Anthropic units
Encyclopedia
Anthropic units are units of measurement which explicitly arose from human physiology
or behavior
. Some were derived directly from the dimensions of the human body, and as such, are commonly referred to as anthropomorphic (meaning "human shaped"). Other anthropic units evolved indirectly from human activities such as walking or farming, or were invented by humans to support human endeavors.
Digit
: Digit is a Latin word meaning finger. As a unit of length, the digit is currently standardized to be a sixteenth of a foot. In English the word “finger
” or “fingerbreadth
” is also a unit of length, although the finger length is slightly larger than the digit. From a practical standpoint, fingerbreadths can easily be used to measure by simply placing ones hand on an object and counting the number of fingerbreadths that cover a specific distance.
Inch
: The English word “inch” was derived from the Latin “uncial” meaning one twelfth, and the inch is defined to be a twelfth of a foot. The historical origin of the inch as a length is disputed, but there is evidence relating it to the width of an average man’s thumb. Other European languages have similarly sized anthropomorphic units with names directly derived from the word for thumb in that language, so it is reasonable to assume that the English inch is an anthropomorphic derivation of the thumb width.{[cn}}
Palm and Hand
: Palm and hand, or handbreadth, have both historically been used in English to refer to specific lengths. The hand or handbreadth is currently standardized to be four inches, whereas the palm is standardized to be three.
Shaftment
: A shaftment is the width of the fist and outstretched thumb. The lengths of poles, staves, etc. can be easily measured by grasping the bottom of the staff with thumb extended and repeating such hand over hand grips along the length of the staff. The shaftment is currently standardized to be six inches, or half of a foot.
Span
: A span is the width of a human hand, from the tip of the thumb to the tip of the pinky finger. The span, from ancient times, has been considered to be 1/2 cubit (as described below). The span is currently standardized to be nine inches.
Foot : The standardized English foot is defined to be twelve inches, although this is larger than what is typically found in human populations.
Cubit
: The cubit is the length of the forearm (from the elbow to the fingertips). The cubit is a very old unit of measurement used in many ancient cultures with different length values. The modern cubit is standardized to be 1.5 feet, or 18 inches.
Fathom
: The fathom is a unit of length derived from an old English word meaning outstretched arms.http://www.etymonline.com/index.php?allowed_in_frame=0&search=fathom&searchmode=none It is currently standardized to be six feet or 72 inches. A number of anthropomorphic techniques have evolved for measuring cords and textiles, and these techniques have resulted in various anthropomorphic measurement units. A technique for measuring ropes is to hold a length of rope taut between one’s hands while holding the left hand out as far as possible to the left side of the body and the right hand out as far as possible to the right side of the body. When the hands are brought together this length of rope will form a loop. This loop may be placed in the left hand while the hands are again outstretched to grasp another length and then brought together to form another loop. The length of each loop will be equal to one fathom; therefore, the total length of the rope in fathoms can be determined by counting the number of loops.
Ell and Yard
: The ell (meaning arm) is the length from a hand to the opposing shoulder, currently standardized to be 45 inches. The yard is the distance from a hand to the center of the chest, currently standardized to be 36 inches. An ell is obtained when the rope is held taut with the left hand outstretched to the left of the body, while the right hand is held close to the right shoulder. A yard is obtained when the left hand is outstretched to the left while the right hand is held near the center of the chest.
, but rather, evolved indirectly from human behaviors such as walking or farming. A few examples are as follows:
rod: The length of the rod may have originated from the typical length of a medieval ox-goad
. The rod is currently standardized as 5.5 yards.
furlong
: The furlong is a unit of length derived from the Old English words furh (furrow) and lang (long). It was originally defined as the length a plough team was to be driven without resting. It was later standardized to be 40 rods or 220 yards.
acre
: The word acre is derived from an old English word meaning an open field. It was approximately the amount of land tillable by one man, behind one ox, in one day. A rectangle of length 1 furlong and width 4 rods (1 chain) has an area of 1 acre. There are 640 acres in a modern square mile.
