D. THE BEGINNING IN TIME

35. First of all, to quote some figures-which aim at nothing else than to give an order of magnitude fixing the dawn of our universe, that is to say, to its beginning in time - science has at its disposal various means, each of which is more or less independent from the other, although all converge. We point them out briefly:

(1) recession of the spiral nebulae or galaxies:

36. The examination of various spiral nebulae, especially as carried out by Edwin W. Hubble at the Mount Wilson Observatory, has led to the significant conclusion, presented with all due reservations, that these distant systems of galaxies tend to move away from one another with such velocity that, in the space of 1,300 million years, the distance between such spiral nebulae is doubled. If we look back into the past at the time required for this process of the "expanding universe," it follows that, from one to ten billion years ago, the matter of the spiral nebulae was compressed into a relatively restricted space, at the time the cosmic processes had their beginning.

(2) The age of the solid crust of the earth:

37. To calculate the age of original radioactive substances, very approximate data are taken from the transformation of the isotope of uranium 238 into an isotope of lead (RaG), or of an isotope of uranium 235 into actinium D (AcD), and of the isotope of thorium 232 into thorium D (ThD). The mass of helium thereby formed can serve as a means of control. This leads to the conclusion that the average age of the oldest minerals is at the most five billion years.

(3) The age of meteorites:

38. The preceding method adopted to determine the age of meteorites has led to practically the same figure of five billion years. This is a result which acquires special importance by reason of the fact that the meteorites come from outside our earth and, apart from the terrestrial minerals are the only examples of celestial bodies which can be studied in scientific laboratories.

(4) The stability of the systems of double stars and starry masses:

39. The oscillations of gravitation between these systems, as also the attrition resulting from tides, again limit their stability within a period of from five to ten billion years. 40. Although these figures may seem astounding, nevertheless, even to the simplest of the faithful, they bring no new or different concept from the one they learned in the opening words of Genesis: "In the beginning . . .," that is to say; at the beginning of things in time. The figures We have quoted clothe these words in a concrete and almost mathematical expression, while from them there springs forth a new source of consolation for those who share the esteem of the Apostle for that divinely inspired Scripture which is always useful "for teaching, for reproving, for correcting, for instructing" (2 Tim., 3, 16).