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An order of magnitude of time is usually a decimal prefix or decimal order-of-magnitude quantity together with a base unit of time, like a microsecond or a million 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 the base 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 have duodecimal or sexagesimal 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 the Planck time―the time light takes to traverse the Planck distance, many decimal orders of magnitude smaller than a second. [1]
The largest realized amount of time, based on known scientific data, is the age of the universe, about 13.8 billion years—the time since the Big Bang as measured in the cosmic microwave background rest 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 length depend on the choice of calendar and are often not regular even with a calendar, e.g., leap years versus regular years in the Gregorian calendar. This makes them problematic for use against a linear and regular time scale such as that defined by the SI, 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 the annum or astronomical 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 the Julian calendar, which has one leap year every four years. According to the geological science convention, this is used to form larger units of time by the application of SI 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 shortest increment of time—see quantum gravity) | 10−14 qs: The length of one Planck time (tP = ≈ 5.39×10−44 s) [3] is the briefest physically meaningful span of time. It is the unit of time in the natural units system known as Planck units. |
10−30 | quectosecond | qs | Quectosecond, ( quecto- + second), is one nonillionth of a second | |
10−27 | rontosecond | rs | Rontosecond, ( ronto- + second), is one octillionth of a second | 300 rs: The mean lifetime of W and Z bosons |
10−24 | yoctosecond | ys [4] | Yoctosecond, ( yocto- + second), is one septillionth of a second | 23 ys: The lower estimated bound on the half-life of isotope 7 of hydrogen (Hydrogen-7) 143 ys: The half-life of the Nitrogen-10 isotope of Nitrogen 156 ys: The mean lifetime of a Higgs Boson |
10−21 | zeptosecond | zs | Zeptosecond, ( zepto- + second), is one sextillionth of one second | 1.3 zs: Smallest experimentally controlled time delay in a photon field. [5] 2 zs: The representative cycle time of gamma ray radiation released in the decay of a radioactive atomic nucleus (here as 2 MeV per emitted photon) 4 zs: The cycle time of the zitterbewegung of an electron () 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 300 nanometres; The time it takes light to travel a distance of 0.3 micrometres (μm). 140 fs: The time needed for electrons to have localized onto individual bromine atoms 6 Ångstrom apart after laser dissociation of Br2. [11] 290 fs: The lifetime of a tauon |
10−12 | picosecond | ps | One trillionth of one second | 1 ps: The mean lifetime of a bottom quark; the time needed for light to travel 0.3 millimetres (mm) 1 ps: The typical lifetime of a transition state one machine cycle by an IBM silicon-germanium transistor 109 ps: The period of the photon corresponding to the hyperfine transition of the ground state of cesium-133, and one 9,192,631,770th of one second by 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 of General 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 a muon 4–16 μs: The time needed to execute one machine cycle by a 1960s minicomputer |
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 typical seek time for a computer hard disk |
10−2 | centisecond | cs | One hundredth of one second | 1–2 cs (=0.01–0.02 s): The human reflex response to visual stimuli 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 |
10−1 | 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 1.4 m/s to walk 1 kilometre |
103 | kilosecond | ks | minutes, hours, days (1 ks = 16 min 40 s = 1,000 s) | 1 ks: The record confinement time for antimatter, specifically antihydrogen, 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 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. |
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 the Baha'i calendar 2.36 Ms (27.32 d): The length of the true month, the orbital period of the Moon 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. |
109 | gigasecond | Gs | decades, centuries, millennia (1 Gs = over 31 years and 287 days = 1,000,000,000 s) | 1.5 Gs: Unix time as of Jul 14 02:40:00 UTC 2017. Unix time being the number of seconds since 1970-01-01T00:00:00Z ignoring leap seconds. 2.5 Gs: (79 a): The typical human life expectancy in the developed world |
1012 | terasecond | Ts | millennia to geological epochs (1 Ts = over 31,600 years = 1,000,000,000,000 s) | 3.1 Ts (100 ka): approximate length of a glacial period of the current Quaternary glaciation epoch 31.6 Ts (1000 ka, 1 Ma): One mega-annum (Ma), or one million years |
1015 | petasecond | Ps | geological eras, history of Earth and the Universe | 2 Ps: The approximate time since the Cretaceous-Paleogene extinction event, believed to be caused by the impact of a large asteroid into Chicxulub 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 the Permian-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-term volcanic eruptions in the area of the Siberian Traps. Also, the approximate time to the supercontinent of Pangaea. Also, the length of one galactic year or cosmic year, the time required for the Sun to complete one orbit around the Milky Way Galaxy. |
