Big Bang Essay, Research Paper
The Origin
Some 12 billion years ago the universe emerged from a hot, dense sea of matter and energy. As the cosmos expanded and cooled, it spawned galaxies, stars, planets and life. Since the beginning of human civilization, people have always questioned the origins of their existence and the creation of the universe. Cosmology, the scientific study of the large scale structure and evolution of the universe, has developed and evolved in response to the human need to know our roots(Silk, Big Bang 1980 456). Within in this field of study, the Big Bang theory has become the most prevalent theory, because the majority of evidence from a variety of different investigations make it extremely likely that something like the Big Bang occurred.
The Big Bang theory of cosmology assumes that the universe began from a singular state of infinite density. As Joseph Silk defines the Big Bang theory, it is a model of the universe in which space-time began with an initial singularity and subsequently expands(Silk, Cosmic Enigmas 56). The theory first referenced in Alexander Friedmann’s complete solution of Albert Einstein’s equations, in 1922. In 1927, Georges Lemaitre used equations to devise a cosmological theory that incorporated the concept that the universe has been expanding from an explosive moment of creation. However, the term “Big Bang,” as a name for the initial cataclysmic event, was chosen by two men named George Gamow and R.A. Alpher due to their discovery of background radiation, a low-temperature radiation that penetrates the universe at microwave wavelengths(58). Its source is now believed to have been the extremely hot fireball with which the universe began, according to the Big Bang theory. Since its initial introduction, much evidence has helped to strengthen its case, and other theories have been added to it, such as the Inflationary theory. This theory seeks to account for the physical events which took place in the very first moments of creation. In short, the Big Bang theory is one which incorporates other theories in its attempt to explain the evolution of the universe. Though much evidence supports, the Big Bang theory, there are still questions which remain unanswered. Other theories that attempt to explain the origin of the universe exist, but the Big Bang theory has become the standard model by which others are measured.
The history of the Big Bang and cosmology was born when Albert Einstein developed his General Theory of Relativity in 1915, and his first cosmological paper in 1917, when Einstein attempted to make the equations of relativity fit together with the incorrect belief that the universe was stable and static, with no beginning nor an end(Monsters 103). Einstein’s theory of gravitation of space-like bodies, general relativity, has identified gravity with the curvature of space-time, the four-dimensional manifold that consists of the three space dimensions combined with time(Silk, Big Bang 1980 13). Any event can be described in terms of its path and location in space-time. In particular, the light from distant galaxies logically follows the shortest possible path, called a geodesic. The manner by which one looks back in time is by geodesics; galaxies are almost like time machines, with the light from most distant galaxies traveling through space-time since before the earth was even formed, 4.6 billion years ago. The most distant galaxies are at a distance of ten billion light years, basically providing a look-back in time of ten billion light years as well.
Einstein’s theory of relativity received solid confirmation in 1919, when the deflection of light from distant stars by the sun was measured during a total eclipse. The cosmological implications of Einstein’s theory of relativity began to receive intensive examination. The idea of the Big bang and an expanding universe which challenged Einstein’s idea of a static and unchanging universe, came primarily from a Russian meteorologist, Alexander Friedmann, and a Belgian cleric and mathematician, Georges Lemaitre. The formulation and prediction of a Big Bang explanation for the universe was remarkable because both men formulated that theory of cosmology without any firm observational evidence for universal expansion(Silk, Big Bang 1980 15). Both men, in different years, independently discovered the solutions to Einstein’s equations of gravitation which described an expanding universe, discarding Einstein’s cosmological constant and his perception of a static universe. Friedmann, in 1922, and Lemaitre, in 1927, demonstrated that the universe could be in a large-scale expansion. To avoid collapse, the expansion of the universe balanced gravitational attraction. The expansion could either continue forever, or eventually reverse into a phase of contraction. A principle assumption of their theory was that the matter content of the universe implied that space was not necessarily Euclidean or analogous to the flatness of a plane in a two-dimensional analogy, but could be curved like the surface of a sphere (with a positive curvature) or a hyperboloid (negative curvature) (Silk Cosmic Enigmas 13) . Since the surface of a sphere is closed and finite while a hyperboloid is open and infinite, it can be inferred that a universe with high matter density should be closed, finite, positively curved and should eventually collapse, while a universe with low matter density should be open, infinite, and negatively curved, expanding indefinitely (14).
