01_-_Origin_of_the_Universe_-The_Big_Bang_and_afterwards

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Origin of the Universe:

Origin of the Universe The universe is commonly defined as the totality of everything that exists, including all matte r and energy , the planets , stars , galaxies , and the contents of intergalactic space .

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Definitions and usage vary and similar terms include the cosmos , the world and nature . Scientific observation of earlier stages in the development of the universe, which can be seen at great distances, suggests that the universe has been governed by the same physical laws and constants throughout most of its extent and history. There are various multiverse theories, in which physicists have suggested that our universe is one among many universes that likewise exist.

Matter:

Matter Matter is a general term for the substance of which all physical objects consist. Typically , matter includes atoms and other particles which have mass . A common way of defining matter is as anything that has mass and occupies volume . Matter is commonly said to exist in four states (or phases ): solid , liquid , gas and plasma . However , advances in experimental techniques have realized other phases

Energy :

Energy In physics , energy ( Ancient Greek : ἐνέργει α energeia "activity, operation") is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems .

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The total energy contained in an object is identified with its mass , and energy (like mass), cannot be created or destroyed. When matter (ordinary material particles) is changed into energy (such as energy of motion, or into radiation), the mass of the system does not change through the transformation process.

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However, there may be mechanistic limits as to how much of the matter in an object may be changed into other types of energy and thus into work , on other systems. Energy , like mass, is a scalar physical quantity. In the International System of Units (SI), energy is measured in joules , but in many fields other units, such as kilowatt-hours and kilocalories , are customary. All of these units translate to units of work, which is always defined in terms of forces and the distances that the forces act through .

Planet :

Planet The term planet is ancient, with ties to history , science , mythology , and religion . The planets were originally seen by many early cultures as divine, or as emissaries of the gods . As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects.

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A planet (from Greek πλα νήτης α στήρ planētēs astēr "wandering star") is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity , is not massive enough to cause thermonuclear fusion , and has cleared its neighbouring region of planetesimals .

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Planets are generally divided into two main types: large, low-density gas giants , and smaller, rocky terrestrials . Under IAU definitions, there are eight planets in the Solar System. In order of increasing distance from the Sun , they are the four terrestrials, Mercury , Venus , Earth , and Mars , then the four gas giants, Jupiter , Saturn , Uranus , and Neptune .

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Six of the planets are orbited by one or more natural satellites . Additionally, the Solar System also contains at least five dwarf planets and hundreds of thousands of small Solar System bodies.

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Planetary-sized objects to scale: Top row: Uranus and Neptune ; second row: Earth , white dwarf star Sirius B , Venus ; bottom row (reproduced and enlarged in lower image) – above: Mars and Mercury ; below: the Moon , dwarf planets Pluto and Haumea

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Artistic comparison of Eris , Pluto , Makemake , Haumea , Sedna , Orcus , 2007 OR 10 , Quaoar , and Earth (scales are outdated)

Star :

Star A star is a massive, luminous sphere of plasma held together by gravity . At the end of its lifetime, a star can also contain a proportion of degenerate matter . The nearest star to Earth is the Sun , which is the source of most of the energy on Earth.

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Other stars are visible from Earth during the night, when they are not obscured by atmospheric phenomena, appearing as a multitude of fixed luminous points because of their immense distance. Historically, the most prominent stars on the celestial sphere were grouped together into constellations and asterisms , and the brightest stars gained proper names.

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Extensive catalogues of stars have been assembled by astronomers, which provide standardized star designations .

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A star-forming region in the Large Magellanic Cloud . NASA / ESA image

People have seen patterns in the stars since ancient times. This 1690 depiction of the constellation of Leo, the lion, is by Johannes Hevelius.:

People have seen patterns in the stars since ancient times. This 1690 depiction of the constellation of Leo, the lion, is by Johannes Hevelius .

Galaxy :

Galaxy A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants , an interstellar medium of gas and dust , and an important but poorly understood component tentatively dubbed dark matter .

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The word galaxy is derived from the Greek galaxias ( γαλαξίας ), literally "milky", a reference to the Milky Way galaxy. Examples of galaxies range from dwarfs with as few as ten million (10 7 ) stars to giants with a hundred trillion (10 14 ) stars, each orbiting their galaxy's own center of mass .