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 the Big Rip according to some models, but this is not favored by existing data. This is one possible scenario for the ultimate 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 increasing negative pressure thereupon |
1021 | zettasecond | Zs | 3 Zs (+100 Ta): The remaining time until the end of Stelliferous Era of the universe under the heat death scenario for the ultimate 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 a black dwarf. After this time has elapsed, the Degenerate Era begins. 9.85 Zs (311 Ta): The entire lifetime of Brahma in Hindu mythology. | |
1024 | yottasecond | Ys | 600 Ys (2×1019 a): The radioactive half-life of bismuth-209 by alpha 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 | quettasecond and beyond | Qs and on | 69 Qs (2.2×1024 a): The radioactive half-life of tellurium-128, the longest known half-life of any elemental isotope. 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 the Mesoamerican Long Count, a date discovered on a stele at the Coba Maya site, believed by archaeologist Linda Schele to be the absolute value for the length of one cycle of the universe [17] [18] 1023 Qs (3.2×1045 years): The largest possible value for the proton half-life, assuming that the Big Bang was inflationary and that the same process that made baryons predominate over antibaryons in the early Universe also makes protons decay [20] |
Multiples | Unit | Symbol |
---|---|---|
6×101 seconds | 1 minute | min |
6×101 minutes | 1 hour | h (hr) |
2.4×101 hours | 1 day | d |
In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch is believed to have lasted from 10−36 seconds to between 10−33 and 10−32 seconds after the Big Bang. Following the inflationary period, the universe continued to expand, but at a slower rate. The re-acceleration of this slowing expansion due to dark energy began after the universe was already over 7.7 billion years old.
The cosmic microwave background is microwave radiation that fills all space in the observable universe. It is a remnant that provides an important source of data on the primordial universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s.
In cosmology, the cosmological constant, alternatively called Einstein's cosmological constant, is the constant coefficient of a term that Albert Einstein temporarily added to his field equations of general relativity. He later removed it; however, much later it was revived and reinterpreted as the energy density of space, or vacuum energy, that arises in quantum mechanics. It is closely associated with the concept of dark energy.
In atomic physics and chemistry, an atomic electron transition is an electron changing from one energy level to another within an atom or artificial atom. The time scale of a quantum jump has not been measured experimentally. However, the Franck–Condon principle binds the upper limit of this parameter to the order of attoseconds.
An attosecond is a unit of time in the International System of Units (SI) equal to 10−18 or 1⁄1 000 000 000 000 000 000 of a second. An attosecond is to a second as a second is to about 31.71 billion years. The attosecond is a tiny unit but it has various potential applications: it can observe oscillating molecules, the chemical bonds formed by atoms in chemical reactions, and other extremely tiny and extremely fast things.
A femtosecond is a unit of time in the International System of Units (SI) equal to 10−15 or 1⁄1 000 000 000 000 000 of a second; that is, one quadrillionth, or one millionth of one billionth, of a second. For context, a femtosecond is to a second as a second is to about 31.71 million years; a ray of light travels approximately 0.3 μm (micrometers) in 1 femtosecond, a distance comparable to the diameter of a virus. The first to make femtosecond measurements was the Egyptian Nobel Laureate Ahmed Zewail, for which he was awarded the Nobel Prize in Chemistry in 1999. Professor Zewail used lasers to measure the movement of particles at the femtosecond scale, thereby allowing chemical reactions to be observed for the first time.
Hawking radiation is the theoretical thermal black-body radiation released outside a black hole's event horizon. This is counterintuitive because once ordinary electromagnetic radiation is inside the event horizon, it cannot escape. It is named after the physicist Stephen Hawking, who developed a theoretical argument for its existence in 1974. Hawking radiation is predicted to be extremely faint and is many orders of magnitude below the current best telescopes' detecting ability.
Doubly special relativity (DSR) – also called deformed special relativity or, by some, extra-special relativity – is a modified theory of special relativity in which there is not only an observer-independent maximum velocity, but also an observer-independent maximum energy scale and/or a minimum length scale. This contrasts with other Lorentz-violating theories, such as the Standard-Model Extension, where Lorentz invariance is instead broken by the presence of a preferred frame. The main motivation for this theory is that the Planck energy should be the scale where as yet unknown quantum gravity effects become important and, due to invariance of physical laws, this scale should remain fixed in all inertial frames.
