Open main menu

The Universe is all of space and time[a] and their contents,[10] including planets, stars, galaxies, and all other forms of matter and energy. While the spatial size of the entire Universe is unknown,[3] it is possible to measure the size of the observable universe, which is currently estimated to be 93 billion light-years in diameter. In various multiverse hypotheses, a universe is one of many causally disconnected[11] constituent parts of a larger multiverse, which itself comprises all of space and time and its contents;[12] as a consequence, ‘the Universe’ and ‘the multiverse’ are synonymous in such theories.

The Hubble Ultra-Deep Field image shows some of the most remote galaxies visible with present technology, each consisting of billions of stars. (Apparent image area about 1/79 that of a full moon)[1]
Age (within Lambda-CDM model)13.799 ± 0.021 billion years[2]
DiameterUnknown.[3] Diameter of the observable universe: 8.8×1026 m (28.5 Gpc or 93 Gly)[4]
Mass (ordinary matter)At least 1053 kg[5]
Average density (including the contribution from energy)9.9 x 10−30 g/cm3[6]
Average temperature2.72548 K[7]
Main contentsOrdinary (baryonic) matter (4.9%)
Dark matter (26.8%)
Dark energy (68.3%)[8]
ShapeFlat with a 0.4% margin of error[9]

The earliest cosmological models of the Universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center.[13][14] Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of universal gravitation, Isaac Newton built upon Copernicus' work as well as Johannes Kepler's laws of planetary motion and observations by Tycho Brahe.

Further observational improvements led to the realization that the Sun is one of hundreds of billions of stars in the Milky Way, which is one of at least hundreds of billions of galaxies in the Universe. Many of the stars in our galaxy have planets. At the largest scale, galaxies are distributed uniformly and the same in all directions, meaning that the Universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters which form immense filaments and voids in space, creating a vast foam-like structure.[15] Discoveries in the early 20th century have suggested that the Universe had a beginning and that space has been expanding since then,[16] and is currently still expanding at an increasing rate.[17]

The Big Bang theory is the prevailing cosmological description of the development of the Universe. Under this theory, space and time emerged together 13.799±0.021 billion years ago[2] and the energy and matter initially present have become less dense as the Universe expanded. After an initial accelerated expansion called the inflationary epoch at around 10−32 seconds, and the separation of the four known fundamental forces, the Universe gradually cooled and continued to expand, allowing the first subatomic particles and simple atoms to form. Dark matter gradually gathered, forming a foam-like structure of filaments and voids under the influence of gravity. Giant clouds of hydrogen and helium were gradually drawn to the places where dark matter was most dense, forming the first galaxies, stars, and everything else seen today. It is possible to see objects that are now further away than 13.799 billion light-years because space itself has expanded, and it is still expanding today. This means that objects which are now up to 46.5 billion light-years away can still be seen in their distant past, because in the past, when their light was emitted, they were much closer to Earth.

From studying the movement of galaxies, it has been discovered that the universe contains much more matter than is accounted for by visible objects; stars, galaxies, nebulas and interstellar gas. This unseen matter is known as dark matter[18] (dark means that there is a wide range of strong indirect evidence that it exists, but we have not yet detected it directly). The ΛCDM model is the most widely accepted model of our universe. It suggests that about 69.2%±1.2% [2015] of the mass and energy in the universe is a cosmological constant (or, in extensions to ΛCDM, other forms of dark energy, such as a scalar field) which is responsible for the current expansion of space, and about 25.8%±1.1% [2015] is dark matter.[19] Ordinary ('baryonic') matter is therefore only 4.84%±0.1% [2015] of the physical universe.[19] Stars, planets, and visible gas clouds only form about 6% of ordinary matter, or about 0.29% of the entire universe.[20]

There are many competing hypotheses about the ultimate fate of the universe and about what, if anything, preceded the Big Bang, while other physicists and philosophers refuse to speculate, doubting that information about prior states will ever be accessible. Some physicists have suggested various multiverse hypotheses, in which our universe might be one among many universes that likewise exist.[3][21][22]


Hubble Space Telescope - Ultra deep field galaxies to Legacy field zoom out
(video 00:50; May 2, 2019)

The physical Universe is defined as all of space and time[a] (collectively referred to as spacetime) and their contents.[10] Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter, and therefore planets, moons, stars, galaxies, and the contents of intergalactic space.[23][24][25] The Universe also includes the physical laws that influence energy and matter, such as conservation laws, classical mechanics, and relativity.[26]

The Universe is often defined as "the totality of existence", or everything that exists, everything that has existed, and everything that will exist.[26] In fact, some philosophers and scientists support the inclusion of ideas and abstract concepts—such as mathematics and logic—in the definition of the Universe.[28][29][30] The word universe may also refer to concepts such as the cosmos, the world, and nature.[31][32]


The word universe derives from the Old French word univers, which in turn derives from the Latin word universum.[33] The Latin word was used by Cicero and later Latin authors in many of the same senses as the modern English word is used.[34]


A term for 'universe' among the ancient Greek philosophers from Pythagoras onwards was τὸ πᾶν, tò pân ("the all"), defined as all matter and all space, and τὸ ὅλον, tò hólon ("all things"), which did not necessarily include the void.[35][36] Another synonym was ὁ κόσμος, ho kósmos (meaning the world, the cosmos).[37] Synonyms are also found in Latin authors (totum, mundus, natura)[38] and survive in modern languages, e.g., the German words Das All, Weltall, and Natur for Universe. The same synonyms are found in English, such as everything (as in the theory of everything), the cosmos (as in cosmology), the world (as in the many-worlds interpretation), and nature (as in natural laws or natural philosophy).[39]

Chronology and the Big Bang

The prevailing model for the evolution of the Universe is the Big Bang theory.[40][41] The Big Bang model states that the earliest state of the Universe was an extremely hot and dense one, and that the Universe subsequently expanded and cooled. The model is based on general relativity and on simplifying assumptions such as homogeneity and isotropy of space. A version of the model with a cosmological constant (Lambda) and cold dark matter, known as the Lambda-CDM model, is the simplest model that provides a reasonably good account of various observations about the Universe. The Big Bang model accounts for observations such as the correlation of distance and redshift of galaxies, the ratio of the number of hydrogen to helium atoms, and the microwave radiation background.

In this diagram, time passes from left to right, so at any given time, the Universe is represented by a disk-shaped "slice" of the diagram.

The initial hot, dense state is called the Planck epoch, a brief period extending from time zero to one Planck time unit of approximately 10−43 seconds. During the Planck epoch, all types of matter and all types of energy were concentrated into a dense state, and gravity—currently the weakest by far of the four known forces—is believed to have been as strong as the other fundamental forces, and all the forces may have been unified. Since the Planck epoch, space has been expanding to its present scale, with a very short but intense period of cosmic inflation believed to have occurred within the first 10−32 seconds.[42] This was a kind of expansion different from those we can see around us today. Objects in space did not physically move; instead the metric that defines space itself changed. Although objects in spacetime cannot move faster than the speed of light, this limitation does not apply to the metric governing spacetime itself. This initial period of inflation is believed to explain why space appears to be very flat, and much larger than light could travel since the start of the universe.

