In the

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which rel ...

superfluidity Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy. When stirred, a superfluid forms vortices that continue to rotate indefinitely. Superfluidity occurs in two i ...

, a boojum is a

geometric Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is ca ...

pattern on the surface of one of the phases of superfluid

helium-3 Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron (the most common isotope, helium-4, having two protons and two neutrons in contrast). Other than protium (ordinary hydrogen), helium-3 is th ...

, whose motion can result in the decay of a

supercurrent A supercurrent is a superconducting current, that is, electric current which flows without dissipation in a superconductor. Under certain conditions, an electric current can also flow without dissipation in microscopically small non-superconductin ...

. A boojum can result from a monopole singularity in the bulk of the liquid being drawn to, and then "pinned" on a surface. Although superfluid helium-3 only exists within a few thousandths of a degree of

absolute zero Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvin. The fundamental particles of nature have minimum vibrati ...

, boojums have also been observed forming in various

liquid crystal Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. The ...

s, which exist at a far broader range of temperatures. The boojum was named by N. David Mermin of

Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to ...

in 1976. He was inspired by

Lewis Carroll Charles Lutwidge Dodgson (; 27 January 1832 – 14 January 1898), better known by his pen name Lewis Carroll, was an English author, poet and mathematician. His most notable works are ''Alice's Adventures in Wonderland'' (1865) and its sequel ...

's poem ''

The Hunting of the Snark ''The Hunting of the Snark'', subtitled ''An Agony in 8 Fits'', is a poem by the English writer Lewis Carroll. It is typically categorised as a nonsense poem. Written between 1874 and 1876, it borrows the setting, some creatures, and eight po ...

''. As in the poem, the appearance of a boojum can cause something (in this case, the supercurrent) to "''softly and suddenly vanish away''". Other, less whimsical names had already been suggested for the phenomenon, but Mermin was persistent. After an exchange of letters that Mermin describes as both "lengthy and hilarious", the editors of ''

Physical Review Letters ''Physical Review Letters'' (''PRL''), established in 1958, is a peer-reviewed, scientific journal that is published 52 times per year by the American Physical Society. As also confirmed by various measurement standards, which include the '' Jou ...

'' agreed to his terminology. Research using the term "boojum" in a superfluid context was first published in 1977, and the term has since gained widespread acceptance in broader areas of physics. Its Russian phonetic equivalent is "budzhum", which is also well accepted by physicists. The plural of the term is "boojums", a word initially disliked by Mermin (who at first used "booja") but one which is defined unambiguously by Carroll in his poem.

References

* A collection of articles by David Mermin, including "''E pluribus boojum''".

External links

* (5.4 MB). ** Reprinted here by Univ of Southampton, dept of Economics: *Transcript of Mermin's 1999 lecture, in which he describes how he made "boojum" an internationally accepted scientific term: {{cite web, url=http://www.lassp.cornell.edu/~cew2/KnightLecture.html , title=Writing Physics , last=Mermin , first=N. David , date=April 19, 1999 , website=Knight Distinguished Lecture in Writing in the Disciplines , publisher=Cornell , accessdate=16 January 2014 , archiveurl=https://web.archive.org/web/20120828183555/http://www.lassp.cornell.edu/~cew2/KnightLecture.html , archivedate=August 28, 2012 , url-status=dead Fluid dynamics Superfluidity