Jacques Maritain Center: Thomistic Institute

Natural Time and Human Time

Juan José Sanguineti
Pontifical Atheneum of the Holy Cross

1. Introduction

Modern philosophical speculations on temporality usually refer to the time of human consciousness opposing it to natural time. There are often doubts concerning the existence of natural time. The object we call 'time', with its topological distinction between past and future, for many authors would be the result of the present, which would be an exclusive characteristic of our consciousness. The present would be the 'now' in flux dividing past from future, our now, i. e. the identity of the 'self' in the sequence of the different mental states. It can be excluded a recourse to absolute time. The constant and linear flow of time belongs, then, to the acts of consciousness. In the extra-mental nature there would be only the earlier-later (prius- posterius) relationship of order(1). Briefly, the introduction of the 'self' would be the cause of the emergence of real time. The direction from past to future then would be merely gnoseological, namely it would emerge from the present of the observer or from the things present to him. The past would exist just in the memory of the mind, and the future in its anticipations. In the real world there would be only our 'now' and everything being simultaneous to it.

This position is not quite satisfactory. The psychological time is also a natural fact, rooted in an ever-growing-old body. The sequence of our mental states is tied to the sequence of our neurophysiological events. The brain enjoys a thermodynamic temporal arrow. If we observers do introduce a temporal dimension, it is because we are in motion as a part of the universe. Our observational acts take place one after another, while the sequence of the external phenomena are measuring the time of the observational acts as well. I do change even on watching the changing landscape, and therefore I am a temporal being. I see the street at 4:00 p.m. and later at 4:30 p.m. As a quiet observer, I am measured by the movement of a clock. I notice however that I have accomplished two acts of observation: then I have moved too. If the street should be motionless, I could myself be regarded as a clock of what's going on in the street.

The attribution of temporality to consciousness in the sense we have described above seems to be linked to the classical dualism between mind and matter. Such a position may be more comprehensible in the scientific frame of classical physics, wherein time appears somewhat irrelevant. Motion in classical mechanics is described according to temporal coordinates, but the reversal of the temporal sense leaves unchanged the dynamic equations. The temporal flux might be referred to an absolute time previous to things, but then it would more plausible to translate it into the psychological time (as Kant did). This psychological time, however, is not completely opposed to physical time, as we have said, since it finds its root in the very nature of physical reality. A pure consciousness without a body would be timeless.

We acknowledge, of course, that the ordinary set-up of physics generally does not take into account the time we might call evolutionary time, which is time in a strong sense (namely a time with the real distinction between past and future, based on an irreversible series of events). Modern physics (classical, but relativity and quantum physics as well) tends to formulate the invariant laws of natural phenomena. This is the ideal of many theoretical scientists, like Einstein or Hawking. Such an ideal ultimately goes back to the ancient Greek paradigm of an everlasting nature despite its many evolving features. An eternal world has no history, lacking a true past and future. The end of the recurring process meets the beginning of the same process. Obviously modern science did not resume the idea of the eternal return, but it remained however open to an 'eternistic' conception when the universe comes to be seen as stationary, in the absence of an evolutionary vision.

Since the nineteenth century, as it is very well-known, the historical perspective in the scientific vision of nature has emerged thanks for the most part to cosmology. This perspective conflicts with the ideal of the 'eternal' description mentioned above. For the dynamic laws any historical fact is simply a particular case. The history of a cosmos would be an instance among many others. The antithesis between law (in itself timeless rather than eternal) and history (in the large sense of the word) stands out. Both are connected through the concept of initial or boundary conditions(2).

A vision of nature as history is obvious in the evolutionary cosmology and in the biological theories of evolution. The attempts to get a 'non-historical' cosmology have been unsuccessful (e. g. the first model of Einstein with the introduction of a special cosmological constant in order to prevent any change, or the stationary theory of Hoyle). Of course, the most typical area in physics where time has been introduced in a compelling (and intriguing) way was thermodynamics. Physical processes (in closed systems) show a law-like irreversible (statistical) tendency to the increment of entropy (II principle). For the nomological frame there is a possibility that yet never occurs in nature: we have never seen closed systems evolving towards the reduction of entropy. A long series of studies on the problem of the direction of time sprang from this further contrast between laws and facts(3). As far as we are now concerned, notice that time, firstly relegated to psychology and nearly absent in nature, then returned in a significant way in the very heart of nature, not as mere succession but in a strong way, namely as an irreversible transit to the future, which is the meaning of 'history'.

