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, ...
