1.
Sneek
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Sneek is a city southwest of Leeuwarden and seat of the former municipality of Sneek in the province of Friesland. As for 2011 it is part of the municipality Súdwest Fryslân, the city has approximately 33,000 inhabitants. Sneek is situated in Southwest-Friesland, close to the Sneekermeer and is known for its canals, the Waterpoort. Sneek is one of the Friese elf steden, the city is very important for the southwest area of Friesland. Sneek was founded in the 10th century on a peninsula at the crossing site of a dike with an important waterway. This waterway was dug when the former Middelzee silted up, the dike can still be traced in the current street pattern and street names like Hemdijk, Oude Dijk and Oosterdijk. Sneek received several city rights in the 13th century, which became official in 1456, Sneek was now one of the eleven Frisian cities. This was also the beginning of a period of blooming trade for the city that would last until about 1550, in 1492 construction of a moat and wall around the city began. In those days Sneek was the walled city in Friesland. The Waterpoort and the Bolwerk remain today, since September 10,1970, Sneek and the Japanese city Kurobe have been sister cities. In 1970, Mayor L. Rasterhoff of Sneek visited the city of Kurobe and was named an Honorary citizen, Mayor H. Terade of Kurobe made a visit to Sneek in 1972. In 2000 delegations of both cities visited each other again, the Japanese showed the citizens of Sneek a Sneekplein which was built in Kurobe. Sneek has its own dialect that dates back to the Dutch language before 1600, snekers is part of the city Frisian dialects. The famous clothingstore C&A started in 1841 with a store in Sneek, the Candyfactory Leaf produces Peppermint under the name KING as well as chewing gum and various other sweets. The name KING has nothing to do with the English word KING, also Sneek has a Steel, Machinery and a Rope factory. Since 1964 theres a factory of Yoshida YKK from Kurobe, besides that, the Supermarket branch Poiesz, Clothing brand Gaastra and Frisian gin called beerenburg from Weduwe Joustra are products that have their roots in Sneek. Sneek is well known as the center of watersports with over 130 watersport companies and 13 Marinas and it also it has a historic inner city replete with houses of old upper-class families. Watergate Town hall Martinichurch, with a carillon of 50 bells Sint-Martinuschurch Tonnema Candy Factory the Wooden bridges across the Rijksweg 7
2.
Leiden
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Leiden is a city and municipality in the Dutch province of South Holland. Leiden is located on the Oude Rijn, at a distance of some 20 kilometres from The Hague to its south, the recreational area of the Kaag Lakes lies just to the northeast of Leiden. A university city since 1575, Leiden houses Leiden University, the oldest university of the Netherlands, Leiden is a city with a rich cultural heritage, not only in science, but also in the arts. One of the worlds most famous painters, Rembrandt, was born, other famous Leiden painters include Lucas van Leyden, Jan van Goyen and Jan van Steen. The city has one of Europes most prominent scientific centres for more than four centuries. Modern scientific medical research and teaching started in the early 18th century in Leiden with Boerhaave, many important scientific discoveries have been made here, giving rise to Leiden’s motto, ‘City of Discoveries’. It is twinned with Oxford, the location of the United Kingdoms oldest university, Leiden University and Leiden University of Applied Sciences together have around 35,000 students. Leiden is a university city, university buildings are scattered throughout the city. Leiden was formed on a hill at the confluence of the rivers Oude. In the oldest reference to this, from circa 860, the settlement was called Leithon, the name is said to be from Germanic *leitha- canal. Leiden has in the past erroneously been associated with the Roman outpost Lugdunum Batavorum and this particular castellum was thought to be located at the Burcht of Leiden, and the citys name was thought to be derived of the Latin name Lugdunum. However the castellum was in closer to the town of Katwijk. The landlord of Leiden, situated in a stronghold on the hill, was subject to the Bishop of Utrecht. This county got its name in 1101 from a domain near the stronghold, Leiden was sacked in 1047 by Emperor Henry III. Early 13th century, Ada, Countess of Holland took refuge here when she was fighting in a war against her uncle, William I. He besieged the stronghold and captured Ada, Leiden received city rights in 1266. In 1389, its population had grown to about 4,000 persons, burgrave Filips of Wassenaar and the other local noblemen of the Hook faction assumed that the duke would besiege Leiden first and send small units out to conquer the surrounding citadels. But John of Bavaria chose to attack the citadels first and he rolled the cannons with his army but one which was too heavy went by ship
3.
