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Multiple Histories
In theoretical physics, top-down cosmology is a proposal to regard the many possible past histories of a given event as having real existence. This idea of multiple histories has been applied to cosmology, in a theoretical interpretation in which the universe has multiple possible cosmologies, and in which reasoning ''backwards'' from the current state of the universe to a quantum superposition of possible cosmic histories makes sense. Stephen Hawking has argued that the principles of quantum mechanics forbid a single cosmic history, and has proposed cosmological theories in which the lack of a past boundary condition naturally leads to multiple histories, called the 'no-boundary proposal', the proposed Hartle–Hawking state. According to Hawking and Thomas Hertog, "The top-down approach we have described leads to a profoundly different view of cosmology, and the relation between cause and effect. Top down cosmology is a framework in which one essentially traces the histories ba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cosmology
Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount (lexicographer), Thomas Blount's ''Glossographia'', and in 1731 taken up in Latin by German philosophy, German philosopher Christian Wolff (philosopher), Christian Wolff, in ''Cosmologia Generalis''. Religious cosmology, Religious or mythological cosmology is a body of beliefs based on Mythology, mythological, Religion, religious, and Esotericism, esoteric literature and traditions of Cosmogony, creation myths and eschatology. In the science of astronomy it is concerned with the study of the chronology of the universe. Physical cosmology is the study of the observable universe's origin, its large-scale structures and dynamics, and the ultimate fate of the universe, including the laws of science that govern these areas. It is investigated by scientists, such as astronomers and physicists, as well as Philosophy, ph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Universe
The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. According to this theory, space and time emerged together ago, and the universe has been expanding ever since the Big Bang. While the spatial size of the entire universe is unknown, it is possible to measure the size of the observable universe, which is approximately 93 billion light-years in diameter at the present day. Some of the earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center. 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's work as well ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boundary Condition
In mathematics, in the field of differential equations, a boundary value problem is a differential equation together with a set of additional constraints, called the boundary conditions. A solution to a boundary value problem is a solution to the differential equation which also satisfies the boundary conditions. Boundary value problems arise in several branches of physics as any physical differential equation will have them. Problems involving the wave equation, such as the determination of normal modes, are often stated as boundary value problems. A large class of important boundary value problems are the Sturm–Liouville problems. The analysis of these problems involves the eigenfunctions of a differential operator. To be useful in applications, a boundary value problem should be well posed. This means that given the input to the problem there exists a unique solution, which depends continuously on the input. Much theoretical work in the field of partial differential eq ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hartle–Hawking State
The Hartle–Hawking state is a proposal in theoretical physics concerning the state of the Universe prior to the Planck epoch. It is named after James Hartle and Stephen Hawking. Hartle and Hawking suggest that if we could travel backwards in time towards the beginning of the Universe, we would note that quite near what might otherwise have been the beginning, time gives way to space such that at first there is only space and no time. According to the Hartle–Hawking proposal, the Universe has no origin as we would understand it: the Universe was a singularity in both space and time, pre- Big Bang. However, Hawking does state "...the universe has not existed forever. Rather, the universe, and time itself, had a beginning in the Big Bang, about 15 billion years ago.", but that the Hartle-Hawking model is not the steady state Universe of Hoyle; it simply has no initial boundaries in time or space. Technical explanation The Hartle–Hawking state is the wave function of the U ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thomas Hertog
Thomas Hertog is a Belgian cosmologist at KU Leuven university and a key collaborator of Professor Stephen Hawking. Early life Thomas Hertog was born on 27 May 1975. He graduated Summa cum laude from KU Leuven in 1997 with an MSc degree in physics. He obtained his Master's degree at the University of Cambridge in Part III of the Mathematical Tripos and obtained a Ph.D. degree at Cambridge with a thesis on the origins of cosmic expansion under the supervision of Stephen Hawking. Career Hertog had the opportunity to conduct research with Stephen Hawking in the field of cosmic inflation, a branch of the Big Bang theory. He then worked as a researcher at the University of California - Santa Barbara in the United States and the Université de Paris VII in France. He became a fellow at CERN in Geneva in 2005. In October 2011, Hertog was appointed professor at the Institute for Theoretical Physics at KU Leuven through the Odysseus program of the Flemish government. He led a rese ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Consistent Histories
In quantum mechanics, the consistent histories (also referred to as decoherent histories) approach is intended to give a modern interpretation of quantum mechanics, generalising the conventional Copenhagen interpretation and providing a natural interpretation of quantum cosmology. This interpretation of quantum mechanics is based on a consistency criterion that then allows probabilities to be assigned to various alternative histories of a system such that the probabilities for each history obey the rules of classical probability while being consistent with the Schrödinger equation. In contrast to some interpretations of quantum mechanics, particularly the Copenhagen interpretation, the framework does not include "wavefunction collapse" as a relevant description of any physical process, and emphasizes that measurement theory is not a fundamental ingredient of quantum mechanics. Histories A ''homogeneous history'' H_i (here i labels different histories) is a sequence of Propositio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multiverse
The multiverse is a hypothetical group of multiple universes. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, information, and the physical laws and constants that describe them. The different universes within the multiverse are called "parallel universes", "other universes", "alternate universes", or "many worlds". History of the concept According to some, the idea of infinite worlds was first suggested by the pre-Socratic Greek philosopher Anaximander in the sixth century BCE. However, there is debate as to whether he believed in multiple worlds, and if he did, whether those worlds were co-existent or successive. The first to whom we can definitively attribute the concept of innumerable worlds are the Ancient Greek Atomists, beginning with Leucippus and Democritus in the 5th century BCE, followed by Epicurus (341-270 BCE) and Lucretius (1st century BCE). In the third century BCE, the philosopher Chrysippus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Cosmology
Quantum cosmology is the attempt in theoretical physics to develop a quantum theory of the universe. This approach attempts to answer open questions of classical physical cosmology, particularly those related to the first phases of the universe. Classical cosmology is based on Albert Einstein's general theory of relativity (GTR or simply GR) which describes the evolution of the universe very well, as long as you do not approach the Big Bang. It is the gravitational singularity and the Planck time where relativity theory fails to provide what must be demanded of a final theory of space and time. Therefore, a theory is needed that integrates relativity theory and quantum theory. Such an approach is attempted for instance with loop quantum cosmology, loop quantum gravity, string theory and causal set theory. In quantum cosmology, the universe is treated as a wave function instead of classical spacetime. See also * String cosmology * Brane cosmology * Loop quantum cosmology * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Physical Cosmology
Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its Cosmogony, origin, structure, Chronology of the universe, evolution, and ultimate fate.For an overview, see Cosmology as a science originated with the Copernican principle, which implies that astronomical object, celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood. Physical cosmology, as it is now understood, began with the development in 1915 of Albert Einstein's general relativity, general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external Galaxy, galaxies beyond the Milky Way; then, work by Vesto Sli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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