the universe} as well as of man with man.
3
What are the assumptions of classical science from which we believe science has freed itself today? Generally those centering around the basic conviction that at some level the world is simple and is governed by time-reversible fundamental laws. This appears as an excessive simplification.
We may compare it to reducing buildings to piles of bricks. Yet out of the same bricks we may construct a factory, a palace, or a
cathedral. It is on the level of the building as a whole that we
apprehend it as a creature of time, as a product of a culture, a
society, a style. But there is the additional and obvious problem that, since there is no one to build nature, we must give to its very "bricks"—that is, to its microscopic activity—a description that accounts for this building process.
The question of classical science is in itself an illustration of a dichotomy that runs throughout the history of Western thought. Only the immutable world of ideas was traditionally recognized as "illuminated by the sun of the intelligible," to use Plato's expression. In the same sense, only eternal laws were seen to express scientific rationality. Temporality was looked down upon as an illusion. This is no longer true today.
"From the point of view of philosophy of science the conception associated with entropy must, I think, be ranked as the great contribution of the nineteenth century to scientific thought. It marked a reaction from the view that everything to which science need pay attention is discovered by a microscopic dissection of objects."[^12]
Science are discoveries at the microscopic level, that of molecules, atoms, or elementary particles. In fact, this success has been so overwhelming that for many scientists the aim of research is identified with this "microscopic dissection of objects."[^13]
The second law of thermodynamics presented the first
challenge to a concept of nature that would explain away the
complex and reduce it to the simplicity of some hidden world.
Perspective is shifting from substance to relation, to communication, to time.
Our universe has a pluralistic, complex character. Structures may disappear, but also they may appear. Some processes are , as far as we know, well described by deterministic equations, but others involve probabilistic processes.
The artificial may be deterministic and reversible. The natural contains essential elements of randomness and irreversibility. This leads to a new view of matter in which matter is no longer the passive substance described in the mechanistic world view but is associated with spontaneous activity. This change is so profound we can really speak about a new dialogue of man with nature.
4
A conceptual transformation of science from the Golden Age of classical science to the present is occurring. This evolution is proceeds on somewhat parallel lines at every level, be it that of elementary particles, chemistry, biology, or cosmology. On every scale self-organization, complexity, and time play a new and unexpected role.society
Our aim is to examine the significance of three centuries of scientific progress from a definite viewpoint. The problem of time is really the center of the research that one of us has been pursuing all his life.
When as a young student at the University of Brussels he came into contact with physics and chemistry for the first time, he was astonished that science had so little to say about time, especially since his earlier education had centered mainly around history and archaeology. This surprise could have led him to two attitudes, both of which we find exemplified in the past: one 6 would have been to discard the problem, since classical science seemed to have no place for time; and the other would have been to look for some other way of apprehending nature, in which time would play a different, more basic role. This is the path Bergson and Whitehead, to mention only two philosophers. of our century, chose. The first position would be a "positivistic" one, the second a "metaphysical" one.
There was, however, a third path, which was to ask whether the simplicity of the temporal evolution traditionally considered in physics and chemistry was due to the fact that attention was paid mainly to some very simplified situations, to the bricks rather than the cathedral.
"The specific and unique versus the repetitive and the universal, the concrete versus the abstract, perpetual movement versus rest, the inner versus the outer, quality versus quantity, culture-bound versus timeless principles, mental strife and self-transformation as a permanent condition of man versus the possibility (and desirability) of peace, order, final harmony and the satisfaction of all rational human wishes—these are some of the aspects of the contrast."[^14]This & that
Classical dynamics seems to express in an especially clear and
striking way the static view of nature. Here time apparently is
reduced to a parameter, and future and past become equivalent.
As early as at the beginning of the nineteenth century, precisely when classical science was triumphant, when the Newtonian program dominated French science and the latter dominated Europe, the first threat to the Newtonian construction loomed into sight. The development of the science of heat, this rival to Newton's science of gravity, starting from the first gauntlet thrown down when Fourier formulated the law governing the propagation of heat. It was, in fact, the first quantitative description of something inconceivable in classical dynamics an irreversible process.
