Overview
The past is contrasted with the present. It is also regarded as the conglomerate of events that happened in a certain point in time, within the Space-time continuum. The aforementioned conception is closely related to Albert Einstein's relativity theory. The past is the object of such fields as history, archaeology, archaeoastronomy, chronology, geology, (historical geology), historical linguistics, law, paleontology, paleobotany, paleoethnobotany, palaeogeography, paleoclimatology, and cosmology.Humans have recorded the past since ancient times, and to some extent, one of the defining characteristics of human beings is that they are able to record the past, recall it, remember it and confront it with the current state of affairs, thus enabling them to plan accordingly for the future, and to theorise about it as well.
Philosophy and science
According to presentism, the past does not strictly exist; however, the methods of all sciences study the world's past, through the process of evaluating evidence. Presentism is compatible with Galilean relativity, in which time is independent of space but is probably incompatible with Lorentzian/Einsteinian relativity in conjunction with certain other philosophical theses which many find uncontroversial.In classical physics the past is just a half of the timeline. In special relativity the past is considered as absolute past or the past cone. In Earth's scale the difference between "classical" and "relativist" past is less than 0.05 s, so it can be neglected in most cases.
In the modern theory of relativity, the conceptual observer is at a geometric point in both space and time at the apex of the 'light cone' which observes events laid out in time as well as space. Different observers can disagree on whether two events at different locations occurred simultaneously depending if the observers are in relative motion (see relativity of simultaneity). This theory depends upon the idea of time as an extended thing and has been confirmed by experiment and has given rise to a philosophical viewpoint known as four dimensionalism. However, although the contents of an observation are time-extended, the conceptual observer, being a geometric point at the origin of the light cone, is not extended in time or space. This analysis contains a paradox in which the conceptual observer contains nothing, even though any real observer would need to be the extended contents of an observation to exist. This paradox is partially resolved in Relativity theory by defining a 'frame of reference' to encompass the measuring instruments used by an observer. This reduces the time separation between instruments to a set of constant intervals.
Quote
See also
References
This article is licensed under the GNU Free Documentation License.
Last updated on Saturday October 11, 2008 at 07:20:27 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation
PAST (short for Polska Akcyjna Spółka Telefoniczna, Polish Telephone Joint-stock Company) was a Polish telephone operator in the period between World War I and World War II. It is notable for its main headquarters in Warsaw, which at the time of its construction was the first and tallest skyscraper in the Russian Empire and the tallest building of Warsaw. The fight for the building during the Warsaw Uprising of 1944 also added to the legend of the place.
The Swedish-owned company Towarzystwo Akcyjne Telefonów "Cedergren" won a competition in 1900 to expand the Warsaw telephone network. For that purpose, two buildings were built at Zielna street in downtown Warsaw, holding the telephone exchange and the company's headquarters. The building, located at 37 Zielna Street, was built between 1904 and 1910 and was constructed in two phases. The lower part, designed by L. Wahiman, I.G. Ciason and B. Brochowicz-Rogoyski, was completed in 1904-1905; the upper part was added in 1907-1910. The building was one of the first reinforced concrete constructions of this magnitude in Europe.
The Cedergren license expired in 1922 and the building was consequently taken over by the PAST company. This is why it was referred to by Varsovians either by the name of Cedergren or PAST, or, colloquially, Pasta (Paste). During the German occupation of Poland, it was the regional telephone center for General Government. During the Warsaw Uprising, on August 20, 1944, the building was captured by Polish insurgents of AK battalion „Kiliński” after 20 days of bloody fighting. The building was severely damaged. It was rebuilt in a simplified architectural form after World War II. The company was not recreated after the war and its assets were nationalized by the Polish communist authorities.
External links
- Old and modern pictures of PAST building
- Old and modern pictures of neighbouring building
- 1938 Warsaw telephone directory published by PAST (large .pdf file)
This article is licensed under the GNU Free Documentation License.
Last updated on Wednesday September 17, 2008 at 20:55:01 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation
The Primeval Structure Telescope (PaST), also called 21 Centimetre Array (21CMA), is a Chinese radio telescope adventure designed to detect the earliest luminous objects in the universe, including the first stars, supernova explosions, and black holes. All of these objects were strong sources of ultraviolet radiation, so they ionised the material surrounding them. The structure of this reionisation reflects the overall density structure at the redshift of luminous-object formation.
PaST will consist an array of some ten-thousand log-periodic antennas spread over several square kilometers. It will capture a detailed radio image of the sky in the range of fifty to two-hundred megahertz. The telescope is built on the high plateau of Ulastai in the west of Xinjiang province, a remote area away from most television and radios signals that may interfere the weak 21 cm background signals.
References
- Peterson, J. B.; Pen, U. L.; Wu, X. P., 2004, " The PrivevAl Structure Telescope".
- Pen, U. L.; Wu, X. P.; Peterson, J. B., 2004, " Forecast for Epoch-of-Reionization as Viewable by the PrimevAl Structure Telescope (PAST)", Chinese Journal of Astronomy and Astrophysics.
This article is licensed under the GNU Free Documentation License.
Last updated on Thursday October 02, 2008 at 18:03:08 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation
Copyright © 2008, Dictionary.com, LLC. All rights reserved.
