Throughout the ages, most people believed that the cosmos had existed for all eternity in an unchanging or static condition, neither expanding nor contracting. One reason individuals held this belief was an absence of scientific data, coupled with the inability to answer questions about the universe through measurement and observation. Another reason was that most individuals’ beliefs tended toward parochialism and traditionalism. They preferred to believe in eternal, absolute truths, which supported their beliefs in an eternal, infinite cosmos created by God. With the arrival of the 20th century, both science and technology had developed to the point where scientists were able to formulate and then explore the empirical validity of what is called the “big bang theory.” According to this theory of the origin of the universe, at one time all space and time were packed into an incredibly small package or dimension. About 14 billion years ago, this package or dimension increased in size at an unimaginable speed, due to a massive explosion (called “singularity”). The primordial universe that was created consisted primarily of strong radiation, which led to the formation of matter and, eventually, to stars, galaxies, solar systems, planets, and moons. The evolution of the cosmos over billions and billions of years produced the right conditions for life to form on earth, leading to the development of thinking beings such as us. Although no one theory perfectly explains—or can explain—everything about the origin and structure of the universe, the big bang theory is convincing. No other theory comes as close in explaining what scientists think happened in the creation of the cosmos. The big bang theory fits both deductions from mathematical models and conclusions from observations of the cosmos.
The First Cosmologies
The Greek philosophers moved the study of the universe away from a strictly religious approach to a more naturalistic one. Aristotle’s ideas influenced philosophers and scientists in the West for centuries. His observations of celestial events convinced him that the earth was spherical rather than flat like a pancake. During lunar eclipses, Aristotle noted that the shadow of the earth on the moon was always round, an impossibility if the earth were flat. A flat planet would have cast an elongated shadow, not a round one (unless he always made his observations when the sun was directly under the earth, an unlikely event). Aristotle made another observation that convinced him of the roundness of earth. He saw the sails of ships coming over the horizon before the rest of the vessel. (On a perfectly flat earth, Aristotle’s first view would have been of the entire ship, not just its mast.) Although some of Aristotle’s conclusions about the universe were accurate, others were not. For example, he remained steadfast in his conviction that the earth was stationary and the moon, sun, other planets, and stars moved in perfectly circular orbits around the earth.
The impact of both religion and philosophy on cosmology diminished with the growth of the physical sciences. Nicholas Copernicus, a Catholic priest, suggested in 1514 that the sun was stationary and the earth and other planets moved in circular orbits around it. Copernicus’s heliocentric view was discounted for nearly a century until two astronomers, the Italian Galileo Galilei and the German Johannes Kepler, reaffirmed Copernicus’s deductions. The invention of the telescope (in Holland) in the early 1600s allowed Galileo to observe stars, planets and their movements, meteors, and comets. It was during his observation of the movement of Venus that he realized Copernicus was right to believe that the earth moved around the sun. Kepler, like Copernicus and Galileo, concluded correctly that planets rotated elliptically around the sun, although he erred by thinking it was magnetic forces that were responsible.
Issac Newton was the first individual to develop a coherent understanding of the physical forces that impact the cosmos. He figured out that the same force that pulled an apple to the ground also attracted humans, animals, other objects, and the planets and moons to one another. In other words, objects in the universe both attracted and were attracted by other objects. Ultimately, Newton developed an understanding of the laws of motion in space and time, as well as a theory of universal gravitation. The gravitational attraction between any two objects is directly proportional to the size of their masses and inversely proportional to the square of the distance between them. For example, if the distance between two objects were to double, the gravitational force between them would only be a fourth of what is was originally. Despite his brilliance, Newton did not understand the full implications of his work for cosmology. He believed the universe was, and always would be, unchanging or static, principally because he believed the universe was infinitely large, containing an infinite number of stars spread uniformly throughout it. Because the universe had no central point, Newton thought a perfect balance of gravitational forces would exist. He failed to realize that in a cosmos of different-sized planets, moons, and stars, these heavenly bodies would always be attracting one another, so that smaller objects would be pulled to larger ones like steel balls to a magnet. (Newton thought that in order to keep the universe perfectly tuned, it would require some tweaking by God, who might have to move a planet a little to the left or a star a little to the right.)