I do not intend to discuss now the problem of time in the natural sciences(4). Whether there exists an arrow of time in the different branches of physics may seem controversial today. Deep metaphysical attitudes (not merely scientific) collide in the debates. Two usual contrary mentalities come out in the confrontation: one 'timeless' and the other 'temporalistic'. Einstein, getting to a real metaphysical level (but unfortunately reductionistic), conceived the cosmos as an immutable block, already given as a total and timeless harmony. The impressions of coming from the past and going to the future would be just illusions of our local perspective(5). The counter position is well represented by I. Prigogine. In stressing the overall comprehensive presence of time in a self-creative nature, he is approaching rather an Epicurean view.

Prigogine emphasised as well the introduction of a strong temporality in natural sciences as a notable fact that helps their reconciliation with human sciences. We can agree with this point, all along with the idea of overcoming the super- dualism between mind and nature, in an Aristotelian approach very much in the line of the current state of natural sciences(6). So we come back to the initial point of this paper: the one-sided attribution of temporality to human consciousness is a sign of the separatist dualism between mind and nature. We should tackle the topic more in consonance with the unity between man and the natural world, though recognising as well the emergence of the spiritual soul of man over the bodily basis.

2. Ontological time

In the next part of this contribution I will follow a philosophical method. Science does not solve the problem of time, but presupposes it and sometimes also hides it (as when Husserl considered Galileo as a genius that "discovered but together hid"). A philosophy of nature regarding the question of time cannot ignore the sciences, but must also focus on the whole intellectual knowledge about reality, both before and after the mediation of the scientific knowledge. Metascientific thought (i. e. philosophy) is necessary since science works always in a particular frame of objectivation.

In our view, the philosophical method is both phenomenological and ontological. We have to consider again and again several and different experiences, together with their mutual confrontation, in order to get some insight and so to argue within the area of what has been understood. Historical horizons are not an obstacle for the knowledge of truth, but rather an aid, though involving the unavoidable limits of human knowledge. Husserl's phenomenology is not sufficient since it is deprived of an ontological weight: it favors consciousness, but it leaves aside nature. The last Husserl anyway approached the 'world of life' (in his work The Crisis of European Science and Transcendental Phenomenology) and in this sense he pointed out a more practicable way of phenomenology in a realistic version.

In the popular knowledge of the Lebenswelt man attains real things, which may be sometimes more relevant than the aspects attained through science. The phenomenological vision is the point of departure for the realistic insight: on observing reality in its manifest being, such vision makes itself ready for the metaphysical comprehension. Firstly, we become aware of natural being, and at the same time we notice our personal being shared with other people. We live in an ordered world, in a cosmos which is open to our common insight. The philosophical intelligence departs from this original experience, trying to grasp which is not immediate for us, or which appears deep amidst shadows.

Let us meet the problem of time with this approach. We use meaningfully the words after and before provided there is a change in a body or in a system of bodies. This is the first experience of time: A1 passes to the situation A2, or a green apple becomes a red apple. For Aristotle the prius and posterius constitute the original temporal relations(7), at once with Leibniz's definition of time as the successive order of events(8). However, the succession involves an endurance: something changes in the whole, but the system remains as well (at least the cosmos). Moreover, every single alteration in a member of a physical system produces a simultaneous alteration in the relationships of the other members, and in this sense it introduces a comprehensive temporality for everybody and for the whole.

The endurance of a mutable thing is its duration. We call time also duration (intervals or periods of time). A number does not last, neither does an abstract timeless object. To persist is to maintain itself in the midst of changes (with a certain resistance or 'hardness' to the undoing, very clear in the Latin names of durus, 'hard' and durare or perdurare, 'to endure'). To change is to be modified while something remains(9). 'Living an hour' means that a certain endurance in life coincides with the duration of the movement of the hands of a clock: these are two durations (intervals) or rather one duration of a unique evolving system. The temporal measure (an hour) is an abstraction based upon the finite interval of a movement (the clock), applicable to the duration of stable or persisting situations.

Time in this sense is the duration of mutable beings. Seen in this way, it can be associated to a prolonged remain. People waiting for a long time in a line which hardly moves tend to say impatiently: This takes too much time! . But also a trip can last a long time. The duration of a physical state hides an ever possible change. A thing of finite duration going on through an interval of time is drawing near to the end, even if it should not change in other senses. A trip close to its terminal point is about to affront its death as a trip. Therefore, everything in the world, even if it passes its time in an apparent rest, cannot escape change since it undergoes internal modifications or submits at least to the changes of the system. Our time passes as we grow older, or as we pass from a day to the other because of the earthly movement, or because in this period many things are changing on the earth and in our daily world. More precisely: our time both with the time of any other being in the world passes because all these things happen together. Temporality would disappear onlyun under the hypothesis of a total stop of everything. We have no experience of such a state of absolute rest.