The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe, was a NASA spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic microwave background (CMB) – the radiant heat remaining from the Big Bang. Headed by Professor Charles L. Bennett of Johns Hopkins University, the mission was developed in a joint partnership between the NASA Goddard Space Flight Center and Princeton University. The WMAP spacecraft was launched on 30 June 2001 from Florida. The WMAP mission succeeded the COBE space mission and was the second medium-class (MIDEX) spacecraft in the NASA Explorer program. In 2003, MAP was renamed WMAP in honor of cosmologist David Todd Wilkinson (1935–2002), who had been a member of the mission's science team. After nine years of operations, WMAP was switched off in 2010, following the launch of the more advanced Planck spacecraft by European Space Agency (ESA) in 2009.
The Friedmann–Lemaître–Robertson–Walker metric is a metric based on an exact solution of the Einstein field equations of general relativity. The metric describes a homogeneous, isotropic, expanding universe that is path-connected, but not necessarily simply connected. The general form of the metric follows from the geometric properties of homogeneity and isotropy; Einstein's field equations are only needed to derive the scale factor of the universe as a function of time. Depending on geographical or historical preferences, the set of the four scientists – Alexander Friedmann, Georges Lemaître, Howard P. Robertson and Arthur Geoffrey Walker – are variously grouped as Friedmann, Friedmann–Robertson–Walker (FRW), Robertson–Walker (RW), or Friedmann–Lemaître (FL). This model is sometimes called the Standard Model of modern cosmology, although such a description is also associated with the further developed Lambda-CDM model. The FLRW model was developed independently by the named authors in the 1920s and 1930s.
In relativistic physics, Lorentz symmetry or Lorentz invariance, named after the Dutch physicist Hendrik Lorentz, is an equivalence of observation or observational symmetry due to special relativity implying that the laws of physics stay the same for all observers that are moving with respect to one another within an inertial frame. It has also been described as "the feature of nature that says experimental results are independent of the orientation or the boost velocity of the laboratory through space".
An order of magnitude is usually a factor of ten. Thus, four orders of magnitude is a factor of 10,000 or 104.
The Dirac large numbers hypothesis (LNH) is an observation made by Paul Dirac in 1937 relating ratios of size scales in the Universe to that of force scales. The ratios constitute very large, dimensionless numbers: some 40 orders of magnitude in the present cosmological epoch. According to Dirac's hypothesis, the apparent similarity of these ratios might not be a mere coincidence but instead could imply a cosmology with these unusual features:
Attosecond physics, also known as attophysics, or more generally attosecond science, is a branch of physics that deals with light-matter interaction phenomena wherein attosecond photon pulses are used to unravel dynamical processes in matter with unprecedented time resolution.
A g-factor is a dimensionless quantity that characterizes the magnetic moment and angular momentum of an atom, a particle or the nucleus. It is the ratio of the magnetic moment of a particle to that expected of a classical particle of the same charge and angular momentum. In nuclear physics, the nuclear magneton replaces the classically expected magnetic moment in the definition. The two definitions coincide for the proton.
In particle physics and string theory (M-theory), the ADD model, also known as the model with large extra dimensions (LED), is a model framework that attempts to solve the hierarchy problem. The model tries to explain this problem by postulating that our universe, with its four dimensions, exists on a membrane in a higher dimensional space. It is then suggested that the other forces of nature operate within this membrane and its four dimensions, while the hypothetical gravity-bearing particle, the graviton, can propagate across the extra dimensions. This would explain why gravity is very weak compared to the other fundamental forces. The size of the dimensions in ADD is around the order of the TeV scale, which results in it being experimentally probeable by current colliders, unlike many exotic extra dimensional hypotheses that have the relevant size around the Planck scale.
Lorentz invariance follows from two independent postulates: the principle of relativity and the principle of constancy of the speed of light. Dropping the latter while keeping the former leads to a new invariance, known as Fock–Lorentz symmetry or the projective Lorentz transformation. The general study of such theories began with Fock, who was motivated by the search for the general symmetry group preserving relativity without assuming the constancy of c.
In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and kB. Expressing one of these physical constants in terms of Planck units yields a numerical value of 1. They are a system of natural units, defined using fundamental properties of nature rather than properties of a chosen prototype object. Originally proposed in 1899 by German physicist Max Planck, they are relevant in research on unified theories such as quantum gravity.
The "axis of evil" is a name given to the apparent correlation between the plane of the Solar System and aspects of the cosmic microwave background (CMB). It gives the plane of the Solar System and hence the location of Earth a greater significance than might be expected by chance – a result which has been claimed to be evidence of a departure from the Copernican principle as assumed in the concordance model.
The term physical constant expresses the notion of a physical quantity subject to experimental measurement which is independent of the time or location of the experiment. The constancy (immutability) of any "physical constant" is thus subject to experimental verification.