Bernard Tan

National University of Singapore




Ancient physics


Before the Rennaisance, science, and physics in particular, functioned largely in harmony with the established state and with organised religion.  In ancient Greece, China and India, astronomical observations of heavenly bodies were sanctioned by the state for the useful functions they could provide, such as the making of calendars and the marking of seasons for agricultural purposes, as well as for navigation at sea.


These observations also supported official religious practices, and in many cases provided a framework for the legitimacy of the ruling elite.  The ability to predict significant heavenly events, such as solar eclipses, helped rulers to keep the populace in awe and to convince them that their rulers had some kind of heavenly mandate.  In many states, rulers were assigned a degree of divinity which had to be confirmed by their ability to forecast these events.  Hence the official state astronomers gained an importance in the state apparatus which enabled observational physics to flourish.


Models of the universe


The need to explain the movements of heavenly bodies gave rise to many models of the universe and the solar system.  In Greek physics, the Ptolemaic system envisioned the planets, the Sun, and the stars as moving in circular orbits around the earth.  However, this model could not account for the actual observed paths which these bodies were seen to take, so it had to be refined with a system of epicycles which became more and more complicated as time went by. 


Eventually, the Copernican model of the solar system was proposed and found to provide a more scientifically satisfying picture of reality.  This model requires the earth to revolve around the Sun and hence came into direct collision with the accepted religious tenet of the Church that the earth and mankind, being the pinnacle of God’s creation, had to occupy the centre of the universe.


Nevertheless, the Copernican model, through its simplicity compared with the complex Ptolemaic cycles and epicycles, became the accepted scientific model of the solar system.  Kepler further refined the Copernican model and published his famous three Laws of planetary motion.  Galileo provided further evidence for the heliocentric nature of the solar system and also propounded the Law of Inertia, i.e. objects which are in motion tend to stay in motion.  Galileo, of course, was to come into direct collision with the Church which forced him to publicly recant the Copernican theory.


Newton and the deterministic universe


Isaac Newton was therefore able to build on these foundations and  propound a theory of gravity which was able to account for the workings of Kepler’s three laws.  In addition, Newton’s three Laws of Motion have become the basis for all of classical physics, and are of course still valid today in the non-quantum world.


Newton’s Laws thus providid the basis for a universe in which, gven the required intitial conditions, one could predict the future state of any physical system, and indeed of the entire universe.  This led to a model of the entire universe as a deterministic system which ran like a well-ordered clockwork machine, whose settings were already predetermined and whose future could be predicted, given that the initial parameters were known.


The consequence of this for religious thought was profound.  In particular, those who believed in a universe in which everything had been predestined found support for their views in scientific determinism.  Naturally, those in favour of a universe in which free will still had meaning found determinism to be a major stumbling block.


Statistical physics and the Laws of Thermodynamics


The notion of cause and effect, which must have profound religious consequences, was also bound up with the clockwork-like determinism of a Newtonian universe.  Strictly speaking, Newtonian physics was not sensitive to time direction.  All the equations of classical physics would work even if time were reversed.  For example, if a movie of a bouncing ball were played in reverse, it should still appear to obey the laws of classical physics.


However, it is apparent that there are many phenomena in nature which are not reversible in time.  For example, a movie of a bowl which shatters when dropped to the ground would not seem to be natural.  Such phenomena, it appears, are intimately connected to the notion of order.  There seems to be a tendency for ordered arrangements to be come disordered in the natural scheme of things.  A pack of cards, if arranged in order, will become disordered when shuffled.  Hence there are natural phenonema which favour one direction of time but not the reverse direction.


The discipline of statistical physics, which arose from the study of thermodynamics or the physics of heat, deals precisely with such phenomena.  Statistical physics deals with the behaviour of large numbers of objects, whose behaviour appears to be random.  For example, individual molecules is a gas move about and collide with each other randomly, but taken as a whole, we can predict their behaviour very accurately. 


The three Laws of Thermodynamics provide the basis for our understanding of the behaviour of physical systems composed of large numbers of randomly behaving objects.  One of the key concepts of statistical physics is entropy, which roughly speaking denotes the degree of disorder of a system.  A pack of cards which is properly arranged in order has low entropy, while a pack which has been shuffled thoroughly has high entropy.  The natural world tends towards an increase of entropy, and in fact the universe should tend towards a final state when all order has been lost, and “Heat Death” is the result.