Thus our duration, even if it may appear static, really includes a continuous and unceasing change. While we exist, the hours pass inexorably. The clock of time never stops. We exist as identities subordinate to continual change: time is unity in diversity, being in the non-being, or more precisely being a little at a time , not in a total and simultaneous manner (as corresponds instead to the concept of eternity). We cannot avoid performing acts with a beginning and an end, living in stable situations that however draw near to the end. And also in the unverifiable hypothesis of an everlasting endurance of mutation, there would be always time, in so far as there would be single acts beginning and ending. A universe without a beginning and an end would also be temporal, stretched out in the ticking of hours, something very different from God's eternity (simultaneous and non-temporal possession of every living perfection).

3. Objective time

The traits we have considered so far refer to natural time, the time of every mutable being. They correspond to the peculiar modality of being (modus essendi) of material things, whose physical existence results from ontological principles. Being in time is not an accidental property of things of the world: it is most specifically their ontological characteristic. Time indicates the continuous transitivity of things persisting without contradiction, their 'being' and 'not being' together. Indeed, we say of a being that it exists, tautologically, while it lasts. Heraclitus, as described by Plato and Aristotle, dissolved being in becoming, whereas Parmenides saw a contradiction in any change and took shelter in the logical immutability of objective thought.

Different from the ontological time is the abstract time grasped by the mind in order to measure the temporal dimension of movement. Hours, days or years do not last as objects of human thought. You can think of an hour in an instant. Human mind is in time and above time(10). Our soul is not completely immersed in temporality, and that's why we are capable of acknowledge our temporal dimension as such, facing death, our limit in time, with anxiety. The peculiar temporal essence of man -historical and metahistorical as well- is a consequence of the substantial union of the spiritual soul with the body. This could constitute a nice argument against the human confinement to temporal limits, since mind is a power which liberates man from those limits. We are open to eternity and just for this reason we dominate time to some extent, we measure it, we cross it forwards and backwards, and we spend it as we like. This natural dominion generates the specificity of human time: the historical existence, something very different from subhuman time. Man is not the lord of history, but he exercises a dominion over a fraction of history and over his own personal time. His superiority consists, partly, in his power to objectify time, that is in having the power to seize the temporal flight in the fixed content of the timeless concept of 'complete time', which is time viewed from its beginning to its end and understood in its ontological sense.

There exists, thus, a natural subhuman time, a subjective time of the mind (in substantial unity with the body) and an objective time of abstract thought (these three modalities correspond to Popper's 'three worlds'). The different features subhuman time can assume depend on the ontological nature of things. The temporal categories present, past and future are used with a certain analogy since the concept of time is not univocal when applied to the different layers of finite being(11). Biological time, for example, is different from inorganic time because of the strong presence of finality in life, from which a particular sense of the future arises. Maybe we should better say that physical time is unique, even if it acquires certain qualities according to the ontological structure of the different beings: thus, future being open, closed, cyclic, determined, undetermined, intentional, free, etc. is not the same kind of future and the notion of time changes analogically in all these modalities.

Now only objective time, as a homogeneous measure of all bodies, makes equal all particular periods in the unity of a common time: a minute of time is in itself equal for humans, living beings and things. Objective time (we borrow this terminology from Husserl(12)) arises from the artificial systems invented for chronometry and it is furtherly developed by technique in connection with scientific knowledge. The history of this time is parallel to the history of culture and science. The measuring of temporal periods is one of the most ancient manifestations of civilization, prior to science. As far as we go back in history, chronometry appears more and more tied to natural phenomena which are immediate to the ordinary life of man. In this sense we approach the true and proper natural time, prior to every metric.

Objective time constituted by man therefore is time as a measure(13), as a number reducing the continuum to discrete quantity in the realm of abstract thought. I think this is the sense of the Aristotelian thesis according to which "there is no time without mind"(14), i. e. no time as a measure, since this time is created by human reason in order to seize temporal potential relations(15). The Aristotelian definition of time as the number of movement according to the before and after(16) refers time as a measure to natural time. However, the first human objectivation of physical time springs from the natural and contingent constitution of man as an inhabitant on earth. Let us now consider more carefully this feature, since in it we find a very intimate relationship between human time and cosmic or natural time. We have reached now the main point of this discussion.