pace: A pace is the measure of a full stride from the position of the heel when it is raised from the ground to the point the same heel is set down again at the end of the step. Thus, a distance can be "paced off" by counting each time the same heel touches ground, or in other words, every other step. In Rome this unit was standardized as five Roman feet (about 1.48 metres or 58.1 English inches).
mile
: The mile is a modern derivation of the Ancient Roman “mille passus” which literally means "a thousand paces" in Latin. The Roman pace was standardized as five Roman feet, so the Roman “mille passus” was 5,000 Roman feet (about 1,480 meters, or 1,618 modern yards). The current definition of a mile as 5,280 feet (as opposed to 5,000) dates to the 13th century.
league
: The league is an ancient unit of length defined as the distance a typical person could walk in an hour. In ancient Rome the league was standardized to be 1.5 Roman miles. In modern times the league is generally standardized to be 3 miles.
The cubit (forearm length), for example, is an ancient unit used in many cultures. A person’s forearm is almost always available, and using one’s forearm to measure distances removes the necessity of carrying additional measuring devices. Also, the forearm is a good standard length for measuring human scaled objects such as buildings and ships. However, one person's forearm length might vary from another person's forearm by as much as a few inches. A boat might be 30 cubits long to a large person but as much as 40 cubits to a small person. This could cause difficulties where collaboration is required. Also, human bodies continually grow and change shape over time, so anthropomorphic measurement systems are inherently unstable.
Natural units have the advantage of being independent of human culture and behavior. Some examples are the circumference of the earth, the duration of a day, the mass of an electron, and the triple-point of water. Since these values are independent of human populations and outside of human control, they can be used as international standards without discriminating against any particular person, group, or nation. Also, unlike the dimensions of the human body, natural values can be determined to a high degree of accuracy and are unlikely to change over time. Therefore, they are ideal for collaboration and standardization.
Natural units, however, have their own unique set of disadvantages. The primary disadvantages is that natural units are often inaccessible to common people and not useful for human purposes. For example, it would be difficult for an untrained person to measure the circumference of the earth to any degree of accuracy. And even if they could, it would be difficult to communicate such lengths in everyday contexts.
There has been a trend in the last few hundred years towards the use of anthropically scaled natural units. In an anthropically scaled system, one chooses a natural unit and then multiplies that unit by a scale factor to obtain a base unit that is useful for human purposes. Anthropically scaled natural units harness the advantage of being both natural and anthropic. Some examples are as follows:
Universal Time
(UT): Our current system of dividing the day into 24 hours, with 60 minutes in each hour and 60 seconds in each minute, is perhaps the oldest example of an anthropically scaled natural system. The day is a natural unit of time, since its duration is beyond human control, but the duration of the day is too long to be suitable for many human time measurements. Therefore, to obtain a set of time units suitable for human activities, the day was divided into hour
s, minute
s, and second
s.
nautical units: The nautical system of length units is another example of an anthropically scaled natural system. The nautical system divides the circumference of the earth into 360 degrees, with each degree being divided into 60 nautical mile
s, and each nautical mile being divided into one thousand nautical fathoms. Also, in analogy to the statutory league, a nautical league is defined to be 3 nautical miles.
grain mass: In many cultures, a grain was a natural unit of measurement of mass that was based upon the mass of a single seed of a typical cereal. These grain mass units were often too small for common human purposes; therefore, a scale factor was used to obtain a larger more useful anthropic mass unit. The avoirdupois pound, for example, was defined to be 7,000 barley grains. The troy pound was defined to be 5,760 barley grains. And the tower pound was defined to be 7,200 wheat grains (or 5,400 barley grains).
Fahrenheit
Temperature: In the early 18th century, when Daniel Fahrenheit manufactured mercury- and alcohol-filled thermometers, he used three temperatures to determine a temperature range: the first temperature was obtained by mixing water and ice with ammonium chloride
, the second by mixing water and ice without ammonium chloride
, and the third by placing the thermometer in the mouth or armpit of a healthy person. However, these three temperatures alone were insufficient for human purposes, so Daniel used a scale factor to obtain additional values. The mixture of water, ice, and ammonium chloride was used to define a temperature of zero degrees Fahrenheit. The human body was used to define a temperature of ninety six degrees Fahrenheit. This placed the freezing point of water at thirty two degrees Fahrenheit.
metric units: When the French invented the original metric system in the late 18th century, they used survey data to estimate the length of one quadrant of the earth (the distance from the equator to the north pole). To achieve a manageable length unit, the French divided the earth’s quadrant into 10 million equal parts. The length obtained through this method was named the metre. The French then used the metre to define other measurement standards. The standard volume, the litre, was defined to be a thousandth of a cubic metre. And the standard mass, the gram, was defined to be a thousandth of the mass of a litre of pure water. These original metric units were all anthropically scaled natural units, based on the circumference of the earth.
