ESSAY IV: BIG BANG AND THE UNIVERSE STORY
Robert J. Schneider
Introduction: Nature's History
I turn now to the Book of Nature, that is, the universe Christians call a creation, to see what scientists are finding in it and how they interpret what they find. The "book" metaphor remains a useful one, for, as German physicist Carl Friedrich von Weizsaker asserted in The History of Nature,
the most important scientific discovery of the twentieth century is that the universe is historical (cited in Haught 180).
And because it has a history, nature exhibits a narrative quality. That is, when scientists describe the universe today, sooner or later they will tell a story. This is the case because they, and most of us, understand the universe far differently from Sir Isaac Newton and his eighteenth-century successors. Newton understood the universe to be static. Space is infinite, time marches on in discrete and unchanging units, and in the three dimensions of space, the solid matter that make up the stars and planets of our galaxy ceaselessly moves according to the Law of Universal Gravitation. Newton and his contemporaries believed that their universe was a created one, and that God was responsible for its making and setting in motion; but the only new thing happening was the motion of matter through space itself. Theirs was a finished universe.
How different from the way scientists understand the universe today! Within the past eighty years scientists discovered that we live in an unfinished universe. It has had a beginning, and if it will have an end, that end is not yet in sight. Far from static, our universe is characterized on the cosmic level by the emergence of new stars and galaxies that have their own life cycles. And on our planet, over its immense age, new forms of living things have continually emerged into existence and lived out their own cycles of life. There is no sign that these evolutionary processes are reaching a conclusion. Hence, paleontologist Pierre Teilhard de Chardin (1881-1955) could often say (as theologian John Haught put it) that the "cosmos is not a fixed body of things, but a genesis—a still unfolding drama rather than merely a frozen agglomeration of spatially related objects. The world is still coming into being" (Haught 180).
|Cartwheel Galaxy A collision between two galaxies (500 million light years from earth). The outer blue ring consists of clouds of dust and newly forming stars. Credits: Kirk Borne (STSc1) and NASA.
Because the universe has a history, the metaphor of the Book of Nature still has its power. But it must be said that nature's book and the story of nature it tells is only as complete as its latest chapter, because the book, like nature, is unfinished: its story is still being written. When they tell the story, scientists can only take it to the present moment. People might speculate about its future on the basis of what science has learned about its past, and have some confidence that the processes by which nature has unfolded over time are likely to continue. Nevertheless, the future remains open, whatever one might venture to speculate about it.
Another quality of nature, as Haught has pointed out, is that its past lives on in the present. Both scientists and historians operate under the valid assumption that "whenever they delve into the past, there is something about reality that fixes forever the facticity of things." For example, while, historically speaking, the dinosaurs are no longer alive, their facticity has not been erased; they remain an essential part of the universe story. Their remains make it possible for scientists not only to know of their existence but also to speculate on their place in the larger history of life. In a sense, then, dinosaurs still live: they live on in the actual existence of their remains, and they live on in the universe's story (Haught 168-169).
What is true of dinosaurs is also true of the cosmos as a whole--and that is why it is correct to describe cosmology as partly a historical science.
Its facticity remains in reality because of another astonishing discovery of the twentieth century, that when we look out into space, we look back in time.
Albert Einstein's insight that space and time are interconnected, confirmed by Edwin Hubble's discoveries about the movement of galaxies, spurred an astonishing revolution in our understanding of the universe—its age, its size, its composition, its history, of the fact that it has a beginning and an as yet uncharted future. Scientists began a series of remarkable discoveries that have led to new speculative hypotheses and solidly grounded theories about the history of the universe. The theories and historical reconstructions continue to be tested, refined, and modified as new facts about the universe and all of its parts continue to be discovered. Some very important things now known about the age and composition of the universe were unknown as recently as the late 1990s. And if the newest finds are any indication, there is more to be discovered.
In this essay, I shall summarize as best I can what is called "the standard Big Bang model" of the origin and development of our present universe and why the great majority of cosmologists and astrophysicists have so much confidence in it. The whole story of both discovery and historical reconstruction is far too complex and detailed to place into a few pages of text, but I intend for the narrative to include enough to help the reader understand that this universe has emerged over an enormous span of time, and why Big Bang is such a well-established and compelling explanation for its beginning and development. Therefore, this exposition will tell two stories. First I shall highlight some of the most important empirical discoveries and theoretical developments that have led to the present standard Big Bang model. In other words, I shall tell a version of the story of how scientists have woven together theory and discovery to read and interpret nature's "text." Second, I shall briefly present what might be called "the revised standard version" of the new universe story, that is, a history of the universe from the Big Bang to the present.
