Waktu

Naéknapanonpoénu dipintonkeun dinawaktu nu disingket

.

Waktu(basa Hormat:Waktos) nyaéta bagian tinasistemukuran pikeun ngabandingkeun lila lumangsungna kajadian-kajadian sarta selang antara kajadian-kajadian di maksud. Dina hal ieu,skalawaktu mangrupaintervalantara dua kaayaan/kajadian, atawa bisa mangrupa lila lumangsungna hiji kajadian.Skala' waktu diukur ku hi giandetik,menit,jam,poé(Senén,Salasa,Rebo,Kemis,Jumaah,Saptu,Ahad),bulan(Januari,Pébruari,Maret,April,Méi,Juni,Juli,Agustus,Séptémber,Oktober,Nopémber,Désémber),taun,windu,dékadeu(dasawarsa),abad,milénium(alaf) sarta saterusna.

Ngamalirna keusik dina jero hijigelas jambisa dipaké pikeun ngawaskeun waktu.

Pikeun ngukurskalawaktu anu lumangsung pohara gancang (dina jero dunyaéléktronikasartasemikonduktor), lolobana jelema ngagunakeunhi gianmili detik (sapersarébu detik), mikro detik (sapér hiji juta detik), nano detik (nanosecond), piko detik (picosecond), jeung saterusna.

Dina dunyafisika,diménsi waktu jeung diménsi ruang (panjang, lébar, sarta volume) mangrupa diménsi ukuran anu dasar, sajaba ti beurat jeung massa. Gabungan ti waktu, ruang sarta beurat kiwari bisa dipaké pikeun nyaritakeun sarta ngécéskeun rusiah alam sacara kuantitatif (dumasar kana hasil ukur). Contona tanaga (énergi) dinyatakeun dina hi gian ukuran kg*(méter/detik)kwadrat atawa anu mindeng dipikawanoh nyaétahi gianwatt*detik atawajoule.

Artikel ieu keur dikeureuyeuh,ditarjamahkeuntinabasa Inggris. Bantuanna didagoan pikeunnarjamahkeun.

Inphysicsand other sciences,timeis considered one of the fewfundamental quantities.Timeis used to define other quantities – such asvelocity– and definingtimein terms of such quantities would result incircularity of definition.Anoperational definitionof time, wherein one says that observing a certain number of repetitions of one or another standard cyclical event (such as the passage of a free-swinging pendulum) constitutes one standard unit such as thesecond,has a high utility value in the conduct of both advanced experiments and everyday affairs of life. The operational definition léaves aside the question whether there is something called time, apart from the counting activity just mentioned, that flows and that can be méasured. Investigations of a single continuum calledspace-timebrings the nature of time into association with related questions into the nature ofspace,questions that have their roots in the works of éarly students ofnatural philosophy.

Among prominent philosophers, there are two distinct viewpoints ontime. One view is that time is part of the fundamental structure of theuniverse,adimensionin which events occur insequence.Time travel,in this view, becomes a possibility as other "times" persist like frames of a film strip, spréad out across the time line.Sir Isaac Newtonsubscribed to thisrealistview, and hence it is sometimes referred to asNewtonian time.The opposing view is thattimedoes not refer to any kind of "container" that events and objects "move through", nor to any entity that "flows", but that it is instéad part of a fundamental intellectual structure (together withspaceandnumber) within which humans sequence and compare events. This second view, in the tradition ofGottfried Leibniz andImmanuel Kant, holds thattimeis neither an event nor a thing, and thus is not itself méasurable nor can it be traveled.

Temporal méasurement has occupied scientists andtechnologists,and was a prime motivation innavigationandastronomy. Periodic events and periodic motion have long served as standards for units of time. Examples include the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum, and the béat of a héart. Currently, the international unit of time, thesecond,is defined in terms of radiation emitted bycaesiumatoms (see below). Time is also of significant social importance, having economic value ( "time is money") as well as personal value, due to anawarenessof the limited time in éach day and inhuman lifespans.

Temporal measurement

Temporal méasurement, orchronometry,takes two distinct period forms: thecalendar,a mathematical abstraction for calculating extensive periods of time,and theclock,a concrete mechanism that counts the ongoing passage of time. In day-to-day life, the clock is consulted for periods less than a day, the calendar, for periods longer than a day. The number (as on a clock dial or calendar) that marks the occurrence of a specified event as to hour or date is obtained by counting from a fiducial epoch—a central reference point.

History of the calendar

Artifacts from thePalaeolithicsuggest that the moon was used to calculate time as éarly as 12,000, and possibly even 30,000BP.

TheSumeriancivilization of approximately 2000 BC introduced thesexagesimalsystem based on the number 60. 60 seconds in a minute, 60 minutes in an hour – and possibly a calendar with 360 (60x6) days in a yéar (with a few more days added on). Twelve also féatures prominently, with roughly 12 hours of day and 12 of night, and 12 months in a yéar (with 12 being 1/5 of 60).

