This year’s May Dialogue, featuring Nobel Laureate PROFESSOR ILYA PRIGOGINE, was the largest for many years – attended by over 375 people at Regent’s College on May 20th. On Thursday we drove straight up to Cambridge, where we had arranged a lecture in the School of the History and Philosophy of Science (HPS) with PROFESSOR MICHAEL REDHEAD. This was attended by over 200 people, ranging from the philosopher and Whitehead specialist PROFESSOR DOROTHY EMMET – at over 90 the oldest person there -to undergraduates and dons who packed into the lecture theatre. We had dinner afterwards in Wolfson with a number of HPS dons.

The following day we drove over to Oxford and had lunch in Green College with SIR CRISPIN TICRELL, SIR ROGER PENROSE and a few other Fellows before the lecture arranged by PROFESSOR DAVID SHERRINGTON in the Department of Physics. This theatre was even larger than in Cambridge, and was once again filled to capacity. These university talks were pitched at a more technical level, while the London presentation explored some of the wider philosophical implications of Prigogine’s work.

His lifelong preoccupation has been with time. What, he asks, do we and a rock have in common? The flow of time, which is both the unifying element and the source or means of diversity The thrust of his current work is the establishment of an evolutionary perspective in physics, which would make it consistent with our understanding of cosmology and biological evolution. At present we have a physics in which time is reversible and essentially an illusion and a biology in which time is crucial: without the reality and irreversibility of time, evolution could not have occurred.

Two of his early philosophical influences were Alfred North Whitehead and Henri Bergson. He sees his work as providing the underpinning in physics of Whitehead’s organic, process view of life. Bergson was convinced that if time existed in us, it must also exist in the universe. And if time is real, so are novelty and creativity. The reality of novelty and creativity implies, in turn, an emergent, evolutionary universe and not a deterministically programmed one. Prigogine’s work starts where Bergson and Whitehead left off, moving from philosophy to physics: if the flow of time and duration are fundamental on most levels of description, then, he argues, they should also be found in basic physics.

Whitehead declared that Western culture had two principal projects: the first was the intelligibility of nature, the ambition ‘to frame a coherent, logical, necessary system of general ideas in terms of which every element of our experience can be interpreted’; then, on the other hand, the humanistic project of democracy, which implied human freedom, creativity and responsibility. As long as the intelligibility of nature is associated with a deterministic description, the two projects appeared to be contradictory.

With this type of background, it was natural that Prigogine turned first to thermodynamics. The legacy of the nineteenth century left us with two conflicting views of nature: the deterministic and time reversible view based on the law of dynamics and the evolutionary views associated with the second law of thermodynamics. Both views have been immensely successful. How could they be related and delineate their respective domains of application? Prigogine considers that there have been two basic steps towards clear classification. The first refers to the macroscopic, thermodynamic level. Traditionally, thermodynamics was mainly applied to equilibrium situations, but Prigogine focused his attention on non-equilibrium systems. His research led to many surprising findings.

An example is Prigogine’s theory of dissipative structures, for which he was awarded the Nobel Prize in Chemistry in 197~, which shows how ever-higher levels of complexity can emerge in nature in far from equilibrium situations. The existence of dissipative structures, therefore, proves the constructive role of the arrow of time associated with irreversibility. In such systems, fluctuations and instabilities lead to bifurcations, points at which the system spontaneously self-organises into a new pattern. And, as the title of an earlier book states, order can emerge out of chaos. Bifurcations introduce a basic element of unpredictability. At these points, several possibilities are open to the system, one of which will actually be realised. Therefore the future involves probabilities, in contrast with stable dynamical systems (such as a pendulum) whose future can be predicted by deterministic laws.

This naturally has essential consequences for the description of evolution. A deterministic view of evolution implies that the film has already been made and is simply unfurling in an entirely predictable sequence. We are automata, but we deceive ourselves into thinking that we are free; our freedom is only apparent. This debate over free will and determinism has a long ancestry. The theological determinism implied in divine omniscience and omnipotence was subsequently translated into various forms of scientific and social determinism ranging from the genetic, neural or biochemical to the psychological and cultural. The key question is whether the future can be predicted with certainty – or is it always essentially a question of probabilities?

We can now restate the dilemma we began with: the irreversible nature of time is asserted in cosmology and biology, but physics is based on a formulation of the laws of nature in which there is no distinction between past and future; in other words time is reversible and therefore illusory, as Einstein implied. The tension or paradox is that the universe itself is full of irreversible transformations which imply an arrow of time (such as ourselves!) and yet the basic laws of physics are said to be reversible. The results mentioned in connection with non-equilibrium thermodynamics show that irreversibility cannot be the result of our approximations. Non-equilibrium structures are as real as equilibrium ones. How then can the arrow of time and limited predictability be introduced into the basic laws of physics? We come now to the second and recent part of the work of Prigogine and his group in Brussels and Austin.

Traditional formulations of the laws of physics for individual cases or experiments in classical mechanics are associated with the idea of trajectories, and in quantum mechanics with the idea of the wave function and its collapse; then for ensembles (a large number of individual cases) there is the corresponding statistical description. It was always assumed that these two descriptions – individual and statistical – were equivalent, but Prigogine has shown that this equivalence is broken for important classes of unstable systems, both in classical and quantum mechanics.