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Galaxies contain varying amounts of star systems , star clusters and types of interstellar clouds . In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays . Dark matter appears to account for around 90% of the mass of most galaxies.

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Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object .

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NGC 4414 , a typical spiral galaxy in the constellation Coma Berenices , is about 55,000 light-years in diameter and approximately 60 million light-years away from Earth.

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There are probably more than 170 billion (1.7 × 10 11 ) galaxies in the observable universe . Most are 1,000 to 100,000 parsecs in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs ). The parsec (symbol: pc ) is a unit of length used in astronomy . It is about 3.26 light-years , or just under 31 trillion (3.1×10 13 ) kilometres (about 19 trillion miles ).

Intergalactic space :

Intergalactic space Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations known as groups and clusters , which, in turn usually form larger superclusters . At the largest scale , these associations are generally arranged into sheets and filaments , which are surrounded by immense voids .

Milky Way:

Milky Way The realization that we live in a galaxy, and that there were, in fact, many other galaxies, parallels discoveries that were made about the Milky Way and other nebulae in the night sky. Milky Way was made up of many stars that almost touch one another and appear to be a continuous image

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The first attempt to describe the shape of the Milky Way and the position of the Sun in it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the solar system close to the center

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The shape of the Milky Way as deduced from star counts by William Herschel in 1785; the solar system was assumed to be near the center.

Big Bang :

Big Bang The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in its present continuously expanding state.

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According to the most recent measurements and observations, this original state existed approximately 13.7 billion years ago, which is considered the age of the Universe and the time the Big Bang occurred. After its initial expansion from a singularity, the Universe cooled sufficiently to allow energy to be converted into various subatomic particles ..

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It would take thousands of years for some of these particles (protons, neutrons, and electrons) to combine and form atoms, the building blocks of matter. The first element produced was hydrogen, along with traces of helium and lithium. Eventually , clouds of hydrogen would coalesce through gravity to form stars, and the heavier elements would be synthesized either within stars or during supernovae

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The Big Bang is a well-tested scientific theory which is widely accepted within the scientific community because it is the most accurate and comprehensive explanation for the full range of phenomena astronomers observe. Since its conception, abundant evidence has arisen to further validate the model. Georges Lemaître first proposed what would become the Big Bang theory in what he called his "hypothesis of the primeval atom ."

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Over time, scientists would build on his initial ideas to form the modern synthesis. The framework for the Big Bang model relies on Albert Einstein's general relativity and on simplifying assumptions (such as homogeneity and isotropy of space). The governing equations had been formulated by Alexander Friedmann .

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In 1929, Edwin Hubble discovered that the distances to far away galaxies were generallyproportional to their redshifts—an idea originally suggested by Lemaître in 1927. Hubble's observation was taken to indicate that all very distant galaxies and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity.

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If the distance between galaxy clusters is increasing today, everything must have been closer together in the past. This idea has been considered in detail back in time to extreme densities and temperatures, and large particle accelerators have been built to experiment on and test such conditions, resulting in significant confirmation of this model. On the other hand, these accelerators have limited capabilities to probe into such high energy regimes.

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There is little evidence regarding the absolute earliest instant of the expansion. Thus , the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the universe going forward from that point on.

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The observed abundances of the light elements throughout the cosmos closely match the calculated predictions for the formation of these elements from nuclear processes in the rapidly expanding and cooling first minutes of the universe, as logically and quantitatively detailed according to Big Bang nucleosynthesis .

Outer space:

Outer space Outer space is the void that exists between celestial bodies , including the Earth . It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium , as well as electromagnetic radiation , magnetic fields , and neutrinos .

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Theory suggests that it also contains dark matter and dark energy . In the space between galaxies, matter density can be as low as a few atoms of hydrogen per cubic meter.

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The baseline temperature, as set by background radiation left over from the Big Bang , is only 3 0 Kelvin ; in contrast, temperatures in the coronae of stars can reach over a million Kelvin .

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Plasma with an extremely low density and high temperature, such as warm-hot intergalactic medium and intracluster medium , accounts for most of the baryonic (ordinary) matter in outer space; local concentrations have evolved into stars and galaxies. Intergalactic outer space takes up most of the volume of the universe , but even galaxies and star systems consist almost entirely of empty space. s.

