BigBang Theory
(essay)
A cosmological model to explain the origins of matter,energy, space, and time, the Big Bang theory asserts that the universe began ata certain point in the distant past—current estimates put it at roughly 13.7 billionyears ago—expanding from a primordial state of tremendous heat and density. Theterm is also used more generally to describe the vast explosion that erupted atthe beginning of space and time, bringing the universe into being. First conceivedby astronomers and physicists in the early twentieth century, the Big Bang was effectivelyconfirmed in the middle and latter years of the century, once new telescopes andcomputers made it possible to peer further into the universe and process the enormousamounts of data those observations generated. The term “big bang” comes from itsunderlying hypothesis, that the universe has not been eternal but emerged out ofa sudden, almost incomprehensibly vast explosion.
Scientists’ understanding of the Big Bang theory emergesout of two separate fields of inquiry: theoretical physics and observational astronomy.According to what are called the Friedmann models, a set of complex metrics namedfor Alexander Friedmann, an early twentieth century Soviet physicist who firstdeveloped them, the Big Bang theory fits in with two of the most important theoriesof twentieth century physics: the cosmological principle (which says that basicphysical properties are the same throughout the universe) and Albert Einstein’sGeneral Theory of Relativity of 1915-1916, which conceives of gravity as a curvaturein space and time. That convergence of ideas, say physicists, provides the theoreticalunderpinning of the Big Bang theory.
Astronomers have made their own confirmations of theBig Bang theory. Analyzing the light coming from other galaxies, they have notedshorter and longer wavelengths proportional to the distances of the galaxies fromEarth, indicating that they are moving away from the Earth and thus that space itselfis expanding. The existence of cosmic microwave radiation, a remnant of hot ionizedplasma of the early universe offers more proof of the Big Bang, as does the distributionof heavier and lighter elements through the universe.
Timeline of the Big Bang
The Big Bang theory hypothesizes that there were time-basedstages in the origins of the universe. The first stage—or, at least, the firststage that cosmologists can theorize about given current understanding of physics—isknown as the Planck era, after the German scientist of the late nineteenth and earlytwentieth centuries who studied the physics that explain it. The Planck era wasextremely brief—just 10-43 seconds (also known as one Planck time). Duringthis period, all four forces of the universe—gravity, electromagnetic energy, andthe weak and strong nuclear forces—were theoretically equal to one another, implyingthat there may have been just one unified force. The Planck era was extremelyunstable, with the four forces quickly evolving into their current forms, startingwith gravity and then the strong nuclear force (what binds protons and neutronstogether in the nucleus of an atom), the weak nuclear force (associated with radioactivedecay, it is some 100 times weaker than the strong force), and finally electromagneticenergy. This process is known as symmetry breaking and led to a longer period inthe universe’s history--though, at one millionth of a second, still extremelybrief in ordinary time--known as the “inflation era.” Physicists, however, arenot certain of the energy force that led to this inflation. At one second in age,the universe now consisted of fundamental energy and sub-atomic particles such asquarks, electrons, photons, and other less familiar particles.
The next stage in the Big Bang—lasting for roughly100,000 years and beginning about three seconds after the Planck era—consisted ofthe process of nucleosynthesis, as protons and neutrons came into being and beganto the form the nuclei of various elements, predominantly hydrogen and helium,the two lightest elements in the periodic table and the two most common elementsin the universe. Yet matter as we know it still did not exist and for thosehundred thousand or so years, the universe essentially consisted of radiation inthe form of light, radio waves, and X-rays. This period, known as the “radiationera,” came to a gradual end as free floating atomic nuclei bonded with free-floatingelectrons to produce the matter with which the universe would subsequently consist.While time was critical to the process so was temperature and density, with thevarious changes corresponding to a gradual cooling of the universe and the gradualdispersing of matter.
It took some 200 million years for gravity to begincoalescing these free-floating atoms into the primordial gas out of which the firststars and galaxies would emerge. Over billions of years, such early stars and galaxiesphased through their lifecycle, using up their nuclear fuel and collapsing in onthemselves, spewing out vast new clouds of matter and energy that would eventuallyform new generations of stars and galaxies. The sun around which the earth andthe solar system rotate is one of these later generation stars, formed roughlyfive billion years ago.Fateof the Universe
The Big Bang theory concerns not just the origins ofthe universe but its ultimate fate. The critical question, of course, is whetherthe universe will continue expanding forever or eventually fall back into itself,creating, perhaps, the conditions for the next Big Bang. Gravity is the criticalfactor here, with three outcomes possible. The first, and most widely acceptedby physicists, is that there is not the critical density, known as omega and estimatedat roughly six hydrogen atoms per cubic meter, necessary to pull the universe backin on itself. In this model, referred to as the “open” model, the universe willcontinue to expand and cool indefinitely. If however, the density of he universeis greater than omega then the universe will eventually, after billions of years,collapse in what physicists call the “big crunch.” A third and highly unlikelypossibility is that omega equals precisely one; in this model, the universe graduallyslows and cools to a static state.
