Editing Dimensionless quantity (section)

== History ==
{{See also|Dimensional analysis#History}}
Quantities having dimension one, ''dimensionless quantities'', regularly occur in sciences, and are formally treated within the field of [[dimensional analysis]]. In the 19th century, French mathematician [[Joseph Fourier]] and Scottish physicist [[James Clerk Maxwell]] led significant developments in the modern concepts of [[dimension]] and [[Unit (measurement)|unit]]. Later work by British physicists [[Osborne Reynolds]] and [[Lord Rayleigh]] contributed to the understanding of dimensionless numbers in physics. Building on Rayleigh's method of dimensional analysis, [[Edgar Buckingham]] proved the [[Buckingham π theorem|{{pi}} theorem]] (independently of French mathematician [[Joseph Bertrand]]'s previous work) to formalize the nature of these quantities.<ref>{{cite journal |author-last=Buckingham |author-first=Edgar |author-link=Edgar Buckingham |date=1914 |title=On physically similar systems; illustrations of the use of dimensional equations |journal=[[Physical Review]] |volume=4 |issue=4 |pages=345–376 |doi=10.1103/PhysRev.4.345 |url=https://babel.hathitrust.org/cgi/pt?id=uc1.31210014450082&view=1up&seq=905 |bibcode=1914PhRv....4..345B |hdl=10338.dmlcz/101743 |hdl-access=free}}</ref>

Numerous dimensionless numbers, mostly ratios, were coined in the early 1900s, particularly in the areas of [[fluid mechanics]] and [[heat transfer]]. Measuring logarithm of ratios as [[level quantity|''levels'']] in the (derived) unit [[decibel]] (dB) finds widespread use nowadays.

There have been periodic proposals to "patch" the SI system to reduce confusion regarding physical dimensions. For example, a 2017 [[op-ed]] in [[Nature (journal)|Nature]]<ref name="nature_2017">{{cite journal |title=Lost dimension: A flaw in the SI system leaves physicists grappling with ambiguous units - SI units need reform to avoid confusion |journal=[[Nature (journal)|Nature]] |date=2017-08-10 |volume=548 |issue=7666 |page=135 |doi=10.1038/548135b |pmid=28796224 |bibcode=2017Natur.548R.135. |s2cid=4444368 |language=en |department=This Week: Editorials |issn=1476-4687 |url=https://www.nature.com/articles/548135b.pdf?error=cookies_not_supported&code=87d78113-7ea0-47c0-a0ac-cd3da87c16ba |access-date=2022-12-21 |url-status=live |archive-url=https://web.archive.org/web/20221221120517/https://www.nature.com/articles/548135b.pdf?error=cookies_not_supported&code=87d78113-7ea0-47c0-a0ac-cd3da87c16ba |archive-date=2022-12-21}} (1 page)</ref> argued for formalizing the [[radian]] as a physical unit. The idea was rebutted<ref name="wendl_2017">{{cite journal |author-last=Wendl |author-first=Michael Christopher |author-link=Michael Christopher Wendl |title=Don't tamper with SI-unit consistency |journal=[[Nature (journal)|Nature]] |date=September 2017 |volume=549 |issue=7671 |pages=160 |doi=10.1038/549160d |pmid=28905893 |s2cid=52806576 |language=en |issn=1476-4687|doi-access=free }}</ref> on the grounds that such a change would raise inconsistencies for both established dimensionless groups, like the [[Strouhal number]], and for mathematically distinct entities that happen to have the same units, like [[torque]] (a [[Cross product|vector product]]) versus energy (a [[Dot product|scalar product]]). In another instance in the early 2000s, the [[International Committee for Weights and Measures]] discussed naming the unit of 1 as the "[[Uno (unit)|uno]]", but the idea of just introducing a new SI name for 1 was dropped.<ref>{{cite web |url=http://www.bipm.fr/utils/common/pdf/CCU15.pdf |title=BIPM Consultative Committee for Units (CCU), 15th Meeting |date=17–18 April 2003 |access-date=2010-01-22 |url-status=dead |archive-url=https://web.archive.org/web/20061130201238/http://www.bipm.fr/utils/common/pdf/CCU15.pdf |archive-date=2006-11-30}}</ref><ref>{{cite web |url=http://www.bipm.fr/utils/common/pdf/CCU16.pdf |title=BIPM Consultative Committee for Units (CCU), 16th Meeting |access-date=2010-01-22 |url-status=dead |archive-url=https://web.archive.org/web/20061130200835/http://www.bipm.fr/utils/common/pdf/CCU16.pdf |archive-date=2006-11-30}}</ref><ref>{{cite journal |author-last=Dybkær |author-first=René |author-link=René Dybkær |title=An ontology on property for physical, chemical, and biological systems |journal=APMIS Suppl. |issue=117 |pages=1–210 |date=2004 |pmid=15588029 |url=http://www.iupac.org/publications/ci/2005/2703/bw1_dybkaer.html}}</ref>