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As of yet, space travel has been limited to the vicinity of the Solar System ; the remainder of outer space remains inaccessible to humans other than by passive observation with telescope

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There is no firm boundary where space begins. However the Kármán line , at an altitude of 100 kilometres above sea level , is conventionally used as the start of outer space for the purpose of space treaties and aerospace records keeping. The framework for international space law was established by the Outer Space Treaty , which was passed by the United Nations in 1963. This treaty precludes any claims of national sovereignty and permits all states to explore outer space freely

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In 1979, the Moon Treaty made the surfaces of objects such as planets, as well as the orbital space around these bodies, the jurisdiction of the international community. Additional resolutions regarding outer space have been drafted by the United Nations, but these have not precluded the deployment of weapons into outer space.

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The boundaries between the Earth's surface and outer space, at the Kármán line , 100 km (62 mi) and exosphere at 690 km (430 mi). Not to scale

Hazards:

Hazards Because of the hazards of a vacuum, astronauts must wear a pressurized spacesuit while outside their spacecraft

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Contrary to popular belief , a person suddenly exposed to a vacuum would not explode, freeze to death or die from boiling blood. However, sudden exposure to very low pressure , such as during a rapid decompression, could cause pulmonary barotrauma —a rupture of the lungs, due to the large pressure differential between inside and outside of the chest.

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Even if the victim's airway is fully open, the flow of air through the windpipe may be too slow to prevent the rupture. Rapid decompression can rupture eardrums and sinuses, bruising and blood seep can occur in soft tissues, and shock can cause an increase in oxygen consumption that leads to hypoxia .

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As a consequence of rapid decompression, any oxygen dissolved in the blood would empty into the lungs to try to equalize the partial pressure gradient. Once the deoxygenated blood arrived at the brain, humans and animals will lose consciousness after a few seconds and die of hypoxia within minutes. aged.

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Blood and other body fluids boil when the pressure drops below 6.3 kPa , and this condition is called ebullism . The steam may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. Ebullism is slowed by the pressure containment of blood vessels, so some blood remains liquid.

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Swelling and ebullism can be reduced by containment in a flight suit . Shuttle astronauts wear a fitted elastic garment called the Crew Altitude Protection Suit (CAPS) which prevents ebullism at pressures as low as 2 kPa . Space suits are necessary to prevent ebullism above 8 kilometres (5.0 mi). Most space suits use around 30–39 kPa of pure oxygen, about the same as on the Earth's surface.

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This pressure is high enough to prevent ebullism , but evaporation of blood could still cause decompression sickness and gas embolisms if not managed. Because humans are optimized for life in Earth gravity, exposure to weightlessness has been shown to have deleterious effects on the health.

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Initially, more than 50% of astronauts experience space motion sickness . This can cause nausea and vomiting , vertigo , headaches , lethargy , and overall malaise. The duration of space sickness varies, but it typically lasts for 1–3 days, after which the body adjusts to the new environment.

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Longer term exposure to weightlessness results in muscle atrophy and deterioration of the skeleton , or spaceflight osteopenia . These effects can be minimized through a regimen of exercise. Other effects include fluid redistribution, slowing of the cardiovascular system , decreased production of red blood cells , balance disorders, and a weakening of the immune system . Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, and puffiness of the face.

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For long duration space travel, radiation can pose an acute health hazard. Exposure to radiation sources such as high-energy, ionizing cosmic rays can result in fatigue, nausea, vomiting, as well as damage to the immune system and changes to the white blood cell count. Over longer durations, symptoms include an increase in the risk of cancer , plus damage to the eyes, nervous system, lungs and the gastrointestinal tract ..

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On a round-trip Mars mission lasting three years, nearly the entire body will be traversed by high energy nuclei, each of which can cause ionization damage to cells. Fortunately , most such particles are significantly attenuated by the shielding provided by the aluminum walls of a spacecraft, and can be further diminished by water containers and other barriers.

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However, the impact of the cosmic rays upon the shielding produces additional radiation that can affect the crew. Further research will be needed to assess the radiation hazards and determine suitable countermeasures

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