Universe
The universe is the set of all physically detectable entities that interact with each other within space-time according to well-defined physical laws. However, the term is also used informally in slightly different contextual senses and refers to concepts such as cosmos, world, nature, or reality. Its study, on the largest scales, is the subject of cosmology, a discipline based on astronomy and science. physics, in which all aspects of this universe with its phenomena are described. The physical sciences model the universe as a closed system that contains energy and matter attached to space-time and that is fundamentally governed by causal principles. Based on observations of the observable universe, physicists attempt to describe the space-time continuum in which we find ourselves, along with all the matter and energy in it.
Experiments suggest that the universe has been governed by the same physical laws, constant throughout its length and history. It is homogeneous and isotropic. The dominant force at cosmic distances is gravity, and general relativity is currently the most accurate theory to describe it. The other three fundamental forces, and the particles on which they act, are described by the Standard Model.
The universe has at least three dimensions of space and one of time, although additional dimensions cannot be ruled out experimentally. Spacetime appears to be simply connected, and space has very little or even no mean curvature, so Euclidean geometry is, as a general rule, accurate throughout the universe.
The currently most accepted theory on the formation of the universe was theorized by the Belgian canon Lemaître, based on Albert Einstein's equations. Lemaitre concluded (in opposition to what Einstein thought) that the universe was not stationary, that the universe had an origin. It is the Big Bang model, which describes the expansion of space-time from a space-time singularity. The universe experienced a rapid period of cosmic inflation that swept away all initial irregularities. Thereafter the universe expanded and became stable, colder, and less dense. Minor variations in the mass distribution resulted in fractal segregation into chunks, which are found in the universe today as galaxy clusters.
Astronomical observations indicate that the universe is 13,799±21 million years old (between 13,778 and 13,820 million years with a 68% confidence interval) and at least 93 billion light-years extension.
Because, according to the theory of special relativity, matter cannot move faster than the speed of light, it may seem paradoxical that two objects in the universe could have been 93 billion light-years apart in a single space. time of only 13 billion years; However, this separation does not conflict with the theory of general relativity, since it only affects movement in space, but not space itself, which can extend at a higher rate, not limited by the speed of light.. Therefore, two galaxies can move away from each other faster than the speed of light if it is the space between them that is expanding.
Recent observations have shown that this expansion is accelerating, and that most of the matter and energy in the universe is called dark matter and dark energy; ordinary (baryonic) matter would only account for just over 5% of the total.
Measurements of the spatial distribution and redshift of distant galaxies, the cosmic microwave background radiation, and the relative percentages of the lightest chemical elements support the theory of the expansion of space, and more generally, the Big Bang theory, which proposes that the universe itself originated at a specific time in the past.
As for its final destination, the evidence indicates that the universe is the totality of space and time, of all forms of matter, energy, momentum, the physical laws and constants that govern them, which seem to support the theories of the permanent expansion of the universe (Big Freeze or Big Rip, Great Tear), which indicates that the expansion of space itself will cause a point to arrive at that the atoms themselves will separate into subatomic particles. Other possible futures that were considered speculated that dark matter could exert enough gravity to stop the expansion and cause all matter to compress again; something that scientists call the Big Crunch or the Great Implosion, but the latest observations point in the direction of the great tear.
Observable or visible portion
Theoretical cosmologists and astrophysicists use the term universe differently, designating either the entire system or only a part of it. The term the universe is often used > to designate the observable part of space-time or the entire space-time.
According to the convention of cosmologists, the term universe frequently refers to the finite part of space-time that is directly observable using telescopes, other detectors, and physical, theoretical, and empirical methods to study the universe. basic components of the universe and their interactions. Cosmological physicists assume that the observable part of co-moving space (also called our universe) corresponds to a part of the whole space and is usually not the whole space.
In the case of the observable universe, this may be only a tiny portion of the existing universe, and therefore it may be impossible to really know whether the universe is being fully observed. Most cosmologists believe that the observable universe is an extremely small part of the actually existing "whole" universe and that it is impossible to see all of space co-moving. Whether this is correct is currently unknown, since according to studies of the shape of the universe, it is possible that the observable universe is close to having the same size as all of space. The question is still being debated.
