Instruct: Given a question, retrieve relevant passages that answer the question.
Query: What is the smallest unit of time?
An Atom of time or "a-tom" (“indivisible” in Greek), refers to the smallest possible unit of time.
A nanosecond (ns) is an SI unit of time equal to one thousand-millionth of a second (or one billionth of a second), that is, / of a second, or 10 seconds.
A nanosecond is equal to 1000 picoseconds or  microsecond. Time units ranging between 10 and 10 seconds are typically expressed as tens or hundreds of nanoseconds.
A flick is a unit of time equivalent to exactly 1/705,600,000 of a second. The figure was chosen so that frequencies of 24, 25, 30, 48, 50, 60, 90, 100 and 120 Hz, as well as 1/1000 divisions of all those, can be represented with integers. The unit was launched in January 2018 by Facebook. A flick is approximately 1.42 × 10 s, which makes it larger than a nanosecond but much smaller than a microsecond.
A microsecond is equal to 1000 nanoseconds or of a millisecond. Because the next SI prefix is 1000 times larger, measurements of 10 and 10 seconds are typically expressed as tens or hundreds of microseconds.
Taking a day to be 24 hours, the smallest time unit, "prāṇa", or one respiratory cycle, equals 4 seconds, a value consistent with the "normal breathing frequency" of 15 breaths/min used in modern medical research. The Surya Siddhanta also described a method of converting local time to the standard time of Ujjain. Despite these early advances, standard time was not widely used outside astronomy. For most of India's history, ruling kingdoms kept their own local time, typically using the Hindu calendar in both lunar and solar units. For example, the Jantar Mantar observatory built by Maharaja Sawai Jai Singh in Jaipur in 1733 contains large sundials, up to 90 ft (27 m) high, which were used to accurately determine the local time.
The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes.
This section is based on the work of Jong-Ping Hsu and Leonardo Hsu. They decided to use the word "Taiji" which is a Chinese word meaning the ultimate principles that existed before the creation of the world. In SI units, time is measured in seconds, but taiji time is measured in units of metres — the same units used to measure space. Their arguments about choosing what units to measure time in, lead them to say that they can develop a theory of relativity which is experimentally indistinguishable from special relativity, but without using the second postulate in their derivation. Their claims have been disputed.
The transformations that they derive involve the factor formula_2 where β is the velocity measured in metres per metre (a dimensionless quantity). This looks the same as (but should NOT be conceptually confused with) the velocity as a fraction of light v/c that appears in some expressions for the Lorentz transformations. Expressing time in metres has previously been done by other authors: Taylor and Wheeler in "Spacetime Physics" and Moore in "Six Ideas that Shaped Physics".
In astronomy, the Julian year is a unit of time; it is defined as 365.25 days of exactly 86,400 seconds (SI base unit), totalling exactly 31,557,600 seconds in the Julian astronomical year.
The Julian year, as used in astronomy and other sciences, is a time unit defined as exactly 365.25 days. This is the normal meaning of the unit "year" (symbol "a" from the Latin "annus") used in various scientific contexts. The Julian century of days and the Julian millennium of days are used in astronomical calculations. Fundamentally, expressing a time interval in Julian years is a way to precisely specify how many days (not how many "real" years), for long time intervals where stating the number of days would be unwieldy and unintuitive. By convention, the Julian year is used in the computation of the distance covered by a light-year.
From 2017, the largest denomination is the 50,000 soʻm banknote (early 2018 worth $6), which made the situation easier. The smallest denomination, the 1 tiyin, is only worth 1/2900 cent U.S. making it the "world's most worthless coin". However, coins and banknotes smaller than 25 soʻm are rare now.
With a mass of approximately and a length of 5 centimetres (2.0 in), the bee hummingbird ("Mellisuga helenae") is the world's smallest bird species and the smallest warm-blooded vertebrate. Called the "zunzún" in its native habitat on Cuba, it is lighter than a Canadian or U.S. penny. It is said that it is "more apt to be mistaken for a bee than a bird". The bee hummingbird eats half its total body mass and drinks eight times its total body mass each day. Its nest is 3 cm across.
The light-nanosecond was popularized as a unit of distance by Grace Hopper as the distance which a photon could travel in one billionth of a second (roughly 30 cm or one foot): "The speed of light is one foot per nanosecond." In her speaking engagements, she was well known for passing out light-nanoseconds of wire to the audience, and contrasting it with light-microseconds (a coil of wire 1,000 times as long) and light-picoseconds (the size of ground black pepper). Over the course of her life, she found many uses for this visual aid, including demonstrating the waste of sub-optimal programming, illustrating advances in computer speed, and simply giving young scientists and policy makers the ability to conceptualize the magnitude of very large and small numbers.
A microbe is an organism that is microscopic.
Hummingbirds are birds native to the Americas and constitute the biological family Trochilidae. They are among the smallest of birds, most species measuring in length. Indeed, the smallest extant bird species is a hummingbird, the bee hummingbird weighing less than .
The smallest turtle is the speckled padloper tortoise of South Africa. It measures no more than in length and weighs about . Two other species of small turtles are the American mud turtles and musk turtles that live in an area that ranges from Canada to South America. The shell length of many species in this group is less than in length.
