Editing Bucket argument (section)

==Background==
These arguments, and a discussion of the distinctions between absolute and relative time, space, place and motion, appear in a scholium at the end of Definitions sections in Book I of Newton's work, ''[[The Mathematical Principles of Natural Philosophy]]'' (1687) (not to be confused with [[General Scholium]] at the end of Book III), which established the foundations of [[classical mechanics]] and introduced his [[law of universal gravitation]], which yielded the first quantitatively adequate dynamical explanation of [[planetary motion]].<ref>See the ''Principia'' on line at [https://archive.org/details/newtonspmathema00newtrich Andrew Motte translation], pp.&nbsp;77–82.</ref>

Despite their embrace of the principle of rectilinear [[inertia]] and the recognition of the kinematical relativity of apparent motion (which underlies whether the [[Geocentric model|Ptolemaic]] or the [[Heliocentrism|Copernican]] system is correct), natural philosophers of the seventeenth century continued to consider true motion and rest as physically separate descriptors of an individual body.  The dominant view Newton opposed was devised by [[René Descartes]], and was supported (in part) by [[Gottfried Leibniz]].  It held that empty space is a metaphysical impossibility because space is nothing other than the extension of matter, or, in other words, that when one speaks of the space between things one is actually making reference to the relationship that exists between those things and not to some entity that stands between them.<ref name="Descartes">{{cite book |author=Descartes |first=René |url=https://books.google.com/books?id=6tNxSphqAYkC&dq=descartes+space+separation&pg=PA191 |title=Descartes: Selected Philosophical Writings |publisher=Cambridge University Press |year=1988 |isbn=0-521-35812-4 |page=191 |translator-last=Cottingham |translator-first=John}}</ref><ref name=Koyre>{{cite book |title=From the Closed World to the Infinite Universe |author=Alexandre Koyre |page=75 |url=https://books.google.com/books?id=gNVB0QnZlXgC&dq=descartes+space+separation&pg=PA75 |isbn=1-60620-143-3 |publisher=Forgotten Books |year=1957}}</ref>  Concordant with the above understanding, any assertion about the motion of a body boils down to a description over time in which the body under consideration is at ''t''<sub>1</sub> found in the vicinity of one group of "landmark" bodies and at some ''t''<sub>2</sub> is found in the vicinity of some other "landmark" body or bodies.<ref name=pricipia>{{cite book |title=[[Principia Philosophiae]] |author=René Descartes |year=1664 |at=Part II, §25}}</ref><ref name=Garber>{{cite book |title=Descartes' Metaphysical Physics |author=Daniel Garber |page=170 |url=https://books.google.com/books?id=ORGKw7CZMQAC&dq=descartes+space+separation&pg=PA170 |isbn=0-226-28219-8 |year=1992 |publisher=University of Chicago Press}}</ref>
[[File:Mach bucket.svg|200px|thumb|Detection of rotation: red flags pop out on flexible arms when either object actually rotates. A: Central object rotates. B: Outer ring rotates, but in opposite direction. C: Both rotate, but in opposite directions. D: Both are locked together and rotate in the same direction.]]

Descartes recognized that there would be a real difference, however, between a situation in which a body with movable parts and originally at rest with respect to a surrounding ring was itself accelerated to a certain angular velocity with respect to the ring, and another situation in which the surrounding ring were given a contrary acceleration with respect to the central object. With sole regard to the central object and the surrounding ring, the motions would be indistinguishable from each other assuming that both the central object and the surrounding ring were absolutely rigid objects. However, if neither the central object nor the surrounding ring were absolutely rigid then the parts of one or both of them would tend to fly out from the axis of rotation.

For contingent reasons having to do with the [[Roman Inquisition#Galileo|Inquisition]], Descartes spoke of motion as both absolute and relative.<ref name=Disalle>{{cite book |title=Understanding Space-time: The philosophical development of physics from Newton to Einstein |author=Robert Disalle |page=19 |year=2006 |publisher=Cambridge University Press |isbn=0-521-85790-2 |url=https://books.google.com/books?id=5rxYBvx7tW0C&dq=descartes+space+separation&pg=PA26}}</ref>{{failed verification|date=April 2018}}

By the late 19th century, the contention that ''all motion is relative'' was re-introduced, notably by [[Ernst Mach]] (German 1883, English translation 1893).<ref name=Mach>{{cite book |title=The Science of Mechanics |author=Ernst Mach |edition=2nd |publisher=The Open Court Publishing Company |pages=233 |url= https://books.google.com/books?id=4OE2AAAAMAAJ&pg=PA233}}</ref><ref name=Wheeler>{{cite book |title=Gravitation and Inertia |author=Ignazio Ciufolini, John Archibald Wheeler |pages=386–387 |url=https://books.google.com/books?id=UYIs1ndbi38C&dq=centrifugal+Einstein+rotating+globes&pg=RA1-PA386 |isbn=0-691-03323-4 |year=1995 |publisher=Princeton University Press}}</ref>
{{Blockquote|When, accordingly, we say that a body preserves unchanged its direction and velocity ''in space'', our assertion is nothing more or less than an abbreviated reference to ''the entire universe''.|[[Ernst Mach]] on p. 233 of ''The Science of Mechanics''; also as quoted by [[Ignazio Ciufolini|Ciufolini]] and [[John Archibald Wheeler|Wheeler]]: ''Gravitation and Inertia'' on p. 387.}}