Editing Philosophy of physics

{{Short description|Truths and principles of the study of matter, space, time and energy}}
{{Use dmy dates|date=April 2017}}
{{original research|date=September 2017}}

In [[philosophy]], the '''philosophy of physics''' deals with conceptual and interpretational issues in [[physics]], many of which overlap with research done by certain kinds of [[Theoretical physics|theoretical physicists]]. Historically, philosophers of physics have engaged with questions such as the nature of space, time, matter and the laws that govern their interactions, as well as the epistemological and ontological basis of the theories used by practicing physicists. The discipline draws upon insights from various areas of philosophy, including [[metaphysics]], [[epistemology]], and [[philosophy of science]], while also engaging with the latest developments in theoretical and experimental physics. 

Contemporary work focuses on issues at the foundations of the three pillars of [[modern physics]]:

* [[Quantum mechanics]]: [[Interpretations of quantum mechanics|Interpretations of quantum theory]], including the nature of quantum states, the [[measurement problem]], and the role of [[Observer (quantum physics)|observers]]. Implications of [[Quantum entanglement|entanglement]], [[Quantum nonlocality|nonlocality]], and the quantum-classical relationship are also explored.
* [[Theory of relativity|Relativity]]: Conceptual foundations of [[Special relativity|special]] and [[general relativity]], including the nature of spacetime, simultaneity, causality, and determinism. Compatibility with quantum mechanics, gravitational singularities, and philosophical implications of [[cosmology]] are also investigated.
* [[Statistical mechanics]]: Relationship between microscopic and macroscopic descriptions, interpretation of probability, origin of irreversibility and the [[arrow of time]]. Foundations of thermodynamics, role of information theory in understanding [[entropy]], and implications for explanation and reduction in physics.

Other areas of focus include the nature of [[Scientific law|physical laws]], [[Symmetry|symmetries]], and [[Conservation law|conservation principles]]; the role of mathematics; and philosophical implications of emerging fields like [[quantum gravity]], [[quantum information]], and [[Complex system|complex systems]]. Philosophers of physics have argued that conceptual analysis clarifies foundations, interprets implications, and guides theory development in physics.

==Philosophy of space and time==
{{Main|Philosophy of space and time}}

The existence and nature of space and time (or space-time) are central topics in the philosophy of physics.<ref name="MaudlinSTa">{{cite book|last1=Maudlin|first1=Tim|title=Philosophy of Physics: Space and Time|date=2012|publisher=Princeton University Press|isbn=978-0691143095|page=xi|url=https://books.google.com/books?id=siyNQV8F0y8C&q=central+topic|access-date=3 October 2017|language=en|quote=...the existence and nature of space and time (or space-time) is a central topic.}}</ref> Issues include (1) whether space and time are fundamental or emergent, and (2) how space and time are operationally different from one another.

===Time===
{{Main| Time in physics}}
[[File:Wooden hourglass.jpg|thumb|right|Time, in many philosophies, is seen as change.]]
In classical mechanics, [[time]] is taken to be a [[fundamental quantity]] (that is, a quantity which cannot be defined in terms of other quantities). However, certain theories such as [[loop quantum gravity]] claim that spacetime is emergent. As [[Carlo Rovelli]], one of the founders of loop quantum gravity, has said: "No more fields on spacetime: just fields on fields".<ref>Rovelli, C. (2004). Quantum Gravity. Cambridge Monographs on Mathematical Physics. p. 71.</ref> Time is [[define]]d via measurement—by its standard time interval. Currently, the standard time interval (called "conventional [[second]]", or simply "second") is defined as 9,192,631,770 [[oscillations]] of a [[Hyperfine structure|hyperfine]] transition in the 133 [[caesium]] [[atom]]. ([[ISO 31-1]]). What time is and how it works [[Logical consequence|follows from]] the above definition. Time then can be combined mathematically with the fundamental quantities of [[space]] and [[mass]] to define concepts such as [[velocity]], [[momentum]], [[energy]], and [[Field (physics)|fields]].

Both [[Isaac Newton]] and [[Galileo|Galileo Galilei]],<ref>[[Roger Penrose]], 2004. ''[[The Road to Reality]]: A Complete Guide to the Laws of the Universe''. London: Jonathan Cape. {{ISBN|0-224-04447-8}} (hardcover), 0-09-944068-7 (paperback).
</ref> as well as most people up until the 20th century, thought that time was the same for everyone everywhere.<ref>{{Citation |last=Rynasiewicz |first=Robert |title=Newton's Views on Space, Time, and Motion |date=2022 |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |url=https://plato.stanford.edu/archives/spr2022/entries/newton-stm/ |access-date=2024-07-28 |edition=Spring 2022 |publisher=Metaphysics Research Lab, Stanford University}}</ref> The modern conception of time is based on [[Albert Einstein]]'s theory of relativity and [[Hermann Minkowski]]'s [[spacetime]], in which rates of time run differently in different inertial frames of reference, and [[space]] and time are merged into [[spacetime]]. Einstein's [[general relativity]] as well as the [[redshift]] of the light from receding distant galaxies indicate that the entire [[Universe]] and possibly space-time itself began about [[Age of the universe|13.8 billion years ago]] in the [[Big Bang]]. Einstein's theory of special relativity mostly (though not universally) made theories of time where there is something metaphysically special about the present seem much less plausible, as the reference-frame-dependence of time seems to not allow the idea of a privileged present moment.