4. The present as co-actual: world and consciousness

In a Cartesian vision, the present closes myself within me: everything I see, could be argued in this line, is in the past, because it has spent some interval of time in order to arrive at the threshold of my consciousness (I say my and not our, since this conception brings to solipsism). The very sensation of my skin is in the past, because it has been transported to the cerebral centre in order to be rendered conscious. My own body would be in my possession only in the past. The phenomenological presence uniquely certifies the actuality of an observer. The apparent actuality of things would be an appearance (phenomenon without being). Through deduction (but what kind of deduction?), I am supposed to arrive to (probably) know what I presently perceive as having existed in the past. I observe the sky and obviously I see phenomena belonging to a remote past.

This strange situation, real in part, is produced when objective time substitutes itself to the natural man's time for the ontological interpretation of immediate reality. We do not intend to diminish the realistic reach of scientific knowledge. The stars we see do really sink in the past. Moreover, we must keep in mind the relativistic effects in order to ascertain the temporal situation of objects in the cosmos submitted to conditions that render themselves inaccessible to our daily experience. However, the scientific frame does not apply univocally to the ordinary knowledge of familiar objects. We cannot pretend to remain closed within the perception of our consciousness. We could claim, no doubt, that the arrival of sensorial information to the retina and afterwards to the occipital lobe of the brain occurs in a minimal and irrelevant time. But this is not enough if we want to tackle the problem as it deserves.

It is our thesis that the psychological present coincides with the natural present of the immediate world to which we have access, the world of our contemporaries, of our body and in general of all terrestrial phenomena, in so far as it can be referred to Husserl's Lebenswelt(17). This human present, which is very different from a mathematical instant, contains a short temporal length and therefore involves a certain simultaneity, in the mutual belonging of intersubjectivity and world(18). It implies then the unity of a natural-human time. This expression illustrates quite well our point. Let us try to justify these ideas.

What is the present? As we said above, several authors hold that the present, belonging to the A-temporal sequence, is exclusive to consciousness, positing a very drastic opposition between the psychological time, which is a directional time (time arrow), and the mere order of physical time (earlier-later: B-series), which would be deprived of a direction. The future and the past could be determined only in relation to a present, and there is no present outside ours. Therefore, the orientation of time has to be decided by a mind. The direction of time, in other words, would be observer-related or mind- dependent(19).

Whatever may be the conventional meaning of terms, we hold that our perception of the present has an ontological connotation and that it is not only epistemological. The present is the actuality of the movement in its process of becoming. Its prius is gone for ever (past) and its posterius is still a possibility (future). Provided the analogous meaning of these terms, the present indicates moreover, an even more normally, our present, the awareness of being in act and at once in flux, which includes the presence of external things to the mind (this is precisely the gnoseological connotation, which is common in ordinary language: 'to be in the presence of somebody' means to be perceived by somebody).

The gnoseological and the ontological meaning of the term now go arm in arm. Through our present we are participating in the actuality of the world, with which we are physically related. The psychic now should better be seen as psychobiological and in some way as cosmological by participation(20). The sentence 'it's raining now' may be fully objective. The consciousness is rooted in the proper body and is lively present in the world, constituting with it a physical unity or a system in movement. We don't need to extend this actuality to the whole cosmos, as the ancient philosophers did by taking light velocity as instantaneous. It is sufficient to refer this psychobiological present mainly to the earth and to our daily world. This local actuality warrants in any case man's participation in the natural world.

The delay in light transmission is quite natural in the structure of a world penetrated by ontological becoming. If everything propagates through movement, even causal physical processes, it is not surprising to find information arriving always a bit late. This is precisely the world of time. Material beings are transitory, lacking immanence (in the Aristotelian sense): they pass and do not stop, though in another sense they are arrested and kept by memory (sensorial consciousness is the first degree in the overcoming of pure physical time) and of course they are timelessly grasped by our intelligence, which is supra tempus. In so far as we are sensitive beings, it is to be expected to receive any information about the world with a certain delay.

Our sensible perception of time, conditioned by the brain rhythm, which constitutes the main bodily clock, includes the so-called psychological present , as we said before. This psychobiological present lasts a very short fraction of time and not an impossible mathematical instant. It has a certain temporal thickness, grasping at once an ordered series of microevents (like a 'Gestalt'). It couldn't be otherwise, since the task of time-perception is to keep in a unity the unceasing information flux arriving to the brain from different sources at a time and within brief intervals. The brain operates a holistic synchronization of registered neural inputs, which include minimal intervals of time in which earlier-later relationships can be assigned to the arriving signals.