First, however, I need to say something generally about the way scientists read and interpret the "Book of Nature," i.e., the universe and its various parts, and challenge a false notion. A student enrolled in my "Science and Faith" class once said to me that science cannot prove there was a Big Bang, because no one was around to see it. He had been instructed in young earth creationism (YEC) by the folks at Answers in Genesis, and had been taught that someone has to be able to observe something in nature for knowledge of it to count as scientific, for there to be any factual basis for theories of origins, including the origin and development of the universe. It is an argument set forth in YEC literature (Ham, cited in Ross, 99-100; Gish 40, cited in Miller 122) and public lectures: "Did you see it?" or "Were you there?" are common refrains in their presentations. I told the student, "That is a very limited and inadequate concept of scientific method," and went on explain that there are many things we cannot see in nature (e.g., elementary particles or molecular bonds), but scientists have good reason to conclude that they exist because they are able to observe their effects, and the theories about them are testable.
It is an old notion perpetuated (though not practiced) by YEC that science operates by gathering facts and then constructing a theory to account for them. This is the inductive or Baconian method, which still has its usefulness. But in fact, the scientific enterprise is far more sophisticated than that. Scientific advances sometimes result from a brilliant act of intuition or imagination that leads to a hypothesis or model that explains the way nature works. For example, Albert Einstein (1879-1955), taking the fact that the speed of light is constant, asked himself what the world would look like to someone riding on a beam of light (Bronowski 247). His answer was formulated as Special Relativity. Certain consequences were suggested by the formula, which, when confirmed, established it as a theory.
This method is sometimes called hypothetical-deductive: from a hypothesis a set of observations are deduced or predicted. When these observations are made, they test the hypothesis and either confirm or modify it (Miller 119).
A well-tested hypothesis becomes a theory: not a "guess" but rather a formulation about nature that explains it better than competing hypotheses. A theory is not a final answer, for it may be falsified by further observations-in that respect science does not "prove" a theory, contrary to the popular notion expressed by my student. But if the theory shares the qualities of (1) agreement with data, (2) coherency, both internally and in agreement with other theories, (3) comprehensiveness, in that it ties together what had been previously disparate data, and (4) fertility, "in providing the framework for an ongoing research program," then scientists have very good reasons to stick with it (Barbour 34).
Some claim that there is a distinction between the so-called "hard" sciences (e.g., chemistry and physics) and the historical sciences (e.g., evolutionary biology, cosmology or paleontology). In the former, scientists observe or make repeatable experiments about natural events going on in the present. Those who make this distinction assert that the historical sciences produce less reliable data and are less subject to the processes of theory and hypothesis testing and confirmation. "Did you see it?" is one of the cruder arguments put forth by advocates for this position. But the distinction is groundless. After all, the chemist does not see chemical bonds nor does the physicist see quarks; they also are observing the effects of past events, however immediate, and inferring causes and theories to explain them. Furthermore, like the hard sciences the historical sciences use the hypothetical-deductive method; the difference is that the subjects of observation and testing are not controlled by the experimenter but by nature. It is the facticity of the past mentioned above that enables the scientific investigator to test new observations in nature against expectations based on previous explanations. Creationists sometimes argue that evolution is not science because it cannot be subjected to repeatable experiments. It is true that scientists cannot repeat the cosmological and evolutionary experiment that nature has undertaken. They are once and for all events. Yet hypotheses and theories about nature's history can still be tested and confirmed from new discoveries (e.g., of a new class of stars or a new species), and useful predictions can be made and tested. "Strict repeatability is thus not a criterion for the testing and revision of hypotheses." "Historical sciences are just as predictive and testable as the 'hard' sciences" (Miller 120-121).