Within the first fraction of a second of the universe's existence, the four fundamental forces had separated. As the universe continued to cool down from its inconceivably hot state, various types of subatomic particles were able to form in short periods of time known as the quark epoch, the hadron epoch, and the lepton epoch. Together, these epochs encompassed less than 10 seconds of time following the Big Bang. These elementary particles associated stably into ever larger combinations, including stable protons and neutrons, which then formed more complex atomic nuclei through nuclear fusion. This process, known as Big Bang nucleosynthesis, only lasted for about 17 minutes and ended about 20 minutes after the Big Bang, so only the fastest and simplest reactions occurred. About 25% of the protons and all the neutrons in the universe, by mass, were converted to helium, with small amounts of deuterium (a form of hydrogen) and traces of lithium. Any other element was only formed in very tiny quantities. The other 75% of the protons remained unaffected, as hydrogen nuclei.

After nucleosynthesis ended, the universe entered a period known as the photon epoch. During this period, the Universe was still far too hot for matter to form neutral atoms, so it contained a hot, dense, foggy plasma of negatively charged electrons, neutral neutrinos and positive nuclei. After about 377,000 years, the universe had cooled enough that electrons and nuclei could form the first stable atoms. This is known as recombination for historical reasons; in fact electrons and nuclei were combining for the first time. Unlike plasma, neutral atoms are transparent to many wavelengths of light, so for the first time the universe also became transparent. The photons released ("decoupled") when these atoms formed can still be seen today; they form the cosmic microwave background (CMB).

As the Universe expands, the energy density of electromagnetic radiation decreases more quickly than does that of matter because the energy of a photon decreases with its wavelength. At around 47,000 years, the energy density of matter became larger than that of photons and neutrinos, and began to dominate the large scale behavior of the universe. This marked the end of the radiation-dominated era and the start of the matter-dominated era.

In the earliest stages of the universe, tiny fluctuations within the universe's density led to concentrations of dark matter gradually forming. Ordinary matter, attracted to these by gravity, formed large gas clouds and eventually, stars and galaxies, where the dark matter was most dense, and voids where it was least dense. After around 100 - 300 million years,[citation needed] the first stars formed, known as Population III stars. These were probably very massive, luminous, non metallic and short-lived. They were responsible for the gradual reionization of the Universe between about 200-500 million years and 1 billion years, and also for seeding the universe with elements heavier than helium, through stellar nucleosynthesis.[43] The Universe also contains a mysterious energy - possibly a scalar field - called dark energy, the density of which does not change over time. After about 9.8 billion years, the Universe had expanded sufficiently so that the density of matter was less than the density of dark energy, marking the beginning of the present dark-energy-dominated era.[44] In this era, the expansion of the Universe is accelerating due to dark energy.

Physical properties

Of the four fundamental interactions, gravitation is the dominant at astronomical length scales. Gravity's effects are cumulative; by contrast, the effects of positive and negative charges tend to cancel one another, making electromagnetism relatively insignificant on astronomical length scales. The remaining two interactions, the weak and strong nuclear forces, decline very rapidly with distance; their effects are confined mainly to sub-atomic length scales.

The Universe appears to have much more matter than antimatter, an asymmetry possibly related to the CP violation.[45] This imbalance between matter and antimatter is partially responsible for the existence of all matter existing today, since matter and antimatter, if equally produced at the Big Bang, would have completely annihilated each other and left only photons as a result of their interaction.[46][47] The Universe also appears to have neither net momentum nor angular momentum, which follows accepted physical laws if the Universe is finite. These laws are the Gauss's law and the non-divergence of the stress-energy-momentum pseudotensor.[48]

Constituent spatial scales of the observable universe
This diagram shows Earth's location in the Universe on increasingly larger scales. The images, labeled along their left edge, increase in size from left to right, then from top to bottom.

Size and regions



The proper distance—the distance as would be measured at a specific time, including the present—between Earth and the edge of the observable universe is 46 billion light-years[50] (14 billion parsecs),[51] making the diameter of the observable universe about 93 billion light-years (28 billion parsecs).[50] The distance the light from the edge of the observable universe has travelled is very close to the age of the Universe times the speed of light, 13.8 billion light-years (4.2×10^9 pc), but this does not represent the distance at any given time because the edge of the observable universe and the Earth have since moved further apart.[52] For comparison, the diameter of a typical galaxy is 30,000 light-years (9,198 parsecs), and the typical distance between two neighboring galaxies is 3 million light-years (919.8 kiloparsecs).[53] As an example, the Milky Way is roughly 100,000–180,000 light-years in diameter,[54][55] and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy, is located roughly 2.5 million light-years away.[56]

Because we cannot observe space beyond the edge of the observable universe, it is unknown whether the size of the Universe in its totality is finite or infinite.[3][57][58] Estimates for the total size of the universe, if finite, reach as high as   megaparsecs, implied by one resolution of the No-Boundary Proposal.[59][b]

Age and expansion

Astronomers calculate the age of the Universe by assuming that the Lambda-CDM model accurately describes the evolution of the Universe from a very uniform, hot, dense primordial state to its present state and measuring the cosmological parameters which constitute the model.[citation needed] This model is well understood theoretically and supported by recent high-precision astronomical observations such as WMAP and Planck.[citation needed] Commonly, the set of observations fitted includes the cosmic microwave background anisotropy, the brightness/redshift relation for Type Ia supernovae, and large-scale galaxy clustering including the baryon acoustic oscillation feature.[citation needed] Other observations, such as the Hubble constant, the abundance of galaxy clusters, weak gravitational lensing and globular cluster ages, are generally consistent with these, providing a check of the model, but are less accurately measured at present.[citation needed] Assuming that the Lambda-CDM model is correct, the measurements of the parameters using a variety of techniques by numerous experiments yield a best value of the age of the Universe as of 2015 of 13.799 ± 0.021 billion years.[2]

Astronomers discovered stars in the Milky Way galaxy that are almost 13.6 billion years old.

Over time, the Universe and its contents have evolved; for example, the relative population of quasars and galaxies has changed[60] and space itself has expanded. Due to this expansion, scientists on Earth can observe the light from a galaxy 30 billion light-years away even though that light has traveled for only 13 billion years; the very space between them has expanded. This expansion is consistent with the observation that the light from distant galaxies has been redshifted; the photons emitted have been stretched to longer wavelengths and lower frequency during their journey. Analyses of Type Ia supernovae indicate that the spatial expansion is accelerating.[61][62]

The more matter there is in the Universe, the stronger the mutual gravitational pull of the matter. If the Universe were too dense then it would re-collapse into a gravitational singularity. However, if the Universe contained too little matter then the self-gravity would be too weak for astronomical structures, like galaxies or planets, to form. Since the Big Bang, the universe has expanded monotonically. Perhaps unsurprisingly, our universe has just the right mass-energy density, equivalent to about 5 protons per cubic meter, which has allowed it to expand for the last 13.8 billion years, giving time to form the universe as observed today.[63]

There are dynamical forces acting on the particles in the Universe which affect the expansion rate. Before 1998, it was expected that the expansion rate would be decreasing as time went on due to the influence of gravitational interactions in the Universe; and thus there is an additional observable quantity in the Universe called the deceleration parameter, which most cosmologists expected to be positive and related to the matter density of the Universe. In 1998, the deceleration parameter was measured by two different groups to be negative, approximately -0.55, which technically implies that the second derivative of the cosmic scale factor   has been positive in the last 5-6 billion years.[17][64] This acceleration does not, however, imply that the Hubble parameter is currently increasing; see deceleration parameter for details.


