Jagat Raya / alam semesta itu berisi matahari, planet, bintang , tata surya, meteor, black hole, galaksi, dll. Tapi lebih jelasnya di bawah ini adalah pengertian dari jagad raya / bisa di sebut UNIVERSE
The Universe comprises everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. However, the term Universe may be used in slightly different contextual senses, denoting such concepts as the cosmos, the world or Nature.
Current interpretations of astronomical observations indicate that the age of the Universe is 13.73 (± 0.12) billion years, and that the diameter of the observable Universe is at least 93 billion light years, or 8.80 × 1026 metres.
It may seem paradoxical that two galaxies on opposite sides can be separated by 93 billion light years after only 13 billion years, since special relativity states that matter cannot be accelerated to exceed the speed of light in a localized region of space-time. However, according to general relativity, space can expand with no intrinsic limit on its rate; thus, two galaxies can separate more quickly than the speed of light if the space between them grows. It is uncertain whether the size of the Universe is finite or infinite.
According to the prevailing scientific model of the Universe, known as the Big Bang, the Universe expanded from an extremely hot, dense phase called the Planck epoch, in which all the matter and energy of the observable Universe was concentrated. Since the Planck epoch, the Universe has been expanding to its present form, possibly with a brief period (less than 10−32 seconds) of cosmic inflation. Several independent experimental measurements support this theoretical expansion and, more generally, the Big Bang theory. Recent observations indicate that this expansion is accelerating because of the dark energy, and that most of the matter and energy in the Universe is fundamentally different from that observed on Earth and not directly observable. The imprecision of current observations has hindered predictions of the ultimate fate of the Universe.
Experiments and observations suggest that the Universe has been governed by the same physical laws and constants throughout its extent and history. The dominant force at cosmological distances is gravity, and general relativity is currently the most accurate theory of gravitation. The remaining three fundamental forces and all the known 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 extremely small additional dimensions cannot be ruled out experimentally. Spacetime appears to be smooth and simply connected, and space has very small mean curvature, so that Euclidean geometry is accurate on the average throughout the Universe. Conversely, on a quantum scale spacetime is highly turbulent.
The word Universe is usually defined as encompassing everything. However, using an alternate definition, some have speculated that this "Universe" is just one of many disconnected "universes", which are collectively denoted as the multiverse. For example, in Bubble universe theory, there are an infinite variety of "universes", each with different physical constants. Similarly, in the many-worlds hypothesis, new "universes" are spawned with every quantum measurement. These universes are usually thought to be completely disconnected from our own and therefore impossible to detect experimentally.
Throughout recorded history, several cosmologies and cosmogonies have been proposed to account for observations of the Universe. The earliest quantitative geocentric models were developed by the ancient Greeks, who proposed that the Universe possesses infinite space and has existed eternally, but contains a single set of concentric spheres of finite size – corresponding to the fixed stars, the Sun and various planets – rotating about a spherical but unmoving Earth. Over the centuries, more precise observations and improved theories of gravity led to Copernicus' heliocentric model and the Newtonian model of the Solar System, respectively. Further improvements in astronomy led to the characterization of the Milky Way, and the discovery of other galaxies and the microwave background radiation; careful studies of the distribution of these galaxies and their spectral lines have led to much of modern cosmology.
Etymology, synonyms and definitions
The word Universe derives from the Old French word Univers, which in turn derives from the Latin word universum.The Latin word was used by Cicero and later Latin authors in many of the same senses as the modern English word is used.The Latin word derives from the poetic contraction Unvorsum — first used by Lucretius in Book IV (line 262) of his De rerum natura (On the Nature of Things) — which connects un, uni (the combining form of unus, or "one") with vorsum, versum (a noun made from the perfect passive participle of vertere, meaning "something rotated, rolled, changed").Lucretius used the word in the sense "everything rolled into one, everything combined into one".
Artistic rendition of a Foucault pendulum showing that the Earth is not stationary, but rotates.
