Editing Luminiferous aether (section)

===Particles vs. waves===
{{main|Wave–particle duality}}
In the 17th century, [[Robert Boyle]] was a proponent of an aether hypothesis. According to Boyle, the aether consists of subtle particles, one sort of which explains the absence of vacuum and the mechanical interactions between bodies, and the other sort of which explains phenomena such as magnetism (and possibly gravity) that are, otherwise, inexplicable on the basis of purely mechanical interactions of macroscopic bodies, "though in the ether of the ancients there was nothing taken notice of but a diffused and very subtle substance; yet we are at present content to allow that there is always in the air a swarm of streams moving in a determinate course between the north pole and the south".<ref>Robert Boyle, ''The Works of the Honourable Robert Boyle'', ed. Thomas Birch, 2nd edn., 6 vols. (London, 1772), III, 316; quoted in E. A. Burtt, ''The Metaphysical Foundations of Modern Science'' (Garden City, New York: Doubleday & Company, 1954), 191–192.</ref>

[[Christiaan Huygens]]'s ''[[Treatise on Light]]'' (1690) hypothesized that light is a wave propagating through an aether. He and [[Isaac Newton]] could only envision light waves as being [[longitudinal wave|longitudinal]], propagating like sound and other [[mechanical wave]]s in [[fluid]]s. However, longitudinal waves necessarily have only one form for a given propagation direction, rather than two [[polarization (waves)|polarization]]s like a [[transverse wave]]. Thus, longitudinal waves can not explain [[birefringence]], in which two polarizations of light are refracted differently by a crystal. In addition, Newton rejected light as waves in a medium because such a medium would have to extend everywhere in space, and would thereby "disturb and retard the Motions of those great Bodies" (the planets and comets) and thus "as it {{bracket|light's medium}} is of no use, and hinders the Operation of Nature, and makes her languish, so there is no evidence for its Existence, and therefore it ought to be rejected".<ref>{{cite book |title=The Metaphysical Foundations of Modern Science |author1=Edwin Arthur Burtt |edition=illustrated, unabridged, reprinted |publisher=Courier Corporation |year=2003 |isbn=978-0-486-42551-1 |page=270 |url=https://books.google.com/books?id=G9WBMa1Rz_kC}} [https://books.google.com/books?id=G9WBMa1Rz_kC&pg=PA270 Extract of page 270]</ref>

Isaac Newton contended that light is made up of numerous small particles. This can explain such features as light's ability to travel in straight lines and [[Reflection (physics)|reflect]] off surfaces. Newton imagined light particles as non-spherical "corpuscles", with different "sides" that give rise to birefringence. But the particle theory of light can not satisfactorily explain [[refraction]] and [[diffraction]].<ref>{{cite book |title=Experimental Mechanics of Solids |author1=Cesar A. Sciammarella |author2=Federico M. Sciammarella |edition= |publisher=John Wiley & Sons |year=2012 |isbn=978-1-119-97009-5 |page=146 |url=https://books.google.com/books?id=aVP6tpNXAf4C}} [https://books.google.com/books?id=aVP6tpNXAf4C&pg=PT146 Extract of page 146]</ref> To explain refraction, Newton's Third Book of ''[[Opticks]]'' (1st ed. 1704, 4th ed. 1730) postulated an "aethereal medium" transmitting vibrations faster than light, by which light, when overtaken, is put into "Fits of easy Reflexion and easy Transmission", which caused refraction and diffraction. Newton believed that these vibrations were related to heat radiation:

<blockquote>Is not the Heat of the warm Room convey'd through the vacuum by the Vibrations of a much subtiler Medium than Air, which after the Air was drawn out remained in the Vacuum?  And is not this Medium the same with that Medium by which Light is refracted and reflected, and by whose Vibrations Light communicates Heat to Bodies, and is put into Fits of easy Reflexion and easy Transmission?<ref group=A name=newton />{{rp|349}}</blockquote>

In contrast to the modern understanding that heat radiation and light are both [[electromagnetic radiation]], Newton viewed heat and light as two different phenomena. He believed heat vibrations to be excited "when a Ray of Light falls upon the Surface of any pellucid Body".<ref group=A name=newton />{{rp|348}} He wrote, "I do not know what this Aether is", but that if it consists of particles then they must be <blockquote>exceedingly smaller than those of Air, or even than those of Light: The exceeding smallness of its Particles may contribute to the greatness of the force by which those Particles may recede from one another, and thereby make that Medium exceedingly more rare and elastic than Air, and by consequence exceedingly less able to resist the motions of Projectiles, and exceedingly more able to press upon gross Bodies, by endeavoring to expand itself.<ref group=A name=newton />{{rp|352}}</blockquote>