International System of Units
: In the subsequent two hundred years since its inception, the metric system has evolved into the International System of Units (SI). There are currently seven base SI units: the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). The definitions for the base units of the metric system have changed over time, but most are still anthropically scaled natural units, the notable exception being the modern kilogram which is defined in terms of an artifact. There is, however, currently a movement in the international community to increase the accuracy of the kilogram by redefining it in terms of an anthropically scaled natural value.
Motions of the Earth
and Moon
: Most of the units used in human time measurement were derived from the motions of the earth and moon. Some examples include the year
, the month
, the day
, the week
(7 days), the hour
(day / 24), the minute
, and the second
. The motions of the earth and moon figure prominently in human lives. These motions cause changes in the weather from one season to the next, and they cause changes in ambient brightness from night to day and from new moon to full moon. Given the profound impact of these motions on human life, it is not surprising that humans have an anthropic preference for using these motions to measure time.
Dimensions of the Earth
: A number of measurement units were derived from the dimensions of the earth. These earth-derived units include the nautical league, the nautical mile, the nautical fathom, the metre, the litre, and the kilogram. Humans live on the earth, and the shape of the earth is an important factor in human endeavors such as navigation. So using the shape of the earth to obtain measurement units is a clear example of an anthropically biased choice.
Triple Point
of Water
: The Kelvin
temperature
scale is obtained by using absolute zero
as the Kelvin zero point, and then setting the triple point of water as the Kelvin scale value of 273.16. This definition may not immediately appear to be anthropically biased. Water is a natural substance, and the triple point is a fundamental property of any natural substance. Therefore, the triple point of water is a fundamental value of nature and not an anthropic value. However, there may be an anthropic bias in the selection of water for this purpose. The earth is the only known planet to have large quantities of water in all three states, solid, liquid, and gas. This abundance of water on earth may have given humans a preconceived notion of the importance of water. Hence, humans have an anthropic bias towards using water to define measurement units.
Carbon-12
Atoms: The mole
is currently defined as the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. The selection of Carbon 12, as the element used in this definition of the mole, is similar to the use of water in the definition of the kelvin described above. Carbon is one of the most important elements for human life. In fact, Carbon is a component in all organic substances. Therefore, humans have a prejudice in favor of the element carbon, and this prejudice may have guided the decision to use carbon in defining the mole.
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
or behavior
Behavior
Behavior or behaviour refers to the actions and mannerisms made by organisms, systems, or artificial entities in conjunction with its environment, which includes the other systems or organisms around as well as the physical environment...
. Some were derived directly from the dimensions of the human body, and as such, are commonly referred to as anthropomorphic (meaning "human shaped"). Other anthropic units evolved indirectly from human activities such as walking or farming, or were invented by humans to support human endeavors.
Anthropomorphic units
Anthropomorphic units are a special subclass of anthropic units. Anthropomorphic units are derived directly from the dimensions of the human body (form), and many have names which reference the specific part of the body from which the unit originated. Some common examples are as follows:Digit
Digit (unit)
The digit or finger is an ancient and obsolete non-SI unit of measurement of length. It was originally based on the breadth of a human finger...
: Digit is a Latin word meaning finger. As a unit of length, the digit is currently standardized to be a sixteenth of a foot. In English the word “finger
Finger (unit)
A finger , is usually seven eighths of an inch or 2.2225 cm . The width of an adult human male finger tip is indeed about two centimetres. The inch, on the other hand, originates in the breadth of a thumb. In English this unit has mostly fallen out of use....
