Van Huyssteen J.W. (editor) Encyclopedia of Science and Religion

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THEOLOGY,THEORIES OF

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The expository mode takes as given, although

not necessarily infallible, some core set of texts or

claims, and seeks to unfold, elaborate, interpret,

and bring them to relevance. Williams’s celebratory

and communicative theologies, Tracy’s systematic

theology, classical biblical theologies, and com-

mentarial theologies in all religions have this mode.

The hypothetico-deductive mode, as illustrated

for instance in Peirce’s “A Neglected Argument for

the Reality of God” and Whitehead’s cosmological

scheme in Process and Reality, elaborates an ab-

stract scheme of conceptions that is then treated as

an hypothesis to explain the world and God or ul-

timate matters. This mode is explicitly derived from

a conception of how science works, and empha-

sizes that the conceptions are hypotheses whose

plausibility consists in their capacity to interpret re-

ality as well as in their consistency and coherence.

Theology in this mode is heavily empirical.

Wolfhart Pannenberg’s proleptic theology, which

says that his particular conception of Christian the-

ology will be proved right in the End Time, and

John Hick’s conception of eschatological verifica-

tion, are empirical in a different sense.

The practical mode of theology combines both

expository and perhaps hypothetico-deductive

philosophy as well as other forms of analysis to in-

terpret the religious situation and to develop strate-

gies for religious response. The situation might call

for reform of social circumstances as in liberation

theologies, the production of art and culture, the

care of a religious congregation or community, or

service to people in times of disaster. Science re-

lates to practical theology both as offering impor-

tant means of analysis of the situation to be ad-

dressed and in some instances as providing

instruments of action.

Theology in the mode of dialectical inquiry fo-

cuses on the topics of theology—God or ultimacy

and the bearing of this on human life—and looks

to all possible sources and to all the modes of ar-

gumentation for learning from these sources. The

word dialectic has been used to mean some kind

of unfolding of reason from within, as in the theo-

ries of Hegel or Thomas J. J. Altizer, but that is not

the meaning here. Dialectical inquiry means com-

bining as many different modes of thinking as exist

in religions, the arts, sciences, and practical do-

mains of experience so as to learn what they might

teach about ultimacy. The combinations and the

limitations of the various modes of thinking can

only be adjudicated in particular arguments. Di-

alectical inquiry is simply making the best case in

the sense articulated by the contemporary histori-

cal theologian Van Harvey in The Historian and

the Believer (1966), and is the mode most appro-

priate for theology in a global public.

See also THOMAS AQUINAS; NATURAL THEOLOGY;

ROCESS THOUGHT; REVELATION

Bibliography

Capra, Fritjof. The Tao of Physics: An Exploration of the

Parallels Between Modern Physics and Eastern Mysti-

cism. Berkeley, Calif.: Shambhala, 1975.

Frei, Hans W. Types of Christian Theology, eds. George

Hunsinger and William C. Placher. New Haven,

Conn.: Yale University Press, 1992.

Gilson, Etienne. Reason and Revelation in the Middle

Ages. New York: Scribners, 1938.

Hartshorne, Charles. The Divine Relativity: A Social Con-

ception of God. New Haven, Conn.: Yale University

Press, 1948.

Harvey, Van A. The Historian and the Believer: The Moral-

ity of Historical Knowledge and Christian Belief. New

York: Macmillan, 1966.

Hick, John. Faith and Knowledge: A Modern Introduction

to the Problem of Religious Knowledge. Ithaca, N.Y.:

Cornell University Press, 1957.

Lindbeck, George A. The Nature of Doctrine: Religion and

Theology in a Post-liberal Age. Philadelphia, Pa.:

Westminster Press, 1984.

Macquarrie, John. Principles of Christian Theology. New

York: Macmillan, 1966.

Murphy, Nancey. Theology in the Age of Scientific Reason-

ing. Ithaca, N.Y.: Cornell University Press, 1990.

Neville, Robert Cummings, ed. Ultimate Realities. A vol-

ume in the Comparative Religious Ideas Project. Al-

bany: State University of New York Press, 2001.

Pannenberg, Wolfhart. Systematic Theology, trans. Geof-

frey W. Bromily. Grand Rapids. Mich.: Eerdmans,

1988–1993.

Peirce, Charles Sanders. “A Neglected Argument for the

Reality of God.” The Hibbert Journal 7 (1908):

90–112. Also in The Collected Papers of Charles

Sanders Peirce, Vol. 6, eds. Charles Hartshorne and

Paul Weiss. Cambridge, Mass.: Harvard University

Press, 1935.

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Polkinghorne, John. Science and Christian Belief: Theolog-

ical Reflections of a Bottom-Up Thinker. London:

SPCK, 1994.

Rahner, Karl. Foundations of Christian Faith: An Intro-

duction to the Idea of Christianity. New York: Cross-

road, 1989.

Taylor, Mark C. Erring: A Postmodern A/Theology.

Chicago: University of Chicago Press, 1984.

Tillich, Paul. Systematic Theology. Chicago: University of

Chicago Press, 1951–1963.

Tracy, David. The Analogical Imagination: Christian The-

ology and the Culture of Modernity. New York: Cross-

road, 1981.

