Editing Antimatter (section)

==Conceptual history==
The idea of [[negative matter]] appears in past theories of matter that have now been abandoned. Using the once popular [[vortex theory of gravity]], the possibility of matter with negative gravity was discussed by [[William Mitchinson Hicks|William Hicks]] in the 1880s. Between the 1880s and the 1890s, [[Karl Pearson]] proposed the existence of "squirts"<ref>
{{cite journal
 |last=Pearson |first=K.
 |date=1891
 |title=Ether Squirts
 |journal=[[American Journal of Mathematics]]
 |volume=13 |issue=4 |pages=309–72
 |doi=10.2307/2369570
 |jstor=2369570
}}</ref> and sinks of the flow of [[Luminiferous aether|aether]]. The squirts represented normal matter and the sinks represented negative matter. Pearson's theory required a fourth dimension for the aether to flow from and into.<ref>
{{cite book
 |last=Kragh |first=H.
 |date=2002
 |title=Quantum Generations: A History of Physics in the Twentieth Century
 |pages=5–6
 |publisher=[[Princeton University Press]]
 |isbn=978-0-691-09552-3
}}</ref>

The term antimatter was first used by [[Arthur Schuster]] in two rather whimsical letters to ''[[Nature (journal)|Nature]]'' in 1898,<ref>{{cite journal
 |last=Schuster
 |first=A.
 |date=1898
 |title=Potential Matter – A Holiday Dream
 |journal=[[Nature (journal)|Nature]]
 |volume=58
 |issue=1503
 |page=367
 |bibcode=1898Natur..58..367S
 |doi=10.1038/058367a0
 |s2cid=4046342
 |url=https://zenodo.org/record/1429382
 |doi-access=free
 |access-date=31 August 2020
 |archive-date=10 October 2021
 |archive-url=https://web.archive.org/web/20211010050639/https://zenodo.org/record/1429382
 |url-status=live
 }}</ref> in which he coined the term. He hypothesized antiatoms, as well as whole antimatter solar systems, and discussed the possibility of matter and antimatter annihilating each other. Schuster's ideas were not a serious theoretical proposal, merely speculation, and like the previous ideas, differed from the modern concept of antimatter in that it possessed [[antigravity|negative gravity]].<ref>{{cite book
 |last=Harrison
 |first=E. R.
 |date=2000-03-16
 |title=Cosmology: The Science of the Universe
 |url=https://books.google.com/books?id=wzpKc3bZqDoC
 |edition=2nd
 |pages=266, 433
 |publisher=[[Cambridge University Press]]
 |isbn=978-0-521-66148-5
 |access-date=31 August 2020
 |archive-date=10 October 2021
 |archive-url=https://web.archive.org/web/20211010050640/https://books.google.com/books?id=wzpKc3bZqDoC
 |url-status=live
 }}</ref>

The modern theory of antimatter began in 1928, with a paper<ref>
{{cite journal
 |last=Dirac |first=P. A. M.
 |date=1928
 |title=The Quantum Theory of the Electron
 |journal=[[Proceedings of the Royal Society A]]
 |volume=117 |issue=778 |pages=610–624
 |bibcode=1928RSPSA.117..610D
 |doi=10.1098/rspa.1928.0023
 |jstor=94981
 |doi-access=free
 }}</ref> by [[Paul Dirac]]. Dirac realised that his [[Dirac equation|relativistic version]] of the [[Schrödinger equation|Schrödinger wave equation]] for electrons predicted the possibility of [[antielectron]]s. Although Dirac had laid the groundwork for the existence of these “antielectrons” he initially failed to pick up on the implications contained within his own equation. He freely gave the credit for that insight to [[J. Robert Oppenheimer]], whose seminal paper “On the Theory of Electrons and Protons” (Feb 14th 1930) drew on Dirac's equation and argued for the existence of a positively charged electron (a positron), which as a counterpart to the electron should have the same mass as the electron itself. This meant that it could not be, as Dirac had in fact suggested, a proton. Dirac further postulated the existence of antimatter in a 1931 paper which referred to the positron as an "anti-electron".<ref>{{Cite journal |last=Dirac |first=Paul |date=1931 |title=Quantised singularities in the electromagnetic field |url=https://royalsocietypublishing.org/doi/10.1098/rspa.1931.0130 |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |language=en |volume=133 |issue=821 |pages=60–72 |bibcode=1931RSPSA.133...60D |doi=10.1098/rspa.1931.0130 |issn=0950-1207}}</ref><ref name=":3">{{Cite web |title=Discovering the positron |url=https://timeline.web.cern.ch/timeline-header/142#416 |access-date=2023-10-23 |website=timeline.web.cern.ch}}</ref> These were discovered by [[Carl David Anderson|Carl D. Anderson]] in 1932 and named [[positron]]s from "positive electron". Although Dirac did not himself use the term antimatter, its use follows on naturally enough from antielectrons, antiprotons, etc.<ref>
{{cite book
 |last1=Kaku |first1=M.
 |last2=Thompson |first2=J. T.
 |date=1997
 |title=Beyond Einstein: The Cosmic Quest for the Theory of the Universe
 |pages=179–180
 |publisher=[[Oxford University Press]]
 |isbn=978-0-19-286196-2
}}</ref> A complete [[periodic table]] of antimatter was envisaged by [[Charles Janet]] in 1929.<ref>
 {{cite journal
 |last=Stewart |first=P. J.
 |date=2010
 |title=Charles Janet: Unrecognized genius of the periodic system
 |journal=[[Foundations of Chemistry]]
 |volume=12 |issue=1 |pages=5–15
 |doi=10.1007/s10698-008-9062-5
|s2cid=171000209
 }}</ref>

The [[Feynman–Stueckelberg interpretation]] states that antimatter and [[antiparticles]] behave exactly identical to regular particles, but traveling backward in time.{{clarify|reason = What would this actually entail? Suppose in a distant galaxy there were antimatter worlds with antimatter beings. What would it mean for these to be "traveling backward in time"?|date=September 2024}} <ref>
{{cite journal
 |last1=Canetti |first1=L.
 |last2=Drewes |first2=M.
 |last3=Shaposhnikov |first3=M.
 |year=2012
 |title=Matter and antimatter in the universe
 |journal=[[New Journal of Physics]]
 |volume=14 |issue=9 |pages=095012
 |arxiv=1204.4186
 |bibcode=2012NJPh...14i5012C
 |doi=10.1088/1367-2630/14/9/095012
|s2cid=119233888
 }}</ref> This concept is nowadays used in modern particle physics, in [[Feynman diagram]]s.<ref>
{{cite book
 |author=Griffiths, D.J. 
 |author-link=David J. Griffiths 
 |page=61 
 |year=2008 
 |title=Introduction to Elementary Particles 
 |edition=2nd 
 |publisher=[[John Wiley & Sons]] 
 |isbn=978-3-527-40601-2
}}</ref>