Editing Absolute space and time (section)

==Differing views==
[[Image:Rotating spheres.svg|thumb|upright=1|Two spheres orbiting around an axis. The spheres are distant enough for their effects on each other to be ignored, and they are held together by a rope. If the rope is under tension, it is because the bodies are rotating relative to absolute space according to [[Rotating spheres|Newton]], or because they rotate relative to the universe itself according to [[Mach's principle|Mach]], or because they rotate relative to local [[Geodesics in general relativity|geodesics]] according to [[general relativity]].]]
Historically, there have been differing views on the concept of absolute space and time. [[Gottfried Leibniz]] was of the opinion that space made no sense except as the relative location of bodies, and time made no sense except as the relative movement of bodies.<ref name="Ferraro">{{citation|title=Einstein's Space-Time: An Introduction to Special and General Relativity|first1=Rafael|last1=Ferraro|publisher=Springer Science & Business Media|date=2007|isbn=9780387699462|bibcode=2007esti.book.....F}}</ref> [[George Berkeley]] suggested that, lacking any point of reference, a sphere in an otherwise empty universe could not be conceived to rotate, and a pair of spheres could be conceived to rotate relative to one another, but not to rotate about their center of gravity,<ref name="Davies">{{cite book |author=Davies |first1=Paul |url=https://books.google.com/books?id=vlmEIGiZ0g4C&pg=PA70 |title=The Matter Myth: Dramatic Discoveries that Challenge Our Understanding of Physical Reality |last2=Gribbin |first2=John |date=2007 |publisher=[[Simon & Schuster]] |isbn=978-0-7432-9091-3 |page=70 |language=en-us}}</ref> an example later raised by [[Albert Einstein]] in his development of general relativity.

A more recent form of these objections was made by [[Ernst Mach]]. [[Mach's principle]] proposes that mechanics is entirely about relative motion of bodies and, in particular, [[mass]] is an expression of such relative motion. So, for example, a single particle in a universe with no other bodies would have zero mass. According to Mach, Newton's examples simply illustrate relative rotation of spheres and the bulk of the universe.<ref name=Wheeler>Ernst Mach; as quoted by {{cite book |title=Gravitation and Inertia |author=Ignazio Ciufolini |author2=John Archibald Wheeler |pages=386–387 |url=https://books.google.com/books?id=UYIs1ndbi38C&pg=RA1-PA386|isbn=978-0-691-03323-5 |date=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''.<br />&mdash;Ernst Mach<ref>as quoted by [[Ignazio Ciufolini|Ciufolini]] and [[John Archibald Wheeler|Wheeler]]: ''Gravitation and Inertia'', p.&nbsp;387</ref></blockquote>

These views opposing absolute space and time may be seen from a modern stance as an attempt to introduce [[operational definition]]s for space and time, a perspective made explicit in the special theory of relativity.

Even within the context of Newtonian mechanics, the modern view is that absolute space is unnecessary. Instead, the notion of [[inertial frame of reference]] has taken precedence, that is, [[preferred frame|a preferred ''set'' of frames of reference]] that move uniformly with respect to one another. The laws of physics transform from one inertial frame to another according to [[Galilean invariance|Galilean relativity]], leading to the following objections to absolute space, as outlined by Milutin Blagojević:<ref name="Blagojević2">{{cite book |author=Blagojević |first=Milutin |url=https://books.google.com/books?id=N8JDSi_eNbwC&pg=PA5 |title=Gravitation and Gauge Symmetries |date=2002 |publisher=[[CRC Press]] |isbn=978-0-7503-0767-3 |page=5}}</ref>

<blockquote>
* The existence of absolute space contradicts the internal logic of classical mechanics since, according to Galilean principle of relativity, none of the inertial frames can be singled out.
* Absolute space does not explain inertial forces since they are related to acceleration with respect to any one of the inertial frames.
* Absolute space acts on physical objects by inducing their resistance to acceleration but it cannot be acted upon.
</blockquote>

Newton himself recognized the role of inertial frames.<ref name="Principia">{{Cite book |last1=Newton |first1=Isaac |url=http://archive.org/details/newtonspmathema00newtrich |title=Newton's Principia : the mathematical principles of natural philosophy |last2=Chittenden |first2=N. W. Life of Sir Isaac Newton |last3=Adee |first3=Daniel |last4=Motte |first4=Andrew |last5=Hill |first5=Theodore Preston Early American mathematics books CU-BANC |date=1846 |publisher=New-York : Published by Daniel Adee |others=University of California Libraries |page=88}}</ref>

<blockquote>The motions of bodies included in a given space are the same among themselves, whether that space is at rest or moves uniformly forward in a straight line.</blockquote>

As a practical matter, inertial frames often are taken as frames moving uniformly with respect to the [[fixed stars]].<ref name="Moeller">{{cite book |author=Møller |first=C. |title=The Theory of Relativity |date=1976 |publisher=[[Oxford University Press]] |isbn=978-0-19-560539-6 |edition=Second |location=Oxford, UK |page=1 |language=en-uk |oclc=220221617}}</ref> See [[Inertial frame of reference]] for more discussion on this.