Measurement
Generally speaking, methods of temporal measurement, orHistory of the calendar
Artifacts from the Paleolithic suggest that the moon was used to reckon time as early as 6,000 years ago.History of other devices
A large variety of devices have been invented to measure time. The study of these devices is called horology. An Egyptian device that dates to c. 1500 BC, similar in shape to a bent T-square, measured the passage of time from the shadow cast by its crossbar on a nonlinear rule. The T was oriented eastward in the mornings. At noon, the device was turned around so that it could cast its shadow in the evening direction. A sundial uses a gnomon to cast a shadow on a set of markings calibrated to the hour. The position of the shadow marks the hour in local time. The idea to separate the day into smaller parts is credited to Egyptians because of their sundials, which operated on a duodecimal system. The importance of the number 12 is due to the number of lunar cycles in a year and the number of stars used to count the passage of night. The most precise timekeeping device of the ancient world was the water clock, or ''clepsydra'', one of which was found in the tomb of Egyptian pharaoh Amenhotep I. They could be used to measure the hours even at night but required manual upkeep to replenish the flow of water. TheUnits
The second (s) is the SI base unit. A minute (min) is 60 seconds in length, and an hour is 60 minutes or 3600 seconds in length. A day is usually 24 hours or 86,400 seconds in length; however, the duration of a calendar day can vary due toDefinitions and standards
A time standard is a specification for measuring time: assigning a number or calendar date to anPhilosophy
Religion
Linear and cyclical
Ancient cultures such as Incan,Time in Greek mythology
The Greek language denotes two distinct principles,Time in Kabbalah
According toIn Western philosophy
Two contrasting viewpoints on time divide prominent philosophers. One view is that time is part of the fundamental structure of theUnreality
In 5th century BCPhysical definition
Until Einstein's reinterpretation of the physical concepts associated with time and space in 1907, time was considered to be the same everywhere in the universe, with all observers measuring the same time interval for any event. Non-relativisticClassical mechanics
In non-relativisticSpacetime
Time has historically been closely related with space, the two together merging into spacetime in Einstein'sDilation
Einstein showed in his thought experiments that people travelling at different speeds, while agreeing onRelativistic versus Newtonian
The animations visualise the different treatments of time in the Newtonian and the relativistic descriptions. At the heart of these differences are theArrow
Time appears to have a direction – the past lies behind, fixed and immutable, while the future lies ahead and is not necessarily fixed. Yet for the most part, the laws of physics do not specify an arrow of time, and allow any process to proceed both forward and in reverse. This is generally a consequence of time being modelled by a parameter in the system being analysed, where there is no "proper time": the direction of the arrow of time is sometimes arbitrary. Examples of this include the cosmological arrow of time, which points away from the Big Bang,Quantization
Time quantization is a hypothetical concept. In the modern established physical theories (the Standard Model of Particles and Interactions andTravel
Time travel is the concept of moving backwards or forwards to different points in time, in a manner analogous to moving through space, and different from the normal "flow" of time to an earthbound observer. In this view, all points in time (including future times) "persist" in some way. Time travel has been a plot device in fiction since the 19th century. Travelling backwards or forwards in time has never been verified as a process, and doing so presents many theoretical problems and contradictive logic which to date have not been overcome. Any technological device, whether fictional or hypothetical, that is used to achieve time travel is known as a time machine. A central problem with time travel to the past is the violation of causality; should an effect precede its cause, it would give rise to the possibility of a temporal paradox. Some interpretations of time travel resolve this by accepting the possibility of travel betweenPerception
The specious present refers to the time duration wherein one'sBiopsychology
The brain's judgment of time is known to be a highly distributed system, including at least theEarly childhood education
Children's expanding cognitive abilities allow them to understand time more clearly. Two- and three-year-olds' understanding of time is mainly limited to "now and not now". Five- and six-year-olds can grasp the ideas of past, present, and future. Seven- to ten-year-olds can use clocks and calendars.Alterations
In addition to psychoactive drugs, judgments of time can be altered by temporal illusions (like theSpatial conceptualization
Although time is regarded as an abstract concept, there is increasing evidence that time is conceptualized in the mind in terms of space. That is, instead of thinking about time in a general, abstract way, humans think about time in a spatial way and mentally organize it as such. Using space to think about time allows humans to mentally organize temporal events in a specific way. This spatial representation of time is often represented in the mind as a Mental Time Line (MTL). Using space to think about time allows humans to mentally organize temporal order. These origins are shaped by many environmental factors––for example,Use
In sociology andSequence of events
A sequence of events, or series of events, is aSee also
* List of UTC timing centers * Time metrologyOrganizations
*Miscellaneous arts and sciences
* Date and time representation by country * List of cycles * Nonlinear narrative * Philosophy of physics * Rate (mathematics)Miscellaneous units
*References
Further reading
External links