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The Templeton Science and Religion Reader
By J. Wentzel van Huyssteen, Khalil Chamcham
Templeton PressCopyright © 2012 Templeton Press
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Case for the Big Bang Joseph Silk
The idea of an expanding universe was a shock to early astronomers, but now the jury is in: the universe is indeed expanding. This is the inevitable consequence of what the America astronomer Edwin Hubble observed (in 1929) as the "redshift" phenomenon. He saw that the light from distant objects in the universe shifted to the red side of the spectrum, which, according to the laws of light waves, means that objects are moving away from the observer.
Curiously, Hubble himself never accepted the radically new idea of an expanding universe, even though it stemmed directly from his work. He rather chose to accept galaxy redshifts as an observable phenomenon without any commitment as to their origin in terms of the properties of space. Perhaps he was confused by the models of other leading cosmologists, who were proposing a static universe. Here, it was suggested that a hypothetical field produced the observed redshift, and indeed in these static models, the universe was seen as devoid of matter, let alone expanding.
The systematic recession of the galaxies is now explained as being due to the expansion of space. Albert Einstein's theory of gravitation, which in 1915 spoke of a curved time-space that could either collapse or expand, certainly predicts this phenomenon. But rather than collapsing, why is space expanding?
This question takes us back to the initial conditions of an infinitesimal patch of matter from which the universe began. That matter must have been in a volatile state, that is, out of equilibrium. This could have been a state of contraction or of expansion. Either way, the density of this primordial patch must have been 1090 grams per cubic centimeter. This is known as the Planck density, after German physicist Max Planck. This density is so high that it takes place only at the interface of quantum theory (in tiny atoms) and general relativity (large-scale gravity). In other words, at the initial conditions, the smallest and largest forces in the universe known today were squeezed together, united and indistinguishable.
The quantum processes were operating in the patch. By quantum jumps, macroscopic clumps of matter could disappear or reappear like the Cheshire Cat in Alice in Wonderland. Black holes, which are so dense with gravity that they attract all the matter around them, could have formed and decayed spontaneously. In this early state, the universe must have been at the most extreme density that can be conceived under known physics. It represents our best guess at the conditions that prevailed near the beginning of time.
After that, the direction of the universe has been quite predictable. It has expanded according to our basic measuring tool, the Hubble diagram, which plots distance compared to the velocity of galaxies as they move away from the central starting point of the universe. We deduce that this expansion began 13.7 billion years ago. The latest data, using supernovae to chart the expansion, have added something surprisingly new to the traditional Hubble diagram: the remotest galaxies are accelerating in recession, speeding up the expansion of the universe, a topic we discuss later.
The ancient age of the universe has also been a surprise to modern science, at least for a century or so. Today, scientists subscribe to the view of a very old universe of about 14 billion years. It is a difficult idea for a substantial minority of the population, especially in North America. Many people prefer a traditional interpretation of the universe drawn from a literal reading of the Bible. In one famous calculation from the King James Bible by seventeenth-century Anglican bishop James Ussher, the universe was created in 4004 BC on Sunday, October 23, at about 7:30 a.m. Today, decades of Gallup polls show that up to 50 percent of Americans think that human life arose fairly recently, according to a literal reading of Genesis, and for many, this would also include the belief in a very young universe.
Fortunately, from the time of Pope Pius XII in the 1940s, guided by the advice of astronomers such as Abbé Lemaître, the Catholic Church and other religious circles have taken a more enlightened approach to modern cosmology, which tries to find a proper balance between theology and science. This view holds that while science is paramount, it presents no challenge to a creed that rests on beliefs that arise from faith. Indeed the converse also applies: the beauty of science and the revelations produced by scientific discovery constitute part of the modern theologian's perspective and toolbox.
Today, for example, the discoveries of modern physics, astronomy, and cosmology reveal intricate details in the physical structure of the universe that seem highly improbable. The proton mass is remarkably close to the neutron mass. Were it very different, stars would not have formed. Further, the force that is accelerating the universe is far weaker than physics leads us to expect. Were this force much stronger, galaxies would never have formed. And in a universe devoid of stars and galaxies, there would not be any observers to marvel at the mysteries of the cosmos. It is not hard to see how theologians might find such discoveries fascinating.
These apparent coincidences in the universe have prompted some to argue that the arrival of human beings on Earth is perhaps not a cosmic accident after all. Indeed, those who employ this reasoning have elevated this human-centered argument into a fundamental principle that governs the universe, which has now been called the anthropic principle, for anthropos, or man. This principle has long held sway in traditional religion. But sadly, in the view of some, the wheel has turned full circle and now physicists too are appealing to the anthropic principle to account for the initial conditions of the big bang. Obviously, the anthropic approach is an unabashedly self-based egocentric worldview.