Spacetimes are the arenas in which all physical events take place. The basic elements of spacetimes are events. In any given spacetime, an event is defined as a unique position at a unique time. A spacetime is the union of all events (in the same way that a line is the union of all of its points), formally organized into a manifold.[65]

The Universe appears to be a smooth spacetime continuum consisting of three spatial dimensions and one temporal (time) dimension (an event in the spacetime of the physical Universe can therefore be identified by a set of four coordinates: (x, y, z, t) ). On the average, space is observed to be very nearly flat (with a curvature close to zero), meaning that Euclidean geometry is empirically true with high accuracy throughout most of the Universe.[66] Spacetime also appears to have a simply connected topology, in analogy with a sphere, at least on the length-scale of the observable Universe. However, present observations cannot exclude the possibilities that the Universe has more dimensions (which is postulated by theories such as the String theory) and that its spacetime may have a multiply connected global topology, in analogy with the cylindrical or toroidal topologies of two-dimensional spaces.[67][68] The spacetime of the Universe is usually interpreted from a Euclidean perspective, with space as consisting of three dimensions, and time as consisting of one dimension, the "fourth dimension".[69] By combining space and time into a single manifold called Minkowski space, physicists have simplified a large number of physical theories, as well as described in a more uniform way the workings of the Universe at both the supergalactic and subatomic levels.



The three possible options for the shape of the Universe

General relativity describes how spacetime is curved and bent by mass and energy (gravity). The topology or geometry of the Universe includes both local geometry in the observable universe and global geometry. Cosmologists often work with a given space-like slice of spacetime called the comoving coordinates. The section of spacetime which can be observed is the backward light cone, which delimits the cosmological horizon. The cosmological horizon (also called the particle horizon or the light horizon) is the maximum distance from which particles can have traveled to the observer in the age of the Universe. This horizon represents the boundary between the observable and the unobservable regions of the Universe.[70][71] The existence, properties, and significance of a cosmological horizon depend on the particular cosmological model.


Observations, including the Cosmic Background Explorer (COBE), Wilkinson Microwave Anisotropy Probe (WMAP), and Planck maps of the CMB, suggest that the Universe is infinite in extent with a finite age, as described by the Friedmann–Lemaître–Robertson–Walker (FLRW) models.[73][67][74][75] These FLRW models thus support inflationary models and the standard model of cosmology, describing a flat, homogeneous universe presently dominated by dark matter and dark energy.[76][77]

Support of life

The Universe may be fine-tuned; the Fine-tuned Universe hypothesis is the proposition that the conditions that allow the existence of observable life in the Universe can only occur when certain universal fundamental physical constants lie within a very narrow range of values, so that if any of several fundamental constants were only slightly different, the Universe would have been unlikely to be conducive to the establishment and development of matter, astronomical structures, elemental diversity, or life as it is understood.[78] The proposition is discussed among philosophers, scientists, theologians, and proponents of creationism.


The Universe is composed almost completely of dark energy, dark matter, and ordinary matter. Other contents are electromagnetic radiation (estimated to constitute from 0.005% to close to 0.01% of the total mass-energy of the Universe) and antimatter.[79][80][81]

The proportions of all types of matter and energy have changed over the history of the Universe.[82] The total amount of electromagnetic radiation generated within the universe has decreased by 1/2 in the past 2 billion years.[83][84] Today, ordinary matter, which includes atoms, stars, galaxies, and life, accounts for only 4.9% of the contents of the Universe.[8] The present overall density of this type of matter is very low, roughly 4.5 × 10−31 grams per cubic centimetre, corresponding to a density of the order of only one proton for every four cubic meters of volume.[6] The nature of both dark energy and dark matter is unknown. Dark matter, a mysterious form of matter that has not yet been identified, accounts for 26.8% of the cosmic contents. Dark energy, which is the energy of empty space and is causing the expansion of the Universe to accelerate, accounts for the remaining 68.3% of the contents.[8][85][86]

The formation of clusters and large-scale filaments in the cold dark matter model with dark energy. The frames show the evolution of structures in a 43 million parsecs (or 140 million light-years) box from redshift of 30 to the present epoch (upper left z=30 to lower right z=0).
A map of the superclusters and voids nearest to Earth

Matter, dark matter, and dark energy are distributed homogeneously throughout the Universe over length scales longer than 300 million light-years or so.[87] However, over shorter length-scales, matter tends to clump hierarchically; many atoms are condensed into stars, most stars into galaxies, most galaxies into clusters, superclusters and, finally, large-scale galactic filaments. The observable Universe contains more than 2 trillion (1012) galaxies[88] and, overall, as many as an estimated 1×1024 stars[89][90] (more stars than all the grains of sand on planet Earth).[91] Typical galaxies range from dwarfs with as few as ten million[92] (107) stars up to giants with one trillion[93] (1012) stars. Between the larger structures are voids, which are typically 10–150 Mpc (33 million–490 million ly) in diameter. The Milky Way is in the Local Group of galaxies, which in turn is in the Laniakea Supercluster.[94] This supercluster spans over 500 million light-years, while the Local Group spans over 10 million light-years.[95] The Universe also has vast regions of relative emptiness; the largest known void measures 1.8 billion ly (550 Mpc) across.[96]

Comparison of the contents of the Universe today to 380,000 years after the Big Bang as measured with 5 year WMAP data (from 2008).[97] (Due to rounding errors, the sum of these numbers is not 100%). This reflects the 2008 limits of WMAP's ability to define dark matter and dark energy.

The observable Universe is isotropic on scales significantly larger than superclusters, meaning that the statistical properties of the Universe are the same in all directions as observed from Earth. The Universe is bathed in highly isotropic microwave radiation that corresponds to a thermal equilibrium blackbody spectrum of roughly 2.72548 kelvins.[7] The hypothesis that the large-scale Universe is homogeneous and isotropic is known as the cosmological principle.[98] A Universe that is both homogeneous and isotropic looks the same from all vantage points[99] and has no center.[100]

Dark energy

An explanation for why the expansion of the Universe is accelerating remains elusive. It is often attributed to "dark energy", an unknown form of energy that is hypothesized to permeate space.[101] On a mass–energy equivalence basis, the density of dark energy (~ 7 × 10−30 g/cm3) is much less than the density of ordinary matter or dark matter within galaxies. However, in the present dark-energy era, it dominates the mass–energy of the universe because it is uniform across space.[102][103]


Dark matter


Ordinary matter







Ordinary matter and the forces that act on matter can be described in terms of elementary particles.[110] These particles are sometimes described as being fundamental, since they have an unknown substructure, and it is unknown whether or not they are composed of smaller and even more fundamental particles.[111][112] Of central importance is the Standard Model, a theory that is concerned with electromagnetic interactions and the weak and strong nuclear interactions.[113] The Standard Model is supported by the experimental confirmation of the existence of particles that compose matter: quarks and leptons, and their corresponding "antimatter" duals, as well as the force particles that mediate interactions: the photon, the W and Z bosons, and the gluon.[111] The Standard Model predicted the existence of the recently discovered Higgs boson, a particle that is a manifestation of a field within the Universe that can endow particles with mass.[114][115] Because of its success in explaining a wide variety of experimental results, the Standard Model is sometimes regarded as a "theory of almost everything".[113] The Standard Model does not, however, accommodate gravity. A true force-particle "theory of everything" has not been attained.[116]









Cosmological models

Model of the Universe based on general relativity




where (r, θ, φ) correspond to a spherical coordinate system. This metric has only two undetermined parameters. An overall dimensionless length scale factor R describes the size scale of the Universe as a function of time; an increase in R is the expansion of the Universe.[126] A curvature index k describes the geometry. The index k is defined so that it can take only one of three values: 0, corresponding to flat Euclidean geometry; 1, corresponding to a space of positive curvature; or −1, corresponding to a space of positive or negative curvature.[127] The value of R as a function of time t depends upon k and the cosmological constant Λ.[125] The cosmological constant represents the energy density of the vacuum of space and could be related to dark energy.[86] The equation describing how R varies with time is known as the Friedmann equation after its inventor, Alexander Friedmann.[128]

The solutions for R(t) depend on k and Λ, but some qualitative features of such solutions are general. First and most importantly, the length scale R of the Universe can remain constant only if the Universe is perfectly isotropic with positive curvature (k=1) and has one precise value of density everywhere, as first noted by Albert Einstein.[125] However, this equilibrium is unstable: because the Universe is known to be inhomogeneous on smaller scales, R must change over time. When R changes, all the spatial distances in the Universe change in tandem; there is an overall expansion or contraction of space itself. This accounts for the observation that galaxies appear to be flying apart; the space between them is stretching. The stretching of space also accounts for the apparent paradox that two galaxies can be 40 billion light-years apart, although they started from the same point 13.8 billion years ago[129] and never moved faster than the speed of light.