The Einsteinian Watershed
Modern cosmology really began in 1905 when a young man by the name of Albert Einstein, working alone in his spare time at his desk in a Swiss patent office, had an opportunity to work through some of his ideas about space, time, gravity, motion, distance, mass, and energy. He wrote four papers that year that were to transform physical science and our understandings of the universe in substantial ways. One of the papers, for which he won a Nobel Prize, showed that light could be understood both as a flow of particles and as a wave, a distinction that laid the basis for the development of quantum mechanics. A second paper showed that the collisions of atoms and molecules are responsible for Brownian motion, the jerky movement of pollen grains or other small particles that are suspended in a liquid. It was his third paper that shook the foundations of physics, altering the prevailing view of the universe. Newton’s system was based on absolutes: A second on earth is identical to a second everywhere else in the universe, and a mile in one place is the same as a mile in every other place. Einstein surmised that Newton’s system was wrong by using what Einstein called “thought experiments.” For example, he wondered how space and time would look to individuals traveling on a train that was going nearly the speed of light (the speed of light is 186,282 miles per second). From his thought experiments, Einstein developed what came to be known as the “special theory of relativity,” which impugned Newton’s absolutist view of space and time. Imagine that a train moving across a prairie at near the speed of light is being chased by a gang of thieves on horseback, who are going almost as fast as the train. The robbers would report later that no matter how fast they rode, the train was still racing ahead of them at an incredible speed. To a stationary observer, however, the robbers were almost keeping up with the train. How could the robbers have an experience so different from the observer’s? Einstein’s answer was that, for the robbers, time itself had actually slowed. The faster you go, the slower time passes relative to a stationary observer. Separate two identical twins, and put one of them on a spaceship that leaves earth at the speed of light. When the rocket returns to earth (also at the speed of light), the rocket twin will be younger than the twin who remained on earth. For the space twin, time slowed, and this individual aged less than the earth twin. Einstein’s fourth paper showed that energy and mass are not separate, but that mass is really compressed energy. Energy is equal to the mass of some object multiplied by the speed of light squared, an incredibly large number. An awesome amount of energy can come from a small amount of mass.
Einstein’s major accomplishment, in all likelihood, was his development of the general theory of relativity, which also modified and extended Newton’s theories. Newton believed that gravity was a force that traveled instantaneously throughout the universe and caused objects to be attracted to one another. Einstein reasoned that this is impossible, because nothing can travel faster than the speed of light. What is actually happening is that gravity is an effect of the curving, warping, or bending of time and space. If a heavy brick is placed on a mattress and a ball is rolled past it, the ball will not travel in a straight line. It is not the force of gravity, however, that accounts for the path of the ball (a ball and a brick have too small a mass to exert much gravitational force on one another). What really happens is that the brick warps or curves the mattress enough that the surface of the bed pushes the ball so that its path is changed. If we replace the brick with the sun and the ball with a planet, we get an understanding of how different general relativity is from Newtonian physics. It is not gravity from the sun that is principally responsible for the way planets rotate around it. What actually happens is that the sun’s mass warps the space around it, and the altered space pushes planets in such a way that they orbit around the sun. Objects in the universe (such as planets or stars) bend space in ways that are similar to the way a heavy object can bend the surface of a mattress. Einstein’s theoretical work paved the way for an understanding of the smallest subatomic forces, as well as for the largest, the big bang of the universe.
The Big Bang
For almost three centuries, views of the origin of the universe had placed the earth, our solar system, and our galaxy at the center of all that happened. When Einstein applied his revolutionary views about gravity, energy, and mass to the cosmos, he recognized that the earlier views could not be correct. In Newton’s view of the universe, stars, moons, and planets were held in perfect balance because of the force of gravity. If true, it means that energy would move in one direction only, from the center outward. As light sped off into the far reaches of the cosmos, it would be lost, never to return. This would mean that the universe would be continually losing energy and decreasing in size. Einstein thought this was unlikely. It neither fit the mathematical models he had developed nor his ideas about time, space, and relativity. Einstein posited the existence of a universe that was finite, boundless, and static, which meant that energy could be recycled. You could start traveling in any direction and eventually come back to where you started, although it could take billions and billions of years. It would be like traveling on earth except on a much larger scale. An individual could circle earth again and again without falling off into space or ever coming to a boundary. Einstein found himself in a quandary. His calculations indicated that the universe had to be expanding, but he, like Newton, preferred to believe it was static. Einstein continued to fiddle with his equations until he got them to fit what he wanted to believe. The universe would be expanding, he reasoned, except for the fact that it was kept in a motionless state by a force that he called the cosmological constant. This provision allowed Einstein to burn his candle at both ends. A potentially expanding universe was actually held in check by some mysterious force.