Following the Evidence
Our concern now is the evidence for the big bang theory of the universe, for we do not want to take it just on hearsay. Four major predictions of the big bang theory have been verified by modern scientific experiments: the recession of galaxies, the abundance of light elements in the universe, the existence of a cosmic background radiation (blackbody) that is uniform, and finally, predicted rates of fluctuations in that same radiation. These four lines of evidence ought to be enough to quench even the most biased critics of what at first sight is a highly implausible theory.
Once the expanding universe had been predicted based on Einstein's theory of gravity, Hubble in 1929 measured this celestial movement. Less well known is Lemaitre's intervention in 1927 when he predicted and derived the very same law that Hubble, unaware of Lemaitre's work, had published two years later. Hubble went on to pioneer and greatly refine the correlation between recession velocities and the distances to remote galaxies. We judge the velocities by the spectra of light in galaxies. The redshift of spectral lines shows the recession velocity. Distances are measured by using so-called standard candles, objects (typically a type of star) that give off the same brightness and whose distances can be judged first in nearby cases, and then can be traced to the same kinds of stars at great distances. Hubble's successor at Mount Wilson, Alan Sandage, delved deeper into the universe with the aid of the two-hundred-inch telescope on Mount Palomar in southern California. By applying Hubble's law farther and farther out, Sandage realized that distant galaxies had recession velocities of 10 percent or more of the speed of light.
The second proof of the big bang comes from the prediction that the early explosion of the universe would produce light elements with the simplest atomic structure. That would mean mostly hydrogen, but also helium and traces of deuterium and lithium. In fact, the universe indeed is abundant with these light elements. This prediction came largely from the insights of George Gamow, a Russian refugee to the United States in 1934. Gamow was a nuclear physicist with a remarkably broad perspective. He initiated our modern understanding of thermonuclear fusion. How could a pair of protons merge together, he asked, to eventually form helium? Resolving this paradox led to our understanding of how stars shine and to the development of the hydrogen bomb.
Eventually Gamow became interested in the big bang theory. Until then, the prevailing view was that the big bang was a cold event that, nevertheless, led to expansion. But the cold theory had a problem. At the cold state, which means a very high density, atoms merge into the most tightly bound nucleus, which is iron. Hence, iron should be the most plentiful atom in the universe, which is certainly not the case.
Gamow realized that a moment of extreme heat could circumvent this problem. The first nuclear reactions, which produce new elements, could not begin until the nuclei of atoms had overcome the heat and then begun to merge with others. At the start of the universe, he reasoned, there was only a small space of time, perhaps only a few minutes, for the light elements so abundant in the universe to form before the cooling down produced the heavy elements. At some early instant, the universe had produced hydrogen, which today remains the predominant element. It must have been a hot beginning.
Following this logic, Gamow was the first to see that cosmology presented the ideal conditions to understand the origin of light elements. Of course, for the light elements to have seeded the many other nuclear reactions that followed, the universe must have been exceedingly hot. But no one had detected any residual heat in the universe, as predicted by a hot big bang, so the prevailing wisdom favored a cold origin. Decades later, the cold theory was still being advanced by the great Russian cosmologist Yaakov Berisovich Zel'dovich, and Gamow's contribution was mostly forgotten.
However, lack of evidence for a hot universe did not deter Gamow's genius for advocating a new way of doing cosmology. He now turned to stars. Gamow believed, erroneously as it turned out, that stars did not have the thermonuclear power necessary to synthesize the chemical elements seen in the universe. He was partly right. Indeed, stars cannot make a significant quantity of light elements, although they can make some. With stars eliminated, Gamow argued, the universe itself was the ideal place for synthesizing the second most abundant element, helium. He proved his prediction by describing how the universe expanded in phases, briefly achieving temperatures above those in the Sun. A phase needed to last only a few minutes, he argued, to produce light elements.
This takes us back to the start of the universe. The only massive particles that could have lived on from the beginning were protons, neutrons, and electrons. Protons and electrons make up hydrogen, which is why that is the most abundant element today. Initially it was too hot for atoms to exist. The dominant constituent of the universe was ionized hydrogen, which meant it now had an electrical charge and was the only chemical element in the early universe. A few neutrons, about one for every proton, were present. For the universe to move toward formation of other chemical elements, a great deal of heat was needed so that nuclear reactions could combine protons and neutrons. With the heat, protons could overcome the force of Coulomb repulsion (that keeps particles apart) and form elements heavier than hydrogen. Gamow had discovered this natural barrier. With his insights, we find the beginning of nuclear physics as a new branch of science. His brilliant idea was that if the universe were, by fiat, initially hot, the required nuclear reactions would have taken place in the first minutes.
He enlisted his student Ralph Alpher and his colleague Robert Herman into the research project, which culminated in predictions of the exact abundance of light elements in the universe. Helium, amounting to some 30 percent of the mass in the universe, was synthesized in the first minutes of the universe. Previously a mystery, the origin of helium—the second most abundant element—was now resolved.