” or “fingerbreadth
Finger (unit)
A finger , is usually seven eighths of an inch or 2.2225 cm . The width of an adult human male finger tip is indeed about two centimetres. The inch, on the other hand, originates in the breadth of a thumb. In English this unit has mostly fallen out of use....
” is also a unit of length, although the finger length is slightly larger than the digit. From a practical standpoint, fingerbreadths can easily be used to measure by simply placing ones hand on an object and counting the number of fingerbreadths that cover a specific distance.
Inch
Inch
An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...
: The English word “inch” was derived from the Latin “uncial” meaning one twelfth, and the inch is defined to be a twelfth of a foot. The historical origin of the inch as a length is disputed, but there is evidence relating it to the width of an average man’s thumb. Other European languages have similarly sized anthropomorphic units with names directly derived from the word for thumb in that language, so it is reasonable to assume that the English inch is an anthropomorphic derivation of the thumb width.{[cn}}
Palm and Hand
Hand (unit)
The hand is a non-SI unit of measurement of length, now used only for the measurement of the height of horses in some English-speaking countries, including Australia, Canada, the UK and the USA. With origins in ancient Egypt, it was originally based on the breadth of a human hand...
: Palm and hand, or handbreadth, have both historically been used in English to refer to specific lengths. The hand or handbreadth is currently standardized to be four inches, whereas the palm is standardized to be three.
Shaftment
Shaftment
The shaftment is a unit of length, 6 - 6½ inches or 2 palms, i.e. 15.24 cm. A shaftment is the width of the fist and outstretched thumb. The lengths of poles, staves, etc...
: A shaftment is the width of the fist and outstretched thumb. The lengths of poles, staves, etc. can be easily measured by grasping the bottom of the staff with thumb extended and repeating such hand over hand grips along the length of the staff. The shaftment is currently standardized to be six inches, or half of a foot.
Span
Span (unit)
A span is the distance measured by a human hand, from the tip of the thumb to the tip of the little finger. In ancient times, a span was considered to be half a cubit...
: A span is the width of a human hand, from the tip of the thumb to the tip of the pinky finger. The span, from ancient times, has been considered to be 1/2 cubit (as described below). The span is currently standardized to be nine inches.
Foot : The standardized English foot is defined to be twelve inches, although this is larger than what is typically found in human populations.
Cubit
Cubit
The cubit is a traditional unit of length, based on the length of the forearm. Cubits of various lengths were employed in many parts of the world in Antiquity, in the Middle Ages and into Early Modern Times....
: The cubit is the length of the forearm (from the elbow to the fingertips). The cubit is a very old unit of measurement used in many ancient cultures with different length values. The modern cubit is standardized to be 1.5 feet, or 18 inches.
Fathom
Fathom
A fathom is a unit of length in the imperial and the U.S. customary systems, used especially for measuring the depth of water.There are 2 yards in an imperial or U.S. fathom...
: The fathom is a unit of length derived from an old English word meaning outstretched arms.http://www.etymonline.com/index.php?allowed_in_frame=0&search=fathom&searchmode=none It is currently standardized to be six feet or 72 inches. A number of anthropomorphic techniques have evolved for measuring cords and textiles, and these techniques have resulted in various anthropomorphic measurement units. A technique for measuring ropes is to hold a length of rope taut between one’s hands while holding the left hand out as far as possible to the left side of the body and the right hand out as far as possible to the right side of the body. When the hands are brought together this length of rope will form a loop. This loop may be placed in the left hand while the hands are again outstretched to grasp another length and then brought together to form another loop. The length of each loop will be equal to one fathom; therefore, the total length of the rope in fathoms can be determined by counting the number of loops.
Ell and Yard
Yard
A yard is a unit of length in several different systems including English units, Imperial units and United States customary units. It is equal to 3 feet or 36 inches...
: The ell (meaning arm) is the length from a hand to the opposing shoulder, currently standardized to be 45 inches. The yard is the distance from a hand to the center of the chest, currently standardized to be 36 inches. An ell is obtained when the rope is held taut with the left hand outstretched to the left of the body, while the right hand is held close to the right shoulder. A yard is obtained when the left hand is outstretched to the left while the right hand is held near the center of the chest.