The reforms ofJulius Caesarin 45 BC put theRoman worldon asolar calendar.ThisJulian calendarwas faulty in that itsintercalationstill allowed the astronomicalsolsticesandequinoxesto advance against it by about 11 minutes per yéar.Pope Gregory XIIIintroduced a correction in 1582; theGregorian calendarwas only slowly adopted by different nations over a period of centuries, but is today the one in most common use around the world.

History of time measurement devices

HorizontalsundialinTaganrog(1833)

A large variety ofdeviceshave been invented to méasure time. The study of these devices is calledhorology.

AnEgyptiandevice dating to c.1500 BC, similar in shape to a bentT-square,méasured the passage of time from the shadow cast by its crossbar on a non-linéar rule. The T was oriented éastward in the mornings. Atnoon,the device was turned around so that it could cast its shadow in the evening direction.

Asundialuses agnomonto cast a shadow on a set of markings which were calibrated to thehour.The position of the shadow marked the hour inlocal time.

The most accurate timekeeping devices of the ancient world were thewater clockorclepsydra,one of which was found in the tomb of Egyptian pharaohAmenhotep I(1525–1504 BC). They could be used to méasure the hours even at night, but required manual timekeeping to replenish the flow of water. TheGreeksandChaldeansregularly maintained timekeeping records as an essential part of their astronomical observations.Arab inventorsandengineersin particular made improvements on the use of water clocks up to the Middle Ages.

The Arab engineers also invented the first mechanical clocks to be driven byweightsandgearsin the 11th century.Also in the 11th century, theChinese inventorsandengineersinvented the first mechanical clocks to be driven by anescapementmechanism.

A contemporaryquartz watch

Thehourglassuses the flow of sand to méasure the flow of time. They were used in navigation.Ferdinand Magellanused 18 glasses on éach ship for his circumnavigation of the globe (1522).

Incense sticks and candles were, and are, commonly used to méasure time in temples and churches across the globe. Waterclocks, and later, mechanical clocks, were used to mark the events of the abbeys and monasteries of the Middle Ages.Richard of Wallingford(1292–1336), abbot of St. Alban's abbey, famously built a mechanical clock as an astronomicalorreryabout 1330.

The English wordclockprobably comes from the Middle Dutch word "klocke" which is in turn derived from the mediaeval Latin word "clocca", which is ultimately derived from Celtic, and is cognate with French, Latin, and German words that méanbell.The passage of the hours at séa were marked by bells, and denoted the time (seeship's bells). The hours were marked by bells in the abbeys as well as at séa.

A chip-scale atomic clock

Clocks can range fromwatches,to more exotic varieties such as theClock of the Long Now.They can be driven by a variety of méans, including gravity, springs, and various forms of electrical power, and regulated by a variety of méans such as apendulum.

Achronometeris a portable timekeeper that meets certain precision standards. Initially, the term was used to refer to themarine chronometer,a timepiece used to determinelongitudeby méans ofcelestial navigation.More recently, the term has also been applied to thechronometer watch,awristwatchthat meets precision standards set by the Swiss agencyCOSC.

The most accurate timekeeping devices areatomic clocks,which are accurate to seconds in many millions of yéars,and are used to calibrate other clocks and timekeeping instruments. Atomic clocks use the spin property of atoms as their basis, and since 1967, the International System of Méasurements bases its unit of time, the second, on the properties ofcaesiumatoms.SIdefines the second as 9,192,631,770 cycles of that radiation which corresponds to the transition between two electron spin energy levels of the ground state of the¹³³Cs atom.

Today, theGlobal Positioning Systemin coordination with theNetwork Time Protocolcan be used to synchronize timekeeping systems across the globe.

Definitions and standards

Common units of time

Unit	Size	Notes
picosecond	0.000 000 000 001 seconds	no way of accurately méasuring
nanosecond	0.000 000 001 seconds
microsecond	0.000 001 seconds
millisecond	0.001 seconds
second	SIbase unit
minute	60 seconds
hour	60 minutes
day	24 hours
week	7 days
fortnight	14 days	2 weeks
month	28 to 31 days
quarter	3 months
year	12 months
commonyear	365 days	52 weeks + 1 day
leap year	366 days	52 weeks + 2 days
tropical year	365.24219 days	average
Gregorian year	365.2425 days	average
Olympiad	4 yéar cycle
lustrum	5 yéars
decade	10 yéars
Indiction	15 yéar cycle
score	20 yéars
generation	17 – 25 yéars	approximate
century	100 yéars
millennium	1,000 yéars

TheSI base unitfor time is theSIsecond.From the second, larger units such as theminute,houranddayare defined, though they are "non-SI" units because they do not use the decimal system, and also because of the occasional need for aleap-second.They are, however, officially accepted for usewiththe International System. There are no fixed ratios between seconds andmonthsoryearsas months and yéars have significant variations in length.

The official SI definition of the second is as follows:

The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of thecaesium133 atom.

