In the physics of superfluidity, a boojum is a geometric pattern on the surface of one of the phases of superfluid helium-3, whose motion can result in the decay of a supercurrent. 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, boojums have also been observed forming in various liquid crystals, which exist at a far broader range of temperatures.
The boojum was named by David Mermin of Cornell University in 1976. He was inspired by Lewis Carroll's poem The Hunting of the Snark. 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 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.
- Frustration in Modulated Phases: Ripples and Boojums, from Europhysics Letters, 5 (4), pp. 327-331 (1988); by J. M. Carlson, S.A. Langer, and J. P. Sethn; archived at Cornell University
- Faculty Highlights: David Mermin, at Cornell University, retrieved March 14, 2011
- N. David Mermin (15 March 1990). Boojums All the Way Through: Communicating Science in a Prosaic Age. Cambridge University Press. p. xii. ISBN 978-0-521-38880-1. A collection of articles by David Mermin, including "E pluribus boojum".
- Mermin, N. David (April 1981). "E Pluribus Boojum: the physicist as neologist" (PDF). Physics Today. pp. 46–53. Archived from the original (PDF) on 3 November 2013. Retrieved 16 January 2014. (5.4 MB).
- Reprinted here by Univ of Southhampton, dept of Economics: http://www.economics.soton.ac.uk/staff/aldrich/boojum.pdf
- Transcript of Mermin's 1999 lecture, in which he describes how he made "boojum" an internationally accepted scientific term: Mermin, N. David (April 19, 1999). "Writing Physics". Knight Distinguished Lecture in Writing in the Disciplines. http://www.lassp.cornell.edu/~cew2/KnightLecture.html: Cornell. Archived from the original on 28 August 2012. Retrieved 16 January 2014.