The historical sciences are also forensic sciences, not only in that they reconstruct a past event but also in that they resemble detective work. If someone had to be present and watch a murder take place in order for the killer to be convicted in court, only a few defendants would ever be found guilty. But those of you who watch the popular "CSI" series or "Cold Case Files" know that by using a variety of scientific instruments and tests forensic scientists can interpret the data from a crime scene accurately enough, even many years later, to build a convincing case against the perpetrator. The use of DNA testing to establish the guilt or innocence of a suspect or convict is a prime example of good forensic science. In much the same way cosmologists, evolutionary biologists and historical geologists patiently gather the facts nature offers and carefully examine and interpret them using methodologies relevant to their particular sciences. The historical sciences, like the forensic, seek to establish a case that is "beyond a reasonable doubt" (Powell), but at the same time these scientists expect to continue to deal with "unresolved problems, inconsistent evidence, or unexplained phenomena" (Miller 121), for that is the way of any science, whether hard or historical. The problems do not lead scientists to abandon a theory; rather, they map out directions for further research. A core of well-established scientific certainties provides a solid base for theories and hypotheses that address the frontiers of scientific discovery. This has been very much the case with the science of cosmology, as I hope to demonstrate below.
Ironically, the claim that a human observer is necessary is an awfully weak reed upon which to build a case against Big Bang theory and the ancient age of our universe. This is because of that other great discovery of the twentieth century: that when we look out into space we look back in time. As astrophysicist Hugh Ross, himself not an evolutionist but an old earth (i.e., old universe) creationist, points out, "Astronomers have only the past—they do not have the present" (Ross 100). It takes time for light to travel from stars to our planet—eight minutes from our sun, 4000 years from the Crab Nebula, 2.9 million years from the Andromeda Galaxy. Thus, any event scientists observe when they look out into space has already happened. In observing and interpreting it, they are telling the story of our universe's past. And thanks to light, that is, to the entire electromagnetic spectrum of both visible and invisible light, they are able to look out using their instruments and see back billions and billions of years in time, close enough to the Big Bang itself to construct a convincing theory about it.
|Tarantula Nebula (Hodge 301) An active starburst region; many old stars have exploded as supernova Credits: Hubble Heritage Team (AURA/STScl/NASA).
A story of discovery
Now, I go on to my first tale, the story of discovery. How did we learn that when we look out into space we look back into time? This discovery was primarily the work of American astronomer Edwin Hubble (1889-1953). When he trained the new 100-inch telescope at the Mt. Wilson Observatory on the heavens in the mid-l920s, it was commonly assumed that our Milky Way Galaxy was pretty much all that existed in the universe. Then, he and other astronomers produced the astonishing evidence that ours is but one of countless galaxies, "islands" widely separated by immense stretches of space in a universe enormously larger than they had assumed. Furthermore, in whatever direction in space Hubble looked, he discovered that aside from our nearest neighbor Andromeda, all of the other galaxies were moving away from ours. He was able to determine this fact by measuring the shift in the signature spectra of certain ionized atoms in the stars of distant galaxies as they receded from our own galaxy: the more proportionately broad the shift, the further the distance. Hubble's law, as it came to be called, expresses a direct and proportionate relationship between the distance and the velocity of another galaxy relative to our own: the further away the galaxy, the faster it appears to be moving (Silk, 1994, 32-35; Morris 13-19).
Hubble made another fundamental discovery about the universe: as he counted galaxies, he realized that the number of galaxies increased proportionately as the volume of space increases. This uniform distribution demonstrated that the "stuff" of the universe is fairly homogeneous on a large scale. Moreover, the evidence was clear that all galaxies are moving away from all other galaxies.
The conclusion was inescapable: we are living in an expanding universe with no discernable center.
This "cosmological principle" has become one of the fundamental assumptions about the universe. Also, since we are looking back in time, there must have been a time when galaxies were much closer together, with less space between them, and even at some point, with no space (Silk, 2001, 22-28, Gribbin 4-9).
If Hubble needed a theory to account for his discoveries, one was already at hand: the General Theory of Relativity formulated by Albert Einstein in 1915. In 1905, Einstein had published his paper on Special Relativity, in which he theorized that the universe is characterized not by three dimensions but four: space and time are bound together not only in his equation but also in reality. In General Relativity Einstein added gravity and its effects: he theorized that heavy objects of matter like the Sun bend and distort spacetime, and photons of light passing near the heavy object will follow a curved trajectory though this region of spacetime (Gribbin 8-9). Physicist John Wheeler put it this way: "Matter tells space how to curve, and space tells matter how to move." Hubble's discoveries and Einstein's theory together offer an excellent example of how theory and data fit together in science.
