The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. It was first proposed as a physical theory in 1931 by Roman Catholic priest and physicist Georges Lemaître when he suggested the universe emerged from a "primeval atom". Various cosmological models of the Big Bang explain the evolution of the observable universe from the earliest known periods through its subsequent large-scale form. These models offer a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure. The uniformity of the universe, known as the flatness problem, is explained through cosmic inflation: a sudden and very rapid expansion of space during the earliest moments.
The cosmic microwave background is microwave radiation that fills all space in the observable universe. It is sometimes called relic radiation. With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s.
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation. The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift, or negative redshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. The main causes of electromagnetic redshift in astronomy and cosmology are the relative motions of radiation sources, which give rise to the relativistic Doppler effect, and gravitational potentials, which gravitationally redshift escaping radiation. All sufficiently distant light sources show cosmological redshift corresponding to recession speeds proportional to their distances from Earth, a fact known as Hubble's law that implies the universe is expanding.
Observations show that the expansion of the universe is accelerating, such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time. The accelerated expansion of the universe was discovered in 1998 by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team, which used distant type Ia supernovae to measure the acceleration. The idea was that as type Ia supernovae have almost the same intrinsic brightness, and since objects that are farther away appear dimmer, the observed brightness of these supernovae can be used to measure the distance to them. The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred; the Hubble law established that the farther away that an object is, the faster it is receding. The unexpected result was that objects in the universe are moving away from one another at an accelerating rate. Cosmologists at the time expected that recession velocity would always be decelerating, due to the gravitational attraction of the matter in the universe. Three members of these two groups have subsequently been awarded Nobel Prizes for their discovery. Confirmatory evidence has been found in baryon acoustic oscillations, and in analyses of the clustering of galaxies.
Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away from Earth. The velocity of the galaxies has been determined by their redshift, a shift of the light they emit toward the red end of the visible light spectrum. The discovery of Hubble's law is attributed to Edwin Hubble's work published in 1929.
This timeline of cosmological theories and discoveries is a chronological record of the development of humanity's understanding of the cosmos over the last two-plus millennia. Modern cosmological ideas follow the development of the scientific discipline of physical cosmology.
The observable universe is a ball-shaped region of the universe consisting of all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. Initially, it was estimated that there may be 2 trillion galaxies in the observable universe. That number was reduced in 2021 to several hundred billion based on data from New Horizons. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical region centered on the observer. Every location in the universe has its own observable universe, which may or may not overlap with the one centered on Earth.
Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors.
The horizon problem is a cosmological fine-tuning problem within the Big Bang model of the universe. It arises due to the difficulty in explaining the observed homogeneity of causally disconnected regions of space in the absence of a mechanism that sets the same initial conditions everywhere. It was first pointed out by Wolfgang Rindler in 1956.
In physical cosmology, the age of the universe is the time elapsed since the Big Bang. Astronomers have derived two different measurements of the age of the universe: a measurement based on direct observations of an early state of the universe, which indicate an age of 13.787±0.020 billion years as interpreted with the Lambda-CDM concordance model as of 2021; and a measurement based on the observations of the local, modern universe, which suggest a younger age. The uncertainty of the first kind of measurement has been narrowed down to 20 million years, based on a number of studies that all show similar figures for the age. These studies include researches of the microwave background radiation by the Planck spacecraft, the Wilkinson Microwave Anisotropy Probe and other space probes. Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time. The range of the estimate is also within the range of the estimate for the oldest observed star in the universe.
The Institute for Creation Research (ICR) is a creationist apologetics institute in Dallas, Texas, that specializes in media promotion of pseudoscientific creation science and interpretation of the Genesis creation narrative as a historical event. The ICR adopts the Bible as an inerrant and literal documentary of scientific and historical fact as well as religious and moral truths, and espouses a Young Earth creationist worldview. It rejects evolutionary biology, which it views as a corrupting moral and social influence and threat to religious belief. The ICR was formed by Henry M. Morris in 1972 following an organizational split with the Creation Science Research Center (CSRC).
The history of the Big Bang theory began with the Big Bang's development from observations and theoretical considerations. Much of the theoretical work in cosmology now involves extensions and refinements to the basic Big Bang model. The theory itself was originally formalised by Father Georges Lemaître in 1927. Hubble's Law of the expansion of the universe provided foundational support for the theory.
The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion, so it does not mean that the universe expands "into" anything or that space exists "outside" it. To any observer in the universe, it appears that all but the nearest galaxies recede at speeds that are proportional to their distance from the observer, on average. While objects cannot move faster than light, this limitation applies only with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.
Distance measures are used in physical cosmology to give a natural notion of the distance between two objects or events in the universe. They are often used to tie some observable quantity to another quantity that is not directly observable, but is more convenient for calculations. The distance measures discussed here all reduce to the common notion of Euclidean distance at low redshift.
In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. Assuming that the lambda-CDM model of cosmology is correct, dark energy is the dominant component of the universe, contributing 68% of the total energy in the present-day observable universe while dark matter and ordinary (baryonic) matter contribute 26% and 5%, respectively, and other components such as neutrinos and photons are nearly negligible. Dark energy's density is very low: 7×10−30 g/cm3, much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the universe's mass–energy content because it is uniform across space.
The International Conference on Creationism (ICC) is a conference in support of young earth creationism, sponsored by the Creation Science Fellowship (CSF). The first conference occurred in 1986 at Duquesne University in Pittsburgh. Subsequent conferences have been held in 1990, 1994, 1998, 2003, 2008, 2013 and 2018.
John G. Hartnett, is an Australian young Earth creationist and cosmologist. He has been active with Creation Ministries International and is known for his opposition to the Big Bang theory and criticism of the dark matter and dark energy hypotheses.
Kevin R. Henke is an American geochemist and former instructor at the University of Kentucky's department of Geology. He currently works as a senior research scientist at the University of Kentucky's Center for Applied Energy Research. He is well known for his criticism of young earth creationism and the scientific arguments they make for a young earth. In particular, he has been critical of the RATE project's results, which claim to show that zircons contain too much helium to be billions of years old, and has argued that Russell Humphreys, a young-earth creationist who was involved in the project, has made errors in his research. These flaws include that, according to Henke, "The vast majority of Humphreys et al.'s critical a, b, and Q/Q0 values that are used in these "dating" equations are either missing, poorly defined, improperly measured or inaccurate." Henke has also accused Humphreys of misidentifying his specimens, fudging his data, and not considering the possibility of helium contamination in this research. He has also criticized John Woodmorappe for arguing that radiometric dating is unreliable. On one occasion, Henke called Kent Hovind on the phone regarding Hovind's $250,000 challenge to "prove" evolution. Hovind told Henke that in order to win the money he would have to recreate the Big Bang in a laboratory. Henke responded by proposing several alternative "proofs" that pertained to geology, but Hovind refused, saying that the project must be chosen by him and it must not pertain to the area in which Henke has scientific expertise. Hovind therefore required Henke to prove that dogs and bananas had a common ancestor, and lowered the award to only $2,000 should he succeed. Henke accepted the challenge, and later drafted a contract, which was then posted on Talk.origins. However, one of Henke's requirements was that the judges be unbiased, and Hovind rejected the challenge for this reason, insisting that he should be the only one who can choose the judges.
Time dilation creationism is a form of young Earth creationism that attempts to harmonize the literal interpretation of the Genesis creation narrative with the existence of distant galaxies. The theory proposes that the universe experienced a rapid passage of time, while the Earth itself experienced six literal days, because of time dilation. It is asserted that the time dilation mainly happened on the fourth day of creation.