The two descendents of the science of heat, the science of energy conversion and the science of heat engines, gave birth to the first "nonclassical" science—thermodynamics. The most original contribution of thermodynamics is the celebrated second law, which introduced into physics the arrow of time.
The nineteenth century was really the century of evolution; biology, geology, and sociology emphasized processes of becoming, of increasing complexity. As for thermodynamics, it is based on the distinction of two types of processes: reversible processes, which are independent of the direction of time, and irreversible processes, which depend on the direction of time. It was in order to distinguish the two types of processes that the concept of entropy was introduced, since entropy increases only because of the irreversible processes.
During the nineteenth century the final state of thermodynamic evolution was at the center of scientific research. This was equilibrium thermodynamics. We now know that far from equilibrium, new types of structures may originate spontaneously. In far-from-equilibrium conditions we may have transformation from disorder, from thermal chaos, into order. New dynamic states of matter may originate, states that reflect the interaction of a given system with its surroundings. We have called these new structures dissipative structures to emphasize the constructive role of dissipative processes in their formation.
Wwhen we move from equilibrium to far-from equilibrium conditions, we move away from the repetitive and the universal to the specific and the unique. Indeed, the laws of equilibrium are universal. Matter near equilibrium behaves in a "repetitive" way. On the other hand, far from equilibrium there appears a variety of mechanisms corresponding to the possibility of occurrence of various types of dissipative structures.
For example, far from equilibrium we may witness the appearance of chemical clocks, chemical reactions which behave in a coherent, rhythmical fashion. We may also have processes of self-organization leading to nonhomogeneous structures to nonequilibrium crystals.
We would like to emphasize the unexpected character of this behavior. Every one of us has an intuitive view of how a chemical reaction takes place; we imagine molecules floating through space, colliding, and reappearing in new forms. We see chaotic behavior similar to what the atomists described when they spoke about dust dancing in the air. But in a chemical clock the behavior is quite different. Oversimplifying somewhat, we can say that in a chemical clock all molecules change their chemical identity simultaneously, at regular time intervals. If the molecules can be imagined as blue or red, we would see their change of color following the rhythm of the chemical clock reaction.
Obviously such a situation can no longer be described in terms of chaotic behavior. A new type of order has appeared. We can speak of a new coherence, of a mechanism of "communication" among molecules. But this type of communication can arise only in far-from-equilibrium conditions. It is quite interesting that such communication seems to be the rule in the world of biology. It may in fact be taken as the very basis of the definition of a biological system.
In addition, the type of dissipative structure depends critically on the conditions in which the structure is formed. External fields such as the gravitational field of earth, as well as the magnetic field, may play an essential role in the selection mechanism of self-organization.
What seems certain is that these far-from-equilibrium phenomena illustrate an essential and unexpected property of matter: physics may henceforth describe structures as adapted to outside conditions. We meet in rather simple chemical systems a kind of prebiological adaptation mechanism. To use somewhat anthropomorphic language: in equilibrium matter is "blind," but in far-from-equilibrium conditions it begins to be able to perceive, to "take into account," in its way of functioning, differences in the external world.
From this perspective life no longer appears to oppose the "normal" laws of physics, struggling against them to avoid its
normal fate—its destruction. On the contrary, life seems to
express in a specific way the very conditions in which our biosphere is embedded, incorporating the nonlinearities of chemical reactions and the far-from-equilibrium conditions imposed
on the biosphere by solar radiation.
We have discussed the concepts that allow us to describe the formation of dissipative structures, such as the theory of bifurcations. It is remarkable that near-bifurcations systems present large fluctuations. Such systems seem to " hesitate" among various possible directions of evolution, and the famous law of large numbers in its usual sense breaks down. A small fluctuation may start an entirely new evolution that will drastically change the whole behavior of the macroscopic system. The analogy with social phenomena, even with history, is inescapable. Far from opposing "chance" and "necessity," we now see both aspects as essential in the description of non-linear systems far from equilibrium.