These concepts have religious resonances in several ways.  The notion of increasing entropy implies that the universe proceeds in a fixed direction of time, towards increasing disorder.  This also implies that the initial state of the universe was one of perfect order, and is continuously being degraded.  Hence entropy appears, to some people, to support the notion of divine creation at the beginning which is being degraded as time progresses.  Conversely, evolution, which implies the increasing of order with time appears to contradict the Third Law of Thermodynamics, i.e. that entropy is increasing all the time.  However, in actual fact, entropy cannot be used to support opposition to evolution, because one has to take the entropy in a system (in this case the solar system or the universe), as a whole.


The classical model of the universe was severely undermined at the beginning of this century by two major developments in Physics - Relativity and Quantum Theory.  These have so profoundly changed the face of physics that we count the genesis of these two Theories as the birth of Modern Physics.




The name we associate most with the Theory of Relativity is Albert Einstein.  The theory is based on a solid observational fact - that the velocity of the speed of light is a constant, not matter what the relative velocities of the light source and the observer may be.  Many careful observations, such as the Michelson-Morley experiment, were made to confirm this suprising conclusion, and many alternative theories, such as the existence of ether, were put forward to explain it.


Hence Einstein’s Theory of Relativity is based on solid experimental fact, and its predictions have been confirmed by careful observation as well.  There are two branches of Relativity theory - Special Relativity and General Relativity.


In Special Relativity, Einstein deals with situations in which objects travel at a constant velocity near the speed of light.  Time becomes just another dimension of space, and can be dealt with likewise.  Many suprising results, such as time dilation and the contraction of objects when seen by a stationary observer, run totally contrary to common sense, which explains why Relativity was so misunderstood by the general public for such a long time.  Special Relativity also profoundly changes our common sense concept of simultaneity, and hence of causuality.  For example, two observers moving at different velocities to another person may observe events happening to that person in different order.


General Relativity theory is even harder to understand than Special Relativity.  However, one important point about it is that it extends Newton’s work on gravitation.  In General Relativity, the effects of gravitation and acceleration are considered to be identical, and hence gravitational force and the force due to acceleration are equivalent to each other.  In this way, gravitational force becomes just a property of space, which is distorted when objects with mass are present.  Hence the earth may be said to attract objects by virtue of its distorting space, thus forcing objects into a path towards it.


Quantum Theory


Quantum Theory, which is the other pillar of Modern Physics, also has profound implications for religious thought.  Like Relativity, this theory also rose from experimental observation.  It had long been observed that so-called “Black bodies” emit a spectrum of radiation which peaks at a certain frequency and then tails off at higher frequencies.  If light and heat are electromagnetic waves, then classical theory predicts that at higher frequencies, such bodies must emit even higher amounts of radiation.


This paradox was overcome only when it was postulated (by Einstein and others) that perhaps light was not a wave motion, but came in small packets of energy, which we now call photons.  By applying this assumption, the problem with the explanation of Black body radiation was overcome.


However, physics now had to face a bigger problem: how could light behave both as a wave and as particles at the same time?  It was undoubtedly true that light behaved as a wave, as phenomena such as diffraction and interference were intrinsic properties of light.  Hence arose the paradox known as the “Wave-particle duality” in which not only light, but every other physical object, has both the properties of waves as well as of particles.  In everyday life, of course, objects such as human bodies are so large that their wave-like properties are unobservable.


Quantum theory therefore developed a whole new formalism to deal with this duality.  The equations of Quantum Theory deal with “Wave functions”, which all objects possess.  It is only at the very smallest level of physical objects that their wave properties become apparent.  One consequence of this duality is the famous “Uncertainty Principle” of Heisenberg, which states that the velocity and position of an object can never be determined perfectly accurately together.


Interpretation of Quantum Theory


The interpretation of the wave function has given rise to much debate in the physics community.  The standard interpretation is that the wave function is a probability function,  in which objects keep their sharply defined particle nature, but whose positions can only be predicted by the probability function.  This seems to satisfy most people, since it implies that the objects are still sharply defined as particles, and that we simply do not know where they are.


However, the probability function implies that we do not know and cannot predict the actual position or location of the partcle, but when we actually attempt to measure its location or momentum, we force the wave function to collapse such that the particle will assume a definite position or momentum. (Of course, subject to the Heisenberg Uncertainty Principle.)


However, Quantum theory seems to imply that the wave-particle duality runs deeper than that, and that each and every particle carries a wave property with it like a kind of ghost.  The Young double-slit experiment showed clearly that interference phenomena occur even when only single photons are involved. 