Evolution
Theory on the origin and formation of the Universe (Big Bang)
The fact that the universe is expanding stems from redshift observations made in the 1920s and quantified by Hubble's law. These observations are the experimental prediction of the Friedmann-Robertson-Walker model, which is a solution of Einstein's field equations of general relativity, which predict the beginning of the universe through a big bang.
The "redshift" is a phenomenon observed by astronomers, which shows a direct relationship between the distance of a remote object (such as a galaxy) and the speed with which it recedes. If this expansion has been continuous throughout the lifetime of the universe, then in the past these distant objects that keep receding must once have been together. This idea gives rise to the Big Bang theory; the dominant model in current cosmology.
During the earliest era of the Big Bang, the universe is believed to be a hot, dense plasma. As the expansion progressed, the temperature decreased to the point where atoms could be formed. At that time, the background energy was decoupled from matter and was free to travel through space. The remaining energy continued to cool as the universe expanded and today forms the cosmic microwave background. This background radiation is remarkably uniform in all directions, a circumstance that cosmologists have tried to explain as reflecting an early period of cosmic inflation after the Big Bang.
Examining small variations in the background microwave radiation provides information about the nature of the universe, including its age and composition. The age of the universe since the Big Bang, according to current information provided by NASA's WMAP, is estimated to be about 13.7 billion years, with a margin of error of 1% (137 millions of years). Other estimation methods offer different age ranges, from 11 billion to 20 billion.
Primal Soup
Until recently, the first hundredth of a second was more of a mystery, preventing scientists from describing exactly what the universe was like. New experiments at RHIC at Brookhaven National Laboratory have given physicists a light on this high-energy curtain so that they can directly observe the types of behavior that may have taken place at that instant.
At these energies, the quarks that make up protons and neutrons were not together, and a superhot dense mixture of quarks and gluons, with a few electrons, was all that could exist in the microseconds before they cooled sufficiently to form the type of matter particles we see today.
Protogalaxies
Rapid advances about what happened after the existence of matter provide much information about the formation of galaxies. The first galaxies are thought to have been faint "dwarf galaxies" that they emitted so much radiation that they would separate gaseous atoms from their electrons. This gas, in turn, was heating up and expanding, and had the potential to gain the mass needed to form the large galaxies we know today.
Final Destination
The final fate of the universe has various models that explain what will happen based on various parameters and observations. According to the general theory of relativity, the most probable final destination will depend on the true value of the density of matter. Depending on this parameter, two types of endings are considered:
- The Big Crunch (Great Implosion) that will happen if the universe has a density of matter above critical density, to the point that it is able to slow down its expansion to stop it and invest it. Thus, matter would condemn in a great implosion guided by gravity.
- The Big Rip (Great Degarration) that will happen if finally density is below a critical value, the clusters of galaxies would end up approaching and forming large black holes, the kind that is supposed to exist in the center of many galaxies. Those black holes can be regarded as a tearing or tearing of space-time.
Since the 1990s it was found that the universe seems to have an accelerated expansion, a fact that within general relativity can only be explained by resorting to a mechanism of the cosmological constant type. It is not known if that fact can lead to a third type of ending.
Big Crunch or the Great Implosion
If the universe is dense enough, it's possible that the gravitational pull of all that matter could eventually stop the initial expansion, so that the universe would contract again, galaxies would start to recede, and eventually collide with each other. The temperature would rise, and the universe would plunge toward a catastrophic fate where it would again be reduced to a point.
Some physicists have speculated that another universe would then form, in which case the process would repeat itself. This theory is known as the oscillating universe theory.
Today this hypothesis seems incorrect, because in light of the latest experimental data, the Universe is expanding more and more rapidly.
Big Rip or Great Tearing
The Great Rip or Eternal Expansion Theory, in English Big Rip, is a cosmological hypothesis about the ultimate fate of the universe. This possible final fate of the universe depends on the amount of dark energy existing in the Universe. If the universe contains enough dark energy, it could end in a tearing apart of all matter.
