(but not necessarily the shortest increment of time-see quantum gravity)ġ0 −20 ys: One Planck time t P = ℏ G / c 5 )Ģ47 zs: an experimentally-measured travel time of a photon across a hydrogen molecule, "for the average bond length of molecular hydrogen" ġ2 as: best timing control of laser pulses. Presumed to be the shortest theoretically measurable time interval Less than one second Units of measure less than a second 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).
Its definition is based on the average length of a year according to the Julian calendar, which has one leap year every four years. Instead, the table uses the annum or astronomical Julian year (365.25 days of 86,400 seconds), denoted with the symbol a. 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.īecause of this, the table below does not include weeks, months, and years. 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. 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. 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. Metric prefixes are defined spanning 10 −24 to 10 24, 48 decimal orders of magnitude which may be used in conjunction with the metric base unit of second. Those amounts of time together span 60 decimal orders of magnitude. 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. 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. 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. Therefore, it is said "a million years" instead of "a mega year". Prefixes are not usually used with a base unit of years. In most cases, the base unit is seconds or years. In other cases, the quantity name implies the base unit, like "century". In some cases, the order of magnitude may be implied (usually 1), like a "second" or "year". JSTOR ( January 2020) ( Learn how and when to remove this template message)Īn 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.Unsourced material may be challenged and removed.įind sources: "Orders of magnitude" time – news
Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.