Netherlands
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The Netherlands, also informally known as Holland is the main constituent country of the Kingdom of the Netherlands. It is a densely populated country located in Western Europe with three territories in the Caribbean. The European part of the Netherlands borders Germany to the east, Belgium to the south, and the North Sea to the northwest, sharing borders with Belgium, the United Kingdom. The three largest cities in the Netherlands are Amsterdam, Rotterdam and The Hague, Amsterdam is the countrys capital, while The Hague holds the Dutch seat of parliament and government. The port of Rotterdam is the worlds largest port outside East-Asia, the name Holland is used informally to refer to the whole of the country of the Netherlands. Netherlands literally means lower countries, influenced by its low land and flat geography, most of the areas below sea level are artificial. Since the late 16th century, large areas have been reclaimed from the sea and lakes, with a population density of 412 people per km2 –507 if water is excluded – the Netherlands is classified as a very densely populated country. Only Bangladesh, South Korea, and Taiwan have both a population and higher population density. Nevertheless, the Netherlands is the worlds second-largest exporter of food and agricultural products and this is partly due to the fertility of the soil and the mild climate. In 2001, it became the worlds first country to legalise same-sex marriage, the Netherlands is a founding member of the EU, Eurozone, G-10, NATO, OECD and WTO, as well as being a part of the Schengen Area and the trilateral Benelux Union. The first four are situated in The Hague, as is the EUs criminal intelligence agency Europol and this has led to the city being dubbed the worlds legal capital. The country also ranks second highest in the worlds 2016 Press Freedom Index, the Netherlands has a market-based mixed economy, ranking 17th of 177 countries according to the Index of Economic Freedom. It had the thirteenth-highest per capita income in the world in 2013 according to the International Monetary Fund, in 2013, the United Nations World Happiness Report ranked the Netherlands as the seventh-happiest country in the world, reflecting its high quality of life. The Netherlands also ranks joint second highest in the Inequality-adjusted Human Development Index, the region called Low Countries and the country of the Netherlands have the same toponymy. Place names with Neder, Nieder, Nether and Nedre and Bas or Inferior are in use in all over Europe. They are sometimes used in a relation to a higher ground that consecutively is indicated as Upper, Boven, Oben. In the case of the Low Countries / the Netherlands the geographical location of the region has been more or less downstream. The geographical location of the region, however, changed over time tremendously
4.
University of Groningen
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The University of Groningen is a public research university in the city of Groningen in the Netherlands. The university was founded in 1614 and is one of the oldest universities in the Netherlands as well as one of its largest, since its inception more than 200,000 students have graduated. It is a member of the distinguished international Coimbra Group of European universities, in April 2013, according to the results of the International Student Barometer, the University of Groningen, for the third time in a row, has been voted the best university of the Netherlands. In 2014 the university celebrated its 400th anniversary, the University of Groningen has ten faculties, nine graduate schools,27 research centres and institutes, and more than 175 degree programmes. There were four faculties – Theology, Law, Medicine, the coat of arms of the university was confirmed by the States of the City and County of Groningen in 1615. It consists of the arms, charged with an open book inscribed with the abbreviated words VER/BVM/DNI LV/CER/NA. The shield is surmounted by a crown of five leaves. The first 75 years of its existence were very fruitful for the University with about 100 students enrolling every year, on average two to three hundred students were registered with the University at any one time during this period. Opportunities and threats followed on each other’s heels during the nineteenth century, in 1815, at the same time as Leiden and Utrecht, the University gained recognition as a national college of higher education, but this was followed by discussions about closure. The situation improved markedly when a new university building, the Academiegebouw, was constructed in 1850. This made the fire completely destroyed this building in 1906 even more poignant. In the meantime, the Higher Education Act of 1876 had radically improved the position of the University, teaching now took place in Dutch as well as in Latin and the University was given a research as well as an educational duty. This laid the foundations for the present research university, the University of Groningen developed apace during the first decades of the twentieth century. The number of faculties and courses grew steadily while the number of students showed an explosive growth, when the University celebrated its first 300 years in 1914 there were 611 registered students, this had already grown to 1000 by 1924. After a drop back during the Depression, and in particular during the Second World War, in 2016 the Dutch chemist Ben Feringa, who worked most of his career at the university, won the Nobel prize for his work on molecular motors. Other strong research groups are in, Nanoscience, Physics, Molecular Biology, Microbiology, Medical Sciences, Neurosciences, Sociology, Philosophy, Theology, Archaeology and Arts. Every year more than 5,000 research publications go to print, the University of Groningen is a member of the so-called Excellence Group of the best universities in Europe. The Excellence Group has 56 members, which is 1.3 percent of the approximately 4,500 European institutions of higher education, the University of Groningen belongs to the top 100 large comprehensive research universities in the world
5.