Third, the curvature index k determines the sign of the mean spatial curvature of spacetime[127] averaged over sufficiently large length scales (greater than about a billion light-years). If k=1, the curvature is positive and the Universe has a finite volume.[131] A Universe with positive curvature is often visualized as a three-dimensional sphere embedded in a four-dimensional space. Conversely, if k is zero or negative, the Universe has an infinite volume.[131] It may seem counter-intuitive that an infinite and yet infinitely dense Universe could be created in a single instant at the Big Bang when R=0, but exactly that is predicted mathematically when k does not equal 1. By analogy, an infinite plane has zero curvature but infinite area, whereas an infinite cylinder is finite in one direction and a torus is finite in both. A toroidal Universe could behave like a normal Universe with periodic boundary conditions.


Multiverse hypothesis

Depiction of a multiverse of seven "bubble" universes, which are separate spacetime continua, each having different physical laws, physical constants, and perhaps even different numbers of dimensions or topologies.

Some speculative theories have proposed that our Universe is but one of a set of disconnected universes, collectively denoted as the multiverse, challenging or enhancing more limited definitions of the Universe.[21][134] Scientific multiverse models are distinct from concepts such as alternate planes of consciousness and simulated reality.

Max Tegmark developed a four-part classification scheme for the different types of multiverses that scientists have suggested in response to various Physics problems. An example of such multiverses is the one resulting from the chaotic inflation model of the early universe.[135] Another is the multiverse resulting from the many-worlds interpretation of quantum mechanics. In this interpretation, parallel worlds are generated in a manner similar to quantum superposition and decoherence, with all states of the wave functions being realized in separate worlds. Effectively, in the many-worlds interpretation the multiverse evolves as a universal wavefunction. If the Big Bang that created our multiverse created an ensemble of multiverses, the wave function of the ensemble would be entangled in this sense.[136]

The least controversial category of multiverse in Tegmark's scheme is Level I. The multiverses of this level are composed by distant spacetime events "in our own universe". If space is infinite, or sufficiently large and uniform, identical instances of the history of Earth's entire Hubble volume occur every so often, simply by chance. Tegmark calculated that our nearest so-called doppelgänger, is 1010115 meters away from us (a double exponential function larger than a googolplex).[137][138] In principle, it would be impossible to scientifically verify the existence of an identical Hubble volume. However, this existence does follow as a fairly straightforward consequence from otherwise unrelated scientific observations and theories.[clarification needed (which ones?)]

It is possible to conceive of disconnected spacetimes, each existing but unable to interact with one another.[137][139] An easily visualized metaphor of this concept is a group of separate soap bubbles, in which observers living on one soap bubble cannot interact with those on other soap bubbles, even in principle.[140] According to one common terminology, each "soap bubble" of spacetime is denoted as a universe, whereas our particular spacetime is denoted as the Universe,[21] just as we call our moon the Moon. The entire collection of these separate spacetimes is denoted as the multiverse.[21] With this terminology, different Universes are not causally connected to each other.[21] In principle, the other unconnected Universes may have different dimensionalities and topologies of spacetime, different forms of matter and energy, and different physical laws and physical constants, although such possibilities are purely speculative.[21] Others consider each of several bubbles created as part of chaotic inflation to be separate Universes, though in this model these universes all share a causal origin.[21]

Historical conceptions



Many cultures have stories describing the origin of the world and universe. Cultures generally regard these stories as having some truth. There are however many differing beliefs in how these stories apply amongst those believing in a supernatural origin, ranging from a god directly creating the Universe as it is now to a god just setting the "wheels in motion" (for example via mechanisms such as the big bang and evolution).[143]


Philosophical models



The Indian philosopher Kanada, founder of the Vaisheshika school, developed a notion of atomism and proposed that light and heat were varieties of the same substance.[148] In the 5th century AD, the Buddhist atomist philosopher Dignāga proposed atoms to be point-sized, durationless, and made of energy. They denied the existence of substantial matter and proposed that movement consisted of momentary flashes of a stream of energy.[149]


Astronomical concepts

3rd century BCE calculations by Aristarchus on the relative sizes of, from left to right, the Sun, Earth, and Moon, from a 10th-century AD Greek copy.


Later Greek philosophers, observing the motions of the heavenly bodies, were concerned with developing models of the Universe-based more profoundly on empirical evidence. The first coherent model was proposed by Eudoxus of Cnidos. According to Aristotle's physical interpretation of the model, celestial spheres eternally rotate with uniform motion around a stationary Earth. Normal matter is entirely contained within the terrestrial sphere.

De Mundo (composed before 250 BC or between 350 and 200 BC), stated, "Five elements, situated in spheres in five regions, the less being in each case surrounded by the greater—namely, earth surrounded by water, water by air, air by fire, and fire by ether—make up the whole Universe".[151]


The Greek astronomer Aristarchus of Samos was the first known individual to propose a heliocentric model of the Universe. Though the original text has been lost, a reference in Archimedes' book The Sand Reckoner describes Aristarchus's heliocentric model. Archimedes wrote:




The only other astronomer from antiquity known by name who supported Aristarchus's heliocentric model was Seleucus of Seleucia, a Hellenistic astronomer who lived a century after Aristarchus.[153][154][155] According to Plutarch, Seleucus was the first to prove the heliocentric system through reasoning, but it is not known what arguments he used. Seleucus' arguments for a heliocentric cosmology were probably related to the phenomenon of tides.[156] According to Strabo (1.1.9), Seleucus was the first to state that the tides are due to the attraction of the Moon, and that the height of the tides depends on the Moon's position relative to the Sun.[157] Alternatively, he may have proved heliocentricity by determining the constants of a geometric model for it, and by developing methods to compute planetary positions using this model, like what Nicolaus Copernicus later did in the 16th century.[158] During the Middle Ages, heliocentric models were also proposed by the Indian astronomer Aryabhata,[159] and by the Persian astronomers Albumasar[160] and Al-Sijzi.[161]


The Aristotelian model was accepted in the Western world for roughly two millennia, until Copernicus revived Aristarchus's perspective that the astronomical data could be explained more plausibly if the Earth rotated on its axis and if the Sun were placed at the center of the Universe.