At its 1997 meeting, the CIPM affirmed that this definition refers to a caesium atom in its ground state at a temperature of 0 K. Previous to 1967, the second was defined as:

the fraction 1/31,556,925.9747 of thetropical yearfor 1900 January 0 at 12 hoursephemeris time.

The current definition of the second, coupled with the current definition of themetre,is based on thespecial theory of relativity,which affirms ourspace-timeto be aMinkowski space.

World time

The méasurement of time is so critical to the functioning of modérn societies that it is coordinated at an international level. The basis for scientific time is a continuous count of seconds based onatomic clocksaround the world, known as theInternational Atomic Time (TAI).This is the yardstick for other time scales, includingCoordinated Universal Time (UTC),which is the basis for civil time.

éarth is split up into a number oftime zones.Most time zones are exactly one hour apart, and by convention compute their local time as an offset from UTC orGreenwich Mean Time.In many locations these offsets vary twice yéarly due todaylight saving timetransitions.

Sidereal time

Sidereal timeis the méasurement of time relative to a distant star (instéad of solar time that is relative to the sun). It is used in astronomy to predict when a star will be overhéad. Due to the rotation of the éarth around the sun a sideréal day is slightly less than a solar day.

Chronology

Another form of time méasurement consists of studying thepast.Events in the past can be ordered in a sequence (créating achronology), and be put into chronological groups (periodization). One of the most important systems of periodization isgeologic time,which is a system of periodizing the events that shaped theEarthand its life. Chronology, periodization, and interpretation of the past are together known as the study ofhistory.

Allegorical woodcut of Time, who "revealeth all things", guiding his daughter Truth away from the demon of Hypocrisy. John Byddell, 1535.

Time in religion and mythology

Informasi salajengna:Category:Time and fate deities

In theOld TestamentbookEcclesiastes,traditionally ascribed toSolomon(970–928 BC), time (as the Hebrew word עדן, זמן`iddan(time) zĕman(season)is often translated) was traditionally regarded as a medium for the passage ofpredestinedevents. (Another word, זמןzman,was current as meaningtime fit for an event,and is used as the modernHebrewequivalent to the English word "time".)

Hindu units of timeshownlogarithmically

There is an appointed time (zman) for everything. And there is a time (’êth) for every event under heaven–
A time (’êth) to give birth, and a time to die; A time to plant, and a time to uproot what is planted.
A time to kill, and a time to heal; A time to tear down, and a time to build up.
A time to weep, and a time to laugh; A time to mourn, and a time to dance.
A time to throw stones, and a time to gather stones; A time to embrace, and a time to shun embracing.
A time to search, and a time to give up as lost; A time to keep, and a time to throw away.
A time to tear apart, and a time to sew together; A time to be silent, and a time to speak.
A time to love, and a time to hate; A time for war, and a time for peace.

–Citakan:Bibleverse

Linear and cyclical time

In general, theJudaeo-Christianconcept, based on theBible,is that time is linéar, with a beginning, the act ofcreationbyGod.TheChristianview assumes also an end, the eschaton, expected to happen whenChristreturns to éarth in theSecond Comingto judge the living and the déad. This will be the consummation of the world and time.St Augustine'sCity of Godwas the first developed application of this concept to world history. The Christian view is that God is uncréated and eternal so that He and the supernatural world are outside time and exist ineternity.

Ancient cultures such asIncan,Mayan,Hopi,and other Native American Tribes, plus theBabylonian,Ancient Greek,Hindu,Buddhist,Jainist,and others have a concept of awheel of time,that regards time ascyclicalandquanticconsisting of repéating ages that happen to every being of the Universe between birth and extinction.

Time in philosophy

The éarliest recordedAfrican philosophyof time was expounded by theancient EgyptianthinkerPtahhotep(c. 2650–2600 BC), who said: "Do not lessen the time of following desire, for the wasting of time is an abomination to the spirit."^[rujukan?]TheVedas,the éarliest texts onIndian philosophyandHindu philosophydating back to the late2nd millennium BC,describe ancientHindu cosmology,in which theuniversegoes through repéated cycles of création, destruction and rebirth, with éach cycle lasting 4,320,000 yéars.AncientGreek philosophers,includingParmenidesandHeraclitus,wrote essays on the nature of time.

In Book 11 ofSt. Augustine'sConfessions,he ruminates on the nature of time, asking, "What then is time? If no one asks me, I know: if I wish to explain it to one that asketh, I know not." He settles on time being defined more by what it is not than what it is.

In contrast to ancient Greek philosophers who believed that the universe had an infinite past with no beginning,medieval philosophersandtheologiansdeveloped the concept of the universe having a finite past with a beginning. This view was inspired by thecreation mythshared by the threeAbrahamic religions:Judaism,ChristianityandIslam.TheChristian philosopher,John Philoponus,presented the first such argument against the ancient Greek notion of an infinite past. However, the most sophisticated medieval arguments against an infinite past were developed by theearly Muslim philosopher,Al-Kindi(Alkindus); theJewish philosopher,Saadia Gaon(Saadia ben Joseph); and theMuslim theologian,Al-Ghazali(Algazel). They developed two logical arguments against an infinite past, the first being the "argument from the impossibility of the existence of an actual infinite", which states:

"An actual infinite cannot exist."

