Determinism or indeterminism?

Modern science has revolutionized our vision of the world. In the eighteenth century, Newton's theory of gravitation could be considered established, and gave rise to a materialistic-deterministic vision of the universe which can be personified in one of the most significant scientists of the time, Pierre-Simon, Marquis de Laplace (1749-1827), whose fields of study covered mathematics, astronomy, chemistry and biology. The success of his studies on the dynamics of the solar system moved him to state that, if we knew the exact initial conditions of the universe, it would be possible to predict all its past and future development. This gave rise to materialistic determinism, so successful in the nineteenth century and still a part of the popular vision of the world, in spite of the three devastating attacks it has suffered during the twentieth century.

The first attack was the principle of uncertainty, formulated in 1927 by Werner Heisenberg. In essence, this principle denies that we can know exactly the conditions of a physical system at any instant in time. With this, Laplace's assumption falls down, for the principle of uncertainty excludes, as a particular case, that we can know the initial conditions of the universe.

There was a way to save a part of Laplace's hypothesis. We may never be able to know the exact initial conditions, but couldn't we know them with sufficient approximation to predict, with a reasonable accuracy, the future development of the cosmos?

The second attack (not necessarily in chronological order) demolished this hope. In 1963, in his studies on meteorology, Edward Lorenz discovered the existence, predicted a few decades before by Poincaré, of dynamic systems where an infinitesimal difference in their initial conditions gives rise to a global discrepancy in the state of the system after some time. The study of these systems is called chaos theory. We now know that the universe, or a relatively small part of it, such as the solar system, is a chaotic system. So we'll never know the initial conditions of the universe with sufficient approximation, because the approximation will never be sufficient. Whatever the number of exact figures we know, even to the maximum allowed by the principle of uncertainty, chaos theory makes certain that, after some time (less than the age of the universe) they would be useless to let us do correct predictions.

Werner Heisenberg

The third attack was even more devastating. Quantum mechanics, developed in the nineteen twenties, states that the basic components of the universe, represented by elementary particles, are not deterministic, but random. Predicting the future of the universe is not only impossible at long range, but also in every step in its existence. Besides the deterministic chaotic macrocosm, whose exact evolution we shall never be able to predict completely, we also have an intrinsically probabilistic microcosm, whose evolution can only be followed with statistics. Both things at the same time, although we still don't know how to put them together.

The material world, the object of study for science, can be represented in this paradigm of modern physics by means of a segment of a straight line, with potentially chaotic determinism at one end, the macroscopic action of gravity, and intrinsic indeterminism at the other, represented by microscopic quantum mechanics.

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Manuel Alfonseca

This is a part of an article which was published in Spanish in the magazine Religión y Cultura, Vol. LIII:240, Jan.-Mar. 2007, pp. 137-153.