However, one thing troubled Einstein about General Relativity: the theory led to the conclusion that spacetime not only bends, it also stretches. Holding on to the common notion that the universe is static, unchanging and eternal, Einstein introduced a cosmological constant into his equation to represent a repulsive force that would counteract the gravitational force of attraction over great distances. Hubble's discoveries would lead him later to regard this addition as one of his greatest blunders. However, two of Einstein's successors in the mathematical modeling business, Russian mathematician Alexander Friedmann (1888-1925), in 1922, and Belgian physicist Georges Lemaitre (1894-1966), in 1927, ignored Einstein's cosmological constant, and from his more simplified field equations each independently derived mathematical models for an expanding universe. Both deservedly can be said to have fathered Big Bang cosmology (Silk, 2001, 25-26). (Lemaitre, by the way, was also a Roman Catholic priest. Remember that the next time someone labels Big Bang theory as "atheistic.")
Hubble apparently was unaware of the Friedmann-Lemaitre model when he made his discoveries, but the relationship of theory, model and data became apparent soon enough.
Together they led to the conclusion that we live in a universe that consists not in an infinite space through which galaxies move, but in a stretching and expanding space in which galaxies are carried along in its matrix.
And now cosmologists had to come to terms with the implications of all this. Mainly, they had to confront the notion that our universe had come into existence at some moment in the past, and that everything in the universe—space, time, matter, and energy—"must have emerged from a single point of zero size and infinite density, a singularity" (Gribbin 11-12).
When did it emerge? Hubble began the dating process; later astronomers greatly improved his figures and refined their techniques. But calculations based on the redshifts of the most distant visible objects took scientists back only 10 billion years. If the universe is older than that, how are scientists able to detect it? They were helped by relying on that part of light that is not visible to the eye, namely, radiation in the form of x-rays and gamma rays on one end of the electromagnetic spectrum, and radio waves on the other. Studies of these forms of light using new instruments able to detect them added other important chapters to this story.
|Dancing Galaxies (NGC 2207, larger, and IC 2163) Billions of years from now the two will become one. Credits: NASA and Hubble Heritage Team (STScl).
Mathematical models of a universe that began with a singularity show that at some point the entire universe was condensed into a "hot fireball" filled with radiation (Gribbin 17). And, as space has expanded so has the radiation; it permeates all of space. As radiation expands, it cools, and if the theory were correct, today it would have a wavelength of light in the microwave band. The story of how this radiation was posited theoretically and eventually discovered is an interesting one, and many scientists were involved in the process, but in the interest of space (not desiring to stretch mine out), I shall move to its discovery by Arno Penzias and Robert Wilson in the 1960s. They had developed a radio telescope to detect signals from communication satellites. What it detected was a much stronger radio signal coming evenly from all over the sky (Silk, 1994, 53). They shared their discovery with Bernard Burke and James Peebles, who had predicted on the basis of the Big Bang theory that the universe should be filled with electromagnetic radiation (radio waves) with a temperature below 10 kelvins. Later the COBE Satellite (see below) refined the background microwave radiation temperature to 2.73 kelvins, barely above absolute zero. Here was the strongest empirical evidence yet for the Big Bang (Silk, 2001, 81, 403; Morris, 7-10).
With such a specific temperature reading, it is possible to work backwards to determine the temperature of the original cosmic fireball, the temperature of the Big Bang. Temperature is important, because certain elements of nature could only come into existence as the hot Big Bang cooled off. Telescopic research showed that the oldest stars shared the same proportion of the most common elements in the universe, hydrogen and helium. According to Big Bang theory, these same two elements arising as a consequence of the initial fireball would have had the same proportions. Once again, theory proved to be consonant with empirical data. But two problems appeared. First, from the cosmic background radiation data it appeared that radiation, hydrogen and helium were evenly and smoothly distributed. If that were the case, then how could gravity bring matter into the clumps that became stars and galaxies within the time frame theory and data suggested? Second, how explain the fact that while galaxies generally are moving away from one another as space expands, some galaxies throughout the universe's history have formed clusters moving around a gravitational center. Is there some unseen, not yet detected matter that provides enough gravitational warping and bending of space to keep these clusters together, scientists asked?
