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Anorder of magnitude oftime is usually adecimal prefix or decimal order-of-magnitude quantity together with a baseunit of time, like amicrosecond or amillion years. In some cases, the order of magnitude may be implied (usually 1), like a "second" or "year." In other cases, the quantity name implies thebase unit, like "century." In most cases, the base unit is seconds or years.
Prefixes are not usually used with a base unit of years. Therefore, it is said "a million years" instead of "a megayear." Clock time and calendar time haveduodecimal orsexagesimal orders of magnitude rather than decimal, e.g., a year is 12 months, and a minute is 60 seconds.
The smallest meaningful increment of time is thePlanck time ― the time light takes to traverse thePlanck distance, many decimal orders of magnitude smaller than a second.[1]
The largest realized amount of time, based on known scientific data, is theage of the universe, about 13.8 billion years — the time since theBig Bang as measured in thecosmic microwave backgroundrest frame.[2] Those amounts of time together span 60 decimal orders of magnitude. Metric prefixes are defined spanning 10−30 to 1030, 60 decimal orders of magnitude which may be used in conjunction with the metric base unit of second.
Metric units of time larger than the second are most commonly seen only in a few scientific contexts such as observational astronomy and materials science, although this depends on the author. For everyday use and most other scientific contexts, the common units of minutes, hours (3 600 s or 3.6 ks), days (86 400 s), weeks, months, and years (of which there are a number of variations) are commonly used. Weeks, months, and years are significantly variable units whose lengths depend on the choice of calendar and are often not regular even with a calendar, e.g., leap years versus regular years in theGregorian calendar. This makes them problematic for use against a linear and regular time scale such as that defined by theSI, since it is not clear which version is being used.
Because of this, the table below does not include weeks, months, and years. Instead, the table uses theannum orastronomical Julian year (365.25 days of 86 400 seconds), denoted with the symbol a. Its definition is based on the average length of a year according to theJulian calendar, which has oneleap year every four years. According to the geological science convention, this is used to form larger units of time by the application ofSI prefixes to it; at least up to giga-annum or Ga, equal to 1 000 000 000 a (short scale: one billion years,long scale: one milliard years).
| Multiple of a second | Unit | Symbol | Definition | Comparative examples & common units |
|---|---|---|---|---|
| 10−44 | Planck time | tP | Presumed to be the shortest theoretically measurable time interval (but not necessarily the shortestincrement of time—seequantum gravity) | 10−14 qs: The length of onePlanck time (tP = ≈5.39×10−44 s)[3] is the briefest physically meaningful span of time. It is the unit of time in thenatural units system known asPlanck units. |
| 10−30 | quectosecond | qs | Quectosecond, (quecto- +second), is onenonillionth of a second | |
| 10−27 | rontosecond | rs | Rontosecond, (ronto- +second), is oneoctillionth of a second | 300 rs: Themean lifetime ofW and Z bosons |
| 10−24 | yoctosecond | ys[4] | Yoctosecond, (yocto- +second), is oneseptillionth of a second | 86 ys: The estimated value on thehalf-life ofisotope 5 of hydrogen (hydrogen-5) 143 ys: Thehalf-life of thenitrogen-10 isotope of nitrogen 156 ys: The mean lifetime of aHiggs boson |
| 10−21 | zeptosecond | zs | Zeptosecond, (zepto- +second), is onesextillionth of one second | 1.3 zs: Smallest experimentally controlled time delay in a photon field.[5] 2 zs: The representative cycle time ofgamma ray radiation released in the decay of a radioactiveatomic nucleus (here as 2MeV per emittedphoton) 4 zs: The cycle time of thezitterbewegung of anelectron () 247 zs: The experimentally measured travel time of a photon across a hydrogen molecule, "for the average bond length of molecular hydrogen"[6] |
| 10−18 | attosecond | as | One quintillionth of one second | 12 as: The best timing control of laser pulses.[7] 43 as: The shortest X-ray laser pulse[8] 53 as: The shortest electron laser pulse[9][10] |