Edwin Hubble, a famed American astronomer of the 1920’s , discovered a linear relation between distance to a remote galaxy and its red-shift in 1929 which provided exciting evidence supporting the idea of the ever expanding universe which came from the Friedmann-Lemaitre model. Hubble s discovery was influenced substantially by the work of a Dutch astronomer, William de Sitter, who in 1917 hypothesized that the universe possessed the peculiar property that the light from the most distant regions became progressively reddened as the distance increased. Hubble’s red-shift is due to a Doppler shift of light from a galaxy which is receding. This explains that the distance of galaxies from us is linearly proportional to their red-shift and therefore linearly proportional to their relative velocity of recession (Silk, Big Bang 1989 374). So basically, galaxies and bodies that are twice as far from us than another, move twice as fast. This idea indicates that it has taken every galaxy the same amount of time to move from a common point of origin to its current position, wherever that might be.
The term “Big Bang” for these theories was coined by the Russian born U.S. nuclear physicist George Gamow in 1946. He was one of the strongest advocates for this theory for the creation of the universe, supporting the work of Einstein, Friedmann, Lemaitre, and Hubble (Peebles 1). Gamow attempted to explain the distribution of chemical elements throughout the universe through a spontaneous thermonuclear reaction. He also proposed that in the beginning of the Big Bang, the universe consisted of a primordial substance called ylem. This ylem was a gas of neutrons which was at extremely high temperatures exceeding 10 billion degrees. Because the neutrons existed in this “free” state, they began decaying into protons, electrons, and neutrinos. The result was a boiling sea of neutrons and protons which merged together to form heavier and heavier elements. In Gamow’s perception, all of the elements in the entire universe formed in this manner during the earliest twenty minutes of the Big Bang. This hypothesis, attempting to account for the origin of helium and hydrogen in the universe, was submitted by Gamow and his partner, Ralph Alpher in 1948(Eldredge 355). Then in a follow up paper, Gamow and Alpher wrote that after the universe was created in a great fiery explosion, as the universe expanded, the radiation would not have persisted but would have been steadily diluted. This would explain the necessary cooling of the universe. But the most important part of this second paper was the prediction of background radiation, a tangible clue to the actual Big Bang. Although in the 1940’s there was no technological way to detect such a faint afterglow, scientists of later decades would be able to prove what Gamow had hypothesized(363).
As cosmology and the Big Bang theory gained acceptance by the scientific community, solid, scientific evidence was found which supported the Big Bang and Gamow’s theory of background radiation. In the spring of 1964, Arno Penzias and Robert Wilson, two researchers at Bell Laboratories, while measuring noise levels from the sky, unexpectedly discovered a signal of microwave radiation which had a temperature equivalent of about 3.5 degrees Kelvin (Smoot 81). The signal was coming from all directions of the sky. The explanation for this signal was that it was a detection of leftover radiation from the creation of the universe, the Big Bang. This conclusion was reached because of the isotropic and blackbody nature of this radiation. Since isotropic means the radiation at the wavelength was equally intense all over the visible sky, it can be inferred that that is exactly what one should expect if left over radiation came from the Big Bang, that since it occurred everywhere simultaneously, the afterglow should be uniform across the heavens (84) . This was a “smoking gun” giving more strength to the Big Bang theory of the creation of the universe and proving Gamow’s hypothesis.
More recently, cosmic microwaves were detected which seemingly originated at the farthest, outer reaches of the universe. These microwaves were incredibly uniform, indicating the homogeneity of the early stages in the creation of the universe. The COBE satellite of NASA which detected these microwaves also discovered changes in temperature and other factors which supported previous calculations based upon the assumptions of the Big Bang theory(Gribben 143). Although, it may never be known for sure whether the Big Bang was the definite manner of creation for the universe, modern scientific thought and evidence, such as that of the COBE satellite, indicate that the Big Bang theory is at the very least, an extremely plausible one.
According to the Big Bang theory, the universe began with one large explosion, which took place about 15 to 20 billion years ago. We now refer to this explosion that began the universe as the ‘Big Bang’ and it is from this theory that we are able to examine the evolution of the universe from the milliseconds of creation to the creation of galaxies, and from the formation of planets to the presence of life on earth. Because almost all astronomical phenomena can be explained entirely within the context of the Big Bang, or if not completely, can be explained to a greater degree than any other mode, this model of the universe has become the most widely accepted up to this point. However, within the framework of the Big Bang theory, there are several different models of the universe.
The standard model of the Big Bang theory takes three possibilities into consideration, displayed in Appendix A. The first one is the open Friedmann-Lemaitre theory on the universe in which hyperbolically curved space is destined to expand forever. The second theory is the closed Friedmann-Lemaitre theory on the universe in which spherically curved space is destined to collapse again. The third one is the Einstein-de-Sitter theory which calculates that the flat space of the universe is destined to continually expand as well. Although these three models do not differ greatly in the initial and beginning fazes of the evolution of the universe, they do differ in their later fazes and as one can see, they predict very different futures for our universe.