As noted by Copernicus himself, the notion that the Earth rotates is very old, dating at least to Philolaus (c. 450 BC), Heraclides Ponticus (c. 350 BC) and Ecphantus the Pythagorean. Roughly a century before Copernicus, the Christian scholar Nicholas of Cusa also proposed that the Earth rotates on its axis in his book, On Learned Ignorance (1440).[162] Al-Sijzi[163] also proposed that the Earth rotates on its axis. Empirical evidence for the Earth's rotation on its axis, using the phenomenon of comets, was given by Tusi (1201–1274) and Ali Qushji (1403–1474).[164]

This cosmology was accepted by Isaac Newton, Christiaan Huygens and later scientists.[165] Edmund Halley (1720)[166] and Jean-Philippe de Chéseaux (1744)[167] noted independently that the assumption of an infinite space filled uniformly with stars would lead to the prediction that the nighttime sky would be as bright as the Sun itself; this became known as Olbers' paradox in the 19th century.[168] Newton believed that an infinite space uniformly filled with matter would cause infinite forces and instabilities causing the matter to be crushed inwards under its own gravity.[165] This instability was clarified in 1902 by the Jeans instability criterion.[169] One solution to these paradoxes is the Charlier Universe, in which the matter is arranged hierarchically (systems of orbiting bodies that are themselves orbiting in a larger system, ad infinitum) in a fractal way such that the Universe has a negligibly small overall density; such a cosmological model had also been proposed earlier in 1761 by Johann Heinrich Lambert.[53][170] A significant astronomical advance of the 18th century was the realization by Thomas Wright, Immanuel Kant and others of nebulae.[166]

In 1919, when Hooker Telescope was completed, the prevailing view still was that the Universe consisted entirely of the Milky Way Galaxy. Using the Hooker Telescope, Edwin Hubble identified Cepheid variables in several spiral nebulae and in 1922–1923 proved conclusively that Andromeda Nebula and Triangulum among others, were entire galaxies outside our own, thus proving that Universe consists of multitude of galaxies.[171]


Map of the observable universe with some of the notable astronomical objects known today. The scale of length increases exponentially toward the right. Celestial bodies are shown enlarged in size to be able to appreciate their shapes.

See also



  1. ^ a b According to modern physics, particularly the theory of relativity, space and time are intimately intertwined and physically meaningless if taken separately from each other.
  2. ^ Although listed in megaparsecs by the cited source, this number is so vast that its digits would remain virtually unchanged for all intents and purposes regardless of which conventional units it is listed in, whether it to be nanometres or gigaparsecs, as the differences would disappear into the error.