| 10−15 | femtosecond | fs | One quadrillionth of one second | 1 fs: The cycle time for ultraviolet light with a wavelength of 300nanometres; the time it takes light to travel a distance of 0.3 micrometres (μm). 7.58 fs: The period of vibration of a hydrogen molecule. 140 fs: The time needed for electrons to have localized onto individualbromine atoms 6Ångstrom apart afterlaser dissociation of Br2.[11] 290 fs: The lifetime of atauon |
| 10−12 | picosecond | ps | One trillionth of one second | 1 ps: The mean lifetime of abottom quark; the time needed for light to travel 0.3 millimetres (mm) 1 ps: The typical lifetime of atransition state one machine cycle by an IBMsilicon-germanium transistor 109 ps: The period of thephoton corresponding to thehyperfine transition of the ground state ofcaesium-133, and one 9,192,631,770th of one secondby definition 114.6 ps: The time for the fastest overclocked processor as of 2014[update] to execute one machine cycle.[12] 696 ps: How much more a second lasts far away from Earth's gravity due to the effects ofgeneral relativity |
| 10−9 | nanosecond | ns | One billionth of one second | 1 ns: The time needed to execute one machine cycle by a 1 GHz microprocessor 1 ns: The time light takes to travel 30 cm (11.811 in) |
| 10−6 | microsecond | μs | One millionth of one second | 1 μs: The time needed to execute one machine cycle by an Intel 80186 microprocessor 2.2 μs: The lifetime of amuon 4–16 μs: The time needed to execute one machine cycle by a 1960sminicomputer |
| 10−3 | millisecond | ms | One thousandth of one second | 1 ms: The time for a neuron in the human brain to fire one impulse and return to rest[13] 4–8 ms: The typicalseek time for a computer hard disk |
| 10−2 | centisecond | cs | One hundredth of one second | 1.6667 cs: The period of a frame at a frame rate of 60 Hz. 2 cs: The cycle time for European 50 Hz AC electricity 10–20 cs (=0.1–0.2 s): The humanreflex response to visual stimuli |
| 10−1 | decisecond | ds | One tenth of a second | 1–4 ds (=0.1–0.4 s): The length of a single blink of an eye[14] |
In this table, large intervals of time surpassing one second are catalogued in order of the SI multiples of the second as well as their equivalent in common time units of minutes, hours, days, and Julian years.
| Multiple of a second | Unit | Symbol | Common units | Comparative examples and common units |
|---|---|---|---|---|
| 101 | decasecond | das | single seconds (1 das = 10 s) | 6 das: One minute (min), the time it takes a second hand to cycle around a clock face |
| 102 | hectosecond | hs | minutes (1 hs = 1 min 40 s = 100 s) | 2 hs (3 min 20 s): The average length of the most popular YouTube videos as of January 2017[15] 5.55 hs (9 min 12 s): The longest videos in the above study 7.1 hs (11 m 50 s): The time for a human walking at average speed of 1.4m/s to walk 1 kilometre 9 hs (14 m): The time for Neutronium-1 to decay |
| 103 | kilosecond | ks | minutes, hours, days (1 ks = 16 min 40 s = 1,000 s) | 1 ks: The record confinement time forantimatter, specificallyantihydrogen, in electrically neutral state as of 2011;[16] 1.477 ks: The longest period in which a person has not taken a breath. 1.8 ks: The time slot for the typical situation comedy on television with advertisements included 2.28 ks: The duration of theAnglo-Zanzibar War, the shortest war in recorded history. 3.6 ks: The length of one hour (h), the time for the minute hand of a clock to cycle once around the face, approximately 1/24 of onemean solar day 7.2 ks (2 h): The typical length of feature films 35.73 ks: the rotational period of planet Jupiter, fastest planet to rotate 38.0196 ks: rotational period of Saturn, second shortest rotational period 57.996 ks: one day on planet Neptune. 62.064 ks: one day on Uranus. 86.399 ks (23 h 59 min 59 s): The length of one day with a removedleap second onUTC time scale. Such has not yet occurred. 86.4 ks (24 h): The length of one day of Earth by standard. More exactly, themean solar day is 86.400 002 ks due totidal braking, and increasing at the rate of approximately 2 ms/century; to correct for this time standards likeUTC useleap seconds with the interval described as "a day" on them being most often 86.4 ks exactly by definition but occasionally one second more or less so that every day contains a whole number of seconds while preserving alignment with astronomical time. The hour hand of an analogue clock will typically cycle twice around the dial in this period as most analogue clocks are12-hour, less common are analogue24-hour clocks in which it cycles around once. 86.401 ks (24 h 0 min 1 s): One day with an addedleap second onUTC time scale. While this is strictly 24 hours and 1 second in conventional units, adigital clock of suitable capability level will most often display the leap second as 23:59:60 and not 24:00:00 before rolling over to 00:00:00 the next day, as though the last "minute" of the day was crammed with 61 seconds and not 60, and similarly the last "hour" was crammed with 3,601 seconds instead of 3,600. 88.775 ks (24 h 39 min 35 s): Onesol of Mars 604.8 ks (7 d): One week of theGregorian calendar |
