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Recombination (cosmology)
In cosmology, recombination refers to the epoch during which charged electrons and protons first became bound to form electrically neutral hydrogen atoms. Recombination occurred about 370,000 yearsRecombination time frames: * Edward L. Wright'Javascript Cosmology Calculator(last modified 23 July 2018). With a default H_0 = (based on ), the calculated age of the universe with a redshift of ''z'' = is in agreement with Olive and Peacock (about 370,000 years). * : "Going forward in time now, the temperature declined, and at ''T''∼3000 K, few of the photons in the radiation field, even in its high-energy tail, had the energy required to ionize a hydrogen atom. Most of the electrons and protons then recombined. Once this happened, at a time ''t''rec = 380,000 yr after the Big Bang, the major source of opacity disappeared, and the Universe became transparent to radiation of most frequencies." * : "The million dollar question is now, 'when did recombination happen? ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cosmology
Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount (lexicographer), Thomas Blount's ''Glossographia'', and in 1731 taken up in Latin by German philosophy, German philosopher Christian Wolff (philosopher), Christian Wolff, in ''Cosmologia Generalis''. Religious cosmology, Religious or mythological cosmology is a body of beliefs based on Mythology, mythological, Religion, religious, and Esotericism, esoteric literature and traditions of Cosmogony, creation myths and eschatology. In the science of astronomy it is concerned with the study of the chronology of the universe. Physical cosmology is the study of the observable universe's origin, its large-scale structures and dynamics, and the ultimate fate of the universe, including the laws of science that govern these areas. It is investigated by scientists, such as astronomers and physicists, as well as Philosophy, ph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quark Epoch
In physical cosmology, the Quark epoch was the period in the evolution of the early universe when the fundamental interactions of gravitation, electromagnetism, the strong interaction and the weak interaction had taken their present forms, but the temperature of the universe was still too high to allow quarks to bind together to form hadrons. The quark epoch began approximately 10−12 seconds after the Big Bang, when the preceding electroweak epoch ended as the electroweak interaction separated into the weak interaction and electromagnetism. During the quark epoch, the universe was filled with a dense, hot quark–gluon plasma, containing quarks, leptons and their antiparticles. Collisions between particles were too energetic to allow quarks to combine into mesons or baryons. The quark epoch ended when the universe was about 10−6 seconds old, when the average energy of particle interactions had fallen below the binding energy of hadrons. The following period, when quarks became ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ranges as microwaves; the above broad definition includes both UHF and EHF (millimeter wave) bands. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz (wavelengths between 0.3 m and 3 mm). In all cases, microwaves include the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum. Frequencies in the microwave range are often referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations. The prefix ' in ''microwave'' is not meant to suggest a wavelength in the micrometer range. Rather, it indicates that microwaves are "small" (having shorter wavelengths), compared to the radio waves used prior to microwave te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in frequency and energy, is known as a negative redshift, or blueshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. In astronomy and cosmology, the three main causes of electromagnetic redshift are # The radiation travels between objects which are moving apart (" relativistic" redshift, an example of the relativistic Doppler effect) #The radiation travels towards an object in a weaker gravitational potential, i.e. towards an object in less strongly curved (flatter) spacetime (gravitational redshift) #The radiation travels through expanding space (cosmological redshift). The observation that all sufficiently distant light sources show redshift corresponding to their distance from Earth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black-body Radiation
Black-body radiation is the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment, emitted by a black body (an idealized opaque, non-reflective body). It has a specific, continuous spectrum of wavelengths, inversely related to intensity, that depend only on the body's temperature, which is assumed, for the sake of calculations and theory, to be uniform and constant., Chapter 13. A perfectly insulated enclosure which is in thermal equilibrium internally contains black-body radiation, and will emit it through a hole made in its wall, provided the hole is small enough to have a negligible effect upon the equilibrium. The thermal radiation spontaneously emitted by many ordinary objects can be approximated as black-body radiation. Of particular importance, although planets and stars (including the Earth and Sun) are neither in thermal equilibrium with their surroundings nor perfect black bodies, black-body radiation is sti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around 1 millimeter (300 GHz) to the nominal red edge of the visible spectrum, around 700 nanometers (430 THz). Longer IR wavelengths (30 μm-100 μm) are sometimes included as part of the terahertz radiation range. Almost all black-body radiation from objects near room temperature is at infrared wavelengths. As a form of electromagnetic radiation, IR propagates energy and momentum, exerts radiation pressure, and has properties corresponding to both those of a wave and of a particle, the photon. It was long known that fires emit invisible heat; in 1681 the pioneering experimenter Edme Mariotte showed that glass, though transparent to sunlight, obstructed radiant heat. In 1800 the astronomer Sir William Herschel discovered ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cosmic Microwave Background Radiation