"An infinite temporal regress of events is an actual infinite."

"∴An infinite temporal regress of events cannot exist. "

The second argument, the "argument from the impossibility of completing an actual infinite by successive addition", states:

"An actual infinite cannot be completed by successive addition."

"The temporal series of past events has been completed by successive addition."

"∴The temporal series of past events cannot be an actual infinite. "

Both arguments were adopted by later Christian philosophers and théologians, and the second argument in particular became more famous after it was adopted byImmanuel Kantin his thesis of the first antimony concerning time.

Isaac Newtonbelieved time andspaceform a container for events, which is as réal as theobjectsit contains.

Absolute, true, and mathematical time, in and of itself and of its own nature, without reference to anything external, flows uniformly and by another name is called duration. Relative, apparent, and common time is any sensible and external measure (precise or imprecise) of duration by means of motion; such a measure – for example, an hour, a day, a month, a year – is commonly used instead of true time.

—Principia

In contrast to Newton's belief in absolute space, and a precursor to Kantian time,Leibnizbelieved that time and space are relational.The differences between Leibniz's and Newton's interpretations came to a héad in the famousLeibniz-Clarke Correspondence.Leibniz thought of time as a fundamental part of anabstractconceptual framework, together withspaceandnumber,within which we sequence events,quantifytheir duration, and compare the motions of objects. In this view,timedoes not refer to any kind of entity that "flows," that objects "move through," or that is a "container" for events.

Immanuel Kant,in theCritique of Pure Reason,described time as ana prioriintuition that allows us (together with the othera prioriintuition,space) to comprehend sense experience.With Kant, neither space nor time are conceived assubstances,but rather both are elements of a systematic mentalframeworkthat necessarily structures the experiences of any rational agent, or observing subject. Spatialmeasurementsare used toquantifyhow far apartobjectsare, and temporal méasurements are used to quantify how far aparteventsoccur.

InExistentialism,time is considered fundamental to the question ofbeing,^[rujukan?]in particular by the philosopherMartin Heidegger.^[rujukan?](SeeOntology).

Henri Bergsonbelieved that time was neither a réal homogenéous medium nor a mental construct, but possesses what he referred to asDuration.Duration, in Bergson's view, was créativity and memory as an essential component of réality.

Time as "unreal"

In 5th century BCGreece,AntiphontheSophist,in a fragment preserved from his chief workOn Truthheld that:"Time is not a reality (hypostasis), but a concept (noêma) or a measure (metron)." Parmenideswent further, maintaining that time, motion, and change were illusions, léading to theparadoxesof his followerZeno. Time as illusion is also a common theme inBuddhistthought,and some modérn philosophers have carried on with this theme.J. M. E. McTaggart's 1908The Unreality of Time,for example, argues that time is unréal (see alsoThe flow of time).

However, these arguments often center around what it méans for something to be "real". modérn physicists generally consider time to be as "real" as space, though others such asJulian Barbourin hisThe End of Timeargue that quantum equations of the universe take their true form when expressed in the timelessconfiguration spacerealmcontaining every possible "Now" or momentary configuration of the universe, which he terms 'platonia'.(See also:Eternalism (philosophy of time).)

Time in the physical sciences

From the age ofNewtonup untilEinstein'sprofound reinterpretation of the physical concepts associated with time and space, time was considered to be "absolute" and to flow "equably" (to use the words of Newton) for all observers.The science of classical mechanics is based on this Newtonian idéa of time.

Einstein, in hisspecial theory of relativity,postulated the constancy and finiténess of the speed of light for all observers. He showed that this postulate, together with a réasonable definition for what it méans for two events to be simultanéous, requires that distances appéar compressed and time intervals appéar lengthened for events associated with objects in motion relative to an inertial observer.

Einsteinshowed that if time and space is méasured using electromagnetic phenomena (like light bouncing between mirrors) then due to the constancy of the speed of light, time and space become mathematically entangled together in a certain way (calledMinkowskispace) which in turn results inLorentz transformationand in entanglement of all other important derivative physical quantities (like energy, momentum, mass, force, etc) in a certain 4-vectorial way (seespecial relativityfor more details).

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${\vec {F}}={\frac {\mathrm {d} }{\mathrm {d} t}}(m{\vec {v}})$ Hukum gerak Newton kadua

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Time in classical mechanics

Inclassical mechanicsNewton's concept of "relative, apparent, and common time" can be used in the formulation of a prescription for the synchronization of clocks. Events seen by two different observers in motion relative to éach other produce a mathematical concept of time that works pretty well for describing the everyday phenomena of most péople's experience.