While Einstein was busy portraying the cosmos as a static system, some other scientists who had familiarized themselves with the principles of relativity were reaching different conclusions. Alexander Friedmann, a Russian meteorologist, worked out equations to show that the universe was actually expanding. He believed the cosmos had started some 15 to 20 billion years ago and had continually expanded to reach its present form. Another individual, working independently from Friedmann, came up with similar conclusions. His name was Georges Lemaitre, a Belgian priest. His prodigious intellectual abilities made it possible for him to build on Einstein’s valid conclusions while avoiding his blunders. Lemaitre reasoned that at some past time and place, all matter was concentrated into a tight bundle—a “primeval atom”—from which the cosmos erupted. Over the billions and billions of years, it expanded to reach its current form, and it would continue to expand for all eternity. The understanding of the cosmos was improving as a result of Einstein’s theory of general relativity and its modifications and extensions by other scientists. However, the data were purely logical, based entirely on mathematical computations.
Nobody had been able to gather much empirical evidence about the nature of the universe, but that was to change. In 1923, Edwin Hubble, a skilled astronomer and mathematician, was viewing a nebula in Andromeda with the aid of the powerful telescope at Mount Wilson Observatory. He spotted Cepheid stars. In 1908, Henrietta Leavitt proved that the speed with which Cepheids get duller or brighter over time correlates directly with how bright they actually are. This knowledge allows scientists to compare how bright a Cepheid star actually is with how bright it appears, allowing them to figure its actual distance from earth. Another physical characteristic of light helped Hubble. Light looks different if it comes from a moving source rather than from a stationary one. If a source is moving away, light looks redder than it is (called “redshift”), and if it is moving closer, it looks bluer (called “blueshift”). By studying Cepheids and redshifts, Hubble was able to determine that the universe was expanding, as well as how quickly it was happening. Those galaxies that were farthest from earth appeared to him to be moving the fastest. (For example, Hubble observed that a galaxy that was twice as far from earth moved twice as fast, and one that was four times as far moved four times as fast.) Hubble’s research indicated that the cosmos was expanding at an accelerated rate, but it neither proved that it began billions of years ago from a “primeval atom” nor that the cosmos would continue to expand for all eternity.
In the 1920s, only a few generally accepted beliefs about the nature of the cosmos existed: Einstein’s theory of relativity was viewed as giving correct information about the shape of the universe, and the universe was viewed as an expanding system in which stars and galaxies were moving away from one another at an accelerated rate. Things changed by the end of the 20th century, as more and more scientists came to view the big bang theory or some variation of it as generally correct. (Oddly, the name “big bang” was coined by British astronomer Fred Hoyle to mock the theory, but the name caught on and is now the preferred one.) According to the big bang theory, about 14 billion years ago, the cosmos was densely packed into an incredibly small, remarkably hot package, dimension, or “seed.” All mass, energy, space, and time were contained inside the “seed.” For some reason, the “seed” exploded, and its contents expanded dramatically and rapidly outward, leading to the creation of atoms, stars, planets, moons, and, ultimately, living things. This big bang was unlike any other explosion, because in ordinary explosions, matter is propelled into some physical space. In the big bang of the cosmos, matter, space, and time were jumbled all together, and they were actually created by the explosion. The primeval cosmos remained dark and without much structure for a long time after its origination. Stars probably did not appear until 100 million years after the initial explosion, and galaxies probably did not form until 1 billion years after it.