The key value is w, the ratio between the pressure of dark energy and its energy density. A w < -1, the universe would eventually be torn apart. First, the galaxies would pull apart, then gravity would be too weak to keep each galaxy together. Planetary systems would lose their gravitational cohesion. In the last minutes, stars and planets will fall apart, and atoms will be destroyed.
The authors of this hypothesis calculate that the end of time would occur approximately 3.5×1010 years after the Big Bang, that is, within 2.0×1010 years.
A modification of this theory called Big Freeze, although little accepted[citation needed], normally states that the universe would continue to expand without cause a Big Rip.
Big Bounce or Great Rebound
Physical description
Size of the universe
Very little is known with certainty about the size of the universe. It can be trillions of light-years across or even infinite in size. A 2003 paper claims to set a lower bound of 24 gigaparsecs (78 billion light-years) for the size of the universe, but there is no reason to. believe that this bound is somehow too tight (See shape of the Universe).
The observable (or visible) universe, which consists of all the matter and energy that could have affected us since the Big Bang given the limitation of the speed of light, is certainly finite. The co-moving distance to the edge of the visible universe is around 46.5 billion light-years in all directions from Earth. Thus, the visible universe can be considered as a perfect sphere with the Earth at its center, and a diameter of about 93 billion light-years. It should be noted that many sources have published a wide variety of incorrect figures for the size of the universe. visible universe: from 13,700 to 180,000 million light years. (See observable universe).
In the Universe, the distances that separate the stars are so great that, if we wanted to express them in meters, we would have to use very large figures. Because of this, the light year is used as the unit of length, which corresponds to the distance that light travels in one year.
Previously, the most commonly accepted model of the universe was the one proposed by Albert Einstein in his General Relativity, in which he proposed a "finite but unlimited" universe, that is, that despite having a volume measurable has no limits, analogous to the surface of a sphere, which is measurable but unlimited. This was characteristic of a spherical universe. Today, thanks to the latest observations made by NASA's WMAP, it is known to have a flat shape. Although a possible flat universe closed on itself is not ruled out. These observations suggest that the universe is infinite.
Shape
An important open question in cosmology is the shape of the universe. Mathematically, which 3-manifold best represents the spatial part of the universe?
If the universe is spatially flat, it is unknown whether the rules of Euclidean geometry will hold on a larger scale. Many cosmologists now believe that the observable Universe is very close to being spatially flat, with local wrinkles where massive objects distort space-time, in the same way that the surface of a lake is nearly flat. This view was reinforced by the latest WMAP data, looking towards "acoustic oscillations" of temperature variations in microwave background radiation.
On the other hand, it is unknown whether the universe is connected. The universe has no spatial bounds according to the standard Big Bang model; however it must be spatially finite (compact). This can be understood using a two-dimensional analogy: the surface of a sphere has no limit, but it does not have an infinite area. It is a two-dimensional surface with constant curvature in a third dimension. The 3-sphere is a three-dimensional equivalent in which all three dimensions are constantly curved into a fourth.
If the universe were compact and boundless, it would be possible, after traveling a sufficient distance, to return to the starting point. Thus light from stars and galaxies could pass through the observable universe more than once. If the universe were multiply connected and small enough (and of an appropriate size, perhaps complex) then one could possibly look once or several times around it in some (or all) directions. Although this possibility has not been ruled out, the results of the latest microwave background radiation research make this seem unlikely.
Colour
Historically it has been believed that the Universe is black, as it is what we observe when looking at the sky on clear nights. In 2002, however, astronomers Karl Glazebrook and Ivan Baldry claimed in a scientific paper that the universe is actually a color they decided to call a cosmic café au lait. This study was based on measuring the spectral range of light. coming from a large volume of the Universe, synthesizing the information provided by a total of more than 200,000 galaxies.
Homogeneity and isotropy
While the structure is considerably fractalized at the local level (ordered in a cluster hierarchy), at the higher orders of distance the universe is very homogeneous. At these scales the density of the universe is very uniform, and there is no preferred or significantly asymmetric direction in the universe. This homogeneity and isotropy is a requirement of the Friedman-Lemaître-Robertson-Walker Metric used in modern cosmological models.