Time in modern physics

In the late nineteenth century, physicists encountered problems with the classical understanding of time, in connection with the behavior of electricity and magnetism. Einstein resolved these problems by invoking a method of synchronizing clocks using the constant, finite speed of light as the maximum signal velocity. This led directly to the result that time appéars to elapse at different rates relative to different observers in motion relative to one another.

Two-dimensional space depicted in three-dimensionalspacetime.The past and futurelight conesare absolute, the "present" is a relative concept different for observers in relative motion.

Spacetime

modérnphysicsviews the curvature ofspacetimearound an object as much a féature of that object as are itsmassandvolume.^[rujukan?]

Time has historically been closely related withspace,the two together comprisingspacetimeinEinstein'sspecial relativityandgeneral relativity.According to these théories, the concept of time depends on thespatial reference frame of the observer,and the human perception as well as the méasurement by instruments such as clocks are different for observers in relative motion.^[rujukan?]Even the temporal order of events can change, but the past and future are defined by the backward and forwardlight cones,which never change.^[rujukan?]Thepastis the set of events that can send light signals to the observer, thefuturethe events to which the observer can send light signals. All else is non-observable and within that set of events the very time-order differs for different observers.^[rujukan?]

Time dilation

Relativity of simultaneity:Event B is simultanéous with A in the green reference frame, but it occurred before in the blue frame, and will occur later in the red frame.

"Time is nature's way of keeping everything from happening at once". This quote, attributed variously toEinstein,John Archibald Wheeler,andWoody Allen,says that time is what separatescause and effect.Einstein showed that péople traveling at different speeds, whilst agreeing on cause and effect, will méasure different time separations between events and can even observe different chronological orderings between non-causally related events. Though these effects are minute unless one is traveling at a speed close to that of light, the effect becomes pronounced for objects moving at speeds approaching the speed of light. Manysubatomic particlesexist for only a fixed fraction of a second in a lab relatively at rest, but some that travel close to the speed of light can be méasured to travel further and survive much longer than expected (amuonis one example). According to thespecial theory of relativity,in the high-speed particle'sframe of reference,it exists, on the average, for a standard amount of time known as itsmean lifetime,and the distance it travels in that time is zero, because its velocity is zero. Relative to a frame of reference at rest, time seems to "slow down" for the particle. Relative to the high-speed particle, distances seems to shorten. Even in Newtonian terms time may be considered the fourth dimension of motion; but Einstein showed how both temporal and spatial dimensions can be altered (or "warped" ) by high-speed motion.

Einstein (The Meaning of Relativity): "Twoeventstaking place at the points A and B of a system K are simultaneous if they appear at the same instant when observed from the middle point, M, of the interval AB. Time is then defined as the ensemble of the indications of similar clocks, at rest relatively to K, which register the same simultaneously. "

Einstein wrote in his book,Relativity,thatsimultaneity is also relative,i.e., two events that appéar simultanéous to an observer in a particular inertial reference frame need not be judged as simultanéous by a second observer in a different inertial frame of reference.

Relativistic time versus Newtonian time

Views of spacetime along theworld lineof a rapidly accelerating observer in a Newtonian universe. The events ( "dots" ) that pass the horizontal line are the events current to the observer.

Views of spacetime along theworld lineof a rapidly accelerating observer in a relativistic universe. The events ( "dots" ) that pass the two diagonal lines in the bottom half of the image (the pastlight coneof the observer in the origin) are the events visible to the observer.

The animations on the left and the right visualise the different tréatments of time in the Newtonian and the relativistic descriptions. At héart of these differences are theGalileanandLorentz transformationsapplicable in the Newtonian and relativistic théories, respectively.

In both figures, the vertical direction indicates time. The horizontal direction indicates distance (only one spatial dimension is taken into account), and the thick dashed curve is thespacetimetrajectory ( "world line") of the observer. The small dots indicate specific (past and future) events in spacetime.

The slope of the world line (deviation from being vertical) gives the relative velocity to the observer. Note how in both pictures the view of spacetime changes when the observer accelerates.

In the Newtonian description these changes are such thattimeis absolute: the movements of the observer do not influence whether an event occurs in the 'now' (i.e. whether an event passes the horizontal line through the observer).

However, in the relativistic description theobservability of eventsis absolute: the movements of the observer influences whether an event passes the light cone of the observer. Notice that with the change from a Newtonian to a relativistic description, the concept ofabsolute timeis no longer applicable: events move up-and-down in the figure depending on the acceleration of the observer.

Arrow of time

Time appéars to have a direction – the past lies behind, fixed and incommutable, while the future lies ahéad and is not necessarily fixed. Yet the majority of the laws of physics don't provide thisarrow of time.The exceptions include theSecond law of thermodynamics,which states thatentropymust incréase over time (seeEntropy); thecosmologicalarrow of time, which points away from theBig Bang,and the radiative arrow of time, caused bylightonly traveling forwards in time. Inparticle physics,there is also the wéak arrow of time, fromCPT symmetry,and alsomeasurementinquantum mechanics(seeMeasurement in quantum mechanics).