These problems were solved in the 1980s by the inflation theory, put forth by physicists Allan Guth, Andre Linde and others. In the words of John Gribbin,
"Inflation says that during the first split-second of the birth of the Universe, a tiny seed containing all the matter and energy in the observable Universe was blown up from a size smaller than that of an individual proton to about that of a basketball" (36).
Following this era (which lasted only about three-thousandth of a second), the expansion decelerated to a still rapid but slower pace. If inflation is correct, then the energy of the expansion, according to Einstein's famous equation E = mc2, would have to be transformed into matter, but this matter would not be the everyday matter that is visible in the form of stars and galaxies. It would be some theoretical dark matter. It would provide the primary contribution to the gravity that eventually pulled atoms of hydrogen and helium together to form stars. Indirect evidence for its existence was accepted.
Yet, something more was needed to account for the creation of galaxies. According to Big Bang theory, "there ought to be irregularities in the background radiation corresponding to the disturbances produced" by the initial abundant elements and the dark matter (Gribbin 39); they would show up as infinitesimal irregularities in the temperature of the background radiation. The Cosmic Background Explorer (COBE) Satellite, launched in 1989, besides providing a more accurate temperature of the background radiation, discovered everywhere throughout the heavens the very tiny wrinkles or ripples in the radiation that theory had predicted. Ripples in time, for COBE was looking back into time, and seeing the universe when it was about 300,000 years old. Scientists could also draw the conclusion that thanks to inflation, space expanded faster than the speed of light; the original fireball of mass and energy was able to expand "to more than 500 million light years across in just 300,000 years…" (Gribbin 41).
In the fourteen years since the launch of COBE, other instruments of discovery have greatly enhanced our knowledge of the universe. They include many powerful ground-based telescopes that capture visible or invisible light, and highly sophisticated cameras attached to them, designed to photograph specific objects in the universe; they also include various space satellites. Of the latter, two have been especially fruitful in expanding our vision and knowledge of the cosmos. The first is the Hubble Space Telescope, placed into an orbit 380 miles above the earth and its restrictive atmosphere in 1990. Thanks to Hubble's stunning photographs we are able to see so much more of this immense universe in so much greater detail. We now may see the huge clouds of matter that spawn galaxies, stars and planetary systems and view these offspring in their births and deaths; we see galaxies forming clusters, even colliding and merging with one another. As this essay was being written, NASA reported that Hubble had photographed the earliest known planet in the Milky Way Galaxy, estimated to be 13 billion years old. Hubble also has greatly enhanced our understanding of such unusual features as quasars, neutron stars, and the massive black holes that fascinate so many. Its "Deep Field" photographs offer a stunning view of a tiny slice of space dotted with a huge array of galaxies. Hubble has enabled astronomers to look even more clearly and deeply into space and back into time (hubblesite.org).
|The Hubble Telescope above Earth The Hubble Telescope above Earth. Credit: NASA.
The knowledge that the Hubble Space Telescope has added to our understanding of the universe and its history has been complemented by another instrument, the Wilkinson Microwave Anisotropy Probe (WMAP). This satellite was placed into an orbit 1.5 million miles from the earth in 2001, and the conclusions drawn from its data reported in the spring of 2003. WMAP has provided invaluable data about the cosmos that has enabled scientists to refine and confirm earlier conclusions about the early universe and its consequent structure and history. It has provided a much sharper image of the microwave background radiation going back to 379,000 years after the Big Bang. It has also detected evidence indicating that the first stars ignited about 200 million years after the initial fireball, earlier than expected. And the team of scientists analyzing the data from WMAP was able to determine a more accurate age for the universe from the Big Bang to the present. The reader has likely encountered estimates stretching from 10 to 20 billion years, with 15 billion a common estimate, and other recent data suggests 13.6 +/- 1.5 billion years (Kirshner 1914). The WMAP data, claimed to be accurate within 1%, gives the age at 13.7 billion years old.
|WMAP Spacecraft after a deployment test.