Gamow's dream of the origin of all of the chemical elements had one problem, however. Only 2 percent of the elements produced in his hot big bang were heavier elements, such as traces of lithium and beryllium. Where did all of the heavy elements come from? As we now know, the heavier elements are made in exploding stars called supernovae, which scatter their ashes around the galaxy. Nevertheless, Gamow was fond of joking that his theory should be considered a success, and rightly so. It explained the nature of 98 percent of the matter in the universe: hydrogen and helium. However, the most important proposal of his theory, the expectation of a hot universe, was to remain forgotten for nearly two decades.
That changed in 1964, when the background radiation of a hot big bang, once predicted, was now discovered quite by accident, resulting in our third piece of evidence for the big bang. In New Jersey, the radio astronomers Arno Penzias and Robert Wilson had gained access to a microwave radio telescope. It was originally designed for the first satellite communications system, but was subsequently overtaken by better technology. Using this old equipment, Penzias and Wilson wanted to survey only the Milky Way galaxy. But they found beyond the Milky Way a pervasive glow that is apparently isotropic, that is, has the same structure in all directions. (Being isotropic is not necessarily the same as being homogeneous, however.) Furthermore, the glow seemed to have no relation to our galaxy. They at first refused to believe their measurements. They tried to explain it away as an experimental artifact but they did not succeed.
Then a bit of news put them into action. When they heard that a rival group at Princeton was searching for the fossil glow of the big bang, Penzias and Wilson realized what they had discovered. They promptly published their measurement of excess radiation—the beginning of a long process of proving Gamow's hot big bang theory. Indeed, Penzias and Wilson were initially unaware of his arguments. Nevertheless, they had found the elusive background from the beginning of the universe.
At last, Gamow and his collaborators were vindicated. However, they never received full recognition for their prediction of an initially hot universe that produced relic radiation. They did not really appreciate the need to connect their theory with microwave astronomy. In their publications as well, they did not use terminology that would have caught the attention of microwave astronomers, such as Penzias and Wilson. I recall once encountering George Gamow surrounded by a small crowd of astronomers, as he declaimed in his high-pitched voice that he "had lost a penny, Penzias and Wilson had found a penny, and was it his penny?"
After the serendipitous discovery by Penzias and Wilson, much of the early debate about the hot big bang came to a climax in early 1967. The chief forum turned out to be a cosmology conference at the Goddard Institute for Space Studies in New York, where the topic was intensely debated. For historical reasons, this meeting was called the Third Texas Symposium on Relativistic Astrophysics, following earlier meetings in a series at Dallas and Austin. These were heady days in astronomy and cosmology. At the first Texas meeting in 1963, the superstars were quasars, just discovered (although their true nature and distance still are debated). The newly named idea of a black hole, a singularity in space of nearly absolute density, much like the start of the universe, was also announced at one of the Texas symposia.
The 1967 New York meeting marked a turning point for acceptance of the big bang theory. Before then, the very name was a kind of slur. It was coined pejoratively by British cosmologist Fred Hoyle, who favored the rival steady state model of the universe. As Hoyle famously told a popular BBC radio broadcast in 1950, the idea of "big bang" was "an irrational process that cannot be described in scientific terms ... [or] challenged by an appeal to observation."
Even after the discovery made by Penzias and Wilson, however, it took another fifteen years to verify the exact nature of this cosmic background radiation. According to predictions, it had to be what we call blackbody radiation. A corollary of the light element interpretation was the prediction that the cosmic microwave background would show a blackbody spectrum, which has so completely mixed the different wavelengths of heat that it approximates the evenness of a perfect furnace. The first prediction of this perfect blackbody temperature was made by Alpher and Herman. But applying such calculations to microwave astronomy did not come for another two decades, when Robert Dicke at Princeton (the rival whom Penzias and Wilson had heard about) was arriving at the best estimates of the background radiation temperature.
Excerpted from The Templeton Science and Religion Reader by J. Wentzel van Huyssteen, Khalil Chamcham. Copyright © 2012 Templeton Press. Excerpted by permission of Templeton Press.
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Table of ContentsIntroduction / 3 J. Wentzel van Huyssteen and Khalil Chamcham Chapter 1: Case for the Big Bang / 13
Joseph Silk Chapter 2: Rocks, Time, Fossils, and Life Itself / 37
Ian Tatt ersall Chapter 3: From Deluge to Biogeography / 59
R. J. Berry Chapter 4: The Human Primate: A Quantum Leap? / 91
Malcolm Jeeves and Warren S. Brown Chapter 5: How Genetics Rescued Darwinian Evolution / 117
Denis R. Alexander Chapter 6: How We Conceive of the Divine / 139
Justin L. Barrett Chapter 7: On Math and Metaphysical Language / 161
Javier Leach Chapter 8: Between Cyberspace and the New Alchemy / 183
Noreen Herzfeld Chapter 9: Medicine Meets Modern Spirituality / 213
Harold G. Koenig Acknowledgments / 237 Contributors / 239 Index / 243