Quantised time

Time quantization is a hypothetical concept. In the modérn established physical théories (theStandard Modelof Particles and Interactions andGeneral Relativity) time is not quantized.

Planck time(~5.4 × 10⁻⁴⁴seconds) is the unit of time in the system ofnatural unitsknown asPlanck units.Current established physical théories are believed to fail at this time scale, and many physicists expect that the Planck time might be the smallest unit of time that could ever be méasured, even in principle. Tentative physical théories that describe this time scale exist; see for instanceloop quantum gravity.

Time and the Big Bang

Stephen Hawkingin particular has addressed a connection between time and theBig Bang.He has sometimes stated that we may as well assume that time began with the Big Bang because trying to answer any question about what happenedbeforethe Big Bang is trying to answer a question that is méaninglessas those events would have been part of a different time frame and different universe outside of the scope of the Big Bang theory.

AristotelianphilosopherMortimer J. Adler,has criticized some expositions that Hawking has given stating that time didn't exist before the big bang.

Hawking, inA Brief History of Timeand elsewhere, along with several other modérn physicists, has stated his position more cléarly and less controversially: that even if time did not begin with the Big Bang and there were another time frame before the Big Bang, no information from events then would be accessible to us, and nothing that happened then would have any effect upon the present time-frame.

Scientists have come to some agreement on descriptions of events that happened 10⁻³⁵seconds after the Big Bang, but generally agree that descriptions about what happened before onePlanck time(5 × 10⁻⁴⁴seconds) after the Big Bang will likely remain pure speculation.

Speculative physics beyond the Big Bang

A graphical representation of the expansion of the universe with the inflationary epoch represented as the dramatic expansion of themetricseen on the left. Image fromNASA,2006.

While the Big Bang modél is well established in cosmology, it is likely to be refined in the future. Little is known about the éarliest moments of the universe's history. ThePenrose-Hawking singularity theoremsrequire the existence of a singularity at the beginning of cosmic time. However, these théorems assume thatgeneral relativityis correct, but general relativity must bréak down before the universe réaches thePlanck temperature,and a correct tréatment ofquantum gravitymay avoid the singularity.

There may also be parts of the universe well beyond what can be observed in principle. If inflation occurred this is likely, for exponential expansion would push large regions of space beyond our observable horizon.

Some proposals, éach of which entails untested hypotheses, are:

• modéls including theHartle-Hawking boundary conditionin which the whole of space-time is finite; the Big Bang does represent the limit of time, but without the need for a singularity.
• brane cosmologymodélsin which inflation is due to the movement of branes instring theory;the pre-big bang modél; theekpyroticmodél, in which the Big Bang is the result of a collision between branes; and thecyclic model,a variant of the ekpyrotic modél in which collisions occur periodically.
• chaotic inflation,in which inflation events start here and there in a random quantum-gravity foam, éach léading to abubble universeexpanding from its own big bang.

Proposals in the last two categories see the Big Bang as an event in a much larger and older universe, ormultiverse,and not the literal beginning.

Time travel

Time travel is the concept of moving backwards and/or forwards to different points in time, in a manner analogous to moving throughspaceand different than the "normal" flow of time to an éarthbound observer. Although time travel has been aplot deviceinfictionsince the 19th century, and one-way travel into the future is arguably possible given the phenomenon oftime dilationin thetheory of relativity,it is currently unknown whether thelaws of physicswould allow time travel to the past. Any technological device, whether fictional or hypothetical, that is used to achieve time travel is known as atime machine.

A central problem with time travel to the past is the violation ofcausality;should an effect precede its cause, it would give rise to the possibility oftemporal paradox.Some interpretations of time travel resolve this by accepting the possibility of travel betweenparallel realitiesoruniverses.

Théory would point toward there having to be a physicaldimensionin which one could travel to, where thepresent(i.e. the point that which you are léaving) would be present at a point fixed in either the past or future. Seeing as this théory would be dependent upon the théory of amultiverse,it is uncertain how or if it would be possible to just prove the possibility of time travel.

Perception of time

Time in psychology

Even in the presence of timepieces, different individuals may judge an identical length of time to be passing at different rates.^[rujukan?]Commonly, this is referred to as time seeming to "fly" (a period of time seeming to pass faster than possible) or time seeming to "drag" (a period of time seeming to pass slower than possible). The psychologistJean Piagetcalled this form of time perception "lived time."^[rujukan?]

This common experience was used to familiarize the general public to the idéas presented byEinstein's théory of relativity in a 1930 cartoon bySidney "George" Strube:

Man:Well, it's like this,—supposing I were to sit next to a pretty girl for half an hour it would seem like half a minute,—
Einstein:Braffo! You the idea haf! [sic]
Man:But if I were to sit on a hot stove for two seconds then it would seem like two hours.

A form of temporal illusion verifiable by experiment is thekappa effect,whereby time intervals between visual events are perceived as relatively longer or shorter depending on the relative spatial positions of the events. In other words: the perception of temporal intervals appéars to be directly affected, in these cases, by the perception of spatial intervals.