The question of anisotropy in the early universe was significantly answered by WMAP, which searched for fluctuations in the intensity of the microwave background. Measurements of this anisotropy have provided useful information and constraints on the evolution of the Universe.
Up to the limit of the observing power of astronomical instruments, objects radiate and absorb energy according to the same physical laws as they do in our own galaxy. Based on this, it is believed that the same laws and physical constants are universally applicable throughout the entire observable universe. No confirmed evidence has been found to show that physical constants have varied since the Big Bang.
Composition
The present observable universe appears to have a geometrically flat space-time, containing a mass-energy density equivalent to 9.9 × 10−30 grams per cubic centimeter. The primary constituents appear to consist of 73% dark energy, 23% cold dark matter, and 4% atoms. Thus, the density of atoms would be equivalent to one single hydrogen nucleus for every four cubic meters of volume. The exact nature of dark energy and cold dark matter remains a mystery. Currently it is speculated that the neutrino, (a very abundant particle in the universe), has a mass, albeit minimal. If this fact is verified, it could mean that dark energy and matter do not exist.
During the early phases of the Big Bang, it is believed that equal amounts of matter and antimatter were formed. Matter and antimatter should mutually eliminate each other on contact, so the actual existence of matter (and the absence of antimatter) is a CP (See CP Violation) symmetry violation, so it can It may be that particles and antiparticles do not have exactly the same or symmetrical properties, or it may simply be that the physical laws that govern the universe favor the survival of matter over antimatter. In this same sense, it has also been suggested that perhaps dark matter is the cause of baryogenesis by interacting differently with matter than with antimatter.
Before the formation of the first stars, the chemical composition of the universe consisted primarily of hydrogen (75% of the total mass), with a minor amount of helium-4 (4He) (24% of the total mass) and the rest of other elements. A small portion of these elements were in the form of the isotope deuterium (²H), helium-3 (³He) and lithium (7Li). Interstellar matter in galaxies has been endlessly enriched by heavier elements, generated by fusion processes in stars, and dispersed as a result of supernova explosions, stellar winds, and the expulsion of the outer shell of stars. ripe.
The Big Bang left behind a background stream of photons and neutrinos. The temperature of the background radiation has steadily decreased with the expansion of the universe and now consists primarily of microwave energy equivalent to a temperature of 2,725 K. The current neutrino background density is 150 per cubic centimeter.
Quantum Structure
According to modern physics, the Universe is an isolated quantum system, a unified field of waves that becomes decoherent upon observation or measurement. In such a virtue, ultimately, the environment of the Universe would be non-local and non-deterministic.
Multiverses
Theoretical cosmologists study models of the spacetime ensemble that are connected, and look for models that are consistent with physical cosmological models of spacetime on the scale of the observable universe. However, recently theories have gained strength that contemplate the possibility of multiverses or several universes coexisting simultaneously. According to the recently enunciated Theory of Multiexplosions, it is intended to explain this aspect, highlighting a possible coexistence of universes in the same space.
The universe, an illusion?
Scientists at King's College London were able to recreate the conditions immediately following the Big Bang through two years' knowledge of the Higgs particle and came to the conclusion that the universe possibly collapsed, until cease to exist almost as soon as it began, which raises the idea that everything we see does not exist and is only the past of the stars.
Structures of the universe
Galaxies
On a large scale, the universe is made up of galaxies and clusters of galaxies. Galaxies are massive groups of stars, and are the largest structures in which matter in the universe is organized. Through the telescope they appear as luminous spots of different shapes. When classifying them, scientists distinguish between the galaxies of the Local Group, made up of the thirty closest galaxies and to which our galaxy (the Milky Way) is gravitationally attached, and all the other galaxies, which they call "outer galaxies".
Galaxies are distributed throughout the universe and present very diverse characteristics, both in terms of their configuration and their age. The smallest encompass around 400,000 million stars, and the largest galaxies can encompass more than a trillion stars. The latter can have a diameter of 170,000 light years, while the former do not usually exceed 6,000 light years.