While it would seem at first glance that the fate ofthe universe—that is, whether matter exceeded omega or not--could be determinedby the admittedly complex but not impossible task of calculating the amount ofmatter and dividing it by the dimensions of the universe, in fact, there is a complicatingfactor. The galaxies and nebulae, or primordial dust clouds out of which stars andgalaxies, do not pull on themselves or on each another as they should. That isto say, they behave as if there was more mass and, hence, gravitational pull thancan be observed. For example, the Andromeda galaxy, the nearest neighbor to ourown Milky Way galaxy, is rushing toward us at 200,000 miles per hour, a speedthat cannot be explained by the gravitational force of the matter in the two galaxies.In fact, the two galaxies are coming together at a pace requiring some 10 timesthat amount of matter. Physicists offer the possibility that there is dark matterin the universe, that is, an unknown type of matter that does not emit or reflectenough electromagnetic energy to be observable by current means. Such dark matter,according to this hypothesis, exists in haloes around galaxies and may be whatcomposes black holes and massive clouds of neutrinos, particles formed from radioactivedecay with little mass and no electric charge. Such dark matter would imply auniverse that eventually collapses in on itself, except for an additional complicatingfactor.
Scientists hypothesize that there is also a dark energyin the universe counteracting both matter and dark matter, a kind of anti-gravitationalforce that is also undetectable with existing technology. While dark matter isbelieved to constitute 22 percent of the universe, dark energy is believe to compose74 percent. These numbers, along with the difficulties of detecting dark matterand energy make it impossible for physicists as of the early twenty-first centuryto come to a definitive conclusion about the ultimate fate of the universe.Pre-TwentiethCentury Ideas of Universe’s Origins
The origins of creation have, of course, preoccupiedhumanity since at least the beginning of civilization itself. Virtually everyculture around the world has created myths to explain how the universe came intobeing, even if they did not necessarily comprehend the universe’s magnitude andcomplexity. These cosmologies, or explanations for the existence of creation, generallyshare four basic ideas. First, there is an intelligence or creator behind creation.Second, the universe came into being at a specific point in time and that what existedbefore the universe came into being is irrelevant as there was no existence ortime before it. A major exception to this model of a universe created at a singlemoment in time comes from Hindu cosmology which states that the universe existsin cycles, of roughly 4.5 billion years, or one day in the life of the Brahma,the creator, endlessly being born, dying, and being reborn. The third componentof most ancient cosmologies was that the Earth stood at the center of creation.
And the final element was that, once the universe wascreated, it remained essentially static--nothing added, nothing taken away, allmatter and energy in perpetual balance. That, too, was the model advanced by Englishscientist Isaac Newton in the late seventeenth and early eighteenth centuries,whose understanding of the laws of the universe dominated physics for more than200 years. But even in Newton’s own time, the idea of a perpetually balanced creationwas questioned by some thinkers, who pointed out that the universe would come apartif just one object should slip out of balance. And while Newton’s laws attemptedto explain how the universe operated, they did not offer much insight into its origins.
Immanuel Kant, a German philosopher of the late eighteenthcentury, was the first major Western thinker to tackle the question that the BigBang theory would eventually answer—had the universe always existed or did it comeinto existence at a specific point in time? Kant concluded that since both argumentswere equally valid on the face of things and that it was impossible to determinewhich was fundamentally true, the question of the universe’s origins, or lackthereof, was beyond human comprehension. Even as nineteenth century astronomersbegan to push back the envelope of what was known about the universe’s scale,they did not have the means or, given their religious faith, the inclination tograpple with Kant’s question.
Early Hypotheses
Early twentieth century physicists and astronomers, ofcourse, would prove Kant wrong. In 1912, an American astronomer named Vesto Sliphernoted a Doppler shift in the wavelengths of light coming from spiral nebulae, anantiquated term for galaxies, dating from before the existence of other galaxieswas confirmed. (It was American astronomer Edwin Hubble who first concluded inthe mid-1920s that the nebulae were, in fact, galaxies similar to our own MilkyWay.) The Doppler shift, named after Christian Doppler, the early nineteenth centuryAustrian mathematician who discovered it, says that waves alter in relation tothe movement of the observer or the object causing the wave. While Slipher notedthat almost all such spiral nebulae were moving away from the Earth, he failedto reach the conclusion that this meant the universe was expanding.
Around the same time, Slipher was making his observations,Friedmann, the Soviet physicist, explained how Einstein’s General Relativity Theorymight prove that the universe was expanding. Einstein’s theory updated and revisedNewton’s gravitational laws, for conditions where enormous mass and energy existed.Newton concluded that gravity was a force between two masses; Einstein argued,correctly as it was proved by later experiments, that gravity was the warping ofspace and time caused by mass. While Newton’s model of gravity was not consistentwith the Big Bang theory—since there was no mass in the primordial state of heatand density at the beginning of time—Einstein’s allowed for the possibility ofgravity itself coming into being, though, ironically, Einstein himself held to astatic view of the universe when he came up with his General Relativity Theory.