We need to thus deal with two conflicting views of the physical universe: the static view of classical dynamics, and the evolutionary view associated with entropy.[12]
For a long time this confrontation was postponed by considering irreversibility as an illusion, as an approximation; it was man who introduced time into a timeless universe. We can no longer avoid this confrontation.
The problem of irreversibility still remains a subject of lively
controversy. How is this possible one hundred fifty years after
the discovery of the second law of thermodynamics? There are
many aspects to this question. There is a cultural component in the mistrust of time. We cite the opinion of Einstein: time (as irreversibility) is an illusion. In fact, Einstein was reiterating what Giordano Bruno had written in the sixteenth century and what had become for centuries the credo of science: "The universe is, therefore, one, infinite, immobile ... It does not move itself locally ... It does not generate itself ... It is not corruptible ... It is not alterable ..."[13] For a long time Bruno's vision dominated the scientific view of the Western world. It is therefore not surprising that the intrusion of irreversibility was received with mistrust.
But there are technical reason in addition to cultural ones. Every attempt to "derive" irreversibility from dynamics necessarily had to fail, because irreversibility is not a universal phenomenon. We can imagine situations that are strictly reversible, such as a pendulum in the absence of friction, or planetary motion. This failure has led to the feeling that, in the end, the whole concept of irreversibility has a subjective origin.
Let us say here that today we can see this problem from a different point of view, since we now know that there are different classes of dynamic systems. The world is far from being homogeneous. Therefore the question can be put in different terms: What is the specific structure of dynamic systems that permits them to "distinguish" past and future? What is the minimum complexity involved {or needed/necessary}?
As we shall see, the second law of thermodynamics corresponds to a selection rule, to a restriction on initial conditions that is then propagated by the laws of dynamics. Therefore the second law introduces a new irreducible element into our description of nature. While it is consistent with dynamics, it cannot be derived from dynamics.
Boltzman already understood that probability and irreversibility had to be closely related. Only when a system behaves in a sufficiently random way may the difference between past and future, and therefore irreversibility, enter into its description.
The arrow of time is a manifestation of the fact that the future is not given, that, as the French poet Paul Valery emphasized, "time is construction."[14]
The experience of our everyday life manifests a radical dif
ference between time and space. We can move from one point
of space to another. However, we cannot turn time around. We
cannot exchange past and future.
Scientifically, permitted states are separated from states that are prohibited by the second law of thermodynamics by means of an infinite entropy barrier. There are other barriers in physics. One is the velocity of light, which in our present view limits the speed at which signals may be transmitted. It is essential that this barrier exist; if not, causality would fall to pieces. Similarly, the entropy barrier is the prerequisite for giving a meaning to communication. Imagine what would happen if our future would become the past for other people!
The recent evolution of physics has emphasized the reality of time. In the process new aspects of time have been uncovered. A preoccupation with time runs all through our century. Think of Einstein, Proust, Freud, Teilhard, Peirce, or Whitehead.
One of the the most surprising results of Einstein's special theory of relativity, published in 1905, was the introduction of a
local time associated with each observer. However, this local time remained a reversible time . Einstein's problem both in the special and the general theories of relativity was mainly that of the "communication" between observers, the way they could compare time intervals.
In classical mechanics time was a number characterizing the position of a point on its trajectory. But time may have a different meaning on a global level. When we look at a child and guess his or her age, this age is not located in any special part of the child's body. It is a global judgment. It has often been stated that science spatializes time. But consider a landscape and its evolution: villages grow, bridges and roads connect different regions and transform them. Space thus acquires a temporal dimension; following the words of geographer B. Berry, we have been led to study the "timing of space."
Perhaps the most important progress is that we now may see the problem of structure, of order, from the perspective of dynamics, be it classical or quantum, there can be no one time-directed evolution. The "information" as it can be defined in terms of dynamics remains constant in time. This sounds paradoxical.