Physics
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Physics is the natural science that involves the study of matter and its motion and behavior through space and time, along with related concepts such as energy and force. One of the most fundamental disciplines, the main goal of physics is to understand how the universe behaves. Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy, Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the mechanisms of other sciences while opening new avenues of research in areas such as mathematics. Physics also makes significant contributions through advances in new technologies that arise from theoretical breakthroughs, the United Nations named 2005 the World Year of Physics. Astronomy is the oldest of the natural sciences, the stars and planets were often a target of worship, believed to represent their gods. While the explanations for these phenomena were often unscientific and lacking in evidence, according to Asger Aaboe, the origins of Western astronomy can be found in Mesopotamia, and all Western efforts in the exact sciences are descended from late Babylonian astronomy. The most notable innovations were in the field of optics and vision, which came from the works of many scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna. The most notable work was The Book of Optics, written by Ibn Al-Haitham, in which he was not only the first to disprove the ancient Greek idea about vision, but also came up with a new theory. In the book, he was also the first to study the phenomenon of the pinhole camera, many later European scholars and fellow polymaths, from Robert Grosseteste and Leonardo da Vinci to René Descartes, Johannes Kepler and Isaac Newton, were in his debt. Indeed, the influence of Ibn al-Haythams Optics ranks alongside that of Newtons work of the same title, the translation of The Book of Optics had a huge impact on Europe. From it, later European scholars were able to build the devices as what Ibn al-Haytham did. From this, such important things as eyeglasses, magnifying glasses, telescopes, Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover what are now considered to be the laws of physics. Newton also developed calculus, the study of change, which provided new mathematical methods for solving physical problems. The discovery of new laws in thermodynamics, chemistry, and electromagnetics resulted from greater research efforts during the Industrial Revolution as energy needs increased, however, inaccuracies in classical mechanics for very small objects and very high velocities led to the development of modern physics in the 20th century. Modern physics began in the early 20th century with the work of Max Planck in quantum theory, both of these theories came about due to inaccuracies in classical mechanics in certain situations. Quantum mechanics would come to be pioneered by Werner Heisenberg, Erwin Schrödinger, from this early work, and work in related fields, the Standard Model of particle physics was derived. Areas of mathematics in general are important to this field, such as the study of probabilities, in many ways, physics stems from ancient Greek philosophy
6.
Big Bang
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The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods through its subsequent large-scale evolution. If the known laws of physics are extrapolated to the highest density regime, detailed measurements of the expansion rate of the universe place this moment at approximately 13.8 billion years ago, which is thus considered the age of the universe. After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, giant clouds of these primordial elements later coalesced through gravity in halos of dark matter, eventually forming the stars and galaxies visible today. Since Georges Lemaître first noted in 1927 that a universe could be traced back in time to an originating single point. More recently, measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating, the known physical laws of nature can be used to calculate the characteristics of the universe in detail back in time to an initial state of extreme density and temperature. American astronomer Edwin Hubble observed that the distances to faraway galaxies were strongly correlated with their redshifts, assuming the Copernican principle, the only remaining interpretation is that all observable regions of the universe are receding from all others. Since we know that the distance between galaxies increases today, it must mean that in the past galaxies were closer together, the continuous expansion of the universe implies that the universe was denser and hotter in the past. Large particle accelerators can replicate the conditions that prevailed after the early moments of the universe, resulting in confirmation, however, these accelerators can only probe so far into high energy regimes. Consequently, the state of the universe in the earliest instants of the Big Bang expansion is still poorly understood, the first subatomic particles to be formed included protons, neutrons, and electrons. Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed, the majority of atoms produced by the Big Bang were hydrogen, along with helium and traces of lithium. Giant clouds of primordial elements later coalesced through gravity to form stars and galaxies. The framework for the Big Bang model relies on Albert Einsteins theory of relativity and on simplifying assumptions such as homogeneity. The governing equations were formulated by Alexander Friedmann, and similar solutions were worked on by Willem de Sitter, extrapolation of the expansion of the universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past. This singularity indicates that general relativity is not a description of the laws of physics in this regime. How closely models based on general relativity alone can be used to extrapolate toward the singularity is debated—certainly no closer than the end of the Planck epoch. This primordial singularity is itself called the Big Bang, but the term can also refer to a more generic early hot. The agreement of independent measurements of this age supports the model that describes in detail the characteristics of the universe. The earliest phases of the Big Bang are subject to much speculation, in the most common models the universe was filled homogeneously and isotropically with a very high energy density and huge temperatures and pressures and was very rapidly expanding and cooling
7.