Ward, Keith. Religion and Creation. Oxford: Clarendon

Press, 1996.

Whitehead, Alfred North. Process and Reality: An Essay in

Cosmology (1929), eds. Donald W. Sherburne and

David Ray Griffin. New York: Free Press, 1978.

Williams, Rowan. On Christian Theology. Oxford: Black-

well, 2000.

ROBERT CUMMINGS NEVILLE

THERMODYNAMICS,SECOND

LAW OF

The Second Law of Thermodynamics expresses a

fundamental and limiting characteristic of all phys-

ical systems: In any closed system, the measure of

disorder, or entropy, of that system must either re-

main the same or increase. Equivalently, in any

isolated system, the amount of energy available for

work—the free energy—must either remain the

same or decrease. Processes in which the entropy

remains the same are reversible; those in which the

entropy increases are irreversible, that is, there is

no realistic possibility of recovering the initial state

of the system. It is principally because of the Sec-

ond Law of Thermodynamics that all physical and

biological systems are destined for eventual disso-

lution or death, even the universe itself. Without

the continual input of work, energy, or material

(food), every system (not necessarily closed)

moves towards equilibrium, which is characterized

by maximum entropy. Organization, order, and life

require that the system in question be maintained

far from equilibrium, and this requires input of en-

ergy from outside—from its environment.

Formulations

Long before the Second Law was expressed in

terms of the change in entropy of a closed system,

Sadi Carnot (1796–1832) formulated it in terms of

heat and work: It is impossible to convert heat

back into work at a given temperature. Although

work can be converted into heat at a given tem-

perature, the reverse cannot be effected without

other changes. Heat will never travel up a temper-

ature gradient on its own. It is only with further

work that heat can be transferred from a body or a

system at a given temperature to one that is either

at the same temperature or at a higher tempera-

ture. Of course, heat can indeed flow from a hot-

ter system to colder system without any work

being necessary. Thus, another formulation of the

Second Law is that heat cannot flow from a given

system to a hotter one without work being done. A

refrigerator must use energy in order to function.

Other expressions of the Second Law are: A perfect

heat engine is impossible to construct (Lord

Kelvin’s formulation), and similarly, it is impossible

to construct a perfect refrigerator (Rudolf Clausius’s

formulation).

The clearest and most applicable formulation

of the Second Law of Thermodynamics, however,

is: During any process the entropy of any isolated

system must either remain the same or increase.

But what is entropy? It is sometimes defined as the

measure of the unavailability of the energy of a

system for work. An isolated system in perfect

equilibrium has maximum entropy and thus has

no energy available for work. It is now more usual,

however, to define entropy by employing the sta-

tistical mechanical underpinnings of thermody-

namics in terms of the number of microstates avail-

able to the system at a given energy. Any given

macroscopic state of a system (given, for instance,

by its temperature, pressure, and volume) corre-

sponds to many different possible microscopic

states of that system (arrangements and velocities

of the molecules constituting it). The larger the

number of possible microstates corresponding to a

given macrostate, the larger the entropy of the sys-

tem, and the larger the disorder of the system. The

maximum entropy—and therefore the maximum

disorder—is given by the situation in which the

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actual macrostate of the system possesses the max-

imum number of accessible microstates for the en-

ergy it contains. This is the state of equilibrium.

Thus, what is really significant is not the absolute

value of the entropy for an isolated system, but

rather how far its entropy is from the maximum—

how far away the system is from equilibrium. As

already mentioned, this also indicates how much

free energy (for work) is available in it.

The determination of the entropy and the max-

imum entropy, and therefore the application of the

Second Law of Thermodynamics to gravitating sys-

tems, such as a cluster of stars, the galaxy, or the

universe, is somewhat more complex than it is for

non-gravitating systems. This is because the total

entropy of such systems must include gravitational

entropy as well as thermodynamic entropy, and

the lowest gravitational entropy state of a system is

realized when it is perfectly homogeneous—

no clustering or clumping. A homogeneous self-

gravitating system is obviously far from equilib-

rium. As the matter gradually coalesces and

clumps, the gravitational entropy increases, releas-

ing free energy through heat and radiation, which

is now capable of being harnessed for work. Even-

tually the cores of some of these mass concentra-

tions become hot enough for the initiation of

nucleosynthesis, and even more free energy is re-

leased. Maximum gravitational entropy is achieved

when the whole system becomes a single black

hole. For that to happen all the free energy of the

system has to be exhausted.

What was the origin of the initial extreme grav-

itational disequilibrium? Possibly it was an infla-

tionary phase of the universe almost immediately

after the Big Bang, during which the universe ex-

panded incredibly fast (exponentially) in a very

short time; perhaps it was certain quantum-gravity

effects even earlier during the Planck era that ren-

dered the initial state of our part of the universe

very smooth. How will the universe as we know it

end? In entropic death or heat death. This will

occur when either the universe evolves to become

something like a single black hole, or when it ex-

pands so much and so rapidly that gravity is no

longer effective in drawing together whatever relic

mass concentrations remain (particles or black

holes). In either case, a state of equilibrium has

been reached; the entropy of the universe is a

maximum, and no useful energy for work or for

nourishment can be found.