In the 1980s, Alan Guth proposed inflation theory, which suggests that moments after the explosion of the big bang or singularity, the universe experienced a striking rate of expansion. If inflation theory (or some variation of it) is true, as most scientists now believe, then the universe must continue to increase in size. If it is bigger today than it was last year, then it was bigger last year than it was the year before that. It seems reasonable to conclude, then, that billions and billions of years ago, the cosmos was a great deal smaller than it is now, suggesting strongly that it has not existed forever and that it did originate at some specific point in time and space. Most scientists also believe that the universe is finite, because a universe containing an infinite number of stars would be incredibly bright all the time and we would never experience the darkness of night.
If a big bang did actually occur, then all of the matter that now exists in the cosmos would had to have been formed in that initial explosion billions of years ago (or at least been created by something that did originate during the big bang). Is this possible? Could a big bang have produced what we see in today’s cosmos? In 1946, a Russian physicist named George Gamow showed how a big bang could indeed have created the cosmos. He theorized that the nascent cosmos was filled with a thick mass of neutrons and these neutrons eventually bound together due to what is called the “strong force.” The strong force can hold even similarly charged particles together into a tight bundle if they are close enough together for the strong force to overcome their natural tendency toward repulsion. The strong force could have been a principal way that both heavy elements (e.g., carbon or oxygen) and light elements (e.g., helium or deuterium) were formed in the universe. (Whether an element is “light” or “heavy” is determined by the number of particles it has in its nucleus.) The prevailing view is that lighter elements joined together to form heavy elements, a hypothesis given support by the fact that light elements are far more abundant in the visible universe than are heavy ones. An additional source of heavy elements could have been stars, because stars were both plentiful and hot enough in the early universe to do the job. Stars warmed and ionized gases, while producing and dispersing heavy elements through the process of thermonuclear fusion that took place in each star’s core. However, lighter elements needed a source other than the stars. Although stars do churn out small amounts of helium from their hydrogen-burning centers, helium is far too abundant in the universe for stars to have been its principal source. Furthermore, the deuterium that comes from stars is destroyed almost as quickly as it is produced. Thus, the existence of any deuterium at all in the cosmos and an abundance of helium mean that these elements had to have been created from something other than stars, and a big bang seems to be a likely source.
Gamow eventually joined forces with two others researchers, Ralph Alpher (a graduate student) and Robert Herman (a colleague). This collaboration led to a more refined picture of the origin of the cosmos. The primeval universe, they argued, initially contained a swirling mass of nothing but neutrons (which Alpher called “ylem”). As this hot, swirling mass expanded, it continued to cool until it hit the pivotal temperature of 6,000 degrees Fahrenheit. This is the perfect temperature for element formation: It is hot enough to energize particles that might otherwise repel one another, but it is not so hot that the particles would move too fast for the strong force to bind them together. With cooler temperatures, a point was reached in which light and energy could escape from the chemical mass, and this radiation then traveled across the cosmos without interference. According to quantum mechanics, particles materialize and then disappear from space all the time. They do not pop into existence as single particles, but always as pairs; a particle and its antimatter counterpart materialize together. In the usual case, as soon as a particle and an antiparticle appear, they bump into one another and instantly disappear. In the early universe, especially under conditions of extreme heat and rapid inflation, things were different. As a particle and its antiparticle partner popped into existence, it was impossible for them to reunite fast enough to dematerialize, so the number of particles went up by two. As more and more particles came into existence, they provided the raw material to create many of the physical structures in the universe. The quarks in the universe (the building block of all matter) would have eventually reached the right temperature to coagulate into neutrons and protons (electrons are quark free). The expanding universe contained structures that varied in their density enough that gravity and the curvature of space worked together to cause the denser regions to slow their expansion and start to contract, leading to the creation of stars, galaxies, solar systems, planets, and moons.