Other anthropic units
Some anthropic units were not directly derived from any part of the human anatomyAnatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
, but rather, evolved indirectly from human behaviors such as walking or farming. A few examples are as follows:
rod: The length of the rod may have originated from the typical length of a medieval ox-goad
Goad
The goad is a traditional farming implement, used to spur or guide lifestock, usually oxen, which are pulling a plough or a cart; used also to round up cattle. It is a type of a long stick with a pointed end, also known as the cattle prod. Though many people are unfamiliar with them today, goads...
. The rod is currently standardized as 5.5 yards.
furlong
Furlong
A furlong is a measure of distance in imperial units and U.S. customary units equal to one-eighth of a mile, equivalent to 220 yards, 660 feet, 40 rods, or 10 chains. The exact value of the furlong varies slightly among English-speaking countries....
: The furlong is a unit of length derived from the Old English words furh (furrow) and lang (long). It was originally defined as the length a plough team was to be driven without resting. It was later standardized to be 40 rods or 220 yards.
acre
Acre
The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. The most common use of the acre is to measure tracts of land.The acre is related...
: The word acre is derived from an old English word meaning an open field. It was approximately the amount of land tillable by one man, behind one ox, in one day. A rectangle of length 1 furlong and width 4 rods (1 chain) has an area of 1 acre. There are 640 acres in a modern square mile.
pace: A pace is the measure of a full stride from the position of the heel when it is raised from the ground to the point the same heel is set down again at the end of the step. Thus, a distance can be "paced off" by counting each time the same heel touches ground, or in other words, every other step. In Rome this unit was standardized as five Roman feet (about 1.48 metres or 58.1 English inches).
mile
Mile
A mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...
: The mile is a modern derivation of the Ancient Roman “mille passus” which literally means "a thousand paces" in Latin. The Roman pace was standardized as five Roman feet, so the Roman “mille passus” was 5,000 Roman feet (about 1,480 meters, or 1,618 modern yards). The current definition of a mile as 5,280 feet (as opposed to 5,000) dates to the 13th century.
league
League (unit)
A league is a unit of length . It was long common in Europe and Latin America, but it is no longer an official unit in any nation. The league originally referred to the distance a person or a horse could walk in an hour...
: The league is an ancient unit of length defined as the distance a typical person could walk in an hour. In ancient Rome the league was standardized to be 1.5 Roman miles. In modern times the league is generally standardized to be 3 miles.
Anthropically-scaled natural units
Anthropic units and natural units each have unique advantages and disadvantages. Anthropic units, which arise from human physiology and behavior, often have the advantage of being accessible to humans and useful for human purposes. The disadvantage of anthropic units is that they are often difficult to standardize.The cubit (forearm length), for example, is an ancient unit used in many cultures. A person’s forearm is almost always available, and using one’s forearm to measure distances removes the necessity of carrying additional measuring devices. Also, the forearm is a good standard length for measuring human scaled objects such as buildings and ships. However, one person's forearm length might vary from another person's forearm by as much as a few inches. A boat might be 30 cubits long to a large person but as much as 40 cubits to a small person. This could cause difficulties where collaboration is required. Also, human bodies continually grow and change shape over time, so anthropomorphic measurement systems are inherently unstable.
Natural units have the advantage of being independent of human culture and behavior. Some examples are the circumference of the earth, the duration of a day, the mass of an electron, and the triple-point of water. Since these values are independent of human populations and outside of human control, they can be used as international standards without discriminating against any particular person, group, or nation. Also, unlike the dimensions of the human body, natural values can be determined to a high degree of accuracy and are unlikely to change over time. Therefore, they are ideal for collaboration and standardization.
Natural units, however, have their own unique set of disadvantages. The primary disadvantages is that natural units are often inaccessible to common people and not useful for human purposes. For example, it would be difficult for an untrained person to measure the circumference of the earth to any degree of accuracy. And even if they could, it would be difficult to communicate such lengths in everyday contexts.