Sometimes people mention that life-generating

or life-maintaining systems do not obey the Second

Law of Thermodynamics, because in generating

order they are lowering the entropy. But, in fact,

they are perfect examples of the application of the

Second Law. The system one must consider in this

case is not just the living organism itself, nor just

the community of living organisms in question,

which are not isolated systems (they are in crucial

and continual interaction with their environment),

but rather the entire ecological system itself as iso-

lated from what occurs outside it. Yes, the entropy

of each organism and community of living organ-

isms is kept relatively low, but only at the expense

of increasing the entropy of their surroundings.

The entropy of the whole isolated ecological sys-

tem is increasing. If one isolates organisms in a

box with a certain limited amount of food and

available energy and no interactions with the

world outside the box, the organisms will live and

reproduce for a certain length of time. But eventu-

ally the available energy will be depleted and the

food supply (both the food they started with and

the food they subsequently produced) will run out,

and everything in the box will reach the equilib-

rium that is death.

Implications for religion

The inescapable limits placed on physical and bi-

ological reality by the Second Law of Thermody-

namics confront theology and religion with a seri-

ous challenge. If all is finite, transient, and

destined for death and dissolution, what meaning

and hope can theology and religion legitimately

assert? How is the eternal destiny proclaimed by

religions to be understood, and how is this seem-

ingly insuperable limit to be transcended? These

are eschatological questions. There are also ques-

tions relating to natural evil. Assuming that God

works through all the laws of nature, including the

Second Law, to create and maintain the world,

how can one conceive God as the creator of a

world in which death, disease, suffering, and the

exploitation of resources is not only pervasive but

essential? Finally, according to religious perspec-

tives, the Second Law of Thermodynamics cannot

have the last word. The “new heavens and the

new earth,” though in continuity with this world,

are promised to be devoid of the transience, suf-

fering, death, and natural evil that accompany

human existence.

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THINKING MACHINES

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See also

BIG BANG THEORY; DEATH; ENTROPY;

SCHATOLOGY

Bibliography

Feynman, Richard P.; Leighton, Robert B.; and Sands,

Matthew. The Feynman Lectures on Physics, Vol. 1.

Reading, Mass.: Addison Wesley, 1963.

Frautschi, Steven. “Entropy in an Expanding Universe.” In

Entropy, Information and Evolution: New Perspectives

on Physical and Biological Evolution, eds. Bruce H.

Weber, David J. Depew, and James D. Smith. Cam-

bridge, Mass.: MIT Press, 1990.

Layzer, David. “Growth of Order in the Universe.” In En-

tropy, Information, and Evolution: New Perspectives

on Physical and Biological Evolution, eds. Bruce H.

Weber, David J. Depew, and James D. Smith. Cam-

bridge, Mass.: MIT Press, 1990.

Puddefoot, John C. “Information Theory, Biology and

Christology.” In Religion and Science: History,

Method, Dialogue, eds. W. Mark Richardson and

Wesley J. Wildman. New York and London: Rout-

ledge, 1996.

Reif, F. Fundamentals of Statistical and Thermal Physics.

New York: McGraw-Hill, 1965.

Russell, Robert John. “Entropy and Evil.” Zygon: Journal

of Science and Religion 19 (1984): 449–468.

WILLIAM R. STOEGER

THINKING MACHINES

The term thinking machine (or intelligent ma-

chine) refers to a computer or a robot that has

human intelligence. No such machine exists as of

2002, and whether it can be built in principle and

how many years of research this would take is a

matter of much dispute. The feasibility of thinking

machines has been promoted by representatives

of strong artificial intelligence (AI), such as John

McCarthy, Marvin Minsky, and Doug Lenat. A prin-

ciple formal argument against conscious and thus

intelligent machines has been posed by mathe-

matician and physicist Roger Penrose. To testify

that a computer agent is a thinking machine it

would have to pass the Turing Test.

See also ARTIFICIAL INTELLIGENCE; ROBOTICS; TURING

TEST

THIEMO KRINK

THOMAS AQUINAS

Thomas Aquinas held that revelation was essential

for grasping truth of faith but he relied on reason

to understand the world that God created. Mindful

of this division, Thomas warned against dogmatic

interpretations in areas of faith that might have to

be abandoned if subsequent natural evidence fal-

sified them. Convinced that Aristotle’s (384–322

B.C.E.) natural philosophy provided the most accu-

rate interpretation of cosmic operations, Thomas

refused to Christianize natural philosophy and, to

the greatest extent possible, he applied reason to

both science and theology.

Life and works

Thomas Aquinas was born near Monte Cassino,

Italy, around 1225. He was the youngest of nine

children. After elementary education in the abbey

of Monte Cassino, Thomas was sent to Naples in

1239, where he studied at the University of Naples.

In 1244, while still at Naples, Thomas entered the

Dominican order, contrary to the wishes of his

family. From 1245 to 1252, Thomas studied at Paris

and then Cologne. At Cologne, and perhaps at

Paris, Thomas’s teacher was Albert the Great (Al-

bertus Magnus) (c. 1206–1280), one of the great

scientists and natural philosophers of the Middle

Ages and a thorough student of Aristotle’s writings.