In June 1964, in a perfect example of serendipity, Arno Penzias and Robert Wilson made a discovery that offered strong support for the big bang theory (they received a Nobel Prize in 1978 for their work). They had started to work for Bell Labs and were trying to measure any radiation coming in from the heavens at a 7.35-cm wavelength. Their initial attempt was simply designed as a test to make certain that the antenna they were using was calibrated correctly. Although they expected to hear only silence, indicating that the antenna was working correctly, this is not what happened. They heard a signal at 3.5 degrees above absolute zero. After discounting the possibility that the radiation was coming from some specific source, either on earth or in the sky, they started searching for flaws in the antenna itself. For several months, they worked to make sure the antenna had not been contaminated. (A family of pigeons had nested in it, and it took a great deal of work to get rid of them and their droppings.) No matter what Penzias and Wilson did, they still picked up radiation with their antenna. They finally concluded that the cosmic microwave background was coming from the universe itself. This background radiation is exactly the temperature it should be if a big bang had occurred, especially in an expanding universe. A similarity in temperature is found in parts of the universe that are so far from one another that they have no reason to have the same temperature, which offers strong evidence that everything reached the same temperature before inflation occurred. Once the different structures from the big bang were spread across the universe—galaxies formed in clusters and in clusters of clusters, separated by huge voids or vacuums where few visible structures are found—they evolved in similar ways with similar temperatures.
The Cosmological Constant, Dark Matter, and the Uncertainty Principle
It is possible that the big bang that formed our universe was simply one moment in a constantly evolving cosmos in which all matter and energy expand and contract for all eternity. Einstein thought that an abundance of high-density matter in a universe would cause space to curve back on itself like a sphere and any expansion in the universe would eventually stop and a collapse would occur (called the “big crunch”). If the density of matter in a universe is low, then space will be shaped more like a saddle or shuttlecock and the universe could expand indefinitely so that no crunch or collapse will occur. With medium density, space would be flat (or nearly so), and whatever expansion occurred would be very gradual for all time. Friedmann studied Einstein’s equations and concluded that more than one possibility existed. The universe could expand and contract only once, or it could grow and shrink repeatedly through multiple beginnings (bangs) and endings (crunches). The prevailing view of our universe is that it is flat (or nearly so). This does not necessarily mean that it resembles a pool table. What it means is that two beings could stand a mile apart and start traveling in the same direction, and they would never cross paths or come in contact with one another; they would always be a mile apart. The exact shape of the “flat” universe is still a mystery, however. A piece of paper that is rolled into a tube is also “flat,” because two paths could be drawn on it that do not converge. The paper could be rolled and shaped into an oval, a circle, or some other shape. These, too, would still be “flat.” A far-distant light in the sky might be nothing more than a reflected image of our own galaxy.
An ongoing series of big bangs might have occurred, which continued to produce new universes in a huge multiverse or metaverse. (Guth calls this possibility “eternal inflation.”) Some theorists speculate that an infinite number of parallel universes exist, each one having its own distinctive history of evolution. In some universe, for example, Abe Lincoln did not get assassinated, Elvis Presley still lives, and the Titanic reached harbor safely. If the number of universes is infinite, all possibilities become realities. Every athletic event or presidential election would replay itself over and over again, and each individual on earth might exist an infinite number of additional times in alternate universes. The gravity from some parallel universe might influence the way galaxies and stars move in our own universe, and black holes might be the entrance or exit from one universe to another. Dimensions might exist in addition to Einstein’s three space dimensions (forward and back, left and right, up and down) and one time dimension, perhaps as many as 10 or 11 space dimensions, but these cannot be seen because they give off no light. This information about eternal inflation and multiple universes—and it does sound more like science fiction than science fact—gives us another way to think about the origin of our universe and the big bang. Two parallel universes could have had intersecting membranes, and these universes could have collided with one another, creating the big bang that created our cosmos.
As galaxies move away from each other, the stars in their outer rims seem to move faster than they should if the force of gravity from visible objects is all that is operating. The term dark matter has been coined to describe the factor that could be responsible. What dark matter is made of—or whether it exists at all—is one of the great scientific mysteries. Without a presumption that something like dark matter exists in the universe and in sufficient quantities, it is difficult to understand how stars and galaxies could have formed as quickly as they have or how our universe could go from a big bang to its present form (i.e., without help from the gravity coming from dark matter, atoms and other elementary particles would have been unable to bind together long enough to create stars and galaxies). Dark matter may even have helped to produce the elements we see in the universe today, particularly light elements such as hydrogen, deuterium, and helium.