An alternative interpretation of unvorsum is "everything rotated as one" or "everything rotated by one". In this sense, it may be considered a translation of an earlier Greek word for the Universe, περιφορα, "something transported in a circle", originally used to describe a course of a meal, the food being carried around the circle of dinner guests.This Greek word refers to an early Greek model of the Universe, in which all matter was contained within rotating spheres centered on the Earth; according to Aristotle, the rotation of the outermost sphere was responsible for the motion and change of everything within. It was natural for the Greeks to assume that the Earth was stationary and that the heavens rotated about the Earth, because careful astronomical and physical measurements (such as the Foucault pendulum) are required to prove otherwise.
The most common term for "Universe" among the ancient Greek philosophers from Pythagoras onwards was το παν (The All), defined as all matter (το ολον) and all space (το κενον).Other synonyms for the Universe among the ancient Greek philosophers included κοσμος (meaning the world, the cosmos) and φυσις (meaning Nature, from which we derive the word physics).[8] The same synonyms are found in Latin authors (totum, mundus, natura)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 hypothesis), and Nature (as in natural laws or natural philosophy).
Big Bang model
The prevailing Big Bang model accounts for many of the experimental observations described above, such as the correlation of distance and redshift of galaxies, the universal ratio of hydrogen:helium atoms, and the ubiquitous, isotropic microwave radiation background. As noted above, the redshift arises from the metric expansion of space; as the space itself expands, the wavelength of a photon traveling through space likewise increases, decreasing its energy. The longer a photon has been traveling, the more expansion it has undergone; hence, older photons from more distant galaxies are the most red-shifted. Determining the correlation between distance and redshift is an important problem in experimental physical cosmology. Other experimental observations can be explained by combining the overall expansion of space with nuclear and atomic physics. As the universe expands, the energy density of the electromagnetic radiation decreases more quickly than does that of matter, since the energy of a photon decreases with its wavelength. Thus, although the energy density of the universe is now dominated by matter, it was once dominated by radiation; poetically speaking, all was light. As the universe expanded, its energy density decreased and it became cooler; as it did so, the elementary particles of matter could associate stably into ever larger combinations. Thus, in the early part of the matter-dominated era, stable protons and neutrons formed, which then associated into atomic nuclei. At this stage, the matter in the universe was mainly a hot, dense plasma of negative electrons, neutral neutrinos and positive nuclei. Nuclear reactions among the nuclei led to the present abundances of the lighter nuclei, particularly hydrogen, deuterium, and helium. Eventually, the electrons and nuclei combined to form stable atoms, which are transparent to most wavelengths of radiation; at this point, the radiation decoupled from the matter, forming the ubiquitous, isotropic background of microwave radiation observed today.
Other observations are not answered definitively by known physics. According to the prevailing theory, a slight imbalance of matter over antimatter was present in the universe's creation, or developed very shortly thereafter, possibly due to the CP violation that has been observed by particle physicists. Although the matter and antimatter mostly annihilated one another, producing photons, a small residue of matter survived, giving the present matter-dominated universe. Several lines of evidence also suggest that a rapid cosmic inflation of the universe occurred very early in its history (roughly 10−35 seconds after its creation). Recent observations also suggest that the cosmological constant (Λ) is not zero and that the net mass-energy content of the universe is dominated by a dark energy and dark matter that have not been characterized scientifically. They differ in their gravitational effects. Dark matter gravitates as ordinary matter does, and thus slows the expansion of the universe; by contrast, dark energy serves to accelerate the universe's expansion.