  1. ^ "Hubble sees galaxies galore". Retrieved April 30, 2017.
  2. ^ a b c Planck Collaboration (2016). "Planck 2015 results. XIII. Cosmological parameters". Astronomy & Astrophysics. 594: A13, Table 4. arXiv:1502.01589. Bibcode:2016A&A...594A..13P. doi:10.1051/0004-6361/201525830.
  3. ^ a b c d Greene, Brian (2011). The Hidden Reality. Alfred A. Knopf.
  6. ^ a b NASA/WMAP Science Team (January 24, 2014). "Universe 101: What is the Universe Made Of?". NASA. Retrieved February 17, 2015.
  7. ^ a b Fixsen, D.J. (2009). "The Temperature of the Cosmic Microwave Background". The Astrophysical Journal. 707 (2): 916–20. arXiv:0911.1955. Bibcode:2009ApJ...707..916F. doi:10.1088/0004-637X/707/2/916.
  8. ^ a b c "First Planck results: the Universe is still weird and interesting". Matthew Francis. Ars technica. March 21, 2013. Retrieved August 21, 2015.
  9. ^ NASA/WMAP Science Team (January 24, 2014). "Universe 101: Will the Universe expand forever?". NASA. Retrieved April 16, 2015.
  10. ^ a b Zeilik, Michael; Gregory, Stephen A. (1998). Introductory Astronomy & Astrophysics (4th ed.). Saunders College Publishing. ISBN 978-0-03-006228-5. The totality of all space and time; all that is, has been, and will be.
  11. ^ "This is Why the Multiverse Must Exist - Starts with a Bang!". March 22, 2019.
  12. ^ Tegmark, Max (May 2003). "Parallel Universes". Scientific American. Vol. 288. pp. 40–51. arXiv:astro-ph/0302131. Bibcode:2003SciAm.288e..40T. doi:10.1038/scientificamerican0503-40. PMID 12701329.
  14. ^ a b c d Thomas F. Glick; Steven Livesey; Faith Wallis. Medieval Science Technology and Medicine: An Encyclopedia. Routledge.
  15. ^ Carroll, Bradley W.; Ostlie, Dale A. (July 23, 2013). An Introduction to Modern Astrophysics (International ed.). Pearson. pp. 1173–74. ISBN 978-1-292-02293-2.
  16. ^ Hawking, Stephen (1988). A Brief History of Time. Bantam Books. p. 125. ISBN 978-0-553-05340-1.
  17. ^ a b "The Nobel Prize in Physics 2011". Retrieved April 16, 2015.
  18. ^ Redd, Nola. "What is Dark Matter?". Retrieved February 1, 2018.
  19. ^ a b Planck 2015 results, table 9
  20. ^ Persic, Massimo; Salucci, Paolo (September 1, 1992). "The baryon content of the Universe". Monthly Notices of the Royal Astronomical Society. 258 (1): 14P–18P. arXiv:astro-ph/0502178. Bibcode:1992MNRAS.258P..14P. doi:10.1093/mnras/258.1.14P. ISSN 0035-8711.: states "less than 10%" but also provides a more exact value of 0.3% of the universe, which is about 6% of baryonic matter [4.9% according to Planck 2015].
  21. ^ a b c d e f g Ellis, George F.R.; U. Kirchner; W.R. Stoeger (2004). "Multiverses and physical cosmology". Monthly Notices of the Royal Astronomical Society. 347 (3): 921–36. arXiv:astro-ph/0305292. Bibcode:2004MNRAS.347..921E. doi:10.1111/j.1365-2966.2004.07261.x.
  22. ^ Palmer, Jason. (August 3, 2011) BBC News – 'Multiverse' theory suggested by microwave background. Retrieved November 28, 2011.
  23. ^ "Universe". Encyclopaedia Britannica online. Encyclopaedia Britannica Inc. 2012. Retrieved February 17, 2018.
  24. ^ "Universe". Merriam-Webster Dictionary. Retrieved September 21, 2012.
  25. ^ "Universe". Retrieved September 21, 2012.
  26. ^ a b Duco A. Schreuder (December 3, 2014). Vision and Visual Perception. Archway Publishing. p. 135. ISBN 978-1-4808-1294-9.
  27. ^ Mermin, N. David (2004). "Could Feynman Have Said This?". Physics Today. 57 (5): 10. Bibcode:2004PhT....57e..10M. doi:10.1063/1.1768652.
  28. ^ Tegmark, Max (2008). "The Mathematical Universe". Foundations of Physics. 38 (2): 101–50. arXiv:0704.0646. Bibcode:2008FoPh...38..101T. doi:10.1007/s10701-007-9186-9. A short version of which is available at Fixsen, D. J. (2007). "Shut up and calculate". arXiv:0709.4024 [physics.pop-ph]. in reference to David Mermin's famous quote "shut up and calculate!"[27]
  31. ^ Paul Copan; William Lane Craig (2004). Creation Out of Nothing: A Biblical, Philosophical, and Scientific Exploration. Baker Academic. p. 220. ISBN 978-0-8010-2733-8.
  34. ^ Lewis, C.T. and Short, S (1879) A Latin Dictionary, Oxford University Press, ISBN 0-19-864201-6, pp. 1933, 1977–1978.
  35. ^ Liddell; Scott. "A Greek-English Lexicon". πᾶς
  36. ^ Liddell; Scott. "A Greek-English Lexicon". ὅλος
  37. ^ Liddell; Scott. "A Greek–English Lexicon". κόσμος
  38. ^ Lewis, C.T.; Short, S (1879). A Latin Dictionary. Oxford University Press. pp. 1175, 1189–90, 1881–82. ISBN 978-0-19-864201-5.
  39. ^ The Compact Edition of the Oxford English Dictionary. II. Oxford: Oxford University Press. 1971. pp. 569, 909, 1900, 3821–22. ISBN 978-0-19-861117-2.
  42. ^ C. Sivaram (1986). "Evolution of the Universe through the Planck epoch". Astrophysics and Space Science. 125 (1): 189–99. Bibcode:1986Ap&SS.125..189S. doi:10.1007/BF00643984.
  43. ^ Richard B. Larson & Volker Bromm (March 2002). "The First Stars in the Universe". Scientific American.
  44. ^ Ryden, Barbara, "Introduction to Cosmology", 2006, eqn. 6.33
  45. ^ "Antimatter". Particle Physics and Astronomy Research Council. October 28, 2003. Archived from the original on March 7, 2004. Retrieved August 10, 2006.
  46. ^ Adamson, Allan (October 19, 2017). "Universe Should Not Actually Exist: Big Bang Produced Equal Amounts Of Matter And Antimatter". Retrieved October 26, 2017.
  47. ^ Smorra C.; et al. (October 20, 2017). "A parts-per-billion measurement of the antiproton magnetic moment" (PDF). Nature. 550 (7676): 371–74. Bibcode:2017Natur.550..371S. doi:10.1038/nature24048. PMID 29052625.
  49. ^ Michio Kaku (March 11, 2008). Physics of the Impossible: A Scientific Exploration into the World of Phasers, Force Fields, Teleportation, and Time Travel. Knopf Doubleday Publishing Group. pp. 202–. ISBN 978-0-385-52544-2.
  50. ^ a b Itzhak Bars; John Terning (October 19, 2018). Extra Dimensions in Space and Time. Springer. pp. 27–. ISBN 978-0-387-77637-8. Retrieved October 19, 2018.
  51. ^ "WolframAlpha". Retrieved October 19, 2018.
  52. ^ Christopher Crockett (February 20, 2013). "What is a light-year?". EarthSky.
  53. ^ a b Rindler, p. 196.
  54. ^ Christian, Eric; Samar, Safi-Harb. "How large is the Milky Way?". Retrieved November 28, 2007.
  55. ^ Hall, Shannon (May 4, 2015). "Size of the Milky Way Upgraded, Solving Galaxy Puzzle". Retrieved June 9, 2015.
  56. ^ I. Ribas; C. Jordi; F. Vilardell; E.L. Fitzpatrick; R.W. Hilditch; F. Edward Guinan (2005). "First Determination of the Distance and Fundamental Properties of an Eclipsing Binary in the Andromeda Galaxy". Astrophysical Journal. 635 (1): L37–L40. arXiv:astro-ph/0511045. Bibcode:2005ApJ...635L..37R. doi:10.1086/499161.
    McConnachie, A.W.; Irwin, M.J.; Ferguson, A.M.N.; Ibata, R.A.; Lewis, G.F.; Tanvir, N. (2005). "Distances and metallicities for 17 Local Group galaxies". Monthly Notices of the Royal Astronomical Society. 356 (4): 979–97. arXiv:astro-ph/0410489. Bibcode:2005MNRAS.356..979M. doi:10.1111/j.1365-2966.2004.08514.x.
  57. ^ "How can space travel faster than the speed of light?". Vannesa Janek. Universe Today. February 20, 2015. Retrieved June 6, 2015.
  58. ^ "Is faster-than-light travel or communication possible? Section: Expansion of the Universe". Philip Gibbs. 1997. Archived from the original on March 10, 2010. Retrieved June 6, 2015.
  59. ^ "Susskind's Challenge to the Hartle-Hawking No-Boundary Proposal and Possible Resolutions"
  60. ^ Phil Berardelli (March 25, 2010). "Galaxy Collisions Give Birth to Quasars". Science News.
  61. ^ Riess, Adam G.; Filippenko; Challis; Clocchiatti; Diercks; Garnavich; Gilliland; Hogan; Jha; Kirshner; Leibundgut; Phillips; Reiss; Schmidt; Schommer; Smith; Spyromilio; Stubbs; Suntzeff; Tonry (1998). "Observational evidence from supernovae for an accelerating universe and a cosmological constant". Astronomical Journal. 116 (3): 1009–38. arXiv:astro-ph/9805201. Bibcode:1998AJ....116.1009R. doi:10.1086/300499.
  63. ^ Sean Carroll; Michio Kaku (2014). "End of the Universe". How the Universe Works. Discovery Channel.
  64. ^ Overbye, Dennis (October 11, 2003). "A 'Cosmic Jerk' That Reversed the Universe". New York Times.
  65. ^ Schutz, Bernard (May 31, 2009). A First Course in General Relativity (2 ed.). Cambridge University Press. pp. 142, 171. ISBN 978-0-521-88705-2.
  66. ^ WMAP Mission: Results – Age of the Universe. Retrieved November 28, 2011.
  67. ^ a b Luminet, Jean-Pierre; Weeks, Jeffrey R.; Riazuelo, Alain; Lehoucq, Roland; Uzan, Jean-Philippe (October 9, 2003). "Dodecahedral space topology as an explanation for weak wide-angle temperature correlations in the cosmic microwave background". Nature (Submitted manuscript). 425 (6958): 593–95. arXiv:astro-ph/0310253. Bibcode:2003Natur.425..593L. doi:10.1038/nature01944. PMID 14534579.
  68. ^ Luminet, Jean-Pierre; Boudewijn F. Roukema (1999). "Topology of the Universe: Theory and Observations". Proceedings of Cosmology School held at Cargese, Corsica, August 1998. arXiv:astro-ph/9901364. Bibcode:1999ASIC..541..117L.
  69. ^ Brill, Dieter; Jacobsen, Ted (2006). "Spacetime and Euclidean geometry". General Relativity and Gravitation. 38 (4): 643–51. arXiv:gr-qc/0407022. Bibcode:2006GReGr..38..643B. CiteSeerX doi:10.1007/s10714-006-0254-9.
  70. ^ Edward Robert Harrison (2000). Cosmology: the science of the universe. Cambridge University Press. pp. 447–. ISBN 978-0-521-66148-5. Retrieved May 1, 2011.
  71. ^ Andrew R. Liddle; David Hilary Lyth (April 13, 2000). Cosmological inflation and large-scale structure. Cambridge University Press. pp. 24–. ISBN 978-0-521-57598-0. Retrieved May 1, 2011.
  72. ^ "What is the Ultimate Fate of the Universe?". National Aeronautics and Space Administration. NASA. Retrieved August 23, 2015.