After training as a theologian, Thomas became a

professor of theology at the University of Paris

(1256–1259). He spent the years between 1259 and

1268 in Italy serving different popes at their papal

courts. During 1269 to 1272, Thomas returned to

another professorship at the University of Paris,

after which he returned to Naples, where his

health began to fail. Thomas died in 1274 while on

his way to the second Council of Lyons.

Thomas was a prolific author who left approx-

imately fifty works that have been thus far identi-

fied. He wrote on numerous topics, the most sig-

nificant of which are his theological treatises,

especially his famous Summa of Theology (Summa

theologiae), commentaries on books of the Bible,

and commentaries on various works of Aristotle,

especially those on natural philosophy, which in-

clude Aristotle’s Physics, On the Heavens, On Gen-

eration and Corruption, Meteorology, and On the

Soul. In addition, Thomas composed sermons, let-

ters, and replies to queries.

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Thomas on the relationship of faith and

reason

Issues of science and religion in the Middle Ages

involve the relationship between natural philoso-

phy and religion. By the time Thomas began writ-

ing, Aristotle’s works on logic and natural philoso-

phy had been adopted as the basic curriculum in

faculties of arts of medieval universities. Because

Aristotle’s natural philosophy raised issues that

were directly relevant to theology and the Catholic

faith, it was inevitable that Thomas, who was both

a theologian and a natural philosopher, would

have to confront those issues in his works on the-

ology and natural philosophy.

When Thomas dealt with issues of science and

religion, he was guided by his overall view of the

relationship between faith and reason. Thomas

emphasized the importance and power of reason,

but insisted that it was inadequate to gain knowl-

edge of unseen things, such as God, for which

faith and divine revelation are essential. For knowl-

edge of the physical cosmos and its regular opera-

tions, however, reason—embodied in the works of

Aristotle—was Thomas’s instrument for under-

standing those operations. But reason was also an

instrument for the study of theology. In the very

first question of his Summa of Theology, Thomas

asked whether theology is a science and replied af-

firmatively. He is usually regarded as the scholar

who gave credence to the claim that theology is a

science, a claim that was widely assumed in the

late Middle Ages.

Two principles derived from the early Christian

leader Augustine of Hippo (354–430

C.E.) and ex-

pressed in the Summa of Theology, guided Thomas

in his explanations of natural phenomena. He in-

sisted: (1) that the truths of Scripture must be held

inviolate, but that (2) no passage in Scripture

should be interpreted rigidly and dogmatically be-

cause it might later be proved false by convincing

arguments, thus leading to a loss of credibility that

would inhibit nonbelievers from adopting the faith.

Thomas and Aristotle

Although Aristotle’s natural philosophy formed the

basic curriculum in the arts faculties of medieval

universities, those aspects of his work that con-

flicted with basic Christian beliefs evoked opposi-

tion through most of the thirteenth century. In the

1260s, and 1270s, when Thomas was writing, the

opposition was led by the Franciscan theologian

Bonaventure (1221–1271), whose neoconservative

Augustinian colleagues eventually prevailed upon

the bishop of Paris to condemn certain of Aristo-

tle’s articles deemed offensive to the faith; thirteen

articles were condemned in 1270 and 219 articles

were condemned in 1277, three years after the

death of Thomas. Since Thomas was a supporter

of Aristotle’s philosophy, as were many Domini-

cans, some of the hostility was plainly directed

against him and his colleagues. It was not until

1325, two years after the canonization of Thomas

Aquinas, that the bishop of Paris, Stephen Bourret,

revoked the condemnation of all articles con-

demned in 1277 that were directed against the

teachings of Thomas.

The most significant idea condemned in 1277

was Aristotle’s claim for the eternity of the world,

which was denounced at least twenty-seven times

in a variety of contexts. In a treatise he titled On

the Eternity of the World, Thomas neither rejected

nor accepted the eternity of the world. By absolute

power, God could have created a world that was

coeternal with God. For as Thomas argued, “The

statement that something was made by God and

nevertheless was never without existence . . . does

not involve any logical contradiction.” If God

wishes, God can choose not to precede any effect

God decides to produce, and thus God can make

the world eternal. Although God could make the

world coeternal with God, an eternal world would

still be a created effect, because it is wholly de-

pendent on an immutable God, thus guaranteeing

that the world cannot be coequal with God. Of the

articles condemned in 1277, Article 99 was proba-

bly directed against Thomas’s interpretation of the

eternity of the world. Thomas’s approach to the

question of the world’s duration proved popular

and found supporters up through the Renaissance.

Bonaventure and others were convinced that Aris-

totle had denied the personal immortality of the

soul, but Thomas thought Aristotle had believed it.

Since Aristotle firmly believed that every mate-

rial thing is derived from previous matter, he

would have been opposed to the Christian doc-

trine of creation from nothing. Article 185 con-

demned the view that something could not be

made from nothing. Indeed, the Fourth Lateran

Council of 1215 had declared belief in creation

from nothing to be an article of faith. On this issue,

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THOMAS AQUINAS

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Thomas, and all Christians, were compelled to re-

ject Aristotle’s interpretation.