Energy
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In physics, energy is the property that must be transferred to an object in order to perform work on – or to heat – the object, and can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the transferred to an object by the mechanical work of moving it a distance of 1 metre against a force of 1 newton. Mass and energy are closely related, for example, with a sensitive enough scale, one could measure an increase in mass after heating an object. Living organisms require available energy to stay alive, such as the humans get from food. Civilisation gets the energy it needs from energy resources such as fuels, nuclear fuel. The processes of Earths climate and ecosystem are driven by the radiant energy Earth receives from the sun, the total energy of a system can be subdivided and classified in various ways. It may also be convenient to distinguish gravitational energy, thermal energy, several types of energy, electric energy. Many of these overlap, for instance, thermal energy usually consists partly of kinetic. Some types of energy are a mix of both potential and kinetic energy. An example is energy which is the sum of kinetic. Whenever physical scientists discover that a phenomenon appears to violate the law of energy conservation. Heat and work are special cases in that they are not properties of systems, in general we cannot measure how much heat or work are present in an object, but rather only how much energy is transferred among objects in certain ways during the occurrence of a given process. Heat and work are measured as positive or negative depending on which side of the transfer we view them from, the distinctions between different kinds of energy is not always clear-cut. In contrast to the definition, energeia was a qualitative philosophical concept, broad enough to include ideas such as happiness. The modern analog of this property, kinetic energy, differs from vis viva only by a factor of two, in 1807, Thomas Young was possibly the first to use the term energy instead of vis viva, in its modern sense. Gustave-Gaspard Coriolis described kinetic energy in 1829 in its modern sense, the law of conservation of energy was also first postulated in the early 19th century, and applies to any isolated system. It was argued for years whether heat was a physical substance, dubbed the caloric, or merely a physical quantity. In 1845 James Prescott Joule discovered the link between mechanical work and the generation of heat and these developments led to the theory of conservation of energy, formalized largely by William Thomson as the field of thermodynamics
8.
Radiation
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In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles, Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules, and break chemical bonds. This is an important distinction due to the difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. The lower-energy, longer-wavelength part of the spectrum including visible light, infrared light, microwaves and this type of radiation only damages cells if the intensity is high enough to cause excessive heating. Ultraviolet radiation has some features of both ionizing and non-ionizing radiation and these properties derive from ultraviolets power to alter chemical bonds, even without having quite enough energy to ionize atoms. The word radiation arises from the phenomenon of waves radiating from a source and this aspect leads to a system of measurements and physical units that are applicable to all types of radiation. This law does not apply close to a source of radiation or for focused beams. Radiation with sufficiently high energy can ionize atoms, that is to say it can knock electrons off atoms, ionization occurs when an electron is stripped from an electron shell of the atom, which leaves the atom with a net positive charge. Because living cells and, more importantly, the DNA in those cells can be damaged by this ionization, thus ionizing radiation is somewhat artificially separated from particle radiation and electromagnetic radiation, simply due to its great potential for biological damage. While an individual cell is made of trillions of atoms, only a fraction of those will be ionized at low to moderate radiation powers. If the source of the radiation is a radioactive material or a nuclear process such as fission or fusion. Particle radiation is subatomic particles accelerated to relativistic speeds by nuclear reactions, because of their momenta they are quite capable of knocking out electrons and ionizing materials, but since most have an electrical charge, they dont have the penetrating power of ionizing radiation. The exception is neutron particles, see below, there are several different kinds of these particles, but the majority are alpha particles, beta particles, neutrons, and protons. Roughly speaking, photons and particles with energies above about 10 electron volts are ionizing, particle radiation from radioactive material or cosmic rays almost invariably carries enough energy to be ionizing. The radiation is invisible and not directly detectable by human senses, as a result, in some cases, it may lead to secondary emission of visible light upon its interaction with matter, as in the case of Cherenkov radiation and radio-luminescence. Ionizing radiation has many uses in medicine, research and construction. Ultraviolet, of wavelengths from 10 nm to 125 nm, ionizes air molecules, causing it to be absorbed by air
9.
