A "fermi" (symbol: fm) is a unit of length used in physics to describe extremely small distances at the atomic and subatomic scale. One fermi is equal to 10^-15 meters or 0.000000000000001 meters. It is named after the Italian physicist Enrico Fermi, who made significant contributions to nuclear physics and particle physics.
The fermi is particularly useful for describing the sizes of atomic nuclei and the distances between particles within atomic nuclei. For example, the typical diameter of an atomic nucleus is on the order of a few femtometers (1 femtometer = 1 fm). It is also used in high-energy particle physics to describe the cross-sectional area of particle interactions.
In summary, the fermi is an essential unit of length for understanding the microscopic world of atoms, nuclei, and subatomic particles, where distances are incredibly small.
The "cubit" (Greek: πῆχυς, pēchys) in ancient Greece was a unit of length used in antiquity for measuring various objects, including architectural dimensions. Like many ancient units of measurement, the length of the Greek cubit could vary over time and by region.
The most commonly referenced Greek cubit is the "common" or "short" cubit, which is believed to have been approximately 45 centimeters (about 17.7 inches) in length. However, there were variations in the length of the cubit in different parts of Greece and during different periods in ancient history.
The Greek cubit was used for measuring building dimensions, as well as in various crafts and trades. It was often based on the length of the forearm from the elbow to the tip of the middle finger, much like other cubits used in different ancient cultures.
It's important to note that the length of the Greek cubit is a matter of historical interpretation and may not be precisely defined due to variations in antiquity.