As the cosmos cooled, dark matter separated from visible matter, and the cooling of hydrogen would have formed a rotating disk of celestial matter and debris. Clumps of dark matter would neither give off much radiation nor lose much energy, so they would scatter throughout the universe. The most compact pockets of gas would eventually develop into stars under the influence of gravity and the curvature of space. Deep in the core of a star is a blast furnace whose phenomenal heat is fueled principally by hydrogen. The heat and pressure would have been so intense in stars in the young universe that ionized hydrogen atoms would have been forced close enough together that the strong force could have bound the protons and neutrons together to create heavy elements. Massive stars (at least 8 times as large as our sun) would have continued to fuse heavier and heavier elements in their cores until iron was eventually produced. The fusion of iron does not give off energy, but uses it up, meaning the star eventually will be without fuel to burn. A dramatic collapse occurs, and what is left of the star is spewed violently into space in a powerful supernova explosion. Although the stars were responsible for creating some essential elements in the primordial universe, they could not be responsible for all the elements that now exist, especially light elements. Because dark matter probably formed before stars, it could have played a major role in the production of both light and heavy elements.
Social scientists are familiar with the “Hawthorne effect”: When you study humans, your observations and measurements can change your subjects in a multitude of ways. You could be creating through your research that which you are trying to uncover. Whereas research methods exist in the social sciences to make it possible to conduct unobtrusive research, this is impossible in the physical sciences because of the uncertainty principle. The uncertainty principle was formulated in 1927 by Werner Heisenberg, a German physicist. It shows that any measurement of the position or velocity of a particle is inherently ambiguous. An observer can never know the precise velocity and position of a particle, because an increase in the accuracy of describing either velocity or position is automatically correlated with a decrease in the accuracy of describing the other. This means that uncertainty is a basic, inescapable quality of the cosmos. If it is impossible to measure the state of the universe without disturbing it to an unknown degree, it is even more difficult to predict what is likely to happen. Heisenberg, Erwin Schrodinger, and Paul Dirac developed quantum mechanics, based heavily on the uncertainty principle. Particles no longer had—or could no longer be viewed as having—fixed positions and velocities. On the contrary, particles were presumed to have a large number of different possible outcomes or positions, and quantum mechanics describes probabilities, not positions. Whether an electron is a wave or a particle, for example, depends on what procedures are used to observe it. In some experiments, electrons act like waves, and in others they act like particles. A tree does not look the same to someone 500 feet in the air as it does to someone leaning against its trunk. The physical world, like the social world, is characterized by enough uncertainty that definitive statements about physical reality are difficult to make.
Heisenberg’s uncertainty principle cautions us against having strong faith that the laws of physics are, have been, or will be uniform in all times and places. Maybe in the far-distant reaches of our uni-verse—or in parallel universes—physical facts and physical laws are different from what they are closer to home. Light, for example, does not have to travel at a constant 186,282 miles per second. If two photons of light left a galaxy 2 billion light-years from earth at exactly the same moment, they would reach earth a minute apart. In some situations, gravity may be able to travel as quickly as light. Hubble’s observations of redshift might mean something other than that the universe is expanding at an accelerated speed. Light might actually lose energy as it travels over the incredible distances involved (called the “tired light theory”), which would make it look red even if it came from a stationary object. (A decrease in energy produces a longer wavelength, making light appear red regardless of the nature or velocity of its source.) Galaxies and stars may have an inherent or natural redshift regardless of whether they are traveling away from earth. (Halton Arp put forth this idea.) If red-shift is an uncertain measure of the state of the universe, if it has nothing to do with whether an object is moving away from earth, then it will offer a tremendous blow to big bang theory and all the efforts to determine how fast galaxies are moving and how old they are.
The Anthropic Principle and Life in the Cosmos
One of the most remarkable things about our universe is that it has developed in such a way that it is capable of sustaining life, especially human life. The anthropic principle is an idea first delineated by Brandon Carter in 1974, and it has both a weak and a strong version. The weak anthropic principle states that because the universe contains human life, it must be the kind of place that can support human life. At its most basic, the weak principle is self-evident: The universe must be a place that can support life, otherwise life could not possibly exist. This is like saying that the park bench on which people are sitting is strong enough for humans to sit on or else they would not be able to sit on it (or think about the experience). The weak version claims that in a universe as expansive as ours, the conditions necessary for the development of intelligent life will exist—will exist only—at particular times and places. In contrast, the strong anthropic principle offers the claim that life-sustaining regions of our universe evolved in order to produce intelligent life.
