Editing Elementary charge (section)

=== Lack of fractional charges ===
[[Paul Dirac]] argued in 1931 that if [[magnetic monopole]]s exist, then electric charge must be quantized; however, it is unknown whether magnetic monopoles actually exist.<ref>{{cite journal|doi=10.1146/annurev.ns.34.120184.002333|doi-access=free|title=Magnetic Monopoles|year=1984|last1=Preskill|first1=J.|journal=[[Annual Review of Nuclear and Particle Science]]|volume=34|issue=1|pages=461–530|bibcode=1984ARNPS..34..461P}}</ref><ref>{{cite news |title=Three Surprising Facts About the Physics of Magnets |url=https://www.space.com/42685-physics-of-magnets-surprising-facts.html |access-date=17 July 2019 |work=Space.com |date=2018 |language=en}}</ref> It is currently unknown why isolatable particles are restricted to integer charges; much of the [[string theory landscape]] appears to admit fractional charges.<ref>{{cite journal |last1=Schellekens |first1=A. N. |title=Life at the interface of particle physics and string theory |journal=Reviews of Modern Physics |date=2 October 2013 |volume=85 |issue=4 |pages=1491–1540 |doi=10.1103/RevModPhys.85.1491|arxiv=1306.5083 |bibcode=2013RvMP...85.1491S |s2cid=118418446 }}</ref><ref>{{cite journal |last1=Perl |first1=Martin L. |last2=Lee |first2=Eric R. |last3=Loomba |first3=Dinesh |title=Searches for Fractionally Charged Particles |journal=[[Annual Review of Nuclear and Particle Science]] |date=November 2009 |volume=59 |issue=1 |pages=47–65 |doi=10.1146/annurev-nucl-121908-122035| doi-access=free|bibcode=2009ARNPS..59...47P }}</ref>

{{see also|Anomaly (physics)#Anomaly cancellation}}