Our sensation of being 'now' fades backwards in the short-term memory and forwards in our projection to the immediate future. We listen for example to a sentence: the intelligence grasps instantaneously the meaning (this instant is not a point in time, but rather a timeless act of a spiritual nature, introduced in the framework of our perceptual apparatus). Nevertheless, the sentence is heard in a period of time. If the phrase is sufficiently long, some parts of it will be clearly in the past and we should recall them with a bit of effort. We do hear now not a single sound, nor a word, but a section of the sentence, brief or long it may be. The distinction between this part and those which are fading away is not precise. It couldn't be exact if time is continuous or dense (not discrete).

One should accept this fact without seeing in it pseudo-contradictions, or such for a rationalistic mentality. A little interval of time is enough for the psychobiological present, with all its undetermined delays. Indeed for this reason, little by little as we leave our surrounding world and address our sight to the stars, the delay in communication becomes more and more relevant, with an ever increasing distance not only in space but in time as well. The time of the whole universe is out of reach for ordinary knowledge. Measuring cosmic (and microphysical) time does not depend on neurophysiological computations. Only mediated scientific knowledge can compute it and investigate its topology. According to the special relativity theory, as we know, time cannot be synchronized by observers situated in different states of relative motion. For objects approaching the light speed, this limitation becomes relevant and those observers will find themselves situated in different local times, i. e. they will not enjoy a common present, since their single times run with a different rhythm (therefore the universe does not exist in a common instant but it is 'fragmented' in different proper times)(21).

Our present then, being co-actual with the environment, in spite of its limitation, is a true and in some way absolute knowledge. What is present does exist and the past does not exist anymore not only for us, but absolutely. We cannot say for example that Caesar is no longer the Consul of Rome just 'from our point of view', such as the moon is above us from our perspective. The past belongs irrevocably to the non-being and so it cannot be attained anew. The concept of time-travel in the sense of being able to interact with past objects (for example with ourselves when we were younger) implies a contradiction: change is only possible in the present, since it creates the present.

5. The unity of human-natural time

The ontological reach of our co-actual present with the surrounding world comprehends a small simultaneous area moving in time (by the way, a pure succession is not intelligible without a certain simultaneity, and both elements are essential in a temporal system). All over the earth, which can be considered an inertial system, such simultaneity makes sense also in relativity theory. We co-exist with the world (having therefore the possibility of interacting in time with other physical things). While we speak, many other things are happening in the world: this 'while' connotes a persisting whole, and this is properly the physical simultaneity, namely the fact of belonging to a common time, as analogically two things can be at the same place.

A common time for many elements is an interval of time taken from the movement of a body and applied to the movement and time of other bodies. To say that my lunch lasts from 2:00 p.m to 2:30 p.m means saying that my lunch is simultaneous with a certain interval of a clock's movements. The coincidence in the duration between both intervals, known through a special synchronization for events far away within a given system of reference (inertial), ultimately presupposes a last all-including system (relatively last), from which we take the measure for all. For human terrestrial life this all-embracing system, natural and previous to every conventional metric system, is the situation itself on earth.

This fact is contingent and constitutes a bridge between the natural and the cultural world. The 'phenomenological' world of the pre-scientific life wherein we live is regulated by the natural clock of the shifting day-night, which is at the foundation of all calendars and chronologies. Also our organism, with its circadian rhythms, is already harmonized with the time of nature. Consequently, the arc of human existence could be defined as the set of all the days, each one divided naturally in day and night. We are contemporary with all beings living on the same day, in the same morning, in the same hour, etc. Simultaneity is relative: it's a matter of choice to take a period of time in order to determine it, without pretending an absolute exactness, since any measure will be invariably limited.

The terrestrial movements and position in the cosmos (its scientific knowledge is not relevant at this level) offer to terrestrial living beings the gift of natural time, a time being for us the natural-human time, with its ontological and gnoseological unity. The psychic impression of the regular 'time passing' arises from the uniformity of the (apparent) celestial movement of day and night. For the Ancients this time of our ordinary perception coincided with the absolute cosmic time. Although we know it is local, this does not render it useless. On this basis the first cultural divisions of time were built, conditioned by scientific knowledge (astronomy, physics) and furtherly by human praxis (religion, work, politics, education, etc.).

Shortly, the natural-human time has its foundation in the unitary system tying man to nature, in the causal coordination between their parts, and manifests itself in our first natural perception of time which is both physical and psychic, in conformity with the unitary structure of human being. From this basis the first objectivation of time arises, when man begins to number the days based on his observations of the earth and the celestial bodies. The book of Genesis narrates the creation in the frame of this natural human time, in order to indicate its ultimate theological meaning. But let us now see the historical time, which is the oriented time of human events.