Credit: NASA/WMAP Science Team
WMAP has also provided greater confirmation for the existence of dark matter, detected in earlier data gathering from ground-based telescopes (Morris 98ff). Astrophysicists are still trying to understand the nature of dark matter, which neither emits nor absorbs light but which is gravitationally self-attractive (Padmanabhan 110-115). It is now clear that, as theorized earlier, dark matter played a crucial role in the early universe in the formation of stars, galaxies, and thus in the present structure of the cosmos. It explains how the cosmic ripples detected first by COBE could grow until ordinary matter could be drawn to dark matter and together form the structures of the universe we can now look out and see (Ostriker and Steinhardt 1909-1910; Silk 183-185).
|The Microwave Sky. Credit: NASA/WMAP
WMAP also confirmed one of the more exciting finds of recent years, the existence of dark energy, first inferred from the study of class Ia supernovas located in the early universe. The light from these supernovas is fainter than expected, leading to the surprising conclusion that the universe must be expanding at a faster rate then previously assumed. Prior to the seven billion year mid-point in the history of the cosmos, the expansion (following the period of inflation during the first second) had been decelerating, and scientists had given the credit for this to dark matter combined with visible matter. But around seven billion years after the Big Bang, some negative, repulsive pressure began to counteract the positive, decelerating pressure of gravitation. Cosmologissts have attributed this phenomenon to dark energy; it adds an important feature to the hot Big Bang model. They are still seeking to understand the nature of dark energy—some have suggested that it is a form of energy represented mathematically by Einstein's cosmological constant, for it strengthens the implications of Einstein's theory that the universe consists not only of the matter we see, and an invisible cold dark matter, but also an invisible dark energy (cf. Krauss 31-39). The acceleration due to dark energy suggests that our universe will go on expanding indefinitely, will take galaxies farther and farther apart until their light is no longer visible to any hypothetical observer. From any point of view the universe will go dark (Kirshner 1914-1918; Hogan, Kirshner and Suntzeff 23-29).
The evidence confirming the existence of both dark matter and dark energy has led the WMAP team to conclude that the universe consists of only 4% of both luminous matter (e.g., stars, galaxies) and non-luminous matter (e.g., the matter sucked into black holes), 23% cold dark matter, and 73% dark energy.
All of the stupendous sights that the Hubble Space Telescope have made possible, all of the amazing images of stars, dust clouds, and galaxies that take our breath away, constitute only a tiny fraction of all the matter and energy that are carried through spacetime. (For details of WMAP, go to map.gsfc.nasa.gov/m_mm.html.)
In this story of discovery I have focused on the large, the expanding universe from the Big Bang. I hope I have demonstrated that Big Bang is not a guess or simply an imaginative hypothesis but a well-established theory that has been repeatedly confirmed by new facts. It is a fact that we live in an expanding universe some 13.7 billion years old, that space is filled with a background radiation left over from the Big Bang, and that galaxies and stars are still coming into existence and passing away. Big Bang theory offers the best explanation for these and other well-established facts that scientists have gathered from the leaves of nature's book. There is another story of discovery that my own constraints of time and space force me to leave off telling: the story of the formulation of quantum theory and the discovery that atoms are not indivisible but composed of many elementary particles. These discoveries also have provided solid evidence not only for understanding the composition of atoms, but also for reconstructing the history of much of the very early seconds of the Big Bang. But I must move on now to the second story in this essay, the history of our universe.
The revised standard version of our universe story (a very brief summary).
Some 13.7 billion years ago, all the matter and energy that we now are able to discern or confidently theorize was compressed into a singularity of zero size and infinite density, governed by laws of physics not yet understood. From this singularity space-time erupted into existence in a cosmic fireball. Within an infinitesimal fraction of a second of its existence, all of the incredible amount of matter and energy in the universe "was compressed within a sphere of radius equal to one-hundredth centimeter, the size of the point of a needle," of which that visible to any hypothetical observer was far smaller than the diameter of an atomic nucleus, and of which the entirety had a density of 1090 kilograms per cubic centimeter (1075 tons per cubic kilometer). Its temperature at this instant of creation was an incredible 1032 kelvins (Silk, 2001, 108, 110).
An infinitesimal moment latter, still very early within the first second of its existence, the universe underwent a period of inflation, which lasted for less time than one could blink one's eye. Inflation substantially affected the rate of expansion of the universe. Fluctuations in the density of matter and energy occurred; the temperature of the universe dropped considerably, and vast homogeneous bubbles of matter and energy were formed throughout. Any preexisting curvature of space was stretched out into a geometrically flat universe.