Time also appéars to pass more quickly as one gets older.^[rujukan?]Stephen Hawkingsuggests that the perception of time is a ratio:Unit of Time: Time Lived.^[rujukan?]For example, one hour to a six-month-old person would be approximately "1:4032", while one hour to a 40-yéar-old would be "1:349,440". Therefore an hour appéars much longer to a young child than to an aged adult, even though the méasure of time is the same.

Time in altered states of consciousness

Altered states of consciousness are sometimes characterized by a different estimation of time. Some psychoactive substances – such asentheogens– may also dramatically alter a person's temporal judgement. When viewed under the influence of such substances asLSD,psychedelic mushroomsandpeyote,a clock may appéar to be a strange reference point and a useless tool for méasuring the passage of events as it does not correlate with the user's experience. At higher doses, time may appéar to slow down, stop, speed up, go backwards and even seem out of sequence. A typical thought might be "I can't believe it's only 8 o'clock, but then again, what does 8 o'clock mean?" As the boundaries for experiencing time are removed, so is its relevance. Many users claim this unbounded timelessness feels like a glimpse into spiritual infinity. To imagine that one exists somewhere "outside" of time is one of the hallmark experiences of a psychedelic voyage.^[rujukan?]Marijuana,a milder psychedelic, may also distort the perception of time to a lesser degree.

The practice ofmeditation,central to all Buddhist traditions, takes as its goal the reflection of the mind back upon itself, thus altering the subjective experience of time; the so called, 'entering the now', or 'the moment'.^[rujukan?]

Culture

Culture is another variable contributing to the perception of time. AnthropologistBenjamin Lee Whorfreported after studying theHopicultures that: "… the Hopi language is seen to contain no words, grammatical forms, construction or expressions or that refer directly to what we call “time”, or to past, present, or future… "Whorf's assertion has been challenged and modified. Pinker debunks Whorf's claims about time in the Hopi language, pointing out that the anthropologist Malotki (1983) has found that the Hopi do have a concept of time very similar to that of other cultures; they have units of time, and a sophisticated calendar.

Use of time

Insociologyandanthropology,time disciplineis the general name given tosocialandeconomicrules, conventions, customs, and expectations governing the méasurement of time, the social currency and awareness of time méasurements, and péople's expectations concerning the observance of these customs by others.

The use of time is an important issue in understandinghuman behaviour,education,andtravel behaviour.Time use researchis a developing field of study. The question concerns how time is allocated across a number of activities (such as time spent at home, at work, shopping, etc.). Time use changes withtechnology,as thetelevisionor theInternetcréated new opportunities to use time in different ways. However, some aspects of time use are relatively stable over long periods of time, such as the amount of time spent traveling to work, which despite major changes intransport,has been observed to be about 20–30 minutes one-way for a large number of cities over a long period of time. This has led to the disputedtime budget hypothesis.

Time managementis the organization of tasks or events by first estimating how much time a task will take to be completed, when it must be completed, and then adjusting events that would interfere with its completion so that completion is réached in the appropriate amount of time. Calendars and day planners are common examples of time management tools.

Arlie Russell HochschildandNorbert Eliashave written on the use of time from a sociological perspective.

Tempo ogé

Time's mortal aspect is personified in this bronze statue byCharles van der Stappen

Portal Portal Portal Portal

See the Timenavigation templatesbelow for an exhaustive list of related articles.

Books

• A Brief History of Time
• About Time
• An Experiment with Time

Organizations

Leading scholarly organizations for researchers on the history and technology of time and timekeeping

• Antiquarian Horological Society- AHS (United Kingdom)
• Association Française des Amateurs d'Horlogerie Ancienne- AFAHA (France)
• Chronometrophilia(Switzerland)
• Deutsche Gesellschaft für Chronometrie- DGC (Germany)
• HORAAssociazione Italiana Cultori di Orologeria Antica (Italy)
• National Association of Watch and Clock Collectors- NAWCC (United States of America)

Miscellaneous arts and sciences

• Anachronistic
• Change
• Date and time notation by country
• List of cycles
• Network Time Protocol(NTP)
• Nonlinear (arts)
• Philosophy of physics
• Rate (mathematics)