6. Historical time

The direction of time is usually indicated with the image of the arrow. This image can have different meanings. An arrow suggests direction, and can indicate the fact that the events follow a specific sequence (they have an orientation), or that they point to something (the problem of finality), or that such order cannot be reversed (the problem of the irreversibility of the time's arrow). The arrow is more genuine if the irreversible direction is open (both aspects coincide in practice), or in other words when change brings out a real novelty ('new', something never seen before, usually implies change and time, in relation to precedent facts). Of course, there are many kinds of novelty (something can pre- exist in a potential way, implicitly, pre-determined, etc.). A merely apparent novelty is the repetition of the same. The utmost novelty is a creation and a free action, since there is no way to retrieve them in the past. A time of novelty is then an open time (or linear time), opposed to closed or circular time.

A strong division between past and future occurs only in open time. Past and future cannot emerge when the earlier-later sequence is recurrent (e. g. the sequence a-b-c-d-a-b-c- d... typical of the cyclical time), even if there is in it a local prius-posterius order relation (think for instance of the order summer-fall-winter-spring). We usually call history the open time, the time that never comes back (a-b-c...). That's why the sequence of the seasons is not historical. History appears clearly, though not exclusively, when the events are free (in a rigorous sense, history means human time, namely the time created by freedom, since in this case events are certainly new and not repetitive). Normally, the two types of time, open and cyclic, are intertwined: a regular repetition can present a novelty (a-b-c-a1-b-c-a2-b1-c...). If these novelties are not cancelled by the cycles, but are kept and do produce new changes, then time is ultimately open rather than cyclic (in the contrary case, it is cyclic and only apparently open).

For ordinary and pre-scientific knowledge, the series of days has no beginning and end: it is indefinite (not infinite). Therefore, in principle such a succession appears to be cyclic, in accordance to its phenomenological and astronomical basis (celestial cycles). A pure prius- posterius recurrence is the natural basis for chronometry or chronology, because the measure of time requires regular sequences of equal periods of time. But no history can be made with monotonous repetitions.

This ultimate task requires the intervention of at least one new phenomenon within a repetitious series. Therefore, the succession of years can be computed departing from a human event (a dynasty, a historical figure, etc.), or even from a natural catastrophe or by the appearance of a rare celestial phenomenon (e. g. a supernova). We need an extraordinary event, a novelty, in order to introduce a finite cut in the indefinite series. This cut divides a past and a future: it creates a history. What matters is the real novelty, different from monotonous cycles, provided the intervals from one event to another are always measured by the recurrent and uniform rhythm of certain facts (for instance, 100 years after the birth of Christ).

We now see the part of truth of the above mentioned distinction between the A and B time series. In fact, without the novelty brought up by open time, there is no way to distinguish the past from the future (unless locally, within the cycles and in this sense 'falsely'). If we normally make this distinction, it is because at least we never fail to introduce our own unrepeatable time, with its constant novelty. This fact is not purely epistemological. For ordinary knowledge, not yet scientific, the physical world appears timeless, not historical, so it is quite natural for the sense of past and future to predominantly proceed from human history (or from the consciousness of having a history behind us).

Obviously, the philosophers of the eternal return, on submitting human events to the eternal cycles, ultimately cancel the past and the future of the human world. This reason explains why the Ancients had a very little historical sense. It is well-known that this historical sense came out for the first time only with the Christian linear conception of time, which is very clear in the history of salvation, from the creation of the universe, through the Incarnation, to the end of time and history in the ultimate stage of God's design.

Moreover, modern science has made us aware of the historicity of nature, as we recalled in the beginning of this paper. Cycles, openings and closings of cosmic processes, of course, can be imagined without end (even with mathematical support), but current science empirically faces a single and irreversible course of the universe. In the cosmological perspective (Big Bang), in astrophysics (genesis of galaxies and stars), in thermodynamics (entropy), as well as in biology (evolution), the cosmos manifests itself as a unified complex process: it is a cosmos (harmony) also regarding time, with a unity of origin and development.

In spite of the relativity fragmentation of local proper times, the universal cosmic transformations (the expansion and the thermodynamical history of the cosmos) achieve a new, unexpected unification of different times in the concept of cosmic coordinate time, with a definite age. What seemed lost in special relativity theory was regained in the generalized one. The latter offered the opportunity of viewing the universe, for the first time in history, as a scientifically treatable concept and not only as a metaphysical and theological knowledge. But right from the beginning Einstein's cosmological approach faced the evolving cosmos (1917), with the expansion as a physical clock, notwithstanding the initial attempt by Einstein to avoid it, as we have said above. The cosmic expansion plays for universal time the same role of the first heaven in Aristotle's rotating cosmos. The only difference is that expansion is most unlikely cyclical. Our cosmos has a history.