It cannot be denied that our universe seems uniquely capable of sustaining life, especially human life. If our universe were even slightly different, it would be a place where complex organisms could not have developed. If the inflation rate of the early cosmos had been altered from what it was, then galaxies would never have formed. If gravity had not been as strong as it was, stars would never have developed or lasted long enough to warm planets. Minor alterations in the forces in the universe would have made it impossible for hydrogen—necessary for both the formation of water and the constant fueling of the sun—to form. A change in the strong force would have made it impossible for protons to form. Minor changes in the universe would have meant that the forces of gravity and electromagnetism would not have been in the correct ratio for our sun to form. If things had been any different in the universe, too little carbon would have been made for organic life to develop. Our universe, with a sun that allowed the existence of a warm planet to sustain human life, with an abundance of water, with sufficient oxygen for living creatures to breathe, with a gravitational force to keep the universe from collapsing too soon, is really an ideal place for life to evolve.
With the universe so finely tuned for human life to develop on earth, is it possible that it all was an accident? According to Karen Fox, the odds of a human-compatible universe happening purely by chance are as likely as a tornado tearing through a junkyard and creating a Boeing 747. It may be even harder for most scientists to accept the claim that our universe was deliberately mapped out in order to sustain intelligent life, the assertion of the strong anthropic principle. Most of the planets in our solar system, a life-sustaining system to be sure, are without both life and the physical conditions necessary for it. If it were true that an infinite number of universes exists, it becomes far easier to accept that one universe could originate by chance that contained a particular solar system with a planet that had all the necessary elements for intelligent life to develop and evolve. It just so happened that our planet, in our solar system, in our galaxy, in our universe, contained all that was needed to sustain beings who could think and wonder about what was happening to them. In fact, it would be surprising if, in a multiverse or metaverse of infinite possibilities, intelligent life had not evolved.
Our solar system formed about 5 billion years ago from a swirling mass of metal, dust, gas, and other debris. Our sun formed in the central part of this nebula, and as the nebula rotated slowly around the sun, it flattened. Specific areas of this mass began to spin like whirlpools in a river. These spinning areas attracted nearby particles of matter and ultimately developed into the planets and moons that now circle the sun. In 1953, Stanley Miller, a graduate student at the University of Chicago, did an experiment that both reflected and reinforced the prevailing view of how life began on earth. He combined water, methane, ammonia, and hydrogen together in a container, heated it, and ran an electric current through it. Within a week, the jar was teeming with microscopic life in the form of amino acids, the building block of proteins. This offered some experimental evidence that the earth was—or at least could have been—created by a slow convergence of rock and other materials over the eons. It seemed clear from Miller’s experiment that the earth started out cold and its inner core did not heat up until radioactive elements slowly turned up the temperature in the center. Iron, unable to melt and sink to the core, would have remained close to the surface for hundreds of millions of years, where it would attract oxygen, making it difficult for carbon dioxide to form. Instead, the carbon would have combined with hydrogen to form methane and ammonia, the chemicals that made the Miller experiment work. If Miller was correct, the earth’s earliest atmosphere, lacking both carbon dioxide and free oxygen, would have been inhospitable to the development of both plants and oxygen-breathing, carbon-based life forms.
In retrospect, it is likely that Miller was wrong and earth was probably formed by violent collisions of celestial debris rather than by some gradual warming process under the influence of gravity. These violent collisions would have melted the iron, sending it plummeting to the earth’s core. Oxygen would then have been available to mix with carbon, making earth’s early atmosphere rich in carbon dioxide (as is the atmosphere of Venus), and it would have been difficult for organic compounds to develop in this environment. One way that life might have developed is that the young planet’s gravitational field and the curvature of space attracted all sorts of material from the cosmos, and the organic building blocks were transported to earth by comets, asteroids, and meteors. Another possibility is that the building blocks of life were transported by interplanetary dust particles that fell down on earth. Even today, countless particles fall to earth like cosmic raindrops, many carrying a load of organic compounds.
