Editing Speed of light (section)

=== Early history ===
[[Empedocles]] (c. 490–430 BCE) was the first to propose a theory of light<ref>
{{Cite book
 |title=Light-Matter Interaction: Physics and Engineering at the Nanoscale |edition=illustrated
 |first1=John
 |last1=Weiner
 |first2=Frederico
 |last2=Nunes
 |publisher=OUP Oxford
 |year=2013
 |isbn=978-0-19-856766-0
 |page=1
 |url=https://books.google.com/books?id=ctpG-kmmK8kC
}} [https://books.google.com/books?id=ctpG-kmmK8kC&pg=PA1 Extract of page 1].</ref> and claimed that light has a finite speed.<ref>
{{Cite book
 |last=Sarton |first=G. |author-link=George Sarton
 |year=1993
 |title=Ancient science through the golden age of Greece
 |url=https://books.google.com/books?id=VcoGIKlHuZcC&pg=PA248
 |page=248
 |publisher=[[Courier Dover]]
 |isbn=978-0-486-27495-9
}}</ref> He maintained that light was something in motion, and therefore must take some time to travel. [[Aristotle]] argued, to the contrary, that "light is due to the presence of something, but it is not a movement".<ref name=Statistics>
{{Cite journal
 |last1=MacKay |first1=R. H. |last2=Oldford |first2=R. W.
 |year=2000
 |title=Scientific Method, Statistical Method and the Speed of Light
 |url=http://sas.uwaterloo.ca/~rwoldfor/papers/sci-method/paperrev/
 |journal=[[Statistical Science (journal)|Statistical Science]]
 |volume=15 |issue=3 |pages=254–278
 |doi=10.1214/ss/1009212817
 |doi-access=free
}} (click on "Historical background" in the table of contents)</ref> [[Euclid]] and [[Ptolemy]] advanced Empedocles' [[Emission theory (vision)|emission theory]] of vision, where light is emitted from the eye, thus enabling sight. Based on that theory, [[Heron of Alexandria]] argued that the speed of light must be [[Infinity|infinite]] because distant objects such as stars appear immediately upon opening the eyes.<ref>{{Cite book |title=Electronic Microwave Imaging with Planar Multistatic Arrays |first1=Sherif Sayed |last1=Ahmed |publisher=Logos Verlag Berlin |year=2014 |isbn=978-3-8325-3621-3 |page=1 |url=https://books.google.com/books?id=ob79AgAAQBAJ}} [https://books.google.com/books?id=ob79AgAAQBAJ&pg=PA1 Extract of page 1]</ref>

[[Early Islamic philosophy|Early Islamic philosophers]] initially agreed with the [[Aristotelian physics|Aristotelian view]] that light had no speed of travel. In 1021, [[Alhazen]] (Ibn al-Haytham) published the ''[[Book of Optics]]'', in which he presented a series of arguments dismissing the emission theory of [[Visual perception|vision]] in favour of the now accepted intromission theory, in which light moves from an object into the eye.<ref>
{{Cite journal
 | last1 = Gross | first1 = C. G.
 | title = The Fire That Comes from the Eye
 | journal = Neuroscientist
 | volume = 5
 | pages = 58–64
 | year = 1999
 | doi = 10.1177/107385849900500108
 | s2cid = 84148912
}}</ref> This led Alhazen to propose that light must have a finite speed,<ref name=Statistics/><ref name=Hamarneh>
{{Cite journal
 |last=Hamarneh |first=S.
 |year=1972
 |title=Review: Hakim Mohammed Said, ''Ibn al-Haitham''
 |journal=[[Isis (journal)|Isis]]
 |volume=63 |issue=1 |page=119
 |doi=10.1086/350861
}}</ref><ref name=Lester>
{{Cite book
 |last=Lester |first=P. M.
 |year=2005
 |title=Visual Communication: Images With Messages
 |pages=10–11
 |publisher=[[Thomson Wadsworth]]
 |isbn=978-0-534-63720-0
}}</ref> and that the speed of light is variable, decreasing in denser bodies.<ref name=Lester/><ref>
{{Cite web
 |first1=J. J.
 |last1=O'Connor
 |author-link1=John J. O'Connor (mathematician)
 |first2=E. F.
 |last2=Robertson
 |author-link2=Edmund F. Robertson
 |url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Al-Haytham.html
 |title=Abu Ali al-Hasan ibn al-Haytham
 |work=[[MacTutor History of Mathematics archive]]
 |publisher=[[University of St Andrews]]
 |access-date=12 January 2010
}}</ref> He argued that light is substantial matter, the propagation of which requires time, even if this is hidden from the senses.<ref>
{{Cite conference
 |last         = Lauginie
 |first        = P.
 |year         = 2004
 |title        = Measuring Speed of Light: Why? Speed of what?
 |url          = http://sci-ed.org/documents/Lauginie-M.pdf
 |conference   = Fifth International Conference for History of Science in Science Education
 |location     = Keszthely, Hungary
 |pages        = 75–84
 |access-date  = 12 August 2017
 |archive-url  = https://web.archive.org/web/20150704043700/http://sci-ed.org/documents/Lauginie-M.pdf
 |archive-date = 4 July 2015
 |url-status=dead
}}</ref> Also in the 11th century, [[Al-Biruni|Abū Rayhān al-Bīrūnī]] agreed that light has a finite speed, and observed that the speed of light is much faster than the speed of sound.<ref>
{{Cite web
 |first1=J. J.
 |last1=O'Connor
 |first2=E. F.
 |last2=Robertson
 |url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Al-Biruni.html
 |title=Abu han Muhammad ibn Ahmad al-Biruni
 |work=MacTutor History of Mathematics archive
 |publisher=University of St Andrews
 |access-date=12 January 2010
}}</ref>

