Tegmark calculated that our nearest so-called doppelgänger, is 1010115 metres away from us (a double exponential function larger than a googolplex). Parmenides denoted this reality as τὸ ἐν (The One). Observationally, the universe appears to be flat (k = 0), with an overall density that is very close to the critical value between recollapse and eternal expansion.[135]. [123], The lepton epoch was the period in the evolution of the early universe in which the leptons dominated the mass of the universe. [175], The modern era of physical cosmology began in 1917, when Albert Einstein first applied his general theory of relativity to model the structure and dynamics of the universe. (Image: © NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team). The Greek astronomer Aristarchus of Samos was the first known individual to propose a heliocentric model of the universe. 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. An atom consists of an atomic nucleus, made up of protons and neutrons, and electrons that orbit the nucleus. In other stories, the universe emanates from fundamental principles, such as Brahman and Prakrti, the creation myth of the Serers,[150] or the yin and yang of the Tao. [42] This was a kind of expansion different from those we can see around us today. Tegmark and others[139] have argued that, 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. [148][149] For example, in one type of story, the world is born from a world egg; such stories include the Finnish epic poem Kalevala, the Chinese story of Pangu or the Indian Brahmanda Purana. Electrons are stable and the most common charged lepton in the universe, whereas muons and taus are unstable particle that quickly decay after being produced in high energy collisions, such as those involving cosmic rays or carried out in particle accelerators. These laws are Gauss's law and the non-divergence of the stress-energy-momentum pseudotensor.[48]. [93] Typical galaxies range from dwarfs with as few as ten million[94] (107) stars up to giants with one trillion[95] (1012) stars. 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. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. [166] Al-Sijzi[167] also proposed that the Earth rotates on its axis. The XDF is a small fraction of the angular diameter of the full Moon. [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. Dark matter is a hypothetical kind of matter that is invisible to the entire electromagnetic spectrum, but which accounts for most of the matter in the universe. Other than neutrinos, a form of hot dark matter, dark matter has not been detected directly, making it one of the greatest mysteries in modern astrophysics. Nevertheless, even the most rapid traveler will not be able to interact with all of space. Seleucus' arguments for a heliocentric cosmology were probably related to the phenomenon of tides. When R changes, all the spatial distances in the universe change in tandem; there is an overall expansion or contraction of space itself. Approximately 10 seconds after the Big Bang, the temperature of the universe had fallen to the point where lepton/anti-lepton pairs were no longer created. 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 truth is, scientists can't put a number on it. This is known as recombination for historical reasons; in fact electrons and nuclei were combining for the first time. Ethnologists and anthropologists who study myths have developed various classification schemes for the various themes that appear in creation stories. The prevailing model for the evolution of the universe is the Big Bang theory. Even though the explosion is as bright as a billion suns, it is so far away that it is just a speck of light. Aristarchus thus believed the stars to be very far away, and saw this as the reason why stellar parallax had not been observed, that is, the stars had not been observed to move relative each other as the Earth moved around the Sun. [46][47] The universe also appears to have neither net momentum nor angular momentum, which follows accepted physical laws if the universe is finite. You will receive a verification email shortly. [74], 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. However, the Penrose–Hawking singularity theorems show that a singularity should exist for very general conditions. 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. [119]:244–66, General relativity is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics. [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. [87][107], The remaining 4.9% of the mass–energy of the universe is ordinary matter, that is, atoms, ions, electrons and the objects they form. 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[131] and never moved faster than the speed of light. Since the Big Bang, the universe has expanded monotonically. Spacetimes are the arenas in which all physical events take place. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. [124] Most leptons and anti-leptons were then eliminated in annihilation reactions, leaving a small residue of leptons. And other parts of the universe, very far away, might be quite different from the universe closer to home. According to the general theory of relativity, far regions of space may never interact with ours even in the lifetime of the universe due to the finite speed of light and the ongoing expansion of space. These are called, respectively, the flat, open and closed universes. Both systems, therefore, agree in denying the objective reality of the categories of Substance and Quality,... and of the relation of Inference uniting them. In general relativity, the distribution of matter and energy determines the geometry of spacetime, which in turn describes the acceleration of matter. Soon after the Big Bang, primordial protons and neutrons formed from the quark–gluon plasma of the early universe as it cooled below two trillion degrees. 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. Scientists measure the size of the universe in a myriad of different ways. About 380,000 years after the Big Bang, the temperature of the Universe fell to the point where nuclei could combine with electrons to create neutral atoms. [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. 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.[138]. [128] A curvature index k describes the geometry. the Earth], ... supposing the heaven to remain at rest and the Earth to revolve in an oblique circle, while it rotates, at the same time, about its own axis, 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. [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. ", "To see the Universe in a Grain of Taranaki Sand", Centre for Astrophysics and Supercomputing, "Unveiling the Secret of a Virgo Dwarf Galaxy", "Hubble's Largest Galaxy Portrait Offers a New High-Definition View", "Earth's new address: 'Solar System, Milky Way, Laniakea, "Astronomers discover largest known structure in the universe is ... a big hole", "Content of the Universe – WMAP 9yr Pie Chart", "Planck captures portrait of the young universe, revealing earliest light", "Three generations of quarks and leptons", "Experiment confirms famous physics model", "Thermal history of the universe and early growth of density fluctuations", "Eternally existing self-reproducing chaotic inflationary Universe", "Relative State Formulation of Quantum Mechanics", "Weird! Aristotle responded to these paradoxes by developing the notion of a potential countable infinity, as well as the infinitely divisible continuum. [28][29][30] The word universe may also refer to concepts such as the cosmos, the world, and nature. [72][73] The existence, properties, and significance of a cosmological horizon depend on the particular cosmological model.
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