There has been a trend in the last few hundred years towards the use of anthropically scaled natural units. In an anthropically scaled system, one chooses a natural unit and then multiplies that unit by a scale factor to obtain a base unit that is useful for human purposes. Anthropically scaled natural units harness the advantage of being both natural and anthropic. Some examples are as follows:
Universal Time
Universal Time
Universal Time is a time scale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time , i.e., the mean solar time on the Prime Meridian at Greenwich, and GMT is sometimes used loosely as a synonym for UTC...
(UT): Our current system of dividing the day into 24 hours, with 60 minutes in each hour and 60 seconds in each minute, is perhaps the oldest example of an anthropically scaled natural system. The day is a natural unit of time, since its duration is beyond human control, but the duration of the day is too long to be suitable for many human time measurements. Therefore, to obtain a set of time units suitable for human activities, the day was divided into hour
Hour
The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...
s, minute
Minute
A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...
s, and second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
s.
nautical units: The nautical system of length units is another example of an anthropically scaled natural system. The nautical system divides the circumference of the earth into 360 degrees, with each degree being divided into 60 nautical mile
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
s, and each nautical mile being divided into one thousand nautical fathoms. Also, in analogy to the statutory league, a nautical league is defined to be 3 nautical miles.
grain mass: In many cultures, a grain was a natural unit of measurement of mass that was based upon the mass of a single seed of a typical cereal. These grain mass units were often too small for common human purposes; therefore, a scale factor was used to obtain a larger more useful anthropic mass unit. The avoirdupois pound, for example, was defined to be 7,000 barley grains. The troy pound was defined to be 5,760 barley grains. And the tower pound was defined to be 7,200 wheat grains (or 5,400 barley grains).
Fahrenheit
Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...
Temperature: In the early 18th century, when Daniel Fahrenheit manufactured mercury- and alcohol-filled thermometers, he used three temperatures to determine a temperature range: the first temperature was obtained by mixing water and ice with ammonium chloride
Ammonium chloride
Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...
, the second by mixing water and ice without ammonium chloride
Ammonium chloride
Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...
, and the third by placing the thermometer in the mouth or armpit of a healthy person. However, these three temperatures alone were insufficient for human purposes, so Daniel used a scale factor to obtain additional values. The mixture of water, ice, and ammonium chloride was used to define a temperature of zero degrees Fahrenheit. The human body was used to define a temperature of ninety six degrees Fahrenheit. This placed the freezing point of water at thirty two degrees Fahrenheit.
metric units: When the French invented the original metric system in the late 18th century, they used survey data to estimate the length of one quadrant of the earth (the distance from the equator to the north pole). To achieve a manageable length unit, the French divided the earth’s quadrant into 10 million equal parts. The length obtained through this method was named the metre. The French then used the metre to define other measurement standards. The standard volume, the litre, was defined to be a thousandth of a cubic metre. And the standard mass, the gram, was defined to be a thousandth of the mass of a litre of pure water. These original metric units were all anthropically scaled natural units, based on the circumference of the earth.
International System of Units
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...
: In the subsequent two hundred years since its inception, the metric system has evolved into the International System of Units (SI). There are currently seven base SI units: the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). The definitions for the base units of the metric system have changed over time, but most are still anthropically scaled natural units, the notable exception being the modern kilogram which is defined in terms of an artifact. There is, however, currently a movement in the international community to increase the accuracy of the kilogram by redefining it in terms of an anthropically scaled natural value.
Anthropically Biased Natural Units
Natural units are intended to be directly derived from nature and to be free of human influence. However, our selection of a particular unit is often driven by a human preference. Therefore, we might use the term “anthropically biased natural units” to designate natural units which were selected because of a particular human prejudice, preconception, bias, or preference. The following are examples of an anthropic bias in the selection of natural units:Motions of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
and Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
: Most of the units used in human time measurement were derived from the motions of the earth and moon. Some examples include the year
Year
A year is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic....
, the month
Month
A month is a unit of time, used with calendars, which was first used and invented in Mesopotamia, as a natural period related to the motion of the Moon; month and Moon are cognates. The traditional concept arose with the cycle of moon phases; such months are synodic months and last approximately...
, the day
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...
, the week
Week
A week is a time unit equal to seven days.The English word week continues an Old English wice, ultimately from a Common Germanic , from a root "turn, move, change"...