Remarkably, this linear time of the cosmos, enclosed as it is within the limits of scientific knowledge, is more in accordance with the human time's arrow. The direction of time does not appear in the most general physical laws (with the exception of the second thermodynamical principle), but it is overwhelmingly clear in the concrete evolution of natural phenomena, which is describable in terms of solutions of the general dynamic equations.

In its complexity, the cosmos has an origin, an evolution and a fate without reversion (this statement is independent of the problem of creation). Now the direction, or in other words the evolution, poses the problem of the first beginning and the final end of the whole process. Remaining at a philosophical and scientific level, the problem is hardly resolvable in a definitive way. If the future reserves a real novelty, this cannot be foreseen by human reason. Whether this novelty will not be a fatal and blind destiny, but something convenient for man, a meaningful future, this can be known only if we turn to an upper source of knowledge, the Revelation of He who is the Lord of time and history(22).

7. Conclusion

I hope the inadequate approach of the dualist separation between psychic and physical time has been sufficiently illustrated in this paper(23). The notion of natural-human time is more consonant with the anthropological substantial unity of mind and body and with the ecological unity of man with his surrounding world, the 'cosmic world for us'. There are not several times, but rather only one time realized in different and analogous ways. Our consciousness, being a part of the soul, which is the act of an evolving organism, experiences a temporal movement coordinated with the natural time. Then we 'objectify' a first common time, belonging to our local cosmos. Modern science enlarges this unity to the whole universe, in so far as we can know it. Ultimately we know that this cosmic time has a strong direction. Without these scientific additions, the arrow of time and the natural-human time would have remained local, but anyway real.

However, we could not regard the 'whole time' as a unity without transcending it, i. e. without having the concept of eternity(24). This is not the naturalistic eternity which is tantamount to an infinite physical duration. Eternity overcomes time in a higher way, as it can be seen in the transcendence of the person, in his inner operations of thought and love. We can grasp God's eternity because we exist in time but also over time (supra tempus).

1. In Analytic philosophy, the earlier-later series is called B-series; the past-present-future sequence adds a new relation and it is called the A-series. The B-account of time is a 'tenseless' theory of time, while the A-account is a 'tensed' one (see R. Le Poidevin and M. MacBeath (eds.), The Philosophy of Time, Oxford University Press, Oxford 1993, and in particular the article by J. M. McTaggart, The Unreality of Time, pp. 23-34). Real time, in our view, necessarily includes the A-series (so we favor the tensed theory). According to this terminology, we are criticizing the idea (sustained e. g. by Russell and Grčnbaum, among others) that A-time would be exclusive of man, and that B-time should be reserved to sub-human nature. This is the core of our article.

2. See S. Weinberg, Dreams of a final Theory, Pantheon Books, New York 1992, pp. 34 and 38.

3. See for example H. Reichenbach, The Direction of Time, University of California Press, Berkeley and Los Angeles 1956; H. B. Hollinger and M. J. Zenzen, The Nature of Irreversibility, Reidel, Dordrecht 1985; P. Kroes, Time: its Structure and Role in Physical Theories, Reidel, Dordrecht 1985; P. Horwich, Asymmetries in Time, MIT Press, Cambridge (Mass.) 1987; H. D. Zeh, The Direction of Time, Springer, Berlino 1992; S. Savitt (ed.), Time's Arrow Today, Cambridge University Press, Cambridge 1995; J. J. Halliwell et al. (ed.), Physical Origins of Time Asymmetry, Cambridge University Press, Cambridge 1996.

4. I am preparing a book on this topic with professor Mario Castagnino. See also M. Castagnino, J. J. Sanguineti, Gnoseology, Ontology, and the Arrow of Time, "Acta Philosophica", 7 (1998), n. 2 (in print).

5. "For us believing physicists, the division into past, present and future has merely the meaning of an albeit obstinate illusion" (quoted by H. D. Zeh, The Direction of Time, Springer, Berlino 1992, p. 164). According to P. Davies, Einstein was the first in introducing a serious notion of time in physics, but his revolution was incomplete and it is still a challenge for the next century (see About Time: Einstein's Unfinished Revolution, London 1995, Viking.). For a very strong timeless view, see also H. Price, Time's Arrow and Archimedes' Point, Oxford University Press, Oxford 1996.