| 106 | megasecond | Ms | weeks to years (1 Ms = 11 d 13 h 46 min 40 s = 1,000,000 s) | 1.6416 Ms (19 d): The length of a month of theBaháʼí calendar 2.36 Ms (27.32 d): The length of the true month, theorbital period of theMoon 2.4192 Ms (28 d): The length of February, the shortest month of theGregorian calendar, in common years 2.5056 Ms (29 d): The length of February in leap years 2.592 Ms (30 d): The length of April, June, September, and November in theGregorian calendar; common interval used in legal agreements and contracts as a proxy for a month 2.6784 Ms (31 d): The length of the longest months of theGregorian calendar 23 Ms (270 d): The approximate length of typical humangestational period 31.5576 Ms (365.25 d): The length of theJulian year, also called theannum, symbola. 5.06703168 Ms: The rotational period of Mercury. 7.600544064 Ms: One year on Mercury. 19.41414912 Ms: One year on Venus. 20.9967552 Ms: The rotational period of Venus. 31.55815 Ms (365 d 6 h 9 min 10 s): The length of the true year, theorbital period of the Earth 126.2326 Ms (1461 d 0 h 34 min 40 s): The elected term of thePresident of the United States or oneOlympiad |
| 109 | gigasecond | Gs | decades, centuries, millennia (1 Gs = over 31 years and 287 days = 1,000,000,000 s) | 2.5 Gs: (79 a): The typical humanlife expectancy in thedeveloped world 3.16 Gs: (100 a): One century 31.6 Gs: (1,000 a, 1 ka): Onemillennium, also called akilo-annum (ka) 194.67 Gs (6.173 ka): The approximate lifespan oftime capsuleCrypt of Civilization, 28 May 1940 – 28 May 8113 363 Gs: (11.5 ka): The time since the beginning of theHolocene epoch 814 Gs: (25.8 ka): The approximate time for the cycle ofprecession of the Earth's axis |
| 1012 | terasecond | Ts | millennia to geologicalepochs (1 Ts = over 31,600 years = 1,000,000,000,000 s) | 3.1 Ts (100 ka): approximate length of aglacial period of the currentQuaternary glaciation epoch 31.6 Ts (1000 ka, 1 Ma): Onemega-annum (Ma), or one million years 79 Ts (2.5 Ma): The approximate time since earliest hominids of genusAustralopithecus 130 Ts (4 Ma): The typical lifetime of abiological species on Earth 137 Ts (4.32 Ma): The length of the mythic unit ofmahayuga, the Great Age, inHindu mythology. |
| 1015 | petasecond | Ps | geologicaleras, history of Earth and theUniverse | 2 Ps: The approximate time since theCretaceous-Paleogene extinction event, believed to be caused by the impact of a largeasteroid intoChicxulub in modern-day Mexico. This extinction was one of the largest in Earth's history and marked the demise of most dinosaurs, with the only known exception being the ancestors of today's birds. 7.9 Ps (250 Ma): The approximate time since thePermian-Triassic extinction event, the actually largest known mass extinction in Earth history which wiped out 95% of all extant species and believed to have been caused by the consequences of massive long-termvolcanic eruptions in the area of theSiberian Traps. Also, the approximate time to thesupercontinent ofPangaea. Also, the length of onegalactic year orcosmic year, the time required for theSun to complete one orbit around theMilky Way Galaxy. 16 Ps (510 Ma): The approximate time since theCambrian explosion, a massive evolutionary diversification of life which led to the appearance of most existingmulticellular organisms and the replacement of the previousEdiacaran biota. 22 Ps (704 Ma): The approximatehalf-life of theuranium isotope235U. 31.6 Ps (1000 Ma, 1 Ga): Onegiga-annum (Ga), one billion years, the largest fixed time unit used in the standardgeological time scale, approximately the order of magnitude of aneon, the largest division of geological time. +1 Ga: The estimated remaining habitable lifetime of Earth, according to some models. At this point in time thestellar evolution of the Sun will have increased itsluminosity to the point that enough energy will be reaching the Earth to cause the evaporation of the oceans and their loss into space (due to the UV flux from the Sun at the top of the atmospheredissociating the molecules), making it impossible for any life to continue. 136 Ps (4.32 Ga): The length of the legendary unitKalpa inHindu mythology, or one day (but not including the following night) of the life ofBrahma. 143 Ps (4.5 Ga): Theage of the Earth by our best estimates. Also the approximate half-life of the uranium isotope238U. 315 Ps (10 Ga): The approximate lifetime of amain-sequence star similar to theSun. 434.8 Ps (13.787 Ga): The approximateage of the Universe |