At 10-10 of its first second, the universe entered into a new phase. The universe was dominated by radiation, and certain elementary particles, including protons and neutrons, were formed. Shortly thereafter, the still tiny universe came to be dominated by photons and other elementary particles including electrons and neutrinos and their antiparticle versions—identical twins except that they carried opposite charges (e.g., the positively charged positrons were antiparticles to the negatively charged electrons). During this phase, an enormous, instantaneous annihilation of particles and their antiparticles released massive amounts of energy in the form of gamma rays. The temperature of the universe dropped from 1012 kelvins to 1010 kelvins (1,000,000,000,000 to 10,000,000,000 kelvins), and while the massive annihilation of matter and antimatter produced a universe full of photons, there were some particles left over that eventually were formed into atoms—lucky for us. So went the first second of our present universe's existence.
Next, during a period from one second to 1000 seconds after the Big Bang, when the temperature of the universe had fallen to 1,000,000,000 kelvins, the process of nucleosynthesis began. Protons, the nuclei of ordinary or "light" hydrogen, and neutrons combined in a process called fusion to form heavy hydrogen nuclei—called deuterium. Nuclei of deuterium from proton-neutron fusion attracted another neutron to make tritium (an even heavier hydrogen); tritium in turn captured another proton, and made helium (Powell; Silk, 2001, 141). The resulting ratio of hydrogen to helium nuclei has been shown to be constant throughout the universe. The nuclei (not yet atoms) of the two most abundant elements in the universe throughout its history were formed in the very first minutes of its existence.
Just a few minutes after the Big Bang, the fiery era of nucleosynthesis ended and the universe embarked on a new and much longer period that scientists call the radiation era or "the Dark Ages." Expansion continued uneventfully for the next 300,000 years; "a dense, hot soup" of primordial matter and radiation evolved without any spectacular fireworks for a hypothetical observer to witness. In fact, a hypothetical observer could not have observed anything, for the universe did not become transparent until after this 300,000-year period (Silk, 2001, 149-150). At the early phase of this period, nuclei and other forms of matter and radiation were in intimate contact; by the end they underwent a decoupling. The temperature dropped to about 4000 kelvins. Radiation now moved independently of matter. And matter, no longer affected as it had been by radiation, undertook another critical and sudden step in the formation of the cosmos. Electrons and protons combined to form hydrogen atoms in a process so efficient that it was completed by the end of the first million years, and during that time, as more and more hydrogen atoms were formed, the universe, which for 300,000 years had been a fog of blackbody radiation coupled with elementary particles, became transparent.
Something else not transparent, cold dark matter, began to add its gravitational force to visible matter. Smaller clouds of hydrogen and helium gas coalesced into larger clouds, and around 200 million years after the Big Bang, the first stars ignited, and galaxies of 100 billion stars or more began to form. The earliest of the estimated 200 billion galaxies were primarily the fairly round elliptical type, which became concentrated in rich clusters. But others, the fairly flat spiral galaxies, like our own, began to appear and, growing in number, were more uniformly distributed throughout space (Silk, 2001, 194-195, 200, 205). Most of the stars in the galaxies were formed during the first 5 billion years of the universe's history; since then star formation has been declining (Silk, 2001, 216). Thanks to the combination of the effects of mass and gravity, some galaxies attracted to one another collided and merged. In many galaxies massive collapsed stars formed black holes, whose gravity is so powerful that light cannot escape them; we see them thanks to the matter that they suck away from nearby visible stars.
|Spiral Galaxy (NGC 4414) Credit: Hubble Heritage Team (AURA/STScl/NASA)
These stellar and galactic processes continue today, some 13.5 billion years later. Many of the first stars were massive; they consumed their fuel rapidly and within a few million years exploded as giant supernovae. These explosions created the heavier elements, from carbon on up, and from the enormous dust clouds created by these explosions, aided by gravity, successive generations of stars appeared. Eventually, thanks to these stellar explosions all of the elements in our universe were created. Planetary systems began to form around some stars even in the earliest years of the universe. Our own Sun, a third-generation star, formed about 5 billion years ago, and our Earth became a planet by about 4.6 billion years ago. Upon it another universe story began, the story of life (see essay V).
|Deep Field Photo 1,500 galaxies at various stages of evolution appear in this very narrow slice of space. Credits: R. Williams (STScl), the Hubble Deep Field Team, and NASA.