Roughly a decade after Friedmann developed his modelsout of Einstein’s General Relativity Theory—models that, while published, generallygot overlooked by other physicists--a Belgian physicist and astronomer GeorgesLemaître, independently coming up with the same theories as Friedmann, usedthem to reach the conclusion that had eluded Slipher—that receding nebulae meantthe universe was expanding. In 1931, Lemaître also hypothesized that theuniverse must have begun with a single atom, an idea that came to be called the“cosmic egg” theory. American astronomer Edwin Hubble, the first to realize thatnebulae were in fact other galaxies, also confirmed that the galaxies all seemedto be moving away from us simultaneously. Extrapolating backward, Hubble believedthat they all had emerged from the same high-density place, exploding outward ina kind of initial fireball. Hubble made his findings by noting shifts in the lightspectrum of distant galaxies that fit in with the Doppler effect.
Despite such findings, a competing theory emerged inthe years after World War II,. The “steady state” model, advocated by British astronomerFrederick Hoyle, held that new matter was created as the universe expanded. A confirmedatheist, Hoyle rejected the “cosmic egg” theory as it seemed to imply the existenceof a creator. Ironically, it was Hoyle who, in the 1950s, coined the term “BigBang,” using it in a radio interview to ridicule Lemaître’sideas. To reconcile his constant universe idea and the observed fact that galaxieswere moving away from each other, Hoyle hypothesized that new galaxies came intobeing as older ones grew apart. While later discounted, Hoyle’s work was usefulin explaining how matter and energy came into existence, a key component of theBig Bang theory.Confirmationof the Big Bang Theory
For two decades the two theories vied with each other,though Lemaître’s steadily gained more advocates. The critical confirmationof the Big Bang theory came in 1964. That year, Arno Penzias and Robert Wilson,two scientists working for Bell Laboratories, noticed that background microwaveradiation, a residual form of energy from the Big Bang, permeated the universe,confirming an idea first propounded by Soviet physicist George Gamow and Americanphysicist Ralph Alpher in the late 1940s.
With the development of ever more powerful computersto crunch the numbers in the 1980s, and the deployment of the Hubble Space telescopein the 1990s, which allowed for observations above the distortions of the Earth’satmosphere and radio waves, astronomers were able to make ever more detailed picturesof the universe and ever more precise timelines for the Big Bang. Key to this wasa worldwide study in the 1980s and 1990s of supernovas, immense outpourings ofradiation caused by the collapse of massive stars, which pointed to yet anotheranomaly about the universe. Rather than expanding at a constant rate, it seemedto be accelerating. This led to the conclusion that there must be a dark energyin the universe working to counteract gravity. One recent hypothesis states thatspace actually consists of negative pressure, which grows as the universe expandsthereby causing that expansion to accelerate since there is not enough matter—evenwith dark matter factored into the equation--to put a brake on the expansion. Accordingto British scientist Robert Caldwell, this accelerating expansion may lead towhat he calls the “big rip,” in which galaxies, stars, and even atoms are eventuallytorn apart by the force of dark energy, leading to the destruction of matter inthe final seconds of time at the end of the universe. Much of this work on darkmatter and energy remains hypothetical, of course, as it has been impossible todetect either of these two phenomena.
As the twenty-first century dawns, scientists—likethe ancients long before them--are still grappling with the very moment of creation,before the radiation, inflation, and Planck eras. Many believe that unveilingthat moment is connected to the development of a Grand Unified Theory, a singleexplanation that fits all of the known laws of the universe—including Einstein’sGeneral Relativity Theory and quantum mechanics, the study of energy and matterat the sub-atomic level—into a single equation. As British physicist Stephen Hawkingnotes, «At the Big Bang, the universe and time itselfcame into existence, so that this is the first cause. If we could understand theBig Bang, we would know why the universe is the way it is. It used to be thoughtthat it was impossible to apply the laws of science to the beginning of the universe,and indeed that it was sacrilegious to try. But recent developments in unifyingthe two pillars of twentieth-century science, Einstein's General Theory of Relativityand the Quantum Theory, have encouraged us to believe that it may be possible tofind laws that hold even at the creation of the universe.»
References
1. Farrell, John. The Day without Yesterday:Lemaître, Einstein, and the Birth of Modern Cosmology. New York: Thunder’sMouth Press, 2005.
2. Fox, Karen C. The Big Bank Theory: What ItIs, Where It Came from, and Why It Works. New York: Wiley, 2002.
3. Hawking, Stephen. A Brief History of Time:From the Big Bang to Black Holes. New York: Bantam, 1988.
4. Levin, Frank. Calibrating the Cosmos: HowCosmology Explains Our Big Bang Universe. New York: Springer, 2007.
5. Singh, Simon. Big Bang: The Origin of theUniverse. New York: Fourth Estate, 2004.