In addition to stars and their associated bodies (planets, asteroids, etc...), galaxies also contain interstellar matter, made up of dust and gas in a proportion that varies between 1 and 10% of their mass.
It is estimated that the universe may be made up of about 100 billion galaxies, although these figures vary depending on the different studies.
Galaxy Shapes
The increasing power of telescopes, which allow more and more detailed observations of the different elements of the universe, has made it possible to classify galaxies by their shape. Five different types have thus been established: elliptical, lenticular, spiral, barred spiral and irregular galaxies.
Elliptical Galaxies
In the form of an ellipse or a spheroid, they are characterized by lacking a defined internal structure and by presenting very little interstellar matter. They are considered the oldest in the universe, since their stars are old and are in a very advanced phase of their evolution.
Lenticular Galaxies
Galaxies of this type were once spiral galaxies, but they consumed or lost much of the interstellar matter, so today they lack spiral arms and only have their nucleus. Although sometimes there is a certain amount of interstellar matter, especially dust, that collects in the form of a disk around it. These galaxies make up about 3% of the galaxies in the universe.
Spiral Galaxies
They are made up of a central nucleus and two or more spiral arms, which start from the nucleus. This is made up of a multitude of stars and hardly any interstellar matter, while in the arms interstellar matter abounds and there are a large number of young stars, which are very bright. About 75% of the galaxies in the universe are of this type.
Barred Spiral Galaxy
It is a subtype of spiral galaxy, characterized by the presence of a central bar from which two spiral arms typically depart. This type of galaxies constitute a significant fraction of the total number of spiral galaxies. The Milky Way is a barred spiral galaxy.
Irregular Galaxies
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They include a great diversity of galaxies, whose configurations do not respond to the four previous forms, although they have some characteristics in common, such as being almost all small and containing a large percentage of interstellar matter. It is estimated that about 5% of the galaxies in the universe are irregular.
The Milky Way
The Milky Way is our galaxy. According to observations, it has a mass of 1012 solar masses and is of the barred spiral type. With an average diameter of about 100,000 light years, it is estimated to contain about 200 billion stars, including the Sun. The distance from the Sun to the center of the galaxy is about 27,700 light years (8, 5kpc) To the naked eye, it appears as a whitish elliptical trail, which can be distinguished on clear nights. What cannot be appreciated are its spiral arms, in one of which, the so-called Orion arm, our solar system is located, and therefore the Earth.
The central core of the galaxy is uniformly thick everywhere except in the center, where there is a large bulge with a maximum thickness of 16,000 light-years, with the average thickness being about 6,000 light-years.
All the stars and interstellar matter that the Milky Way contains, both in the central core and in the arms, are located within a disk 100,000 light-years in diameter, which rotates on its axis at a higher linear speed at 216 km/s.
The constellations
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Only three galaxies other than our own are visible to the naked eye. We have the Andromeda Galaxy, visible from the Northern Hemisphere; the Large Magellanic Cloud, and the Small Magellanic Cloud, in the Southern Celestial Hemisphere. The rest of the galaxies are not visible to the naked eye without the aid of instruments. Yes, they are, on the other hand, the stars that are part of the Milky Way. These stars often draw recognizable patterns in the sky, which have received various names in relation to their appearance. These groups of stars with an identifiable profile are known as constellations. The International Astronomical Union officially grouped the visible stars into 88 constellations, some of them very large, such as Hydra or the Big Dipper, and others very small, such as Arrow and Triangle.
The stars
They are the most prominent constituent elements of galaxies. Stars are huge spheres of gas that shine due to their gigantic nuclear reactions. When due to the gravitational force, the pressure and the temperature of the interior of a star that is intense enough, the nuclear fusion of its atoms begins, and they begin to emit a dark red light, which later moves towards the superior state, which It is the one in which our Sun is, to later, when the internal nuclear reactions are modified, it expands and finally cools down.
When the hydrogen runs out, nuclear reactions of heavier, more energetic elements take place, which turn the star into a red giant. Over time, it becomes unstable, spewing most of the stellar material into outer space. This process can last 100 million years, until all nuclear energy is used up, and the star contracts under the effect of gravity until it becomes small and dense, in the form of a white, blue or brown dwarf. If the initial star is several times more massive than the Sun, its cycle may be different, and instead of a giant, it may become a supergiant and end its life with an explosion called a supernova. These stars can end as neutron stars. Even larger-sized stars can burn out all their fuel very quickly, transforming into a supermassive entity called a black hole.