  73. ^ Roukema, Boudewijn; Zbigniew Buliński; Agnieszka Szaniewska; Nicolas E. Gaudin (2008). "A test of the Poincare dodecahedral space topology hypothesis with the WMAP CMB data". Astronomy and Astrophysics. 482 (3): 747–53. arXiv:0801.0006. Bibcode:2008A&A...482..747L. doi:10.1051/0004-6361:20078777.
  74. ^ Aurich, Ralf; Lustig, S.; Steiner, F.; Then, H. (2004). "Hyperbolic Universes with a Horned Topology and the CMB Anisotropy". Classical and Quantum Gravity. 21 (21): 4901–26. arXiv:astro-ph/0403597. Bibcode:2004CQGra..21.4901A. doi:10.1088/0264-9381/21/21/010.
  76. ^ "Planck reveals 'almost perfect' universe". Michael Banks. Physics World. March 21, 2013. Retrieved March 21, 2013.
  77. ^ Mark Isaak, ed. (2005). "CI301: The Anthropic Principle". Index to Creationist Claims. TalkOrigins Archive. Retrieved October 31, 2007.
  78. ^ Fritzsche, Hellmut. "electromagnetic radiation | physics". Encyclopædia Britannica. p. 1. Retrieved July 26, 2015.
  79. ^ "Physics 7:Relativity, SpaceTime and Cosmology" (PDF). Physics 7:Relativity, SpaceTime and Cosmology. University of California Riverside. Archived from the original (PDF) on September 5, 2015. Retrieved July 26, 2015.
  80. ^ "Physics – for the 21st Century". Harvard-Smithsonian Center for Astrophysics Annenberg Learner. Retrieved July 27, 2015.
  81. ^ "Dark matter – A history shapes by dark force". Timothy Ferris. National Geographic. 2015. Retrieved December 29, 2015.
  82. ^ Redd,, Nola Taylor. "It's Official: The Universe Is Dying Slowly". Retrieved August 11, 2015.
  83. ^ Will Parr; et al. "RIP Universe – Your Time Is Coming… Slowly | Video". Retrieved August 20, 2015.
  84. ^ a b Sean Carroll, Ph.D., Caltech, 2007, The Teaching Company, Dark Matter, Dark Energy: The Dark Side of the Universe, Guidebook Part 2 p. 46, Accessed October 7, 2013, "...dark matter: An invisible, essentially collisionless component of matter that makes up about 25 percent of the energy density of the universe... it's a different kind of particle... something not yet observed in the laboratory..."
  85. ^ a b Peebles, P.J. E. & Ratra, Bharat (2003). "The cosmological constant and dark energy". Reviews of Modern Physics. 75 (2): 559–606. arXiv:astro-ph/0207347. Bibcode:2003RvMP...75..559P. doi:10.1103/RevModPhys.75.559.
  86. ^ Mandolesi, N.; Calzolari, P.; Cortiglioni, S.; Delpino, F.; Sironi, G.; Inzani, P.; Deamici, G.; Solheim, J.-E.; Berger, L.; Partridge, R.B.; Martenis, P.L.; Sangree, C.H.; Harvey, R.C. (1986). "Large-scale homogeneity of the Universe measured by the microwave background". Nature. 319 (6056): 751–53. Bibcode:1986Natur.319..751M. doi:10.1038/319751a0.
  88. ^ Staff (2019). "How Many Stars Are There In The Universe?". European Space Agency. Retrieved September 21, 2019.
  89. ^ "The Structure of the Universe". doi:10.1007/978-1-4614-8730-2_10. Cite journal requires |journal= (help)
  91. ^ "Unveiling the Secret of a Virgo Dwarf Galaxy". European Southern Observatory Press Release. ESO: 12. May 3, 2000. Bibcode:2000eso..pres...12. Retrieved January 3, 2007.
  92. ^ "Hubble's Largest Galaxy Portrait Offers a New High-Definition View". NASA. February 28, 2006. Retrieved January 3, 2007.
  93. ^ Gibney, Elizabeth (September 3, 2014). "Earth's new address: 'Solar System, Milky Way, Laniakea'". Elizabeth Gibney. doi:10.1038/nature.2014.15819. Retrieved August 21, 2015.
  94. ^ "Local Group". Fraser Cain. Universe Today. May 4, 2009. Retrieved August 21, 2015.
  95. ^ Devlin, Hannah; Correspondent, Science (April 20, 2015). "Astronomers discover largest known structure in the universe is ... a big hole". The Guardian.
  96. ^ "Content of the Universe – WMAP 9yr Pie Chart". Retrieved July 26, 2015.
  97. ^ Rindler, p. 202.
  99. ^ Livio, Mario (2001). The Accelerating Universe: Infinite Expansion, the Cosmological Constant, and the Beauty of the Cosmos. John Wiley and Sons. p. 53. ISBN 978-0-471-43714-7. Retrieved March 31, 2012.
  101. ^ Paul J. Steinhardt; Neil Turok (2006). "Why the cosmological constant is small and positive". Science. 312 (5777): 1180–83. arXiv:astro-ph/0605173. Bibcode:2006Sci...312.1180S. doi:10.1126/science.1126231. PMID 16675662.
  102. ^ "Dark Energy". Hyperphysics. Retrieved January 4, 2014.
  103. ^ Carroll, Sean (2001). "The cosmological constant". Living Reviews in Relativity. 4 (1): 1. arXiv:astro-ph/0004075. Bibcode:2001LRR.....4....1C. doi:10.12942/lrr-2001-1. PMC 5256042. PMID 28179856. Archived from the original on October 13, 2006. Retrieved September 28, 2006.
  104. ^ "Planck captures portrait of the young Universe, revealing earliest light". University of Cambridge. March 21, 2013. Retrieved March 21, 2013.
  107. ^ G. 't Hooft (1997). In search of the ultimate building blocks. Cambridge University Press. p. 6. ISBN 978-0-521-57883-7.
  108. ^ Clayton, Donald D. (1983). Principles of Stellar Evolution and Nucleosynthesis. The University of Chicago Press. pp. 362–435. ISBN 978-0-226-10953-4.
  109. ^ Veltman, Martinus (2003). Facts and Mysteries in Elementary Particle Physics. World Scientific. ISBN 978-981-238-149-1.
  111. ^ Close, Frank (2012). Particle Physics: A Very Short Introduction. Oxford University Press. ISBN 978-0-19-280434-1.
  112. ^ a b R. Oerter (2006). The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern Physics (Kindle ed.). Penguin Group. p. 2. ISBN 978-0-13-236678-6.
  113. ^ Onyisi, P. (October 23, 2012). "Higgs boson FAQ". University of Texas ATLAS group. Retrieved January 8, 2013.
  114. ^ Strassler, M. (October 12, 2012). "The Higgs FAQ 2.0". Retrieved January 8, 2013. [Q] Why do particle physicists care so much about the Higgs particle?
  115. ^ Steven Weinberg (April 20, 2011). Dreams of a Final Theory: The Scientist's Search for the Ultimate Laws of Nature. Knopf Doubleday Publishing Group. ISBN 978-0-307-78786-6.
  116. ^ a b Allday, Jonathan (2002). Quarks, Leptons and the Big Bang (Second ed.). IOP Publishing. ISBN 978-0-7503-0806-9.
  117. ^ "Lepton (physics)". Encyclopædia Britannica. Retrieved September 29, 2010.
  118. ^ Harari, H. (1977). "Beyond charm". In Balian, R.; Llewellyn-Smith, C.H. (eds.). Weak and Electromagnetic Interactions at High Energy, Les Houches, France, Jul 5 – Aug 14, 1976. Les Houches Summer School Proceedings. 29. North-Holland. p. 613.
  119. ^ Harari H. (1977). "Three generations of quarks and leptons" (PDF). In E. van Goeler; Weinstein R. (eds.). Proceedings of the XII Rencontre de Moriond. p. 170. SLAC-PUB-1974.
  120. ^ "Experiment confirms famous physics model" (Press release). MIT News Office. April 18, 2007.
  121. ^ "Thermal history of the Universe and early growth of density fluctuations" (PDF). Guinevere Kauffmann. Max Planck Institute for Astrophysics. Retrieved January 6, 2016.
  122. ^ "First few minutes". Eric Chaisson. Havard Smithsonian Center for Astrophysics. Retrieved January 6, 2016.
  123. ^ "Timeline of the Big Bang". The physics of the Universe. Retrieved January 6, 2016.
  124. ^ a b c d Zeilik, Michael; Gregory, Stephen A. (1998). "25-2". Introductory Astronomy & Astrophysics (4th ed.). Saunders College Publishing. ISBN 978-0-03-006228-5.
  125. ^ Raine & Thomas (2001, p. 12)
  126. ^ a b Raine & Thomas (2001, p. 66)
  127. ^ Friedmann A. (1922). "Über die Krümmung des Raumes" (PDF). Zeitschrift für Physik. 10 (1): 377–86. Bibcode:1922ZPhy...10..377F. doi:10.1007/BF01332580.
  129. ^ Raine & Thomas (2001, pp. 122–23)
  130. ^ a b Raine & Thomas (2001, p. 70)
  131. ^ Raine & Thomas (2001, p. 84)
  132. ^ Raine & Thomas (2001, pp. 88, 110–13)
  133. ^ Munitz MK (1959). "One Universe or Many?". Journal of the History of Ideas. 12 (2): 231–55. doi:10.2307/2707516. JSTOR 2707516.
  134. ^ Linde A. (1986). "Eternal chaotic inflation". Mod. Phys. Lett. A. 1 (2): 81–85. Bibcode:1986MPLA....1...81L. doi:10.1142/S0217732386000129.
    Linde A. (1986). "Eternally existing self-reproducing chaotic inflationary Universe" (PDF). Phys. Lett. B. 175 (4): 395–400. Bibcode:1986PhLB..175..395L. doi:10.1016/0370-2693(86)90611-8. Retrieved March 17, 2011.
  135. ^ Everett, Hugh (1957). "Relative State Formulation of Quantum Mechanics". Reviews of Modern Physics. 29 (3): 454–62. Bibcode:1957RvMP...29..454E. doi:10.1103/RevModPhys.29.454.
  136. ^ a b Tegmark M. (2003). "Parallel universes. Not just a staple of science fiction, other universes are a direct implication of cosmological observations". Scientific American. 288 (5): 40–51. arXiv:astro-ph/0302131. Bibcode:2003SciAm.288e..40T. doi:10.1038/scientificamerican0503-40. PMID 12701329.
  137. ^ Tegmark, Max (2003). J. D. Barrow; P.C.W. Davies; C.L. Harper (eds.). "Parallel Universes". Scientific American: "Science and Ultimate Reality: From Quantum to Cosmos", Honoring John Wheeler's 90th Birthday. 288 (5): 40–51. arXiv:astro-ph/0302131. Bibcode:2003SciAm.288e..40T. doi:10.1038/scientificamerican0503-40. PMID 12701329.
  138. ^ Ellis G. F (2011). "Does the Multiverse Really Exist?". Scientific American. 305 (2): 38–43. Bibcode:2011SciAm.305a..38E. doi:10.1038/scientificamerican0811-38. PMID 21827123.
  139. ^ Clara Moskowitz (August 12, 2011). "Weird! Our Universe May Be a 'Multiverse,' Scientists Say". livescience.
  140. ^ Gernet, J. (1993–1994). "Space and time: Science and religion in the encounter between China and Europe". Chinese Science. 11. pp. 93–102.
  141. ^ Blandford R. D. (2015). "A century of general relativity: Astrophysics and cosmology". Science. 347 (6226): 1103–08. Bibcode:2015Sci...347.1103B. doi:10.1126/science.aaa4033. PMID 25745165.
  145. ^ (Henry Gravrand, "La civilisation Sereer -Pangool") [in] Universität Frankfurt am Main, Frobenius-Institut, Deutsche Gesellschaft für Kulturmorphologie, Frobenius Gesellschaft, "Paideuma: Mitteilungen zur Kulturkunde, Volumes 43–44", F. Steiner (1997), pp. 144–45, ISBN 3-515-02842-0
  146. ^ B. Young, Louise. The Unfinished Universe. Oxford University Press. p. 21.
  147. ^ Will Durant, Our Oriental Heritage:




  149. ^ Donald Wayne Viney (1985). "The Cosmological Argument". Charles Hartshorne and the Existence of God. SUNY Press. pp. 65–68. ISBN 978-0-87395-907-0.
  150. ^ Aristotle; Forster, E. S.; Dobson, J. F. (1914). De Mundo. Oxford: The Clarendon Press. p. 2.
  151. ^ Boyer, C. (1968) A History of Mathematics. Wiley, p. 54.
  152. ^ Neugebauer, Otto E. (1945). "The History of Ancient Astronomy Problems and Methods". Journal of Near Eastern Studies. 4 (1): 166–173. doi:10.1086/370729. JSTOR 595168. the Chaldaean Seleucus from Seleucia
  153. ^ Sarton, George (1955). "Chaldaean Astronomy of the Last Three Centuries B. C". Journal of the American Oriental Society. 75 (3): 166–73 (169). doi:10.2307/595168. JSTOR 595168. the heliocentrical astronomy invented by Aristarchos of Samos and still defended a century later by Seleucos the Babylonian
  156. ^ Bartel (1987, p. 527)
  157. ^ Bartel (1987, pp. 527–29)
  158. ^ Bartel (1987, pp. 529–34)
  159. ^ Bartel (1987, pp. 534–7)
  160. ^ Nasr, Seyyed H. (1993) [1964]. An Introduction to Islamic Cosmological Doctrines (2nd ed.). 1st edition by Harvard University Press, 2nd edition by State University of New York Press. pp. 135–36. ISBN 978-0-7914-1515-3.
  161. ^ Misner, Thorne and Wheeler, p. 754.
  162. ^ Ālī, Ema Ākabara. Science in the Quran. 1. Malik Library. p. 218.
  163. ^ Ragep, F. Jamil (2001), "Tusi and Copernicus: The Earth's Motion in Context", Science in Context, 14 (1–2): 145–63, doi:10.1017/s0269889701000060
  164. ^ a b Misner, Thorne and Wheeler, pp. 755–56.
  165. ^ a b Misner, Thorne and Wheeler, p. 756.
  167. ^ Olbers HWM (1826). "Unknown title". Bode's Jahrbuch. 111.. Reprinted as Appendix I in Dickson FP (1969). The Bowl of Night: The Physical Universe and Scientific Thought. Cambridge, MA: M.I.T. Press. ISBN 978-0-262-54003-2.
  168. ^ Jeans, J. H. (1902). "The Stability of a Spherical Nebula" (PDF). Philosophical Transactions of the Royal Society A. 199 (312–320): 1–53. Bibcode:1902RSPTA.199....1J. doi:10.1098/rsta.1902.0012. JSTOR 90845. Archived from the original (PDF) on July 20, 2011. Retrieved March 17, 2011.
  169. ^ Misner, Thorne and Wheeler, p. 757.
  170. ^ Sharov, Aleksandr Sergeevich; Novikov, Igor Dmitrievich (1993). Edwin Hubble, the discoverer of the big bang universe. Cambridge University Press. p. 34. ISBN 978-0-521-41617-7. Retrieved December 31, 2011.
  171. ^ Einstein, A (1917). "Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie". Preussische Akademie der Wissenschaften, Sitzungsberichte. 1917. (part 1): 142–52.


External links

Listen to this article (4 parts) · (info)
Part 1 • Part 2 • Part 3 • Part 4
This audio file was created from a revision of the article "Universe" dated 2012-06-13, and does not reflect subsequent edits to the article. (Audio help)