6. This kind of Cartesian dualism is frequent in many authors, due to the lack of a philosophy of nature in modern philosophy. Nor phenomenology was able to overcome it. The approach to a real cosmological time goes ahead with the current impact of natural sciences and with the suggestions for a realistic account of science.

7. Aristotle, Phys., 219 b 1: time is "a number of change with respect to the before and after".

8. See P. Wiener (ed.), Leibniz: Selections, Scribner, New York 1951, pp. 201- 202. This is called the 'relational' theory of time, to which is opposed the 'substantival' theory (time as a substance, or 'absolute time'), followed by Newton: see Q. Smith and L. Nathan Oaklander, Time, Change and Freedom, Routledge, London and New York 1995, pp. 35-44.

9. When Bergson conceives the duration as a result of the introduction of conscience unifying the earlier-later relation, he is still affected by the mind- matter dualism (see above). Cfr. Durée et simultanéité, Alcan, Paris 1931, pp. 60, 62, 88: on peut pas parler d une réalite qui dure sans y introduire de la conscience (p. 60).

10. See Thomas Aquinas, S. Th., I, q. 75, a. 6; C.G., II, 96 and III, 84; Q. disp. de Anima, q. un., a. 14. Humana anima non est forma in materia corporali immersa, vel ab ea totaliter comprehensa, propter suam perfectionem (S. Th., I, q. 76, a. 1, ad 4; see also C.G., II, 68).

11. For an interpretation of time according to the principle of progressive integration of different hierarchical levels of reality, see J. T. Fraser, The Genesis and Evolution of Time, The Harvester Press, Brighton 1982. Fraser is the founder of the International Society for the Study of Time.

12. See E. Husserl, Zur Phenomenologie des Inneren Zeitbewusstseins, Husserliana, vol. X (R. Boehm, ed.).

13. On the soul measuring time, see Augustine's deep insight in Confessions, 11, 16; 11, 21; 11, 27.

14. Aristotle, Phys., 223 a 20-30.

15. This is the solution suggested by Aristotle to the question posed by himself (see Phys., ibidem).

16. Aristotle, Phys., 219 b 1-5.

17. Following Husserl and Heidegger, Merleau-Ponty described very well some aspects of this 'world presence' to the conscience in its intrinsic temporality. But his approach lacks of a solid cosmological basis. Cfr. Phénomenologie de la perception, Gallimard, Paris 1945, pp. 469-495.

18. See A. Vergote, Le temps psychologique, in Groupe de synthèse de Louvain, Temps et devenir, Presses Universitaire Louvain- la-Neuve, Louvain-la-Neuve 1984, p. 212.

19. Some authors try to detect a physical orientation of time, for example in the irreversible increase of entropy (Reichenbach) or in the expansion of the universe. An irreversible natural process could decide the direction towards the future without the intervention of psychology. Nonetheless, we think that the psychological present remains essential for the arrow of time, but we claim as well in this paper that this present is natural and realistic, and not merely epistemological or subjective. The problem can be illustrated in dating things or events: we can say that the French Revolution occurred in 1786 after Christ's birth (B-series), but we couldn't say that the French Revolution is in the past unless we take our present as a reference point (A-series). That's why we assert that the French Revolution did occur (tensed theory).

20. Therefore, it is not surprising the contingent correlation between the psychological and the thermodynamical arrow. This is the answer to Reichenbach's question: Why is the flow of psychological time identical with the direction of increasing entropy? (The Direction of Time, p. 269). We prefer to speak of correlation instead of identity, also because the link is contingent (or empirical).

21. According to Bohm, absolute time does not belong to 'common sense'. There is a continuity between special relativity theory and our psychological micro-perception of time. Both are in search of invariances within the different presentations. See D. Bohm, The Special Theory of Relativity, Routledge, London/New York 1996, pp. 185 ff.

22. See Acts 1, 7. In Christian faith, the revelation of the mystery of time doesn t concern only the end of time, but it has already begun with Christ: 'Thanks to God s coming on earth, human time, which began at Creation, has reached its fullness. The fullness of time is in fact eternity, indeed, it is the One who is eternal, God himself. Thus, to enter in the fullness of time means to reach the end of time and to transcend its limits, in order to find time's fulfilment in the eternity of God' (John Paul II, Tertio Millennio Adveniente, n. 9).

23. Ricoeur notices in the history of philosophy a reciprocal concealment between cosmological and phenomenological time (Aristotle-Augustine; Kant- Husserl; Heidegger): cfr. Temps et récit, vol. 3, Ed. du Seuil, Paris 1985, pp. 439 ff.

24.

See Qoelet, 3, 11.