Gravitation Gravitation, or gravity, is a natural phenomenon by which all physical bodies attract each other. It is most commonly recognized and experienced as the agent that gives weight to physical objects, and causes physical objects to fall toward the ground when dropped from a height. During the grand unification epoch, gravity separated from the electronuclear force. Gravity is the weakest of the four fundamental forces, and appears to have unlimited range (unlike the strong or weak force). The gravitational force is approximately 10-38 times the strength of the strong force (i.e., gravity is 38 orders of magnitude weaker), 10-36 times the strength of the electromagnetic force, and 10-29 times the strength of the weak force. As a consequence, gravity has a negligible influence on the behavior of sub-atomic particles, and plays no role in determining the internal properties of everyday matter. History of gravitational theory Scientific revolution Newton's theory of gravitation General relativity
Religious cosmology Biblical cosmology[edit] The Bible was formed over many centuries, by many authors, and reflects shifting patterns of religious belief; consequently, its concepts of cosmology are not always consistent.[1][2] Nor should the Biblical texts be taken to represent the beliefs of all Jews or Christians at the time they were put into writing: the majority of those making up Hebrew Bible or Old Testament in particular represent the beliefs of only a small segment of the ancient Israelite community, the members of a late Judean religious tradition centered in Jerusalem and devoted to the exclusive worship of Yahweh.[3] Christianity/modern Judaism[edit] Around the time of Jesus or a little earlier, the Greek idea that God had actually created matter replaced the older idea that matter had always existed, but in a chaotic state. This concept, called creatio ex nihilo, is now the accepted orthodoxy of most denominations of Judaism and Christianity. Mormon cosmology[edit] Islamic cosmology[edit]
Newton's law of universal gravitation Newton's law of universal gravitation states that any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. (Separately it was shown that large spherically symmetrical masses attract and are attracted as if all their mass were concentrated at their centers.) This is a general physical law derived from empirical observations by what Isaac Newton called induction.[2] It is a part of classical mechanics and was formulated in Newton's work Philosophiæ Naturalis Principia Mathematica ("the Principia"), first published on 5 July 1687. (When Newton's book was presented in 1686 to the Royal Society, Robert Hooke made a claim that Newton had obtained the inverse square law from him – see History section below.) In modern language, the law states the following: History[edit] Early History[edit] Plagiarism dispute[edit] Hooke's work and claims[edit] Vector form[edit]
List of cosmologists This is a list of people who have made noteworthy contributions to cosmology (the study of the history and large-scale structure of the universe) and their cosmological achievements. A[edit] Tom Abel (1970–) studied primordial star formationRoberto Abraham (1965–) studied the shapes of early galaxiesHannes Alfvén (1908–1995) theorized that galactic magnetic fields could be generated by plasma currentsRalph A. B[edit] Ja'far ibn Muhammad Abu Ma'shar al-Balkhi (787–886) conveyed Aristotle's theories from Persia to EuropeJames M. C[edit] Bernard J. D[edit] E[edit] F[edit] Sandra M. G[edit] George Gamow (1904–1968) argued that observed proportions of hydrogen and helium in the universe could be explained by the big bang model, modeled the mass and radius of primordial galaxiesMargaret J. H[edit] Stephen W. I[edit] Jamal Nazrul Islam (1939–2013) published seven books on Cosmology K[edit] L[edit] M[edit] N[edit] Jayant Narlikar (1938–) promoted steady state theories P[edit] R[edit] S[edit]
High-energy astronomy High energy astronomy is the study of astronomical objects that release EM radiation of highly energetic wavelengths. It includes X-ray astronomy, gamma-ray astronomy, and extreme UV astronomy, as well as studies of neutrinos and cosmic rays. The physical study of these phenomena is referred to as high-energy astrophysics.[1] Astronomical objects commonly studied in this field may include black holes, neutron stars, active galactic nuclei, supernovae, supernova remnants, and Gamma ray bursts. Missions[edit] Some space and ground based telescopes that have studied high energy astronomy include the following:[2] External links[edit] References[edit]
Flat Earth The paradigm of a spherical Earth appeared in Greek philosophy with Pythagoras (6th century BC), although most Pre-Socratics retained the flat Earth model. Aristotle accepted the spherical shape of the Earth on empirical grounds around 330 BC, and knowledge of the spherical Earth gradually began to spread beyond the Hellenistic world from then on.[2][3][4][5] The modern misconception that educated Europeans at the time of Columbus believed in a flat Earth, and that his voyages refuted that belief, has been referred to as the myth of the flat Earth.[6] Historical development[edit] Ancient Near East[edit] The Jewish conception of a flat earth is found in biblical and post-biblical times.[7][8][9] In early Egyptian[10] and Mesopotamian thought the world was portrayed as a flat disk floating in the ocean. Ancient Mediterranean[edit] Poets[edit] Philosophers[edit] Possible rendering of Anaximander's world map[25] Historians[edit] Ancient India[edit] Norse and Germanic[edit] Ancient China[edit]
Cosmology The Hubble eXtreme Deep Field (XDF) was completed in September 2012 and shows the farthest galaxies ever photographed by humans. Except for the few stars in the foreground (which are bright and easily recognizable because only they have diffraction spikes), every speck of light in the photo is an individual galaxy, some of them as old as 13.2 billion years; the observable universe is estimated to contain more than 200 billion galaxies. Cosmology (from the Greek κόσμος, kosmos "world" and -λογία, -logia "study of"), is the study of the origin, evolution, and eventual fate of the universe. Physical cosmology is the scholarly and scientific study of the origin, evolution, large-scale structures and dynamics, and ultimate fate of the universe, as well as the scientific laws that govern these realities.[1] Religious cosmology (or mythological cosmology) is a body of beliefs based on the historical, mythological, religious, and esoteric literature and traditions of creation and eschatology.
Infinite divisibility In philosophy[edit] Zeno questioned how an arrow can move if at one moment it is here and motionless and at a later moment be somewhere else and motionless, like a motion picture. Zeno's reasoning, however, is fallacious, when he says that if everything when it occupies an equal space is at rest, and if that which is in locomotion is always occupying such a space at any moment, the flying arrow is therefore motionless. This is false, for time is not composed of indivisible moments any more than any other magnitude is composed of indivisibles.[1] In reference to Zeno's paradox of the arrow in flight, Alfred North Whitehead writes that "an infinite number of acts of becoming may take place in a finite time if each subsequent act is smaller in a convergent series":[2] In physics[edit] Until the discovery of quantum mechanics, no distinction was made between the question of whether matter is infinitely divisible and the question of whether matter can be cut into smaller parts ad infinitum.