Time translation symmetry or temporal translation symmetry (TTS) is a mathematical transformation in physics that moves the times of events through a common interval. Time translation symmetry is the hypothesis that the laws of physics are unchanged, (i.e. invariant) under such a transformation. Time translation symmetry is a rigorous way to formulate the idea that the laws of physics are the same throughout history. Time translation symmetry is closely connected, via the Noether theorem, to conservation of energy. In mathematics, the set of all time translations on a given system form a Lie group.
The smallest known planet is PSR B1257+12A, one of the first extrasolar planets discovered, which was found in 1992 in orbit around a pulsar. Its mass is roughly half that of the planet Mercury. The smallest known planet orbiting a main-sequence star other than the Sun is Kepler-37b, with a mass (and radius) slightly higher than that of the Moon.
The following example concerns definitions of quantities and units. The (average) velocity ("v") of an object is defined as the quantitative physical property of the object that is directly proportional to the distance ("d") traveled by the object and inversely proportional to the time ("t") of travel, i.e., "v" = "kd"/"t", where "k" is a constant that depends on the units used. Suppose that the meter (m) and the second (s) are base units; then the kilometer (km) and the hour (h) are noncoherent derived units. The meter per second (mps) is defined as the velocity of an object that travels one meter in one second, and the kilometer per hour (kmph) is defined as the velocity of an object that travels one kilometer in one hour. Substituting from the definitions of the units into the defining equation of velocity we obtain, 1 mps = "k" m/s and 1 kmph = "k" km/h = 1/3.6 "k" m/s = 1/3.6 mps. Now choose "k" = 1; then the meter per second is a coherent derived unit, and the kilometer per hour is a noncoherent derived unit. Suppose that we choose to use the kilometer per hour as the unit of velocity in the system. Then the system becomes noncoherent, and the numerical value equation for velocity becomes {"v"} = 3.6 {"d"}/{"t"}. Coherence may be restored, without changing the units, by choosing "k" = 3.6; then the kilometer per hour is a coherent derived unit, with 1 kmph = 1 m/s, and the meter per second is a noncoherent derived unit, with 1 mps = 3.6 m/s.
In large-scale natural science, there is need for another time perspective, independent from human activity, and indeed spanning a far longer period (mainly prehistoric), where "geologic era" refers to well-defined time spans. 
The next-larger division of geologic time is the eon. The Phanerozoic Eon is subdivided into eras. There are currently three eras defined in the Phanerozoic; the following table lists them from youngest to oldest (BP is an abbreviation for "before present").
While comparing between various classes of animals, a different unit is used, body length per second for organisms. The fastest organism on earth, relative to body length, is the South Californian mite "Paratarsotomus macropalpis", which has a speed of 322 body lengths per second. The equivalent speed for a human running as fast as this mite would be . This is far in excess of the previous record holder, the Australian tiger beetle, "Cicindela eburneola", the fastest insect in the world relative to body size, which has been recorded at or 171 body lengths per second. The cheetah, the fastest land mammal, scores at only 16 body lengths per second while Anna's hummingbird has the highest known length-specific velocity attained by any vertebrate
He explains the rationale for 14 minutes as follows: ""It's one minute less than the smallest unit of schedulistically significant time. No calendar has a finer granularity than 15 minutes. No one ever has a meeting that starts at 5 or 10 or 14 minutes before or after the hour. You have no excuse not to do this. Time-wise, it doesn't even register.""
In his day, atoms were proposed to be the smallest division of matter. Within Leibniz’s theory, however, substances are not technically real, so monads are not the smallest part of matter, rather they are the only things which are, in fact, real. To Leibniz, space and time were an illusion, and likewise substance itself. The only things that could be called real were utterly simple beings of psychic activity “endowed with perception and appetite.” The other objects, which we call matter, are merely phenomena of these simple perceivers. “Leibniz says, ‘I don't really eliminate body, but reduce [revoco] it to what it is. For I show that corporeal mass [massa], which is thought to have something over and above simple substances, is not a substance, but a phenomenon resulting from simple substances, which alone have unity and absolute reality.’ (G II 275/AG 181)” Leibniz’s philosophy is sometimes called “‘panpsychic idealism’ because these substances are psychic rather than material”. That is to say, they are mind-like substances, not possessing spatial reality. "In other words, in the Leibnizian monadology, simple substances are mind-like entities that do not, strictly speaking, exist in space but that represent the universe from a unique perspective.” It is the harmony between the perceptions of the monads which creates what we call substances, but that does not mean the substances are real in and of themselves.
In medieval philosophical writings, the atom was a unit of time referred to as the smallest possible division of time. The earliest known occurrence in English is in Byrhtferth's "Enchiridion" (a science text) of 1010–1012, where it was defined as 1/564 of a "momentum" (1½ minutes), and thus equal to 15/94 of a second. It was used in the "computus", the process of calculating the date of Easter.
Planck time (~ 5.4 × 10 seconds) is the unit of time in the system of natural units known as Planck units. Current established physical theories 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 measured, even in principle. Tentative physical theories that describe this time scale exist; see for instance loop quantum gravity.