Another interesting thought experiment is the Schrodinger’s cat experiment (named for Erwin Schrodinger, one of the founders of Quantum Physics), whose life or death seems to depend on the state of the wave function of a single electron which triggers off a series of events releasing a poison gas into the container where the cat is kept.  Since the wave function’s values are indeterminate until we force it to collapse, and the cat’s life or death depends on definite values of the wave function, is the cat alive or dead before the wave function is forced to collapse by our observation?


Einstein  himself was never comfortable with the probability interpretation of Quantum Theory, or that the wave function implied that there hidden variables which we could never see.  As he famously said, “God does not play dice with the universe.”


A small number of physicists have looked for alternative interpretations of Quantum Physics.  David Bohm and others have propounded alternative models which have recently attracted renewed interest in alternatives to the probability function interpretation of Quantum Physics (usually known as the Copenhagen interpretation, after the Danish physicist Neils Bohr). Bohm himself has proposed a quantum model in which every particle possesses a so-called ''pilot wave'' which can account for the particle's wave properties.


An interesting alternative interpretation is the so-called “Many-Worlds” model of the universe in which an infinite number of parallel universes exist, is proposed. In the standard Copenhagen interpretation, the wave function which represents the sum of all possible configurations of the particle, collapses into just one configuration when a measurement or observation is made.  In the Many Worlds theory, ALL of these outcomes will actually be realized in parallel universes which exist alongside our own.  Such a bizarre model of the universe must surely have profound philosophical and theological implications.


Chaos Theory


In studying physical systems which obey the classical laws of physics, physicists have assumed that for all such systems, a given defined starting point would lead to predictable outcomes. If such systems comprised large numbers of individual objects behaving randomly and unpredictably, then they would obey the laws of statistical physics predictably. However, it has since been discovered that there are many systems in the real world which do not exhibit such predictable behaviour, but also are not random systems describable by the laws of statistics. Such systems are known as Chaotic systems, and they abound in nature.  One characteristic of such systems, which is quite counter-intuitive, is that extremely small starting differences can make very large differences in outcomes.


The meteorologist Edward Lorenz discovered that the global climate system was just such a Chaotic system.  For example, a butterfly flapping its wings could trigger off a hurricane on the other side of the world.  Such an outcome, which one would not expect in classical physics, is a common feature of Chaotic systems.  Hence in such systems, causuality may run counter to what is common-sense, and hence have important implications for theological ideas of predestination and free will.


Chaos theory has provided physicists with new insights into the nature of physical systems and of nature, which contradict previously held views about randomness and determinism.  Chaos theory has also provided new ways of looking at the universe and nature, through such topics as fractals and the Mandelbrot set.  The Mandelbrot set, which shows that wholly unexpected and amazing results can come from very simple mathematical assumptions, is well known through the many startlingly beautiful patterns which it can create. 


The most surprising feature of these patterns is their ability to create complex patterns within complex patterns, in a self-repeating way.  These patterns have properties which are so complex that they consitute a class of objects midway between a normal line and a plane.  Another amazing feature is the way in which these patterns appear to mirror natural objects such as clouds and plants.  These patterns seem to imply that there are worlds within worlds which can constitute an infinite regress as we examine them closer and closer, and must have resonances in theological thought about the infinite resources of a divine creator.


Complexity and the holistic universe


Chaos theory and its many related concepts are now seen as part of an increasing interest in the Theory of Complexity.  Many of these ideas tend towards a holistic view of the universe as a whole, such that every part of it is somehow related and connected to every other part.  The recording of images using holography is a precursor of such a concept, for the holographic image resides in the hologram in such a way that every part of the image is in every part of the hologram, unlike a normal photograph.


This holistic view of the universe, which Bohm and other physicists have strongly espoused, has major implications for theological thought.  Such a universe may appear to provide support for a divine creator, though many physicists still believe that divine intervention does not need to be invoked for the universe to run as it does.  Those who hold to a pantheistic world view may also find support for their position in such a holistic universe.


In this short talk, I have not attempted to cover all of present day physics, for that would be an impossible task.  I have not covered, for example, theories regarding the origins of the universe, such as the big bang and the steady state theory, nor have I covered the latest developments in the physics of elementary particles.  There are many exciting advacnces in these areas, such as string theory, but I must leave that for another time.


What I have tried to do is to give a coherent picture of the development of physical thought from earliest times to the present, particularly with respect to the very fundamental ideas which have had and are having such a profound impact on philosophical and theological thinking on determinism and free will.   I hope that this talk will stimulate you to examine more closely the relationships between science and Christian theology which could benefit both scientists and theologians.