Multiverse
Some speculative theories have proposed that this universe is but one of a set of disconnected universes, collectively denoted as the multiverse, altering the concept that the universe encompasses everything.By definition, there is no possible way for anything in one universe to affect another; if two "universes" could affect one another, they would be part of a single universe. Thus, although some fictional characters travel between parallel fictional "universes", this is, strictly speaking, an incorrect usage of the term universe. The disconnected universes are conceived as being physical, in the sense that each should have its own space and time, its own matter and energy, and its own physical laws - that also challenges the definition of parallellity as these universes don't exist synchronously (since they have own time) or in a geometrically parallel way (since there's no interpretable relation between spatial positions of the different universes). Such physical disconnected universes should be distinguished from the metaphysical conception of alternate planes of consciousness, which are not thought to be physical places and are connected through the flow of information. The concept of a multiverse of disconnected universes is very old; for example, Bishop Étienne Tempier of Paris ruled in 1277 that God could create as many universes as he saw fit, a question that was being hotly debated by the French theologians. There are two scientific senses in which multiple universes are discussed. First, disconnected spacetime continua may exist; presumably, all forms of matter and energy are confined to one universe and cannot "tunnel" between them. An example of such a theory is the chaotic inflation model of the early universe.Second, according to the many-worlds hypothesis, a parallel universe is born with every quantum measurement; the universe "forks" into parallel copies, each one corresponding to a different outcome of the quantum measurement. However, both senses of the term "multiverse" are speculative and may be considered unscientific; no experimental test in one universe could reveal the existence or properties of another non-interacting universe.
Broadest definition: reality and probability
The broadest definition of the Universe is found in De divisione naturae by the medieval philosopher Johannes Scotus Eriugena, who defined it as simply everything: everything that exists and everything that does not exist. Time is not considered in Eriugena's definition; thus, his definition includes everything that exists, has existed and will exist, as well as everything that does not exist, has never existed and will never exist. This all-embracing definition was not adopted by most later philosophers, but something not entirely dissimilar reappears in quantum physics, perhaps most obviously in the path-integral formulation of Feynman. According to that formulation, the probability amplitudes for the various outcomes of an experiment given a perfectly defined initial state of the system are determined by summing over all possible paths by which the system could progress from the initial to final state. Naturally, an experiment can have only one outcome; in other words, only one possible outcome is made real in this Universe, via the mysterious process of quantum measurement, also known as the collapse of the wavefunction (but see the many-worlds hypothesis below in the Multiverse section). In this well-defined mathematical sense, even that which does not exist (all possible paths) can influence that which does finally exist (the experimental measurement). As a specific example, every electron is intrinsically identical to every other; therefore, probability amplitudes must be computed allowing for the possibility that they exchange positions, something known as exchange symmetry. This conception of the Universe embracing both the existent and the non-existent loosely parallels the Buddhist doctrines of shunyata and interdependent development of reality, and Gottfried Leibniz's more modern concepts of contingency and the identity of indiscernibles.
Definition as reality
More customarily, the Universe is defined as everything that exists, has existed, and will exist. According to this definition and our present understanding, the Universe consists of three elements: space and time, collectively known as space-time or the vacuum; matter and various forms of energy and momentum occupying space-time; and the physical laws that govern the first two. These elements will be discussed in greater detail below. A related definition of the term Universe is everything that exists at a single moment of cosmological time, such as the present, as in the sentence "The Universe is now bathed uniformly in microwave radiation".
The three elements of the Universe (spacetime, matter-energy, and physical law) correspond roughly to the ideas of Aristotle. In his book The Physics (Φυσικης, from which we derive the word "physics"), Aristotle divided το παν (everything) into three roughly analogous elements: matter (the stuff of which the Universe is made), form (the arrangement of that matter in space) and change (how matter is created, destroyed or altered in its properties, and similarly, how form is altered). Physical laws were conceived as the rules governing the properties of matter, form and their changes. Later philosophers such as Lucretius, Averroes, Avicenna and Baruch Spinoza altered or refined these divisions; for example, Averroes and Spinoza discern natura naturans (the active principles governing the Universe) from natura naturata, the passive elements upon which the former act.
Definition as connected space-time
It is possible to conceive of disconnected space-times, each existing but unable to interact with one another. An easily visualized metaphor 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. According to one common terminology, each "soap bubble" of space-time is denoted as a universe, whereas our particular space-time is denoted as the Universe, just as we call our moon the Moon. The entire collection of these separate space-times is denoted as the multiverse. In principle, the other unconnected universes may have different dimensionalities and topologies of space-time, different forms of matter and energy, and different physical laws and physical constants, although such possibilities are currently speculative.
sumber : http://en.wikipedia.org/wiki/Universe.
Sherly Cynthia D.T
XH/26
XH/26