In the 13th century, [[Roger Bacon]] argued that the speed of light in air was not infinite, using philosophical arguments backed by the writing of Alhazen and Aristotle.<ref name=Lindberg>
{{Cite book
 |last=Lindberg |first=D. C.
 |year=1996
 |title=Roger Bacon and the origins of Perspectiva in the Middle Ages: a critical edition and English translation of Bacon's Perspectiva, with introduction and notes
 |url=https://books.google.com/books?id=jSPHMKbjYkQC&pg=PA143
 |page=143
 |isbn=978-0-19-823992-5
 |publisher=Oxford University Press
}}</ref><ref>
{{Cite book
 |last=Lindberg |first=D. C.
 |year=1974
 |chapter=Late Thirteenth-Century Synthesis in Optics
 |editor=Edward Grant
 |title=A source book in medieval science
 |chapter-url=https://books.google.com/books?id=fAPN_3w4hAUC&q=roger-bacon%20speed-of-light&pg=RA1-PA395
 |page=396
 |publisher=Harvard University Press
 |isbn=978-0-674-82360-0
}}</ref> In the 1270s, [[Witelo]] considered the possibility of light travelling at infinite speed in vacuum, but slowing down in denser bodies.<ref name=Marshall>
{{Cite journal
 |last=Marshall |first=P.
 |year=1981
 |title=Nicole Oresme on the Nature, Reflection, and Speed of Light
 |journal=[[Isis (journal)|Isis]]
 |volume=72 |issue=3 |pages=357–374 [367–374]
 |doi=10.1086/352787
 |s2cid=144035661
}}</ref>

In the early 17th century, [[Johannes Kepler]] believed that the speed of light was infinite since empty space presents no obstacle to it. [[René Descartes]] argued that if the speed of light were to be finite, the Sun, Earth, and Moon would be noticeably out of alignment during a [[lunar eclipse]]. Although this argument fails when aberration of light is taken into account, the latter was not recognized until the following century.<ref>{{Cite journal |last=Sakellariadis |first=Spyros |date=1982 |title=Descartes' Experimental Proof of the Infinite Velocity of Light and Huygens' Rejoinder |url=https://www.jstor.org/stable/41133639 |journal=[[Archive for History of Exact Sciences]] |volume=26 |issue=1 |pages=1–12 |doi=10.1007/BF00348308 |jstor=41133639 |s2cid=118187860 |issn=0003-9519}}</ref> Since such misalignment had not been observed, Descartes concluded the speed of light was infinite. Descartes speculated that if the speed of light were found to be finite, his whole system of philosophy might be demolished.<ref name=Statistics /> Despite this, in his derivation of [[Snell's law]], Descartes assumed that some kind of motion associated with light was faster in denser media.<ref>{{Cite book |last=Cajori |first=Florian |url=https://books.google.com/books?id=XNtUAAAAYAAJ |title=A History of Physics in Its Elementary Branches: Including the Evolution of Physical Laboratories |date=1922 |publisher=Macmillan |pages=76 |language=en}}</ref><ref>{{Cite journal |last=Smith |first=A. Mark |date=1987 |title=Descartes's Theory of Light and Refraction: A Discourse on Method |url=https://www.jstor.org/stable/1006537 |journal=[[Transactions of the American Philosophical Society]] |volume=77 |issue=3 |pages=i–92 |doi=10.2307/1006537 |jstor=1006537 |issn=0065-9746}}</ref> [[Pierre de Fermat]] derived Snell's law using the opposing assumption, the denser the medium the slower light travelled. Fermat also argued in support of a finite speed of light.<ref>{{Cite book|author-link=Carl Benjamin Boyer |first=Carl Benjamin |last=Boyer |title=The Rainbow: From Myth to Mathematics |year=1959 |pages=205–206 |publisher=Thomas Yoseloff |oclc=763848561}}</ref>