(7 days), the hour
Hour
The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...
(day / 24), the minute
Minute
A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...
, and the second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
. The motions of the earth and moon figure prominently in human lives. These motions cause changes in the weather from one season to the next, and they cause changes in ambient brightness from night to day and from new moon to full moon. Given the profound impact of these motions on human life, it is not surprising that humans have an anthropic preference for using these motions to measure time.
Dimensions of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
: A number of measurement units were derived from the dimensions of the earth. These earth-derived units include the nautical league, the nautical mile, the nautical fathom, the metre, the litre, and the kilogram. Humans live on the earth, and the shape of the earth is an important factor in human endeavors such as navigation. So using the shape of the earth to obtain measurement units is a clear example of an anthropically biased choice.
Triple Point
Triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium...
of Water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
: The Kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
scale is obtained by using absolute zero
Absolute zero
Absolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means....
as the Kelvin zero point, and then setting the triple point of water as the Kelvin scale value of 273.16. This definition may not immediately appear to be anthropically biased. Water is a natural substance, and the triple point is a fundamental property of any natural substance. Therefore, the triple point of water is a fundamental value of nature and not an anthropic value. However, there may be an anthropic bias in the selection of water for this purpose. The earth is the only known planet to have large quantities of water in all three states, solid, liquid, and gas. This abundance of water on earth may have given humans a preconceived notion of the importance of water. Hence, humans have an anthropic bias towards using water to define measurement units.
Carbon-12
Carbon-12
Carbon-12 is the more abundant of the two stable isotopes of the element carbon, accounting for 98.89% of carbon; it contains 6 protons, 6 neutrons, and 6 electrons....
Atoms: The mole
Mole (unit)
The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...
is currently defined as the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. The selection of Carbon 12, as the element used in this definition of the mole, is similar to the use of water in the definition of the kelvin described above. Carbon is one of the most important elements for human life. In fact, Carbon is a component in all organic substances. Therefore, humans have a prejudice in favor of the element carbon, and this prejudice may have guided the decision to use carbon in defining the mole.
See also
- Anthropic principleAnthropic principleIn astrophysics and cosmology, the anthropic principle is the philosophical argument that observations of the physical Universe must be compatible with the conscious life that observes it. Some proponents of the argument reason that it explains why the Universe has the age and the fundamental...
- AnthropocentrismAnthropocentrismAnthropocentrism describes the tendency for human beings to regard themselves as the central and most significant entities in the universe, or the assessment of reality through an exclusively human perspective....
- AnthropometryAnthropometryAnthropometry refers to the measurement of the human individual...
- Hand (unit)Hand (unit)The hand is a non-SI unit of measurement of length, now used only for the measurement of the height of horses in some English-speaking countries, including Australia, Canada, the UK and the USA. With origins in ancient Egypt, it was originally based on the breadth of a human hand...
- History of measurementHistory of measurementUnits of measurement were among the earliest tools invented by humans. Primitive societies needed rudimentary measures for numerous tasks such as: constructing dwellings of an appropriate size and shape, fashioning clothing, or bartering food or raw materials....
- ProtagorasProtagorasProtagoras was a pre-Socratic Greek philosopher and is numbered as one of the sophists by Plato. In his dialogue Protagoras, Plato credits him with having invented the role of the professional sophist or teacher of virtue...
Man is the measure of all things - Natural unit
- Span (unit)Span (unit)A span is the distance measured by a human hand, from the tip of the thumb to the tip of the little finger. In ancient times, a span was considered to be half a cubit...
- Units of measurementUnits of measurementA unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of...
- Vitruvian ManVitruvian ManThe Vitruvian Man is a world-renowned drawing created by Leonardo da Vinci circa 1487. It is accompanied by notes based on the work of the famed architect, Vitruvius. The drawing, which is in pen and ink on paper, depicts a male figure in two superimposed positions with his arms and legs apart and...
Measure of man in art
External links
- General table of units of measure - NIST - pdf
- This NIST website(National Institute of Standards and TechnologyNational Institute of Standards and TechnologyThe National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
) gives a brief history of the SI. - Rowlett's A Dictionary of Units of Measurement