All during the billions of years of our universe's existence the galaxies and their clusters continued to be carried by the expanding space, and at this point, no end of the process is in sight. Looking out into space we see a visible universe that presently is about 28 billion light-years across, and which contains an estimated 70,000,000,000,000,000,000,000,000 stars; looking back in time we see the remnants of its earliest moments 13.7 billion years ago. At this point, the evidence suggests that the expansive power of the mysterious dark energy will overcome the gravitational power of matter, and that the universe will go on expanding forever.
While writing this essay, I attended the 2003 meeting of the American Scientific Affiliation. Its theme was "Cosmology and Astronomy," and I saw and heard presentations on many of the features of the universe's history that are laid out in this essay. Cosmologists, astronomers, and astrophysicists presented some of their own recent research on such topics as the evolution of stars and galactic formation in the early universe, dark matter, elliptical galaxies, and superstring cosmology. These scientists, all of whom openly profess their Christian faith, brought their audiences up to date on the most recent developments in this story of an evolving and unfinished universe (for the program, go the ASA Home Page at www.asa3.org). This latest version is by no means the final one. New facts will be brought to light, old hypotheses modified or abandoned and new hypotheses formulated. A new revised standard version of hot Big Bang may not be far off. And there are other alternatives to this model, and other hypotheses regarding the earliest milliseconds of the universe's beginning. But scientists are convinced that in its general outlines and its most important details, the story given here is an accurate one.
In a later essay I shall show how Christian theologians are incorporating this universe story into new theologies of creation. Let me say for now, as the scientist-believers at the ASA meeting attested, that there is nothing in this newest "portrait" of creation that conflicts with biblical creation as the great majority of Bible scholars interpret it (see the first essay), or with the theology of creation the historic Church has developed over the centuries (see the second essay). There is nothing in this reading of the Book of Nature that cannot be reconciled with the Book of Scripture. Christians may look out at this new portrait of the universe in the stunning photographs of the Hubble Space Telescope, and proclaim, perhaps with even greater wonder than the Psalmist, "O Lord, how manifold are your works!" (Ps. 104:25).
|Carina Nebula (NGC 3372) Located about 8,000 light years from earth. Credits: NASA, the Hubble Heritage Team (AURA/STScl).
(In addition to the sources cited in this essay, "Resources" lists other Internet sources that provide much detailed and useful information about astronomy and Big Bang cosmology.)
58th Annual Meeting of the American Scientific Affiliation: "Cosmology and Astronomy." Colorado Christian University, Lakewood, Colorado, July 25-28, 2003 (www.asa3.org).
Barbour, Ian G., Religion and Science: Historical and Contemporary Issues. San Francisco: Harper, 1997.
Bronowski, Jacob, The Ascent of Man. Boston: Little, Brown, 1973.
Gribbin, John, In the Beginning: After COBE and Before the Big Bang. Boston: Little, Brown, 1993.
Haught, John F., Deeper Than Darwin: The Prospect for Religion in the Age of Evolution. Boulder, CO: Westview Press, 2003.
Hogan, C. J., R. Kirshner, and N. B. Suntzeff, "Surveying Spacetime with Supernovae," in The once and future cosmos. Scientific American Special Edition, 2002, 22-29.
Kirshner, Robert, "Throwing Light on Dark Energy," in Science 300 (2003) 1914-1918.
Krauss, Lawrence M., "Cosmological Antigravity," in The once and future cosmos, 30-39.
Miller, Keith B., "The Similarity of Theory Testing in the Historical and 'Hard' Sciences," Perspectives on Science and Christian Faith 54 (2002) 119-122.
Morris, Richard, Cosmic Questions. New York: Wiley, 1993.
National Aeronautics and Space Administration: Hubble Site (hubblesite.org).
National Aeronautics and Space Administration: Wilkinson Microwave Anisotropy Probe (map.gsfc.nasa.gov/index.html).
Ostriker, Jeremiah and Paul Steinhardt, "New Light on Dark Matter," in Science 300 (2003) 1909-1913.
Padmanabhan, T., After the First Three Minutes: The Story of Our Universe. Cambridge: University Press, 1998.
Ross, Hugh, Creation and Time. Colorado Springs: Navpress, 1994.
Silk, Joseph, The Big Bang. 3rd Edition. New York: W. H. Freeman, 2001.
Silk, Joseph, A Short History of the Universe. New York: W. H. Freeman, 1994.