When we mix two liquids, there would occur no "evolution" in spite of the fact that we cannot, without using some external device, undo the effect of the mixing.
On the contrary, the entropy law describes the mixing as the evolution toward a "disorder," toward the most probable state. To speak about information, or order, we have to redefine the units we are considering. The important new fact is that we now may establish precise rules to go from one type of unit to the other. In other words, we have achieved a microscopic formulation of the evolutionary paradigm expressed by the second law.
5
Erwin Schrödinger once wrote, to the indignation of many phi
losophers of science:
... there is a tendency to forget that all science is bound up with human culture in general, and that scientific findings, even those which at the moment appear the most advanced and esoteric and difficult to grasp, are meaningless outside their cultural context. A theoretical science, unaware that those of its constructs considered relevant and momentous are destined eventually to be framed in concepts and words that have a grip on the educated community and become part and parcel of the general world picture—a theoretical science, I say, where this is forgotten, and where the initiated continue musing to each other in terms that are, at best, understood by a small group of close fellow travellers, will necessarily be cut off from the rest of cultural mankind; in the long run it is bound to atrophy and ossify however virulently esoteric chat may continue within its joyfully isolated groups of experts.[15]
We wish to apply a strong intermingling of the issues proper to culture as a whole and the internal conceptual problems of science in particular. We find questions about time at the very heart of science. Becoming, irreversibility—these are questions to which generations of philosophers have also devoted their lives. Today, when history—be it economic, demographic, or political—is moving at an unprecedented pace, new questions and new interests require us to enter into new dialogues, to look for a new coherence.
However, we know the progress of science has often been described in terms of rupture, as a shift away from concrete experience toward a level of abstraction that is increasingly difficult to grasp. We believe that this kind of interpretation is only a reflection, at the epistemological level, of the historical
situation in which classical science found itself, a consequence of its inability to include in its theoretical frame vast areas of the relationship between man and his environment.
The rediscovery of time has roots both in the internal history of science and in the social context in which science finds itself today. Discoveries such as those of unstable elementary particles or of the expanding universe clearly belong to the internal history of science, but the general interest in nonequilibrium situations, in evolving systems, may reflect our feeling that humanity as a whole is today in a transition period.
Asserting this receptiveness to cultural content runs counter to the traditional conception of science. In this view science develops by freeing itself from outmoded forms of understanding nature; it purifies itself in a process that can be compared to an "ascesis" of reason. But this in turn leads to the conclusion that science should be practiced only by communities living apart, uninvolved in mundane matters. In this view, the ideal scientific community should be protected from the pressures, needs, and requirements of society. Scientific progress ought to be an essentially autonomous proces s that any " outside" influence, such as the scientists's participation in other cultural, social, or economic activities, would merely disturb or delay.
This ideal of abstraction, of the scientist's withdrawal, finds an ally in still another ideal, this one concerning the vocation
of a "true" researcher, namely, his desire to escape from
worldly vicissitudes. Einstein describes the type of scientist
who would find favor with the "Angel of the Lord" should the
latter be given the task of driving from the "Temple of Science" all those who are "unworthy"—it is not stated in what
respects. They are generally
... rather odd, uncommunicative, solitary fellows, who despite these common characteristics resemble one another really less than the host of the banished.
What led them into the Temple? . . . one of the strongest motives that lead men to art and science is flight from everyday life with its painful harshness and wretched dreariness, and from the fetters of one's own shifting desires. A person with a finer sensibility is driven to escape from personal existence and to the world of objective observing (Schauen) and understanding. This motive can be compared with the longing that irresistibly pulls the town-dweller away from his noisy, cramped quarters and toward the silent, high mountains, where the eye ranges freely through the still, pure air and traces the calm contours that seem to be made for eternity.
With this negative motive there goes a positive one. Man seeks to form for himself, in whatever manner is suitable for him, a simplified and lucid image of the world (Bild der Welt), and so to overcome the world of experience by striving to replace it to some extent by this image.[16]
The incompatibility between the ascetic beauty sought after
We are aware that