Thomas’s conception of the physical world

and its operations was basically the same as that

held by Aristotle, from whom he derived it. In his

commentaries on Aristotle’s natural philosophy,

Thomas considered the numerous problems Aris-

totle presented, accepting most of Aristotle’s solu-

tions, but disagreeing on some important issues.

Although Thomas believed with Aristotle that the

existence of void spaces was impossible, he dis-

agreed with the absurd consequence Aristotle de-

duced from the assumption of motion in a vac-

uum, namely that because of an absence of

material resistance, a body would move instanta-

neously in a vacuum and, as a consequence, no

ratio could obtain between motions in a hypothet-

ical void and motions in a space filled with matter.

Thomas rejected these conclusions. A body falling

or moving in a void space would have a definite

speed and take a definite time to move succes-

sively between two distant points. This is so, ar-

gued Thomas, because any distance in a three-

dimensional void has prior and posterior parts that

a body must traverse to get from one point to an-

other, which requires time. Hence there could in-

deed be a ratio between motions in a vacuum and

motions in a plenum.

In a letter to a soldier, Thomas explained how

bodies could perform actions that do not follow

from the nature of their constituent elements, as,

for example, the attraction of a magnet for iron.

Thomas regarded such actions as occult, explain-

ing the causes of such phenomena by the behavior

of two kinds of superior agents: (1) celestial bod-

ies, or (2) separate spiritual substances, which in-

cluded celestial intelligences, angels, and even

demons. A superior agent can either communicate

the power to perform the action directly to an in-

ferior body, as is the case with the magnet; or the

superior agent can, by its own motion, cause the

body in question to move, as, for example, the

moon causes the ebb and flow of the tides.

Whatever disagreements Thomas had with

Aristotle, whether doctrinal or otherwise, it is obvi-

ous that Thomas was an Aristotelian in natural phi-

losophy. As an Aristotelian natural philosopher and

a professional theologian, one may appropriately

inquire how Thomas related natural philosophy

and theology, the medieval equivalent of the rela-

tions between science and religion. Thomas fol-

lowed in the path of his teacher, Albert the Great,

and generally refrained from introducing theologi-

cal ideas into his treatises on natural philosophy,

whereas he did not hesitate to introduce natural

philosophy to elucidate his theological discussions.

As a theologian doing natural philosophy, Thomas

could easily have resorted to theological appeals

and arguments in his natural philosophy, but he

did not think it appropriate to do so. As he ex-

plained in a reply to one of forty-three questions

sent to him by the master general of the Domini-

can order, “I don’t see what one’s interpretation of

the text of Aristotle has to do with the teaching of

the faith.” Thomas refused to Christianize Aristo-

tle’s natural philosophy and to confuse natural phi-

losophy with theology. In this, Thomas followed

the practice of most medieval theologians and nat-

ural philosophers.

See also ARISTOTLE; AUGUSTINE; CHRISTIANITY, ROMAN

CATHOLIC, ISSUES IN SCIENCE AND RELIGION;

REATIO EX

NIHILO; CREATION; GOD

Bibliography

Copleston, Frederick C. Aquinas. Harmondsworth, UK:

Penguin Books, 1955.

Thomas Aquinas. Summa Theologiae, Vol. 10: Cosmogony,

trans. and ed. William A. Wallace. London: Blackfri-

ars, 1967.

Dijksterhuis, E. J. The Mechanization of the World Picture,

trans. C. Dikshoorn. Oxford: Clarendon Press, 1961.

Gilson, Etienne. History of Christian Philosophy in the

Middle Ages. London: Sheed and Ward, 1955.

Pegis, Anton C., ed. Introduction to Saint Thomas

Aquinas. New York: Modern Library, 1948.

Wallace, William A. “Aquinas on Creation: Science, Theol-

ogy, and Matters of Fact.” Thomist 38 (1974): 485-523.

Wallace, William A. “Aquinas, Saint Thomas.” In Dictio-

nary of Scientific Biography, Vol. 1, ed. Charles C.

Gillispie. New York: Scribner, 1970.

Weisheipl, James A. Friar Thomas d’Aquino: His Life,

Thought, and Work. Garden City, N.Y.: Doubleday,

1974.

Weisheipl, James A. “Motion in a Void: Aquinas and Aver-

roes.” In St. Thomas Aquinas 1274-1974, Commemo-

rative Studies, ed. A. A. Mauer. Toronto: Pontifical In-

stitute of Medieval Studies, 1974.

