The word universe derives from the Old French word ‘Univers’, which in turn derives from the Latin word universum. It is 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"). An alternative interpretation of unvorsum is "everything rotated as one" or "everything rotated by one". It can be related to the God as the One who rotates the total universe regularly. The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space.The Universe here is referred to as the entire creation and existence, visible and invisible; material and living; approachable and unapproachable for the beings. It also includes all terms like cosmos, the worldand the nature.
Col Dr Dalvinder Singh Grewal
The concepts ‘known universe’, ‘observable universe’, or ‘visible universe’ are often used to describe the part of the universe that we can see or otherwise observe. But there is much more than whatever we observe. Observable universe is the spatial region within which we can affect and be affected. It is also termed as the universe visible to human eye while the unobservable or invisible universe is the one which is not visible to human eye. The observable universe depends on the location of the observer. This visibility to the eyes has been extended by the use of various telescopes. The studies conducted by various telescopes and other astronomical instruments have been included here for fathoming the observable universe.
The universe is immensely large and possibly infinite in volume. The limits of the boundaries of universe have not been fathomed, hence is called limitless. Philosophers like Aristotle philosophisized at the God’s wonder world; the phenomena of the moon and those of the sun and the stars, and about the origin of the universe.  Derek Parfit, a contemporary philosopher, declared that "No question is more sublime than why there is a Universe: why there is anything rather than nothing." Philosopher Gottfried Wilhelm Leibniz philosophized that ‘the existence of a metaphysically necessary being which carries within itself the sufficient reason for its own existence and which constitutes the sufficient reason for the existence of everything else in the world’. Bertrand Russell in his BBC radio debate with Frederick Copleston thought it to be beyond any philosophy. He simply said "The universe is just there, and that's all." Visualising the universe, Guru Nanak exclaimed in wonder: ‘Wah’
No one can actually understand the limit of this darkness. The being is too small to understand the vastness of the nature of the Lord and the darkness spread around. For this, one needs to understand the originator of the universe; one has to become one with Him; to understand Him. History has records of only a few who could reach Him; Lords Rama, Krishna, Buddha, Mahavir and God’s own Christ, Mohammed, Sikh Gurus and some Rishis and Saints are stated to be the ones who could reach and know Him and His entire universe.
Scientists too, have been trying to fathom limits of the boundaries. Most of the recent Nobel prizes in physics including in 2006, have been won on measurement tools of the distances to the farthest stars in the universe. But so far no verifiable records exist to reply ‘wh’ questions about this universe. There is nothing to confirm if it originated itself or someone else created it. No account gives the length, breadth, depth or height of the universe. No one has seen the ends of The Universe. None knows time of creation. No one even correctly knows whether the universe is expanding or contracting. Yet there is so much written about ‘wh’s of the universe because we are inquisitive and we want to know the truth about the universe of which we are part and parcel. Similarly no one can definitely state about life whether it came from egg, earth, water, air or from elsewhere. Yet there are numerous sciences and philosophies which base their theories and experiments on the life in The Universe. Similarly no one knows how the life in the universe was originated or came into existence.
Scientists have been basing their results on whatever is observable or calculable. But the solution to the two main questions lies in what is not observable or calculable. The answer remains in the dark. Modern science teaches us that the entire universe is made of energy, which keeps on changing forms from one form to another. The observable or perceivable energy in the form of materials is our observable world; the remaining is the dark matter or dark energy. It is an irony of nature that the most abundant form of energy the dark energy, in the universe is also the most mysterious for the scientists.
The scientist community describes it as the dark matter or dark energy. Measurements of the cosmic microwave background (CMB), most recently by the WMAP satellite are consistent with a Universe made up of 74% dark energy, 22% dark matter, and 4% ordinary matter. According to them, ’the observable or visible universe is only about 4%. The dark matter component has vastly more mass than the "visible" component of the universe’. ‘The remaining 74% is thought to consist of dark energy, an even stranger component, distributed diffusely in space’. In Sri Guru Granth Sahib Ji word ‘dhundhukara’; the darkness prevalent in the universe in the form of dark matter and dark energy.
Dark matter refers to hypothetical matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. According to present observations of structures, larger than galaxy-sized as well as Big Bang cosmology, dark matter accounts for the vast majority of mass in the observable universe. Evidence suggests that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation: the remainder is called the "dark matter component". The dark matter component has vastly more mass than the "visible" component of the universe. Astronomers have long been aware of a missing-energy problem: the luminous mass of galaxies and clusters falls far short of the gravitational mass. This difference is attributed to the presence of dark matter - a cold, non-relativistic material most likely in the form of exotic particles that interact very weakly with atoms and light. The composition of dark matter is unknown, but may include new elementary particles such as WIMPs, axions, and ordinary and heavy neutrinos, as well as astronomical bodies such as dwarf stars and planets (collectively called MACHOs), and clouds of non-luminous gas. Current evidence favours models in which the primary component of dark matter is new elementary particles, collectively called non-baryonic dark matter. Although dark matter was detected by its gravitational lensing in August 2006, many aspects of dark matter remain speculative.
