Chapter 3

Stars and galaxies

But since molecular hydrogen is stable, what the Second Law of Thermodynamics would predict at this stage is an even distribution of hydrogen molecules through the universe. There was nothing in the initial explosion which would imply eddies in the light that originally fled from the center of the exploding body, and certainly not vast numbers of eddies. True, the universe was small at the time, and so the "fleeing" light was also "returning" light, which was what produced the interference that gave rise to the particles and eventually hydrogen atoms and molecules. This return on itself of the light might account for eddies; but it must be remembered that the universe was expanding very rapidly, as an explosion expands. There was nothing from outside pressing inward; it was simply that the universe was small, and was growing larger.

Be that as it may, one might conclude that evolution should have stopped at this point, with perhaps a few coagulations of hydrogen clouds, rapidly dissipating as the universe grew larger and larger.

But in fact somehow--and once again I detect the intervention of God, directing everything according to its laws, but using chance to bring about the further stage--there were areas in which the hydrogen collected into rather dense clouds, in spite of the extremely weak gravitational field of each molecule.

As it happens, the gravitational field has the property of being "additive": that is, the more mass there is, the stronger the gravitational field of the whole. So as a cloud was formed, it would tend to attract more and more molecules into itself, becoming denser and more compact, with the molecules falling toward the center of mass of the cloud.

And as these molecules moved toward the common center of greatest mass, they followed curved paths, making the whole cloud turn around an axis as it grew denser and denser; the whole moving away from the center of the initial explosion.

And as the cloud moved through space, its increasing gravitational field collected more and more hydrogen into its mass, making it still larger and its field still stronger, and the tendency of all of it to spiral in toward the center even greater, meanwhile sweeping its environs clean of gas.

This gravitational pressure toward the center of mass of the cloud forced the hydrogen molecules at the center to strike each other so hard that they broke the molecular bond and became hydrogen atoms again; and as the pressure increased, the atoms became stripped of their electrons, which escaped toward the outside, leaving the center simply a mass of protons whizzing past (and around) each other, repelled from collision by their like positive charges. But as still more material collected from outside increased the total mass and the pressure toward the center, finally the protons were forced into collision with each other, and they destroyed each other back into electromagnetic radiation.

Once again, the stage for further advance is set by a setback, this time past the previous stages of atoms and particles, all the way back, it would seem, to the beginning.

But the destruction was not complete; it was not like a proton meeting an anti-proton, in which each is totally annihilated as such and transformed into radiation. In this collision only some of the mass of the proton-proton collision was converted into radiation, because both were particles of the same charge. This was a new, a productive self-destruction, which allowed the "strong force" to create a helium nucleus of two protons, which existed at a considerably lower energy level than that of the protons that made it up. It was the excess energy not needed by this new body that was radiated out as light.

And so the center of the hydrogen cloud became a hydrogen bomb, and a star was born.

A cloud mass becomes a star when the radiation pressure from the center more or less balances the gravitational pressure toward the center. This happened not once but billions of times, and the universe became populated with glowing stars, now radiating light in our visible spectrum. And stars, of course, are with us at present, from our sun to all the stars so far away that they appear to us as mere points of light.

A star, however, is not really in equilibrium, because as its central hydrogen explodes into helium, it collapses into a denser mass, forcing the helium nuclei into closer encounters with each other, until--to summarize a very long story--they too fuse into the nuclei of heavier elements, once again radiating out light which slows the further collapse. Depending on the total mass of the cloud from which the star is formed, its internal evolution takes a longer or shorter time, and follows different pathways. Some stars swell to "red giants" and then collapse and explode into ever-expanding gas clouds; others reach a stage of cataclysmic collapse into a neutron star or a "black hole": a body so dense that it becomes a small universe unto itself, because the light around it is so tightly confined that it cannot pass beyond a small distance without curving back onto itself.

The point, of course, is that a star is in process, using up its fuel until it is all spent, at which point it stops glowing and exists in equilibrium as a kind of cosmic pile of ashes, or until it spews out all of the left-over elements into the surrounding space.

All the while a star evolves, the energy radiated from it is degenerating, according to the Second Law of Thermodynamics, much of it in that very low energy state called heat, from which very little can come. Once energy reaches its lowest condition, of course, it is then in equilibrium, and no more change occurs. Stars glow because they are not in equilibrium, and they are losing energy to reach this lowest state, whatever it is, based on the initial amount of excess energy in the body; and once that is reached, the process stops.

As I say, just as this went on from the beginning of the first star, it is going on now, in all the stars that now exist.(1) Just as the expansion of the universe is sti1l going on, just as cosmic radiation is still with us, just as hydrogen clouds are still forming and becoming stars, so stars are still evolving. Evolution didn't just happen in the past; the "past" evolution is going on as I write this.

What is to be noted here, however, is that it is the forcible destruction of the nuclei of each element that creates by fusion the nuclei of the heavier elements. All elements in the universe were formed by the destructive force in the center of stars; and each gave itself up, as it were, to become a component in the more complex nucleus.

Note further that it was the tiniest element whose minuscule gravitational force produced the largest bodies in the universe which are the factories for all of the material complexity of the universe. And this could not have happened without turbulence somehow introduced into the initial explosion.

The turbulences that produced stars, however, also produced systems of stars. Many stars in our galaxy are close enough together that they orbit each other in pairs; and some are in small clusters of several stars. This is not surprising, since the gravitational field of a star is extremely strong, and so it could reach out enormous distances to capture another star.

In fact what happened is that the stars seem to have collected into clusters of millions and millions of stars and gas clouds called galaxies, all orbiting a common center and producing the various spiral shapes that astronomers are familiar with. Recently formed galaxies (speaking in millions of years now) are full of gas and have rather extended arms; older galaxies consist (of course) of older stars and very few if any gas clouds, and seem to have already wound themselves up into an egg shape.

Each of these galaxies or small clusters of galaxies (our own Milky Way, the galaxy made of all the stars we can see as stars plus the cloud of stars we see as the milky way itself, has a companion galaxy visible from the southern hemisphere) are moving apart from each other due to the effect of the initial explosion; moving more and more slowly as the millennia of millennia go on. Once again, we do not know if this will stop and then collapse, or if it will continue indefinitely, or until God arrests it.

Eventually, as I said, barring divine intervention, all the fuel in all the stars in all the galaxies will burn out, and the universe will reach its "heat death," with a more or less even distribution of the radiation lost from the stars, then in such a low-energy state that nothing can be formed from it. And so we can even now point to the purpose(2) of cosmic evolution: A vast space, whose total temperature is rather evenly just a couple of degrees above absolute zero, possibly including the stable detritus of the magnificent stellar bodies that originally made it up.



1. Not necessarily all the stars that we can see, because some are so far away that it takes millions of years for their light to reach us so that we can see them; and some, we know from observing novas and supernovas, blow up, which means that some will have already blown up and we will not see the explosion for perhaps hundreds or thousands of years.

2. I remind you of the sense of "purpose" in this book, which I discussed in Chapter 4 of Section 3 of the second part 2.3.4. It simply means the end of a process, not something "intended" or even "good."