The proof of this statement requires appropriate mathematical tools which have been developed only recently. In short, the statistical description leads to new solutions that are irreducible to classical trajectories or quantum wave functions. To obtain these solutions we need function spaces (rigged Hilbert spaces, Gelfand spaces) going beyond the ‘nice’ functions associated with the Hilbert space familiar to physicists. This is not the place to describe the technical aspects of this approach. But let us emphasise that, as a result, the meaning of the fundamental laws of physics is changed. They no longer express certainties but possibilities and time symmetry is broken, making the process irreversible rather than reversible. We, therefore, obtain an extension of Newton’s and Schrodinger’s dynamics to account for unstable dynamic systems. In the classic Popperian sense of a new formulation containing but transcending the existing one, Prigogine’s theory suggests that stable systems are actually a subset of unstable systems and not vice-versa as was previously assumed.

Prigogine quotes his friend Leon Rosenfeld that ‘no physical concept is sufficiently defined without the knowledge of its domain of validity’. It is precisely this domain of validity of the basic concepts of physics which he is delineating in relation to instability and chaos; it is also important to stress that his co-workers have recently validated some of the main predictions of his approach by an extensive computer programme.

Irreversibility, which is an emergent property like phase transitions, is, therefore, a fundamental property of nature, since, according to Prigogine, it is intrinsic to unstable chaotic systems. In other words, the statistical description is not simply an expression of our ignorance. Many physicists like Murray Gell-Mann still claim that irreversibility can be explained by ‘coarse graining’, that is by saying that it results from our limited human approximations, and that for a really well-informed observer the world would appear perfectly time reversible. Prigogine strongly contests this view, maintaining that ‘irreversibility subsists, whatever the precision of our experiments

An important illustration of this controversy can be found in Prigogine’s understanding of the quantum measurement problem and the well-known conundrum of the role of the observer in the measurement of quantum systems. He refers to a recent article in the *Scientific American *in which Steven Weinberg highlights ‘a stubborn duality in the role of intelligent life in the universe’: on the one hand, when a system is not observed it behaves in a perfectly deterministic (and reversible) way in agreement with Schrodinger’s equation of quantum mechanics; on the other hand, when the system is actually measured by an external observer, it violates this determinism. In this second case, possible outcomes of measurements can no longer be predicted with certainty in advance, but can only be expressed in terms of probabilities.

In this view irreversibility is introduced by the observer or experimenter rather than being inherent in the basic physics. This makes us the ‘fathers of time’ rather than its children clearly a nonsense! Prigogine’s conceptual scheme involves instability or chaos leading to probability and in turn to irreversibility. It is these notions of instability, probability and irreversibility which now become fundamental, so that the ideas of trajectory or wave function become particular cases which are only relevant for stable systems. The duality inherent in the traditional formulas of quantum mechanics on the one hand Schrodinger’s equation – on the other the collapse of the wave function – is therefore avoided.

At his lecture in Cambridge, Prigogine asked the poignant question: would Newton have approved of all this? His answer was in the affirmative, as he saw Newton’s allowing for occasional divine intervention in the universe as implying an openness to an evolutionary view – strongly rejected by Leibniz with his theory of pre-established harmony.

The wider implications of this new point of view in physics are far-reaching and promise to reconcile the scientific and humanistic projects of Whitehead mentioned earlier. Classical science emphasised stability and equilibrium. Now we discover fluctuations, instabilities and evolutionary patterns at all levels. This is not only true in science as the second half of the century has been characterised by social instability and a crisis of control and planning, as well as by recent self organising phenomena like the Internet. This change of perspective requires new approach. We have to find a ‘narrow passage’ between the Scylla of determinism and Charybdis of randomness.

These points were taken up by our other speakers at the May Dialogue – PROFESSOR BRIAN GOODWIN of the Open University and REV. PROFESSOR JOHN POLKINGHORNE, President of Queens’ College, Cambridge and formerly Professor of Mathematical Physics in the University. Brian gave a wonderful illustration of the application of Professor Prigogine’s ideas to biology when he described the behaviour of ants in a colony as ‘technically chaotic’. However, when the density of ants crosses a critical threshold, the chaos is transformed into a dynamic, holistic order. He concluded that the exploration of creativity required disorder.

John Polkinghorne supported Ilya Prigogine’s call for an enlargement of physics, adding that he would like to see an ontological revaluation within the discipline and an openness to metaphysical questions. Our rationality is based on causality and intentionality, which meant recognising holistic top-down causation and pattern- forming capacities. An enlarged imagination would allow for a broader physical interpretation, which would understand much of our current knowledge as a particular limiting case within a new framework of understanding – just as fractal geometry has contained and transcended Euclidian geometry.

One of the overall conclusions of a rich day was that we are not at the end of physics, but rather at the end of predictability and certainty, which means including novelty and creativity. And a science in which creativity and participation in the construction of the world are intrinsic is a science, which overcomes the widespread alienation associated with the traditional scientific outlook. In Prigogine’s ‘new rationality’, probability will no longer be seen as ignorance or science as equivalent to certainty. Time is real and the future is open: we live not simply in an ‘open society’ but also in an open universe.