| 1018 | exasecond | Es | future cosmological time | All times of this length and beyond are currently theoretical as they surpass the elapsed lifetime of the known universe. 1.08 Es (+34 Ga): Time to theBig Rip according to some models, but this is not favored by existing data. This is one possible scenario for theultimate fate of the Universe. Under this scenario,dark energy increases in strength and power in a feedback loop that eventually results in the tearing apart of all matter down to subatomic scale due to the rapidly increasingnegative pressure thereupon 300 – 600 Es (10 – 20 Ta): The estimated lifetime of low-mass stars (red dwarfs) |
| 1021 | zettasecond | Zs | 3 Zs (+100 Ta): The remaining time until the end ofStelliferous Era of the universe, under theheat death scenario for theultimate fate of the Universe, which is the most commonly accepted model in the current scientific community. This is marked by the cooling-off of the last low-mass dwarf star to ablack dwarf. After this time has elapsed, theDegenerate Era begins. 9.85 Zs (311 Ta): The entire lifetime ofBrahma inHindu mythology. | |
| 1024 | yottasecond | Ys | 600 Ys (2×1019 a): The radioactive half-life ofbismuth-209 byalpha decay, one of the slowest-observed radioactive decay processes. | |
| 1027 | ronnasecond | Rs | 3.16 Rs (1×1020 a): The estimated time until all stars are ejected from their galaxies or consumed by black holes. 32 Rs (1×1021 a): Highest estimate of the time until all stars are ejected from galaxies or consumed by black holes. | |
| 1030and onward | quettasecondand beyond | Qs and on | 69 Qs (2.2×1024 a): The radioactive half-life oftellurium-128, the longest known half-life of any elementalisotope. 1,340,009 Qs (4.134105×1028 years): The time period equivalent to the value of 13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.0.0.0.0 in theMesoamerican Long Count, a date discovered on a stele at theCoba Maya site, believed by archaeologistLinda Schele to be the absolute value for the length of one cycle of the universe[17][18] 2.6×1011 Qs (8.2×1033 years): The smallest possible value forproton half-life consistent with experiment[19] 1023 Qs (3.2×1045 years): The largest possible value for theproton half-life, assuming that theBig Bang wasinflationary and that the same process that madebaryons predominate overantibaryons in the early Universe also makes protons decay[20] 6×1043 Qs (2×1066 years): The approximatelifespan of a black hole with the mass of the Sun[21] 4×1063 Qs (1.3×1086 years): The approximate lifespan ofSagittarius A*, if uncharged and non-rotating[21] 5.4×1083 Qs (1.7×10106 years): The approximate lifespan of asupermassive black hole with a mass of 20 trillionsolar masses[21] Qs:Estimated time for iron star formation if protons do not decay.[22] Qs: The scale of an estimatedPoincaré recurrence time for the quantum state of a hypothetical box containing an isolated black hole of stellar mass[23] This time assumes a statistical model subject to Poincaré recurrence. A much simplified way of thinking about this time is that in a model in which historyrepeats itself arbitrarily many times due toproperties of statistical mechanics, this is the time scale when it will first be somewhat similar (for a reasonable choice of "similar") to its current state again. Qs: The scale of an estimated Poincaré recurrence time for the quantum state of a hypothetical box containing a black hole with the mass of the observable Universe.[23] Qs ( years): The scale of an estimated Poincaré recurrence time for the quantum state of a hypothetical box containing a black hole with the estimated mass of the entire Universe, observable or not, assuming Linde'sChaotic Inflationary model with aninflaton whose mass is 10−6Planck masses.[23] |
| Multiples | Unit | Symbol |
|---|---|---|
| 6×101 seconds | 1 minute | min |
| 6×101 minutes | 1 hour | h(hr) |
| 2.4×101 hours | 1 day | d |
| Quantity | |
|---|---|
| See also | |
| Related | |
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