Big Bang

Big Bang

The big bang is the cosmic event that is theorized to have marked the origin of the universe. At that instant all matter and energy in the entire physical universe, and the four dimensions of time and space, were created from a state of enormous density, temperature, and pressure. Big bang theory is the widely held set of scientific explanations relating to the primordial big bang. Cosmology is the study of the creation, evolution, present structure, and ultimate fate of the universe; the big bang theory is, at present, the central, unifying model that guides cosmology.

Three subdivisions of cosmology (quantum, particle, and standard cosmology) deal with the big bang according to the length of time after the big bang event.

Quantum cosmology ranges from about 10-43 seconds to about 10-11 seconds after the big bang. Because no agreed-upon physical theory exists among scholars for this time period (called the Planck epoch), the process and events contained therein remain highly speculative. In addition, the uncertainty principle of quantum mechanics prevents speculation on times shorter than 10-43 seconds after the big bang.

Particle cosmology deals with the period from about 10 -11 seconds to one hundredth of a second after the big bang. This area of cosmology is less speculative; involving some estimated equations and unverified assumptions.

Standard cosmology studies the period from about one hundredth of a second after the big bang to the present day. This subdivision has withstood many tests and provides a reliable basis for the bulk of information related to cosmological development and evolution.

Big bang theory is essentially based on two major theoretical assumptions. The first assumption, derived from German-American physicist Albert Einstein's general theory of relativity, correctly describes the gravitational interaction of all matter and radiation. The second assumption, called the cosmological principle, states that at sufficiently large scales, the average properties of different regions of the universe are the same. As a result, even though average densities of matter and radiation vary wildly within small regions, such as the Milky Way galaxy, over vast volumes of space the average densities and types of matter are the same from one region to another. These two premises allow physicists to make determinations regarding the history of the universe (from the Planck epoch) using field equations that were developed by Russian physicist Alexander (Aleksandr Aleksandrovich) Friedmann (also spelled as Fridman, 1888-1925). Field equations are solutions mathematically derived from Einstein's general theory of relativity. In addition, in 1929 American astronomer Edwin Hubble provided supporting evidence for the theory with his discovery that the light of galaxies is universally red-shifted. His studies showed that galaxies are generally moving away from each other and that the universe is uniformly expanding. During the 1940s Russian-born American cosmologist and nuclear physicist George Gamow developed the modern version of the big bang model that fit with Friedmann's solutions.

Super-dense theory, another name for the big bang theory, proposes that approximately 10-20 billion years ago the universe was composed of a very high concentration of matter and radiation mixed in an extremely dense conglomerate at very high temperatures. This initial singularity, or "primordial atom", then expanded rapidly in its first 10-32 second, to about 1050 times its original size. The universe then slowed its expansion and cooled, allowing the single force that existed at the beginning of the universe to separate into the forces of gravity, electromagnetism, the strong nuclear force, and the weak nuclear force. Temperatures quickly dropped below 1012 K as the production of protons and heavy particles, and then electrons and light particles, rapidly decreased. At about one second into the life of the universe, the majority of existing particles and antiparticles had been destroyed to produce photons of electromagnetic radiation. The domination of photons during this time was called the radiation era. During this expansion radiation quickly lost energy and energy density, causing matter to overtake radiation in total energy density after an elapse of approximately 10,000 years and at a temperature of about 10,000K. This change of domination from energy to matter began the matter era. The matter was composed primarily of an ionized gas of electrons, protons, and helium nuclei. At a temperature of about 3,000K electrons combined with protons to form neutral hydrogen. At around 100,000 years after the big bang this formation of neutral hydrogen brought about a cooling of radiation that has continued to the present at the cosmic microwave background radiation observed at 2.7K. The expansion of the universe also caused red-shifting of traces of early radiation. With matter no longer coupled with radiation, existing matter was able to form planets, stars, galaxies, and other large-scale structures observed today. The heavier elements were created later within the interiors of stars and spread widely in supernova explosions.

A widely accepted version of the big bang theory, one that solves a number of problems within cosmology, involves an inflationary model that predicts the universe can be either open or closed. The theory was advanced in the 1980s by Alan Harvey Guth and was elaborated upon by Paul Steinhardt, Andrei Linde, and Andreas Albrecht. If the universe is open (with the amount of matter less than a critical density), it will expand forever ultimately leading to both entropic death and a universe filled with subatomic particles too far apart to form larger atomic structures. If the universe is closed (with the amount of matter more than a critical density), the expansion of the universe will eventually stop and then reverse to begin a contraction leading to an eventual collapse termed the big crunch. The inflationary model currently predicts that the universe is on the boundary between being open and closed, with scientists differing upon whether there is sufficient matter and mass in the universe to meet the requirements of critical mass.

The 1965 observation of the 2.7K microwave background radiation by Arno Penzias and Robert Wilson from Bell Laboratories was a critical confirmation big bang based cosmological models. In cosmological analysis, because the laws of physics break down as one regressively approaches the time of the big bang, there is no satisfactory explanation for the cause the big bang itself.