In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all space. It is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination when the first atoms were formed. With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark (see: Olbers' paradox). However, a sufficiently sensitive radio telescope shows a faint background brightness, or glow, almost uniform, that 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, and earned t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Free Stream
In astronomy, a free streaming particle, often a photon, is one that propagates through a medium without scattering. Use in defining surfaces Defining an exact surface for an object such as the Sun is made difficult by the diffuse nature of matter which constitutes the Sun at distances far from the stellar core. An often used definition for the surface of a star is based on the path that photons take. Inside a star, photons travel by random walk, constantly interacting with matter, and the surface of the star is defined as the point at which photons encounter little resistance from the matter in the stellar atmosphere, or in other words, when photons stream freely. The light which constitutes the cosmic microwave background comes from the surface of last scattering. This is, on average, the surface at which primordial photons last interacted with matter in the universe, or in other words, the point at which photons started free streaming. Similarly, the surface of the cosmic neutr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decoupling (cosmology)
In cosmology, decoupling refers to a period in the development of the universe when different types of particles fall out of thermal equilibrium with each other. This occurs as a result of the expansion of the universe, as their interaction rates decrease (and mean free paths increase) up to this critical point. The two verified instances of decoupling since the Big Bang which are most often discussed are photon decoupling and neutrino decoupling, as these led to the cosmic microwave background and cosmic neutrino background, respectively. Photon decoupling is closely related to recombination, which occurred about 378,000 years after the Big Bang (at a redshift of ''z'' = ), when the universe was a hot opaque ("foggy") plasma. During recombination, free electrons became bound to protons (hydrogen nuclei) to form neutral hydrogen atoms. Because direct recombinations to the ground state (lowest energy) of hydrogen are very inefficient, these hydrogen atoms generally for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lyman Series
In physics and chemistry, the Lyman series is a hydrogen spectral series of transitions and resulting ultraviolet emission lines of the hydrogen atom as an electron goes from ''n'' ≥ 2 to ''n'' = 1 (where ''n'' is the principal quantum number), the lowest energy level of the electron. The transitions are named sequentially by Greek letters: from ''n'' = 2 to ''n'' = 1 is called Lyman-alpha, 3 to 1 is Lyman-beta, 4 to 1 is Lyman-gamma, and so on. The series is named after its discoverer, Theodore Lyman. The greater the difference in the principal quantum numbers, the higher the energy of the electromagnetic emission. History The first line in the spectrum of the Lyman series was discovered in 1906 by Harvard physicist Theodore Lyman, who was studying the ultraviolet spectrum of electrically excited hydrogen gas. The rest of the lines of the spectrum (all in the ultraviolet) were discovered by Lyman from 1906-1914. The spectrum of radiation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ground State
The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state. In quantum field theory, the ground state is usually called the vacuum state or the vacuum. If more than one ground state exists, they are said to be degenerate. Many systems have degenerate ground states. Degeneracy occurs whenever there exists a unitary operator that acts non-trivially on a ground state and commutes with the Hamiltonian of the system. According to the third law of thermodynamics, a system at absolute zero temperature exists in its ground state; thus, its entropy is determined by the degeneracy of the ground state. Many systems, such as a perfect crystal lattice, have a unique ground state and therefore have zero entropy at absolute zero. It is also possible for the highest excited state to have absolute zero temper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metric Expansion Of Space
The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not expand "into" anything and does not require space to exist "outside" it. This expansion involves neither space nor objects in space "moving" in a traditional sense, but rather it is the metric (which governs the size and geometry of spacetime itself) that changes in scale. As the spatial part of the universe's spacetime metric increases in scale, objects become more distant from one another at ever-increasing speeds. To any observer in the universe, it appears that all of space is expanding, and that all but the nearest galaxies (which are bound by gravity) recede at speeds that are proportional to their distance from the observer. While objects within space cannot travel faster than light, this limitation does not apply to the effects of ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