EDWARD GRANT

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TIME:PHYSICAL AND BIOLOGICAL ASPECTS

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TIME

See SPACE AND TIME

TIME:PHYSICAL AND

BIOLOGICAL ASPECTS

Insofar as science aims at reconstructing the laws

of nature, which describe the temporal develop-

ment of nature’s physical constituents and allow

for predicting future events out of data derived

from past events, time is a fundamental and crucial

notion of empirical sciences. Science, however,

does not deal with time itself, but with changes

and events in time. Consequently, what really mat-

ters in science “is not how we define time, but

how we measure it” (Feynman, p. 5-1). As such,

time constitutes the realm, rather than the object,

of scientific investigation. The nature and character

of time must be derived from interpretation of the

basic structure of science and its method. And be-

cause time does not refer to external objects of in-

vestigation, but to the presupposed internal order

of physical phenomena, it is closely related to

human experience and the human perception of

time, which is the sequential, nonspatial order of

events, structured by the relation of cause and ef-

fect. Unlike space, time as sequential order shows

a fundamental asymmetry between the past (fixed

in documents, which can be investigated) and the

future (still to come and not totally fixed—it can

only be predicted). People can remember the past

but not the future; people can alter the future, but

not the past. The astronomer Arthur S. Eddington

(1882–1944) was the first to speak of the “arrow of

time,” which points from the past to the future, to

symbolize this fundamental asymmetry.

The physics of time

The crucial question of the interpretation of time in

physics and biology is whether this asymmetry is

due to physical laws, or whether it is a subjective

illusion due to the human experience of time. The

laws of both classical and relativistic physics, as

well as the basic equations of quantum physics,

are time reversal invariant and provide no scientific

ground for an arrow of time. On the other hand,

an irreversible directedness of time does turn up in

empirical sciences related to different phenomena:

(1) According to the Second Law of Thermody-

namics, disorder (entropy) increases in a

closed system from past to future.

(2) The measurement of quantum events consti-

tutes an irreversible difference between past

and future.

(3) Biological systems and their evolution con-

stitute a historical development from past to

future.

(4) The universe is expanding in time.

Because time and irreversibility seem to have

different meanings in different physical theories,

and because the notions of causality involved are a

matter of dispute as well, a comprehensive and

commonly accepted interpretation of time in natural

sciences is neither at hand nor in sight. This entry

will refer to some aspects of an ongoing discussion.

Newtonian time of classical physics. In his

Mathematical Principles of Natural Philosophy,

Isaac Newton (1642–1727) distinguishes between

absolute and relative time: “Absolute, true, and

mathematical time . . . flows equably without rela-

tion to anything external, and by another name is

called duration: relative, apparent, and common

time, is some sensible and external (whether accu-

rate or unequable) measure of duration by the

means of motion, which is commonly used instead

of true time; such as an hour, a day, a month, a

year” (p. 6). The notion of absolute time is crucial

for Newtonian physics because its First Law of Mo-

tion implies that a body on which no forces act

moves uniformly in a straight line at constant

speed, or it is at rest. Only against the background

of absolute time and space can rest and equable

translation as free from external influence stand

out against those deformations of motion that indi-

cate external forces. Thus, absolute time in New-

tonian physics is an a priori presupposition, and it

is essential for the frame of reference, against

which all forces are determined. Newton himself

considered that in reality there might exist no ab-

solutely equable form of motion representing this

absolute time: It might not be the time of a partic-

ular clock. But still, the assumed flowing of ab-

solute time should not be liable to any change.

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However, the laws of classical mechanics,

which describe the motions of massive bodies, do

not distinguish a direction of absolute time: No fea-

ture of the mechanical world would change, if time

were reversed. Because the basic differential equa-

tions of classical mechanics are time reversal invari-

ant, the future development of any mechanical sys-

tem is in principle derivable from its past state, and

vice versa. Thus, development from past to future

and from future to past are physically equivalent.

The arrow of time in thermodynamics. But

what people experience in reality are often

processes, which appear to be irreversibly “di-

rected,” such as the cooling of hot water or the

erosion of a rock. Especially inanimate natural sys-

tems show a tendency to spontaneously evolve to

equilibrium of order, energy, or temperature,

where these macroscopic parameters remain ap-

proximately stable, and they never leave this state,

provided no external intervention takes place. The

physics to describe such processes is called ther-

modynamics. Elaborated in the mid-nineteenth

century, classical thermodynamics is based on two

laws, the second of which expresses the tempo-

rally asymmetric behavior of all isolated (adiabatic)

systems, with the universe as the biggest of them,

to approach equilibrium in due course of time. The

universe thus faces heat death, the equilibrium

state in which no energy differences remain and all

physical processes come to an end, as its final fate.

In order to express this fundamental law, Rudolf

Clausius (1822–1888) coined the term entropy

(from Greek entrope, turning toward) as a measure

of dispersed and irretrievable energy that becomes

unavailable for producing work. Clausius further

stated that the entropy of the universe strives to-

ward a maximum. Because entropy is at a maxi-

mum when the molecules of a system are at the

same energy level, entropy can be understood as a

measure of disorder. Thus, the Second Law of

Thermodynamics implies the increase of disorder

in due course of time, ruling out all reverse

processes that could create order spontaneously

within a closed system.

When James Maxwell (1831–1879) and others

developed the kinetic theory of heat and gases,

Ludwig Boltzmann (1844–1906) tried to reduce

thermodynamics to mechanical laws and interpret

the Second Law as only statistical: Systems gener-

ally develop toward states of higher entropy be-

cause such states are more probable than others.