Pulsars are sources of radio waves that emit with regular periods. The word "pulsar" means pulsating radio source. They are detected by radio telescopes and extremely precise clocks are required to detect their changes in rhythm. Studies indicate that a pulsar is a small, rapidly rotating neutron star. The best known is in the Crab Nebula. Its density is so great that a quasar sample the size of a ballpoint pen would have a mass of about 100,000 tons. Its very intense magnetic field is concentrated in a small space. This speeds it up and causes it to emit a large amount of energy in beams of radiation that we receive here as radio waves.
The word quasar is an acronym for quasi stellar radio source. They were identified in the 1950s. They were later found to display a larger redshift than any other known object. The cause was the Doppler Effect, which shifts the spectrum towards red when objects move away. The first quasar studied, named 3C 273, is 1.5 billion light-years from Earth. Since 1980 thousands of quasars have been identified, some traveling away from us at speeds of 90% of light.
Quasars have been discovered 12 billion light-years from Earth; practically the age of the universe. Despite the enormous distances, the energy that arrives in some cases is very large, equivalent to that received from thousands of galaxies: as an example, the s50014+81 it is about 60,000 times brighter than the entire Milky Way.
The planets
Planets are bodies that revolve around a star and that, according to the definition of the International Astronomical Union, must also meet the condition of having cleared their orbit of other important rocky bodies, and of having enough mass to its force of gravity generates a spherical body. In the case of bodies that orbit around a star that do not meet these characteristics, we speak of dwarf planets, planetesimals, or asteroids. In our Solar System there are 8 planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, considering Pluto as a dwarf planet since 2006. By the end of 2009, more than 400 extrasolar planets had been detected outside our solar system, but technological advances are allowing this number to grow apace.
The satellites
Natural satellites are bodies that revolve around the planets. Earth's only natural satellite is the Moon, which is also the closest satellite to the Sun. The main satellites of the planets of the solar system are listed below (Pluto is included in the list, considered by the IAU as a dwarf planet).
- Earth: 1 satellite → Moon
- Mars: 2 satellites → Fobos, Deimos
- Jupiter: 92 satellites → Metis, Adrastea, Amaltea, Tebe, Io, Europe, Ganimedes, Calisto, Leda, Himalia, Lisitea, Elara, Ananké, Carmé, Pasífae, Sinope...
- Saturn: 83 satellites → Pan, Atlas, Prometheus, Pandora, Epimetheus, Jano, Mimas, Encélado, Tetis, Telesto, Calipso, Dione, Helena, Rea, Titan, Hiperion, Jápeto, Febe...
- Uranus: 27 satellites → Cordelia, Ofelia, Bianca, Crésida, Desdémona, Julieta, Porcia, Rosalinda, Belinda, Puck, Miranda, Ariel, Umbriel, Titania, Oberón.
- Neptune: 14 satellites → Nayade, Talasa, Despina, Galatea, Larisa, Proteo, Tritón, Nereida
- Pluto: 5 satellites → Caronte, Nix, Hidra, Cerbero and Estigia
Asteroids and comets
In those areas of a star's orbit where, for various reasons, the grouping of the initial matter into a single dominant body or planet has not occurred, asteroid disks appear: rocky objects of many different sizes they orbit the star in large numbers, eventually colliding with each other. When the rocks have diameters less than 50 m they are called meteoroids. As a result of collisions, some asteroids can vary their orbits, adopting very eccentric trajectories that periodically bring them closer to the star. When the composition of these rocks is rich in water or other volatile elements, the approach to the star and its consequent increase in temperature cause part of its mass to evaporate and be dragged by the solar wind, creating a long tail of bright material at as the rock gets closer to the star. These objects are called comets. In our solar system there are two large asteroid disks: one located between the orbits of Mars and Jupiter, called the Asteroid Belt, and another much fainter and more scattered at the edges of the solar system, about a light-year away, called Oort cloud.
