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Scientists seem more difficult to please than the golden-haired girl of fairy-tale fame. While Goldilocks troubled herself over the just-right porridge, chair, and bed, astronomers appear preoccupied with the size of the universe.
In the days before telescopes, when an observer could count a few thousand stars in the night sky, many considered the universe too small and unimpressive to be the work of an almighty, all-knowing Creator. Only an infinite cosmos, they said, would befit an infinite deity. But then, others argued, an infinite cosmos might eliminate the need for a Creator.
Thanks to the Hubble space telescope, scientists now see that the universe contains roughly 200 billion large- and medium-sized galaxies and about a hundred times as many dwarf galaxies. The stars in those galaxies add up to about fifty billion trillion, and they comprise a mere one percent of the mass of the observable universe.
Because of the travel time of light, the universe humans can observe is really the universe of the past. What researchers know about the expansion and geometry of the universe informs us that the universe of today is at least several hundred times more enormous than the universe we can see. The universe is trillions of trillions of times larger and more spectacular than what the earliest astronomers presumed!
And yet, this new knowledge of the vastness of the universe has led to new complaints. In his book, God: The Failed Hypothesis, Victor Stenger says, "If God created the universe as a special place for humanity, he seems to have wasted an awfully large amount of space." Stephen Hawking, in the best-selling science book of all time, A Brief History of Time, shares Stenger's view: "Our solar system certainly is a prerequisite for our existence. . . . But there does not seem to be any need for all these other galaxies." So now the universe is too big to befit the all-wise, all-powerful God of the Bible.
If Wrong Mass, Wrong Elements
Those who have not had the privilege of studying astrophysics may not realize that the universe must be as massive as it is in order for human life, or any kind of life, to be possible within it. There are at least two reasons for this necessity. The first concerns the production of life-essential elements.
The hot big bang model (now firmly established by observations) tells us that at the moment of cosmic creation, the universe was infinitely or near-infinitely hot and compressed, and all the ordinary matter existed in the form of hydrogen. As the universe expanded, it cooled. The rate at which the universe expanded and cooled depended in large part on its mass—the greater the mass, the slower the expansion and cooling rate. The slower the expansion and cooling rate, the more time the universe would spend in the temperature range (13–150 million degrees Centigrade) at which nuclear fusion can occur.
Because of its mass, the universe spent about twenty seconds in the nuclear fusion temperature range when it was between three and four minutes old. As a result, 24.77 percent of the universe's hydrogen (by mass) fused into helium. Thus, when stars began to form—about 380,000 years later—they started off composed of about 75 percent hydrogen, 25 percent helium, and trace amounts of deuterium, lithium, and beryllium.
In the nuclear furnaces of the stars themselves, more hydrogen fused into helium, and, in addition to the extra helium, all the rest of the elements that appear in the periodic table were synthesized (created). The capacity of stellar nuclear furnaces to produce an abundance of elements heavier than helium (all but two of the elements) depended critically on how much of the universe's initial hydrogen was fused into helium and heavier elements during the first several minutes after the cosmic creation event. How much fusion of the universe's primordial hydrogen actually occurred at this time depended, in turn, on the universe's mass or mass density.
If the universe's mass (or cosmic mass density) had been even the slightest bit less than a hundred times the fifty billion trillion stars occupying the observable universe, nuclear fusion during the first several minutes of its existence would have proceeded less efficiently. Thus, the cosmos would have been forever incapable of generating elements heavier than helium—elements such as carbon, nitrogen, oxygen, phosphorus, sodium, and potassium—all of which are essential for any conceivable kind of physical life.
On the other hand, if the universe's mass had been even the slightest bit greater, nuclear fusion during the first several minutes after its beginning would have been too productive, and all the hydrogen in the universe eventually would have been fused (after just two generations of stars) into elements as heavy as iron or heavier. Again, all the most life-essential elements, including hydrogen itself, would have ceased to exist.
Given the laws of physics by which the universe operates, the cosmic mass must have been no different from exactly what astronomers observe, or we wouldn't be here to observe and discuss it. A universe any more massive or less massive would not have permitted the existence of physical life. To put it another way, for even one planet like Earth to exist, the observable universe must contain no more and no less than about fifty billion trillion stars and about a hundred times more mass in other forms.
If Wrong Mass, Wrong Expansion Rate
The second reason the universe must be as enormously massive as it is comes from the effect of the cosmic expansion rate on star formation. As noted above, the rate of cosmic expansion depends on the universe's mass. This dependence follows from the law of gravity.
The more mass the universe contains, the closer together will be its bits and pieces of mass. The law of gravity says that the closer two massive bodies are to one another, the more powerfully those bodies are attracted to each other. Therefore, the closer the bits and pieces of mass were to one another in the early universe, the more powerfully gravity would have acted as a "brake" to slow down cosmic expansion. Conversely, the farther apart those bits and pieces were, the faster the universe would have expanded.
Let's ignore for a moment something called "dark energy," the mysterious self-stretching property of the cosmos. (As researchers learn more about it, they recognize that it demands even more remarkable fine-tuning, by far, than any other feature of the universe.) If the universe had contained a lesser mass density, its expansion would have been so rapid that gravity could not pull together enough gas and dust to form stars such as the Sun and planets such as Earth. On the other hand, if the cosmic mass density had been any greater, gravity would have caused gas and dust to condense too effectively. In such a universe, all the stars would be much larger than the Sun, and any planets orbiting such stars would be unsuitable for life. The temperature, radiation, and luminosity of such stars, and of neighboring supergiant stars, would be unstable, and that would rule out the possibility of life on their surrounding planets.
Even a very small amount of extra mass in the universe would cause such a slowing of its expansion that all its stars would quickly turn into black holes or neutron stars. Given that the surface density of black holes and neutron stars exceeds two billion tons per level teaspoon (a half billion tons per cubic centimeter), no molecules would be possible in their environs. Even atoms would be impossible. Thus, life would be impossible. In addition, the radiation and gravitational disturbances emanating from black holes and neutron stars would make physical life impossible virtually anywhere in the universe. The bottom line is that physical life cannot exist in a universe with either a lesser or greater mass density than the value we observe in the cosmos.
A Just-Right Universe
Some might argue that sheer coincidence explains the "just-right" mass density of the universe. And yet, scientists observe Goldilocks values on two counts or more. For one, the mass of the universe must be fine-tuned to produce the just-right abundance and diversity of elements essential for life. For another, the mass density must be precisely fixed to allow for the just-right rates of expansion throughout cosmic history so that the just-right kinds of stars and planets will form at the just-right times and in the just-right locations for life. The combination of these astronomical improbabilities clearly defies any explanation other than transcendent intentionality.
This degree of cosmic fine-tuning also declares the worth of human beings. It tells us that the Creator of the universe considered humans to be of such value that he willingly and meticulously crafted a universe of fifty billion trillion stars, and a hundred times more mass besides, just to produce an appropriate planet to be their home. Such benevolent preparation permits us to live and thrive on a pale blue dot where we can discover our eternal significance and destiny. •
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