The name "dark energy" here refers to the fact that some kind of "stuff" must fill the vast reaches of mostly empty space in the Universe in order to be able to make space accelerate in its expansion. In this sense, it is a "field" just like an electric field or a magnetic field, both of which are produced by electromagnetic energy. But this analogy can only be taken so far because we can readily observe electromagnetic energy via the particle that carries it, the photon. Dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. Dark energy causes expansion because it has strong negative pressure. The exact nature of this dark energy is a matter of speculation. It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity. Since it is not very dense—roughly 10−29 grams per cubic centimeter—it is hard to imagine experiments to detect it in the laboratory. Dark energy can only have such a profound impact on the universe, making up 74% of all energy, because it uniformly fills otherwise empty space. Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously, and quintessence, a dynamic field whose energy density can vary in time and space. The type Ia supernovae provide the most direct evidence for dark energy.
Dark matter can become dark energy and vice versa. Dark energy may become dark matter when buffeted by baryonic particles, thus leading to particle-like excitations in some type of dynamicalfield, referred to as quintessence. Quintessence differs from the cosmological constant in that it can vary in space and time. In order to avoid clumping and to form structure like matter, it must be very light so that it has a large Crompton wavelength. The universe is expanding and the density of dark matter in this expanding universe disappears more quickly than dark energy, and eventually the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved but the density of dark energy is nearly unchanged.
Analogy of dark and light is also given to the ignorance and knowledge or enlightenment. It has been noted that the names "dark matter" and "dark energy" serve mainly as expressions of our ignorance, much as the marking of early maps with “terra incognita” . Spiritually speaking, the entire universe is the same as the matter of human body (Jo brihmande soi pinde: Sri Guru Granth Sahib Ji, p.). We cannot know about the universe until we realize our innerself. Matter of ignorance of truth is darkness, knowledge is light. Ignorance and knowledge are related to mind. Thus it is the mind energy which is most affected subtly. If you see the actual construction of body, you can divide it into 4 parts; the physical body; the energy or aural body; the mind body and the spirit. The spirit is the controller of mind. The mind is the controller of the energy/aural body which in turn controls physical body. It also affects the human behaviour and the impact on the activities and their outcome. If the mind is attached too much with the world, the being loses the actual mission of life i.e., to merge into the One wherefrom the being has come; the True Lord, the Ultimate truth. The entire world is enveloped by the darkness of egotistical pride. It does not like the Truth. Love and emotional attachment to Maya brings total darkness.(Sri Guru Granth Sahib Ji, M 3, p.880) Due to Maya the mortal has fallen into the deep, dark pit, and is entangled in the darkness of doubt, and the bondage of emotional attachment; (Sri Guru Granth Sahib Ji, M 5, p.823) of household attachment; the horrible, dark hell. (Sri Guru Granth Sahib Ji, M 5, p. 1223).
We remain in dark because we do not do anything to attain light or enlightenment; the knowledge, and submersion into God. We need someone to guide us out of this dark hell. A Guru or a guide can provide us this light in this world full of darkness. If we do not submerge into the Lord we continue taking birth, living life and dying. Alternatively we go on changing from dark matter to dark matter; dark matter to visible matter and back to dark matter and dark energy; cyclically. The transmigration is the journey from dark to dark as no one knows where one goes after death. The vast world of dark has countless souls searching for the True Lord; the ultimate truth; the true Light. Once a person attains enlightenment, he is in a position to merge into light ‘Jyoti jyot milai, sampooran thia Ram”. Thereafter ends the journey in darkness.
As per scientific or astronomical observations the region visible from Earth (the observable universe) is a sphere with a radius of about 46 billion light years , based on where the expansion of space has taken the most distant objects observed. For comparison, the diameter of a typical galaxy is only 30,000 light-years, and the typical distance between two neighboring galaxies is only 3 million light years. As an example, our Milky Way Galaxy is roughly 100,000 light years in diameter, and our nearest sister galaxy, the Andromeda Galaxy, is located roughly 2.5 million light years away. There are probably more than 100 billion (1011) galaxies in the observable universe. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (1012) stars, all orbiting the galaxy's center of mass. A 2010 study by astronomers estimated that the observable universe contains 300 sextillion (3×1023) stars. Known universe is one known to the man while the unknown universe is the one not known to the man till date. There are various multi-verse theories, in which physicists have suggested that our universe is one among many universes that likewise exist.