But the discussion about the statistical interpreta-

tion of thermodynamics revealed that the time re-

versal invariance of the mechanical laws cannot

model the irreversible phenomena of macroscopic

systems striving toward equilibrium. In the light of

classical mechanism, the irreversible direction of

time from past to future, the arrow of time as indi-

cated by the Second Law of Thermodynamics,

seems to rest on no physical ground.

Time in Special and General Theory of Relativ-

ity. The direction of time from past to future

seemed to become even more illusionary when Al-

bert Einstein’s (1879–1955) Theory of Relativity

succeeded in overcoming the Newtonian notion of

absolute time. In his 1905 Special Theory of Rela-

tivity, Einstein stated that the time interval (and the

distance) between two events depends on the ob-

server’s velocity relative to the events, while the

velocity cannot exceed the speed of light.

In Einstein’s theory, space and time together

constitute the four-dimensional space-time, while

each reference frame of an observer divides space-

time differently into a temporal and a spatial com-

ponent relative to its state of velocity. There is no

simultaneity of events and absolute duration of

time for every observer, as well as no absolute spa-

tial distance. Still, there is an objective causal con-

nection between events, because one event cannot

interact with another instantaneously, but only me-

diated by forces, whose propagation speed is final

and equals or is less than the speed of light. Thus

temporal as well as spatial intervals between

causally related events cannot become zero, and

their causal relation cannot be reversed. Relativis-

tic time still represents the order of causal chains.

Shortly after Einstein’s discovery, the Russian

mathematician and physicist Hermann Minkowski

(1864–1909) united space and time into one four-

dimensional continuum, the space-time of the so-

called Minkowksi-world: “Henceforth space by it-

self, and time by itself, are doomed to fade away

into mere shadows, and only a kind of union of

the two will preserve an independent reality”

(Space and Time, p. 75). This view of the physical

world, in which no independent time exists, sug-

gests that the world is to be envisioned as a four-

dimensional being, rather than a becoming within

three-dimensional space. Then, as Einstein himself

stated, for a physicist “the distinction between past,

present and future is only an illusion, however per-

sistent” (quoted in Davies, 1983, p.128).

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Time in quantum theory. In the Schrödinger-

equation, which is the basic formula of quantum

mechanics, time is not an observable, but just a pa-

rameter. Although it is time reversal invariant, in its

common interpretation, the equation refers to

probabilities and only allows for the determination

of probabilities for certain states. When a state is

measured, the Schrödinger wave-function of an

object, which is derived from the Schrödinger-

equation, “collapses,” and a certain value for an

observable is provided. Some physicists interpret

this as a new notion of irreversible physical time:

“The concept of becoming acquires a meaning in

physics: The present, which separates the future

from the past, is the moment when that which was

undetermined becomes determined, and ‘becom-

ing’ means the same as ‘becoming determined’”

(Reichenbach, p. 269).

Thus, quantum theory seems to include two

concepts of time: time in the form of a classical, re-

versible parameter of continuous time, in which

the realm of probabilities unfolds; and time in the

form of the discontinuous interaction between ob-

jects, which reduces knowledge of possible states

into factual, documented knowledge. Because of

fundamental theoretical reasons and because of

the very precise empirical data available, a dynam-

ical description of the transition from the probabil-

ity description to the factual description cannot be

modeled within the theory. Thus quantum-meas-

urement seems to establish a fundamental distinc-

tion between past and future within physics, with

past and future being closely related, but without

the possibility of completely deriving the factual

future out of the factual past, and vice versa.

Time and biological systems

According to the Second Law of Thermodynamics,

flows of energy arise far from equilibrium in order

to compensate energy differences and to increase

entropy. The Earth, for example, receives a con-

stant flow of energy from the sun and dissipates

energy into its cold surroundings. This energy flow

establishes a direction of time, which can be iden-

tified as the source of the temporality of complex

systems, biological systems in particular. Such sys-

tems are able to exploit energy flows to locally in-

verse the increase of entropy and to maintain

themselves in a steady state far from equilibrium

by functional closure against their environment.

They may even develop toward states of increased

order and organization, as the contingent and irre-

versible evolution of life on the planet shows. Bio-

logical systems can differentiate, interact, and or-

ganize themselves; they can form populations,

families, and ecosystems; and, in the case of

human beings, they can begin to establish history

as the temporal unfolding of rational, self-con-

scious, and moral social agency.

The cosmological foundation of time

All manifestations of irreversible time can be seen

as a consequence of the fact that the universe

started off with the Big Bang in a smooth and or-

ganized state of low entropy. The interplay of its

expansion with the contracting force of gravitation,

which agglomerates matter into bodies of high den-

sity that start to radiate and disperse their energy

into the expanding void, is responsible for the cos-

mos still being far away from equilibrium. It re-

mains a matter of dispute whether cosmic time will

end in a final collapse of the universe, when gravi-

tation will have superseded expansion and reversed

it into contraction, or whether expansion will go on

forever, until all order and structure of the universe

has been dissolved into an ever dispersing radiation

field with decaying minimal fluctuations. But the

expansion of the universe establishes a cosmic

time, which is the origin of the large-scale arrow of

time, in whose due course, in a favored niche far

away from equilibrium, biological systems could

evolve and develop into conscious beings, who

start wondering what time is all about.