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Hints of a beginning
The general theory of relativity, which was published by Albert Einstein in 1916, implied that the cosmos was either expanding or contracting. But this concept was totally opposed to the notion of a static universe, then accepted even by Einstein himself. Hence, he included in his calculations what he called the "cosmological constant," an adjustment by which he tried to reconcile his theory with the accepted idea of a static and unchanging universe. However, certain discoveries that occurred in the 1920s led Einstein to say that the adjustment he had made to his theory of relativity was the "biggest mistake of his life." These discoveries were made thanks to the installation of a huge 254-centimeter telescope on Mount Wilson (California). Observations made in the 1920s with the help of this instrument showed that the universe is expanding.
Until then, the largest telescopes could only identify the stars in our galaxy, the Milky Way, and although blobs of light, called nebulae, were seen, they were generally taken to be eddies of gas in our galaxy. Thanks to the greater power of the telescope on Mount Wilson, Edwin Hubble was able to distinguish stars in those nebulae. The blots were eventually found to be the same as the Milky Way: galaxies. Today it is believed that there are between 50 and 125 billion galaxies, each containing hundreds of billions of stars.
In the late 1920s, Hubble also discovered that galaxies are receding from us, and that they are receding faster the further away they are. Astronomers calculate the recession rate of galaxies using the spectrograph, an instrument that measures the spectrum of light from the stars. To do this, they direct the light that comes from distant stars towards a prism, which breaks it down into the colors that make it up.
The light from an object is reddish (phenomenon called redshift) if it moves away from the observer, and bluish (blueshift) if it approaches it. It should be noted that, except for a few nearby galaxies, all known galaxies have red-shifted spectral lines. From this, scientists infer that the universe expands in an orderly manner. The rate of such expansion is determined by measuring the degree of redshift. What conclusion has been drawn from the expansion of the cosmos? Well, one scientist invited the public to look at the process in reverse—like a movie of the expansion projected backwards—in order to observe the early history of the universe. Seen in this way, the cosmos would appear to be in recession or contraction, instead of expanding, and would eventually return to a single point of origin.
Physicist Stephen Hawking concluded in his 1993 book Black Holes and Small Universes (and Other Essays): "Science could claim that the universe had to have known a beginning." But years ago, many experts rejected that the universe had a beginning. The scientist Fred Hoyle did not accept that the cosmos had arisen through what he mockingly called a big bang (“a big explosion”). One of the arguments he put forward was that, had there been such a dynamic beginning, residues of that event would have to be preserved somewhere in the universe: there would have to be fossil radiation, so to speak; a slight afterglow.
The New York Times (March 8, 1998) reported that around 1965 "astronomers Arno Penzias and Robert Wilson discovered the ubiquitous background radiation: the afterglow of the primal explosion". The article added: "Everything indicated that the [Big Bang] theory had triumphed."
But in the years after the find, this objection was raised: If the big bang model was correct, why hadn't slight irregularities in the radiation been detected? (The formation of galaxies would have required a universe with colder, denser areas that allowed matter to melt.) Indeed, the experiments carried out by Penzias and Wilson from the Earth's surface did not reveal such irregularities.
For this reason, NASA launched the Cosmic Background Explorer (COBE) satellite in November 1989, whose discoveries were described as crucial. “The waves detected by their differential microwave radiometer corresponded to the fluctuations that left their mark on the cosmos and that billions of years ago led to the formation of galaxies.”
Other terms
Various words have been used throughout history to denote "all space", including the equivalents and variants in various languages of "heavens", "cosmos& #3. 4; and "world". The macrocosm has also been used for this effect, although it is more specifically defined as a system that reflects on a large scale one, some, or all of these system components or parts. Similarly, a microcosm is a system that reflects on a small scale a much larger system of which it is a part.
Although words like world and its equivalents in other languages almost always refer to the planet Earth, in ancient times they referred to everything that existed (could be seen). In that sense it was used, for example, by Copernicus. Some languages use the word "world" as part of the word "outer space". An example in German is the word "Weltraum".
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