One of the most interesting thoughts which arises out of this framework, is that the universe was not always in the state which we see it currently. To examine how the universe evolved, we must trace back through the expansion of the universe, coming as close as possible to the exact moment of the Big Bang. Probably the most astounding fact is that we are know in a position to describe the universe as it existed during most of the first second of existence. (Trefil 20)
In its early stages, according the Big Bang theory, the universe was in thermal equilibrium. A searing light pervaded all locations and traveled in every direction, with the characteristics and qualities of a blackbody at exceedingly high temperatures. Early on in creation, the temperature was in the trillions of degrees because it was in a highly compressed, primordial state. At this extremely early stage of creation, particles of opposite charge freely moved around independently of one another, in a state of matter called a plasma(Trefil 23). As the space expanded according the Big Bang theory from a single point of origin, the wavelengths of light stretched out as well. Likewise, the expansion of the space stretched the wavelengths shifting the extremely high temperature blackbody spectrum to that of a lower temperature. Blue light shifted to the cooler red light region, and the universe cooled. As the universe cooled, certain forms of nuclei, definite amounts of helium, hydrogen, and lithium were formed, as well as other forms of elementary particles. About 1,000,000 years later, and almost 15 billion years ago, the universe became cool enough for atoms to finally form.
Soon after the formation of atoms and the subsequent attraction of particles of opposite charges, another natural process began(Trefil 45). Under the expanding new materials began to come together in clumps. As the universe expanded, matter was being brought together in these clumps by the force of attraction in gravity. Within each clump, the gravitational forces continued to operate, drawing large clouds of gases together to form nebulae. Eventually, the clumps and clouds of gas would form stars through a process known as fusion.
A gas cloud had little choice but to collapse and fragment into what we now know as stars. Only the random motion of its atoms provides a pressure that can resist gravity for only a very short time, with atoms colliding, radiating because of the presence of heavy atoms such as carbon, losing their kinetic energy of motion, and eventually causing a cool down and a collapse. As the gas clouds collapse into little clumps; these clumps merge together into larger, mixed fragments, and grew by accreting gas from their surroundings (Silk, Cosmic Enigmas 65). This collapsing gas soon became sufficiently dense to begin radiating energy from atomic collisions, and thus the first stars were born.
Over time many of the star clusters dissolved because of disruptive gravitational forces exerted by other clouds, and a galaxy emerged which resembled the Milky Way (Silk, Cosmic Enigmas 69). The most prominent feature of this early galaxy was a rotating disk of stars and gas clouds, along with a compact central spheroid shape of stars which developed from those collapsing gas clouds. Five billion more years would go by before one of these interstellar clouds would birth our solar system, condensed from the remnants of earlier stars. Finally, simply put, chemical processes would occur to link atoms, which were billions of years in the making from the origin of the universe, together to form molecules, and then eventually complicated solids and liquids, and finally bringing us to where humans stand now.
With our ability to observe other regions, not just the optical region, we have discovered much evidence that supports the Big Bang theory. Probably the most persuasive evidence for this theory is the presence of cosmic microwave background radiation, which can only be detected by radio telescopes. Cosmic microwave background radiation is diffuse isotropic radiation whose spectrum is that of a blackbody at 3 degrees Kelvin and consequently is most intense in the microwave region of the spectrum (Silk, Big Bang 1989 456). This radiation is thought to come from the cooled residue of the initial explosion from which the universe evolved. Because microwaves are of shorter wavelengths, only several centimeters wide, and are thus not in the optical window, we are not able to directly observe these. Microwave radiation also does not usually produce heat, except at extremely high intensity, making it difficult to detect. However, our entire universe is a great source of these microwaves and it was not until the production of a small radio horn for satellite communication, created in 1965 at Bell Laboratories in Holmdel, New Jersey that radiation was detected.
The discovery of cosmic microwave background radiation, was significant because it fit in with George Gamow’s theory that the elements of the universe had been created 5 minutes after the ‘Big Bang’ and thus primordial radiation should be scattered across the universe. He also hypothesized that due to expansion, the temperature of radiation should have cooled to about 5 degrees above 0. When scientists detected this radiation it became evident that it contained a high degree of uniformity which proves its origins are from the farthest points of the universe (Silk, Big Bang 1980 102).
Cosmic microwave background radiation has also been found to have almost a perfect blackbody radiation, meaning that the intensity distribution of its radiation is that of a blackbody. Its temperature now is about 3 degrees Kelvin, inferring that it is very cold. This fits in very well with the notion that the universe has been expanding. Indeed, if the blackbody radiation is traced backward in time, it becomes hotter and hotter until it reaches the conditions to create blackbody radiation; a state of perfect equilibrium between radiation and matter. Evidence is also provided from small deviations from the blackbody spectrum of about 5 degrees(Monsters 4). They provide important information on the small imperfections of the Big Bang, which are responsible for the structure of the universe. This discovery of cosmic microwave background radiation is probably the most significant evidence that supports the Big Bang theory.