Jacques Maritain Center: Thomistic Institute

Time and Universe

Mario Castagnino
Instituto de Astronomía y Física del Espacio.
Buenos Aires, Argentina

This talk is not a philosophical essay. It is just a physical rough material, about the concepts of time and universe, prepared by a physicist to be used by the philosophers in eventual speculations. Because, in fact, these two concepts: time and universe and their interconnection, open the ways of, what we believe, is the most interesting philosophical speculation. Metaphysics must be based in Physics, and since Metaphysics tries to reach the widest possible scenario, it must be based on the biggest physical object: the universe considered as a whole. Moreover time is one of the essential and most intriguing components of the universe.

We will consider three problems:

1.- The nature of time.

From the very beginning of scientific history two lines of thought define the nature of time in different ways. Aristotle, Leibnitz and Mach, consider the time as a concept derived from the motion. Newton, Poincaré and Prigogine consider the time as a primitive concept. Based on the ideas of Mach, and using Barbour's modern view of these ideas, we will conclude that time is a derived concept.

2.- Had the universe an origin?

Also, from the very beginning of human thought, the universe has being considered in two different ways: endowed with a beginning (and eventually an end) by most religious cosmogonies, and as an eternal object, by the greeks and all the scientists up to this century. Based on cosmological observation we will conclude that the universe had an origin (namely the "big-bang"). This conclusion introduces another question: Can be the universe be originated in the "nothingness"? (more precisely in the vacuum). Is this possible, since we use to think that from nothing only nothing can be obtained?. Nevertheless, the analysis of Einstein equation allows us to see that it is possible to extract something (matter, energy, and geometry) from the vacuum. This fact leads to consider as unstable the original state of the universe.

3.- The arrow of time.

All the laws of physics (with negligeable exceptions) are time symmetric. For these laws past is identical to future. Nevertheless the universe is time-asymmetric and allows to establish a clear difference between past and future. How can we explain these contradiction?. Simply because the universe as an object is time-asymmetric, even if the laws that establish its evolution are time-symmetric.

Causality is the best feature of the universe that shows its time asymmetry and causality was studied, in great detail, by Reichenbach, who introduced a global model of the universe, which contains branch subsystems. We will show how Gibbs ideas about irreversibility can be inscribed in Reichenbach global system and how the instability of the branch subsystem and those of the universe complete the scenario. Then we can see how the object-universe turns out to be clearly time-asymmetric and how the unstable initial state of the universe plays a fundamental role in the game.

4.- Conclusion.

The three features above give us a clear idea of the universe and its time-evolution. This image is based in Einstein equation of general relativity, where time is a derived concept, in agreement to 1. The universe began in an unstable state: the vacuum, in agreement with 2. As a consequence the universe is time symmetric answering, question 3.

To elaborate this rough material would be the task of philosophers...