See also ENTROPY; PHYSICS, QUANTUM; RELATIVITY,

ENERAL THEORY OF; RELATIVITY, SPECIAL THEORY

; SPACE AND TIME; THERMODYNAMICS, SECOND

LAW OF ; TIME: RELIGIOUS AND PHILOSOPHICAL

ASPECTS

Bibliography

Albert, David Z. Time and Chance. Cambridge, Mass.:

Harvard University Press, 2000.

Callender, Craig, and Edney, Ralph. Introducing Time.

Cambridge, UK: Icon, 2001.

Davies, Paul C. God and the New Physics. New York:

Simon & Schuster, 1983.

Davies, Paul C. About Time: Einstein’s Unfinished Revolu-

tion. London: Viking, 1995.

Denbigh, Kenneth G. Three Concepts of Time. Berlin and

New York: Springer-Verlag, 1981.

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Eddington, Arthur S. The Nature of the Physical World.

Cambridge, UK: Cambridge University Press, 1928.

Feynman, Richard. The Feynman Lectures on Physics, Vol.

1. Reading, Mass.: Addison-Wesley, 1963.

Friedman, Michael. Foundations of Space-Time Theories:

Relativistic Physics and Philosophy of Science. Prince-

ton, N.J.: Princeton University Press, 1983.

Hawking, Stephen, and Penrose, Roger. The Nature of

Space and Time. Princeton, N.J.: Princeton University

Press, 1996.

Macey, Samuel L. Time: A Bibliographic Guide. New York:

Garland, 1991.

Minkowski, Hermann. Space and Time (1908). In The

Principle of Relativity, ed. Albert Einstein, et al. New

York: Dover, 1952.

Newton, Isaac. The Mathematical Principles of Natural

Philosophy (1729), trans. Andrew Motte. Facsimile

Reprint. London: Dawson, 1968.

Reichenbach, Hans. The Direction of Time. Berkeley and

Los Angeles: University of California Press, 1956.

Turetzky, Philip. Time. London: Routledge, 1998.

DIRK EVERS

TIME:RELIGIOUS AND

PHILOSOPHICAL ASPECTS

According to Augustine of Hippo (354–430) time

cannot be satisfactorily described using one single

definition. In his words: “What, then, is time? If no

one asks me, I know: if I wish to explain it to one

that asketh, I know not” (Confessions 11, c. 14).

The attempt to establish a conclusive definition of

time ultimately leads to confusion. Time is not de-

finable by any other concepts. Time, in its fullness,

is unique and sui generis. This view is now gener-

ally accepted among philosophers of time. No at-

tempt to clarify the concept of time is claimed to

be more than an accentuation of some aspects of

time at the expense of others. The statement of

Plato (428–347

B.C.E.) that time is the “moving

image of eternity” and Aristotle’s (384–322

B.C.E.)

suggestion that “time is the number of motion with

respect to earlier and later” are no exceptions.

Time and eternity

Many philosophical and religious schools have as-

sumed that no beginning or end can be attributed

to time. For instance, in Indian thought the uni-

verse is largely conceived as undergoing repeated

creation and dissolution. According to this cosmo-

logical model, each world-cycle has to be meas-

ured in terms of billions of humans years (Balslev,

p. 140 ff.). Ancient Greek thought includes the

even stronger idea of cyclic time according to

which not only the cosmological processes but all

individual destinies are repeated in every detail in

time (Whitrow, p. 14 ff.). Jewish, Christian, and

Muslim philosophers have had to reject this idea of

cyclic time because it leaves no room for genuine

progress or final salvation. Augustine, in particular,

was very clear about this: “Heaven forbid, I repeat,

that we should believe that. For Christ died once

for our sins, but rising from the dead he dies no

more, and death shall no longer have domain over

him” (De Civitate Dei 12; vol. 4, p. 63)

Some Muslim thinkers such as al-Farabi

(873–950) and Avicenna (980–1037) held that the

act of creation should be conceived as atemporal

and purely logical. In Judaism and Christianity,

however, most philosophers have rejected this

view maintaining that God’s creation of the world

was in fact its temporal beginning. In Judaic

thought some have argued that time existed and

the Torah was created before the creation of the

world. This view of time would allow the notion of

the universe being created in time. However, ac-

cording to the most common view in traditional

medieval philosophy, time is considered to be re-

lational; that is, there can only be time in relation

to a world of events. With this view of time, cre-

atio ex nihilo means that the universe does not

owe its existence to anything in the physical world,

and it can only be explained by reference to some-

thing that is not a part of this temporal world. The

idea of the absolute beginning of the universe does

not imply any change from one state to another.

Medieval writers typically held that time itself

began with creation. Thomas Aquinas (c.

1225–1274) stated this view in the following way:

“The phrase about things being created in the be-

ginning of time, means that the heavens and earth

were created together with time” (Summa Theo-

logica 1a, 46, 3). A similar view had been ex-

pressed earlier by the great Jewish scholar Moses

Maimonides (1135–1204), according to whom the

biblical statement of God’s existence before the

creation of the world has to be interpreted in terms

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