Galaxy formation and evolution
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Galaxy formation is hypothesized to occur, from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. Because of the inability to conduct experiments in space, the only way to “test” theories. Explanations for how galaxies formed and evolved must be able to predict the properties and types of galaxies. Edwin Hubble created the first galaxy classification scheme known as the Hubble tuning-fork diagram and it partitioned galaxies into ellipticals, normal spirals, barred spirals, and irregulars. These groups divide into blue star-forming galaxies that are more like spiral types, spiral galaxies are quite thin, dense, and rotate relatively fast, while the stars in elliptical galaxies have randomly-oriented orbits. The majority of mass in galaxies is made up of matter, a substance which is not directly observable. The majority of giant galaxies contain a black hole in their centers. The black hole mass is tied to the host galaxy bulge or spheroid mass, metallicity has a positive correlation with the absolute magnitude of a galaxy. This is not the case instead the tuning fork diagram shows an evolution from simple to complex with no temporal connotations intended, astronomers now believe that disk galaxies likely formed first, then evolved into elliptical galaxies through galaxy mergers. The earliest stage in the evolution of galaxies is the formation, when a galaxy forms, it has a disk shape and is called a spiral galaxy due to spiral-like arm structures located on the disk. There are different theories on how these disk-like distributions of stars develop from a cloud of matter, however, at present, olin Eggen, Donald Lynden-Bell, and Allan Sandage in 1962, proposed a theory that disk galaxies form through a monolithic collapse of a large gas cloud. The distribution of matter in the universe was in clumps that consisted mostly of dark matter. These clumps interacted gravitationally, putting tidal torques on each other that acted to give them some angular momentum, as the baryonic matter cooled, it dissipated some energy and contracted toward the center. With angular momentum conserved, the matter near the center speeds up its rotation, then, like a spinning ball of pizza dough, the matter forms into a tight disk. Once the disk cools, the gas is not gravitationally stable and it breaks, and these smaller clouds of gas form stars. Since the dark matter does not dissipate as it only interacts gravitationally, observations show that there are stars located outside the disk, which does not quite fit the pizza dough model. It was first proposed by Leonard Searle and Robert Zinn that galaxies form by the coalescence of smaller progenitors, known as a top-down formation scenario, this theory is quite simple yet no longer widely accepted. More recent theories include the clustering of dark matter halos in the bottom-up process and this still results in disk-like distributions of baryonic matter with dark matter forming the halo for all the same reasons as in the top-down theory
10.
Galaxy cluster
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They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. One of the key features of clusters is the intracluster medium, the ICM consists of heated gas between the galaxies and has a peak temperature between 2–15 keV that is dependent on the total mass of the cluster. Galaxy clusters should not be confused with star clusters, such as clusters, which are structures of stars within galaxies, or with globular clusters. Small aggregates of galaxies are referred to as groups of galaxies rather than clusters of galaxies, the groups and clusters can themselves cluster together to form superclusters. Notable galaxy clusters in the relatively nearby Universe include the Virgo Cluster, Fornax Cluster, Hercules Cluster, a very large aggregation of galaxies known as the Great Attractor, dominated by the Norma Cluster, is massive enough to affect the local expansion of the Universe. Notable galaxy clusters in the distant, high-redshift Universe include SPT-CL J0546-5345 and SPT-CL J2106-5844, using the Chandra X-ray Observatory, structures such as cold fronts and shock waves have also been found in many galaxy clusters. Galaxy clusters typically have the properties, They contain 100 to 1,000 galaxies, hot X-ray- emitting gas. Details are described in the Composition section, the distribution of the three components is approximately the same in the cluster. They have total masses of 1014 to 1015 solar masses and they typically have a diameter from 2 to 10 Mpc. The spread of velocities for the galaxies is about 800–1000 km/s. There are three components of a galaxy cluster. They are tabulated below, Stars, Star clusters, Galaxies, Galaxy clusters, Super clusters Abell catalogue Intracluster medium List of Abell clusters
11.