Universe has been governed by the same physical laws and constants throughout most of its extent and history. The observable matter is spread homogeneously (uniformly) throughout the universe, when averaged over distances longer than 300 million light-years.  However, on smaller length-scales, matter is observed to form "clumps", i.e., to cluster hierarchically; many atoms are condensed into stars, most stars into galaxies, most galaxies into clusters, super-clusters and, finally, the largest-scale structures such as the Great Wall of galaxies. The observable matter of the universe is also spread isotropically, meaning that no direction of observation seems different from any other; each region of the sky has roughly the same content. The universe is also bathed in a highly isotropic microwave radiation that corresponds to a thermal equilibrium blackbody spectrum of roughly 2.725-kelvins. The hypothesis that the large-scale universe is homogeneous and isotropic is known as the cosmological principle, which is supported by astronomical observations.
The universe is believed to be mostly composed of dark energy and dark matter, both of which are poorly understood at present. Less than 5% of the universe is ordinary matter, a relatively small contribution. The present overall density of the universe is very low, roughly 9.9 × 10−30 grams per cubic centimetre. This mass-energy appears to consist of 73% dark energy, 23% cold dark matter and 4% ordinary matter. Thus the density of atoms is on the order of a single hydrogen atom for every four cubic meters of volume. The properties of dark energy and dark matter are largely unknown. Dark matter gravitates as ordinary matter, and thus works to slow the expansion of the universe; by contrast, dark energy accelerates its expansion.
The recent estimate of the universe’s age is 13.73±0.12 billion years old, based on observations of the cosmic microwave background radiation.  Independent estimates (based on measurements such as radioactive dating) agree at 13–15 billion years. Guru Nanak calculated it to 1,37,96,80,00,000 years (36 Yugas). The universe has not been the same at all times in its history; for example, the relative populations of quasars and galaxies have changed and space itself appears to have expanded. This expansion accounts for how Earth-bound scientists can observe the light from a galaxy 30 billion light years away, even if that light has travelled 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 red-shifted; the photons emitted have been stretched to longer wavelengths and lower frequency during their journey. The rate of this spatial expansion is accelerating, based on studies of Type Ia supernovae and corroborated by other data.
The relative frictions of different chemical agents — particularly the lightest atoms such as hydrogen, deuterium and helium — seem to be identical throughout the universe and throughout its observable history.  The universe seems to have much more matter than ante-matter, an asymmetry possibly related to the observations of CP violation. The universe appears to have no net electric charge, and therefore gravity appears to be the dominant interaction on cosmological length scales. The universe also appears to have neither net momentum nor angular momentum. The absence of net charge and momentum would follow from accepted physical laws (Gauss's law and the non-divergence of the stress- energy-momentum, respectively), if the universe were finite.
According to Standard Model of physics, all matter is composed of three generations of leptons and quarks, both of which are fermions. The elementary particles, the six leptons and six quarks comprise most of the matter from which the universe is constructed; for example, the protons and neutrons of atomic nuclei are composed of quarks, and the ubiquitous electron is a lepton. These particles interact via the gauge bosons each corresponding to a particular type of gauge symmetry. The Higgs boson, under investigation at CERN, is believed to confer mass on the particles with which it is connected. The gravitron is a supposed gauge boson for gravity. These elementary particles interact via at most three fundamental interactions: the electronweak interaction which includes electromagnetic and the weak nuclear force; the strong nuclear force described by quantum chrono-dynamics; and gravity, which is best described at present by general relativity. The first two interactions can be described by renominalised quantum field theory and are mediated by gauge bosons that correspond to a particular type of gauge symmetry. A renominalised quantum field theory of general relativity has not yet been achieved, although various forms of string theory promising. The theory of special relativity is believed to hold throughout the universe, provided that the spatial and temporal length scales are sufficiently short; otherwise, the more general theory of general relativity must be applied. There is no explanation for the particular values that physical constant appear to have throughout our universe, such as Plank’s constant h or the gravitational constant G. Several conservation laws have been identified, such as the conservation of charge, momentum, angular momentum and energy; in many cases, these conservation laws can be related to symmetries or mathematical identities. The universe appears to behave in a manner that regularly follows a set of physical laws and physical constants.
Everything that exists physically is included in the Cosmos. The hierarchy that deals with the physical entities within the Universe are arranged below by a progression of decreasing sizes. That hierarchy, in its simplest form, is:
“?? --> The Absolute Vacuum (The Cosmos) --> Our Universe (Perhaps Other Universes)-->The Intergalactic Medium (Voids Containing Gas, Photons and Other Particles) --> Galactic Clusters --> Galaxies --> Intragalactic Gases --> Star Clusters --> Stars --> Planetary Systems --> Planets --> Satellites (Moons) --> First Order Surficial and Interior Features on Planets --> Local Features --> Individual Entities (For Example, Humans) --> Atoms And Molecules --> Subatomic Particles --> Superstrings -->?”
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