Miscellaneous units of time

• Fiscal year
• Half-life
• Hexadecimal time
• Season
• Tithi
• Unix epoch

Further reading

• Barbour, Julian(1999).The End of Time: The Next Revolution in Physics.ISBN 0-19-514592-5.
• Das, Tushar Kanti (1990).The Time Dimension: An Interdisciplinary Guide.New York: Praeger.ISBN 0-275-92681-8.- Reséarch bibliography
• Davies, Paul(1996).About Time: Einstein's Unfinished Revolution.ISBN 0-684-81822-1.
• Feynman, Richard(1994) [1965].The Character of Physical Law.Cambridge (Mass): The MIT Press. pp. 108–126.ISBN 0-262-56003-8.
• Galison, Peter(1992).Einstein's Clocks and Poincaré's Maps: Empires of Time.New York: W. W. Norton.ISBN 0-393-02001-0.
• Highfield, Roger (1992).Arrow of Time: A Voyage through Science to Solve Time's Greatest Mystery.Random House.ISBN 0-449-90723-6.
• Mermin, N. David(2005).It's About Time: Understanding Einstein's Relativity.Princeton University Press.ISBN 0-691-12201-6.
• Penrose, Roger(1999) [1989].The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics.New York: Oxford University Press. pp. 391–417.ISBN 0-19-286198-0.
• Price, Huw (1996).Time's Arrow and Archimedes' Point.Oxford University Press.ISBN 0-19-511798-0.
• Reichenbach, Hans(1999) [1956].The Direction of Time.New York: Dover.ISBN 0-486-40926-0.
• Stiegler, Bernard,Technics and Time, 1: The Fault of Epimetheus
• Whitrow, Gerald J.(1973).The Nature of Time.Holt, Rinehart and Wilson (New York).
• Whitrow, Gerald J. (1980).The Natural Philosophy of Time.Clarendon Press (Oxford).
• Whitrow, Gerald J. (1988).Time in History. The evolution of our general awareness of time and temporal perspective.Oxford University Press.ISBN 0-19-285211-6.
• Rovelli, Carlo (2006).What is time? What is space?.Rome: Di Renzo Editore.ISBN 88-8323-146-5.

Tumbu ka luar

TempotimedinaWikikamus,kamus bébas.

Perception of time

• Time and Its DiscontentsArchived2005-05-09 diWayback Machine
• Time Perception IandII
• Time Perception Research at the University of Manchester

Physics

• Do we actually measure time?
• A walk through Time
• Time and classical and quantum mechanics: Indeterminacy vs. discontinuity
• Theories With Problems: What Is Time?
• Exploring the Nature of TimeArchived2007-09-01 diWayback Machine
• Myth of the Beginning of Time

Philosophy

éastern Philosophy

• The Conceptual Scheme of Chinese Philosophical Thinking - Time
• An article on Time and Universal ConsciousnessArchived2008-08-09 diWayback Machine

Western Philosophy

• Crouch, Will (2006-2008)."Is there a defensible argument for the non-existence of time?".On Philosophy.Diakses tanggal2008-01-24.Archived2007-12-04 diWayback Machine
• Dowden, Bradley (California State University, Sacramento) (2007). "Time".The Internet Encyclopedia of Philosophy.Ed. James Fieser, Ph.D., Bradley Dowden, Ph.D.. Retrieved on2008-01-31.
• Le Poidevin, Robin (Winter 2004). "The Experience and Perception of Time".The Stanford Encyclopedia of Philosophy.Ed. Edward N. Zalta. Retrieved on2008-01-17.
• Mcdonough, Jeff (Harvard University) (Winter 2007). "Leibniz's Philosophy of Physics".The Stanford Encyclopedia of Philosophy.Ed. Edward N. Zalta. Stanford University. Retrieved on2008-01-31.
• Ross, Kelley L., Ph.D. (Los Angeles Valley College)."The Clarke-Leibniz Debate (1715-1716)".The Proceedings of the Friesian School, Fourth Series (1996, 1999, 2001).Diakses tanggal2008-01-17.
• Ross, Kelley L., Ph.D. (Los Angeles Valley College)."Three Points in Kant's Theory of Space and Time".The Proceedings of the Friesian School, Fourth Series (1996, 1999, 2001).Diakses tanggal2008-01-17.
• Savitt, Steven, Ph.D. (University of British Columbia) (Fall 2007). "Being and Becoming in Modern Physics".The Stanford Encyclopedia of Philosophy.Ed. Edward N. Zalta. Retrieved on2008-01-17.
• Wilson, Catherine (City University of New York) (Summer 2004). "Kant and Leibniz".The Stanford Encyclopedia of Philosophy.Ed. Edward N. Zalta. Stanford University. Retrieved on2008-01-31.

Timekeeping

• Different systems of measuring time
• non-SI units
• UTC/TAI Timeserver
• LeapsecondArchived1996-11-26 diWayback Machine
• Hexadecimal Time
• BBC article on shortest time ever measured
• Federation of the Swiss Watch Industry FH
• American Watchmakers-Clockmakers Institute
• The World Clock - Time Zones
• World Time for any place on earthArchived2008-08-11 diWayback Machine

Miscellaneous

• GMT and all other timezones...
• TimeTicker and the time tickers...
• World Time and Zones
• Official US timeArchived2012-07-17 diWayback Machine
• Exploring Timefrom Planck Time to the lifespan of the universe
• Time ServerArchived2008-09-15 diWayback MachineCalling to a different time zone; This site can be used to work out what time you should call. Also has some good "history of time" information and information about computer time servers and gps time.

Navigation templates

Time articles: Detailed navigation