Charles Darwin postulated that life on earth started in a warm little pond. He was probably right about the water but wrong about its temperature and its location. It was in the ocean where life first formed, not in a pond, and the region where life formed was hot, not warm. Initially, earth’s surface would have been so hot that any moisture that fell would instantly turn into steam. This moisture absorbed some of the heat and helped to cool the planet, and the cloud masses that formed from the evaporating water would have kept the sun’s warmth from reaching earth’s surface. After thousands of years, the planet cooled enough that it reached the freezing point of rock (1,000 to 2,000 degrees Fahrenheit), and a crust formed. The time eventually came when the earth cooled to beneath the boiling point of water. The moisture did not evaporate into steam but started to accumulate on the planet. It may have taken a billion years to fill the crevices enough to form oceans.
The epicenter of life on the primitive earth was, in all likelihood, what are now called “hydrothermal vents.” These are cracks in the ocean floor, leading to subterranean areas of molten rock. Cold water rushes into the vents, and hot water gushes out in a series of endless undersea geysers. High temperatures and all the underwater energy could have provided the conditions necessary to make life. The hotter it is, it seems, the easier it is for life to flourish, although researchers have found no organisms living in temperatures hotter than 235 degrees Fahrenheit. The organisms that now anchor the food chain around the hydrothermal vents are sulfur-eating organisms, creatures that probably look very much like the first living organisms on the planet. It is possible that rather than being the birthplace of life on earth, hydrothermal vents were only its nursery. Living organisms that originated elsewhere might have migrated to the vents for protection and nourishment. They survived because the deep water made it possible for them to survive any intergalactic calamity—radiation from exploding stars or environmental changes produced by collisions with asteroids and meteors—that wiped out their surface-dwelling relatives. Some of the larger asteroids that ploughed into earth would have generated enough heat to vaporize rock, boil oceans, and fill the atmosphere with debris and steam. These environmental changes would have made it impossible for life to survive, so life might have started but then disappeared many times on earth before it finally took root. The Chilean biologist Humberto Maturana coined the word autopoiesis, meaning “self-creation,” to emphasize that a key feature of life is that it is organized to create and re-create itself.
When life on earth was established well enough to reproduce itself, it came in stages. The first organisms probably resembled current-day viruses, bacteria, and fungi. These original organisms could reproduce, but they could not breathe oxygen because there was not much to breathe. They broke down chemicals in the oceans through a process of fermentation. A characteristic byproduct of fermentation is carbon dioxide, which eventually reached a saturation point in the oceans of the young planet. The carbon-dioxide-rich environment became a starting point for new forms of life containing chlorophyll. These living organisms survived through a process of photosynthesis: Carbon dioxide, water, and sunlight are converted into sugar, which serves as food for chlorophyll-containing forms of life. Photosynthesis produces oxygen as a waste product. Oxygen seeped through the water in which the first plants grew and accumulated in the atmosphere. The conditions were finally right for the evolution of oxygen-breathing organisms, first in the oceans, and then later on land. Mutations would have occurred, most of which would have perished because of their inability to adapt to prevailing environmental conditions. However, some of these mutations would have survived and developed into successful breeders, eventually supplanting the creatures from which they were descended. Higher life forms evolved, such as fish, amphibians, reptiles, mammals, and, eventually, humans. Recent discoveries in anthropology have suggested that the hominid line really began about 5 million years ago, when Ardepithecus ramidus and, later, Australopithecus africanus abandoned their arboreal existence to walk upright on the savanna of eastern Africa, which required them to adapt to a new and constantly changing natural environment. Upright posture, complex brains, successful breeding, tool use, cultural innovations and modifications, group living arrangements, advanced cognitive and emotional capabilities, and the refined ability to invent and use symbols and language—all these made it possible for humans to become remarkably successful at surviving on earth. The relationship of humans to their environment is characterized by world-openness (an idea proposed by Peter Berger and Thomas Luckmann). Humans are found all across the planet, having started their geographic expansion millions of years ago, and they show great adaptability and flexibility in regard to the physical world and the various social situations in which they find themselves. They continue to search for a more thorough understanding of the origins of the universe and life in it. The big bang theory can help them in their quest.
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