Cosmic microwave background
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The cosmic microwave background is the electromagnetic radiation left over from the time of recombination in Big Bang cosmology. In older literature, the CMB is also known as cosmic microwave background radiation or relic radiation. The CMB is a cosmic radiation that is fundamental to observational cosmology because it is the oldest light in the universe. With a traditional optical telescope, the space between stars and galaxies is completely dark, however, a sufficiently sensitive radio telescope shows a faint background glow, almost isotropic, that is not associated with any star, galaxy, or other object. This glow is strongest in the region of the radio spectrum. The discovery of CMB is landmark evidence of the Big Bang origin of the universe, when the universe was young, before the formation of stars and planets, it was denser, much hotter, and filled with a uniform glow from a white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler, when the universe cooled enough, protons and electrons combined to form neutral hydrogen atoms. These atoms could no longer absorb the radiation, and so the universe became transparent instead of being an opaque fog. This is the source of the alternative term relic radiation, precise measurements of the CMB are critical to cosmology, since any proposed model of the universe must explain this radiation. The CMB has a black body spectrum at a temperature of 2. 72548±0.00057 K. The spectral radiance dEν/dν peaks at 160.23 GHz, in the range of frequencies. In particular, the radiance at different angles of observation in the sky contains small anisotropies, or irregularities. This is an active field of study, with scientists seeking both better data and better interpretations of the initial conditions of expansion. Although many different processes might produce the form of a black body spectrum. As a result, most cosmologists consider the Big Bang model of the universe to be the best explanation for the CMB. The high degree of uniformity throughout the universe and its faint but measured anisotropy lend strong support for the Big Bang model in general. Moreover, the fluctuations are coherent on angular scales that are larger than the apparent cosmological horizon at recombination, either such coherence is acausally fine-tuned, or cosmic inflation occurred. The cosmic microwave radiation is an emission of uniform, black body thermal energy coming from all parts of the sky
12.
Dark energy
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In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate. Assuming that the model of cosmology is correct, the best current measurements indicate that dark energy contributes 68. 3% of the total energy in the present-day observable universe. The mass–energy of dark matter and ordinary matter contribute 26. 8% and 4. 9%, respectively, the density of dark energy is very low, much less than the density of ordinary matter or dark matter within galaxies. However, it comes to dominate the mass–energy of the universe because it is uniform across space, contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant can be formulated to be equivalent to the zero-point radiation of space i. e. the vacuum energy, scalar fields that change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow. High-precision measurements of the expansion of the universe are required to understand how the rate changes over time. In general relativity, the evolution of the rate is estimated from the curvature of the universe. Measuring the equation of state for energy is one of the biggest efforts in observational cosmology today. The equilibrium is unstable, if the universe expands slightly, then the expansion releases vacuum energy, likewise, a universe which contracts slightly will continue contracting. These sorts of disturbances are inevitable, due to the distribution of matter throughout the universe. Further, observations made by Edwin Hubble in 1929 showed that the universe appears to be expanding, einstein reportedly referred to his failure to predict the idea of a dynamic universe, in contrast to a static universe, as his greatest blunder. Alan Guth and Alexei Starobinsky proposed in 1980 that a negative pressure field, similar in concept to dark energy, inflation postulates that some repulsive force, qualitatively similar to dark energy, resulted in an enormous and exponential expansion of the universe slightly after the Big Bang. Such expansion is a feature of most current models of the Big Bang. It is unclear what relation, if any, exists between energy and inflation. Even after inflationary models became accepted, the constant was thought to be irrelevant to the current universe. Nearly all inflation models predict that the density of the universe should be very close to the critical density. During the 1980s, most cosmological research focused on models with critical density in matter only, usually 95% cold dark matter, then in 2001, the 2dF Galaxy Redshift Survey gave strong evidence that the matter density is around 30% of critical
