Quantum Theory and the Laws of Nature

Of course, theories and experimental results do get established, and a moderately competent scientist can trust and use them once they have been published by a thinker of genius and accepted by a reputable peer group. But those thinkers of genius will always be looking for what has been missed, for counterexamples that current theories cannot explain, and for anomalies and discrepancies that point to the need for new and possibly revolutionary forms of theoretical explanation.

None of that means that there are no laws of nature. But it does mean that we should not be too sure that we really know what they are or that we are on the verge of explaining absolutely everything by means of them or that we may not get a huge surprise at any time that may disprove all previous theories.

This happened to Newton's laws with the advent of quantum theory in the early twentieth century. The principles of Newtonian mechanics were not shown to be totally incorrect. They had worked well for over two hundred years and were a pretty reliable guide to how middle-sized objects, moving slowly relative to the speed of light, behave. But Einstein's theory of relativity subsumed those laws under a wider set of more fundamental laws and showed them to offer only a limited and incomplete explanation of gravitational attraction. They do not work for very small or very fast particles. And they omit all mention of the basic nuclear and electromagnetic forces that play a large part in determining the behavior of all fundamental particles.

In the light of discoveries in physics since 1905, when Einstein published his paper on the photoelectric effect, it has become accepted by all competent physicists that Newton's laws of motion and gravitation do not provide a complete, closed, and deterministic account of the physical universe. They are not complete because they fail to account for many physical phenomena. They do not form a closed system, for there are many factors they do not even mention—like dark energy, dark matter, quantum fields, and nonlocality—that modify the operation of Newton's laws in major ways. And they do not offer a deterministic account because we now know that it is impossible in principle to predict the future completely.

This is because Heisenberg's principle of indeterminacy means that we can never determine both the position and the momentum of a subatomic particle. So, we can never have precise knowledge of all the properties of an initial physical state. Not only that. On the "Copenhagen interpretation" of quantum events, there is nothing—certainly nothing knowable by us—that precisely determines a change in quantum state of a subatomic particle. Exactly the same physical state of an atom can have a number of alternative future states. That is, the same cause can have different effects, and we can assign no physical cause for which effect is actualized.

This finding undermines a highly cherished dogma of classical physicists, the dogma that every cause (every initial state) can have one and only one effect; that is, that causes sufficiently determine their effects. This is the dogma of physical determinism. Given an initial state and the laws of physics, all effects follow by necessity from their causes. No alternatives are permitted.

This dogma cannot be proved in any way. The most we could say, before the rise of quantum physics, was that, as far as we have been able to determine, the same initial states always give rise to the same effects—as Hume might say, unalterably and uniformly. Some philosophers (Immanuel Kant, for example) have thought that this principle of sufficient causality is entailed by the rationality of the universe and is a precondition of scientific research, for, if we introduced uncaused causes into the universe, we would have introduced a principle of nonrational anarchy.

Copenhagen indeterminacy undermines this argument. It introduces vast numbers of particular events that are not determined by any law that we know about. The reason this does not bring anarchy into the universe is that there are stochastic or probabilistic laws that govern the behavior of large assemblies of subatomic particles and that make the observable universe seem deterministic, insofar as all "random" quantum fluctuations usually cancel each other out when large numbers are involved.

However, they do not always cancel out. Chaos theory (which uses fully deterministic equations) shows that very small fluctuations in initial conditions can produce very large and unpredictable changes in macromolecular states. A common illustration is a metal ball poised precariously on top of a semicircular metal ring. The smallest force applied to the ball will tip it one way or the other, but it will fall either onto a switch that will ignite a nuclear bomb or onto another switch that will dispense a million dollars. This is an example of a tiny change that will produce hugely different effects. For quantum theory, there are millions of such tiny changes, and some of them will produce unpredictable effects on a large scale.

So, now we know that extraordinary and highly improbable events are possible without breaking any laws of physics. They will, in fact, happen but only rarely. To say that an event is highly improbable is not to say that it cannot happen. It is to say that it will happen but not very often. Most of the time the quantum indeterminacy of the universe will be invisible, and we will not observe the slight distortions of time and space that they, in fact, constantly involve. Stochastic laws are still laws of physics, but they allow extraordinary things to happen.

These would, of course, not be miracles if there were no God. But, if the prevailing interpretation of quantum theory is accepted, two dogmas of determinism have been comprehensively undermined—that every cause has one and only one possible effect and that all causes can be exhaustively specified and their effects, at least in principle, predicted.

There are laws, and, without them, there could be no science. But quantum theory has rendered obsolete a widely held eighteenth-century view that the universe is wholly determined by inflexible and universal laws that exclude any other causal influence and that completely explain everything that will ever happen.

John Polkinghorne speaks of "the patchwork character of scientific understanding" (2005, 11). Modern physics does not offer "a single causal web of known and determinating character." There is, Polkinghorne says, a major gap between the quantum realm and the realm of classical physics that has not yet been bridged by a fully integrated account. And quantum theory and general relativity have never been perfectly reconciled to one another. So, he concludes, "science has not demonstrated the causal closure of the natural world" (2005, 37). There may be an "intrinsic fuzziness" or "ontological openness" in nature that allows the operation of further, largely unknown, causal principles.

It looks as though modern physics is mainly concerned with establishing a set of precisely measurable regular relationships between artificially isolated phenomena under strictly controlled conditions. That such relationships exist and can be mathematically described is an amazing fact about our world, which did not have to be true. Einstein remarked that "the eternal mystery of the world is its comprehensibility" (1970, 61).

But the supposition that these relationships (these "laws") govern absolutely all phenomena without exception, that they are wholly unbreakable and unchangeable, and that there are no other causal factors to be taken into account in the real world is not supported by modern physics. As Polkinghorne says, "We therefore have no compelling grounds for regarding current theories as being more than a form of approximation to actual physical reality as it is encountered in the limit of effective isolatability" (2005, 34).

There is probably no statement about the fit between modern physics and the objective world that is not contentious. But we can confidently say that a closed and deterministic view of nature is neither a presupposition of nor a deduction from the practice and established findings of modern physics. Universal physical determinism was suggested to many by the work of Newton, though he did not subscribe to it himself. Contemporary views tend to be much more agnostic about the universal applicability and all-encompassing range of physical laws. There is, after all, no firm and unalterable experience that establishes the existence of unbreakable and deterministic laws of nature.

As far as physics is concerned, there could be forms of spiritual causality in nature, though the methodology of physics would preclude a study of them within physics proper. The strongest arguments against miracles will not come from a belief that there are closed, absolute, and inflexible laws of nature. They will come from the difficulty of establishing that any spiritual causes have ever been reliably observed. And that is where David Hume concentrates his attack.

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