Genesis: The origin of the universe

National Forum, Winter 1996 by Wersinger, J-M

It took time, observational evidence, and careful verification of predictions made by the Big Bang model to convince the scientific community to accept the idea of a cosmic genesis. Not only did the Big Bang model seem to give in to the Judeo-Christian idea of a beginning of the world, but it also seemed to have to call for an act of supernatural creation at some point. How else to explain the appearance of a whole universe? One of the fundamental rules of science is the impossibility of getting something from nothing. This rule appears to place the very moment of creation of the universe outside the realm of the scientific debate and force scientists to treat the existence of the universe as a given.

Not only is it difficult to figure out how a whole universe could appear from nothing, but also no plausible explanation for the mechanism of the explosion itself springs to mind. The only known force in nature capable of affecting the universe as a whole is gravity. Gravity is, however, an attractive force, whereas the explosion requires a repulsive force. The mystery of the explosion lies in the first fraction of a second of the life of the universe. At such early times, the universe was in a state of incredibly high temperature and density, a situation so foreign to laboratory conditions that it is impossible to extrapolate known physics to that realm. The cause of the explosion is shrouded in the extreme conditions of the very early universe. For a while cosmology treated the existence of the universe as a given and concentrated on the consequences of the explosion rather than its cause.

In the course of the scientific step-by-step reconstruction of the chronology of the universe, a number of puzzling paradoxes surfaced, of which two are of interest here. The first deals with the strength of the explosion. The push of the Bang was exquisitely well fine-tuned, allowing for the existence of a universe with galaxies, stars, planets, and life. Any other push would have meant either a structureless universe or a universe collapsing back onto itself after a brief existence. Why was the Bang so well engineered?

The second paradox deals with the large-scale properties of the universe. The extreme large-scale smoothness of the temperature and of the density of matter cannot be explained by the standard Big Bang model. No known physical process can account for it. What is the origin of this conspiracy? Is our universe very peculiar, that is, did it just start this way by sheer luck -- in the scientific jargon, with very special initial conditions -- or are there mechanisms that can account for the fine-tuned push of the explosion and for the smoothness of the universe?

Two diametrically opposite schools of thought have addressed these paradoxes. The proponents of the so-called anthropic principle state that if the universe were not so fine-tuned, there could be no life in it, and we humans would not be there to witness it. Although this statement is correct, it does not attempt to resolve the paradoxes in terms of physical mechanisms, but relegates them to the status of special initial conditions. In other words, that is the way the universe started because if it had not, we would not be there to witness it. The other school of thought has refused to accept special initial conditions but rather has searched for mechanisms that could account for the observed peculiarities. It is the purpose of this essay to present and to discuss some of the latest models advanced by the second school.

The Big Bang

When Einstein applied his newly created theory of General Relativity to the universe, he discovered to his dismay that the universe was not static as everybody, including himself, liked to believe at that time. His universe was either contracting or expanding. Rather than exploring the consequences of his findings, Einstein introduced an ad-hoc term into his equation that he called the cosmological term. The cosmological term provides for an antigravity term compensating for the overall gravity of the matter that tends to pull the universe together. Einstein created thus an artificially static universe that other mathematicians pointed out to be unstable, to no avail. Einstein later regretted the way he handled the problem, calling it the greatest blunder of his life.

Indeed, a decade later, the American astronomer, Edwin Hubble, using the newly built and largest existing 200-inch telescope on Mount Wilson, discovered the existence of galaxies other than our own and found that distant galaxies were all racing away from us. Actually, the farther away the galaxy, the faster it recedes from Earth. The truth of the matter finally hit Einstein: he had the key to the overall behavior of the universe in his equation ten years earlier and could have claimed another first had he not been blinded, like most other physicists, by the belief in a static universe. The universe is not static but expanding.

The fact that we see distant galaxies all racing away from us does not put us in a special position in the universe: we are not at the center of anything. Rather, the whole universe is expanding uniformly (at the same rate everywhere) and thus the larger the distance between any two galaxies, the faster they move away from each other. Imagine having a rubber balloon marked with dots representing galaxies. As the balloon is inflated, dots all move away from each other. The larger the separation between two dots the faster they move apart -- there is more rubber stretching between them than between two dots closer together. The analogy can be pushed correctly a step further. The rubber of the balloon represents space. As the balloon is inflated there is more rubber surface created, thus dots move apart. Translating this for the universe, we will say that rather than moving into more space, galaxies move apart as more space is created by the expanding universe] This is the correct picture provided by General Relativity. As time marches on the expanding universe stretches the fabric of space and creates the room required for galaxies to move apart. We witness the creation of more and more space in the universe as time goes on.