===Space===
{{Main|Space}}

Space is one of the few fundamental quantities in physics, meaning that it cannot be defined via other quantities because there is nothing more fundamental known at present. Thus, similar to the definition of other fundamental quantities (like [[time]] and [[mass]]), space is defined via measurement. Currently, the standard space interval, called a standard metre or simply metre, is defined as the [[speed of light|distance traveled by light in a vacuum]] during a time interval of 1/299792458 of a second (exact).

In [[classical physics]], space is a three-dimensional [[Euclidean space]] where any position can be described using three [[coordinate system|coordinate]]s and parameterised by time.  Special and general relativity use four-dimensional [[spacetime]] rather than three-dimensional space; and currently there are many speculative theories which use more than three spatial dimensions.

==Philosophy of quantum mechanics==
{{Main|Quantum foundations}}
[[Quantum mechanics]] is a large focus of contemporary philosophy of physics, specifically concerning the correct interpretation of quantum mechanics. Very broadly, much of the philosophical work that is done in quantum theory is trying to make sense of superposition states:<ref>{{cite web|url=https://www.youtube.com/watch?v=J8k_2oD66mI&t=128| archive-url=https://ghostarchive.org/varchive/youtube/20211211/J8k_2oD66mI| archive-date=2021-12-11 | url-status=live|title=Eleanor Knox (KCL) – The Curious Case of the Vanishing Spacetime|last=BristolPhilosophy|date=19 February 2013|access-date=7 April 2018|via=YouTube}}{{cbignore}}</ref> the property that particles seem to not just be in one determinate position at one time, but are somewhere 'here', and also 'there' at the same time. Such a radical view turns many common sense metaphysical ideas on their head. Much of contemporary philosophy of quantum mechanics aims to make sense of what the very empirically successful formalism of quantum mechanics tells us about the physical world.

===Uncertainty principle===
{{Main|Uncertainty principle}}
The [[uncertainty principle]] is a mathematical relation asserting an upper limit to the accuracy of the simultaneous measurement of any pair of [[conjugate variables]], e.g. position and momentum. In the formalism of [[Operator (physics)#Operators in quantum mechanics|operator notation]], this limit is the evaluation of the [[Canonical commutation relation|commutator]] of the variables' corresponding operators.

The uncertainty principle arose as an answer to the question: How does one measure the location of an electron around a nucleus if an electron is a wave?  When quantum mechanics was developed, it was seen to be a relation between the classical and quantum descriptions of a system using wave mechanics.

==="Locality" and hidden variables===
{{main|EPR paradox|Bell's theorem}}
[[Bell's theorem]] is a term encompassing a number of closely related results in physics, all of which determine that [[quantum mechanics]] is incompatible with [[Local hidden-variable theory|local hidden-variable theories]] given some basic assumptions about the nature of measurement. "Local" here refers to the [[principle of locality]], the idea that a particle can only be influenced by its immediate surroundings, and that interactions mediated by [[Field (physics)|physical fields]] cannot propagate faster than the [[speed of light]]. "[[Hidden-variable theory|Hidden variables]]" are putative properties of quantum particles that are not included in the theory but nevertheless affect the outcome of experiments. In the words of physicist [[John Stewart Bell]], for whom this family of results is named, "If [a hidden-variable theory] is local it will not agree with quantum mechanics, and if it agrees with quantum mechanics it will not be local."<ref>{{cite book  | first = John S. | last = Bell | author-link = John Stewart Bell | title = Speakable and Unspeakable in Quantum Mechanics | publisher = Cambridge University Press | date = 1987  | page = 65 | isbn = 9780521368698 | oclc = 15053677}}</ref>

The term is broadly applied to a number of different derivations, the first of which was introduced by Bell in a 1964 paper titled "On the [[EPR paradox|Einstein Podolsky Rosen Paradox]]". Bell's paper was a response to a 1935 [[thought experiment]] that [[Albert Einstein]], [[Boris Podolsky]] and [[Nathan Rosen]] proposed, arguing that quantum physics is an "incomplete" theory.<ref name="EPR">{{cite journal | title = Can Quantum-Mechanical Description of Physical Reality be Considered Complete? | date = 1935-05-15 | first1 = A. | last1 = Einstein |first2=B. |last2 = Podolsky |first3=N. |last3 = Rosen | author-link1 = Albert Einstein | author-link2 = Boris Podolsky | author-link3 = Nathan Rosen | journal = [[Physical Review]] | volume = 47 | issue = 10 | pages = 777–780 | bibcode = 1935PhRv...47..777E |doi = 10.1103/PhysRev.47.777 | doi-access = free }}</ref><ref name=Bell1964>{{cite journal | last1 = Bell | first1 = J. S. | author-link = John Stewart Bell | year = 1964 | title = On the Einstein Podolsky Rosen Paradox | url = https://cds.cern.ch/record/111654/files/vol1p195-200_001.pdf | journal = [[Physics Physique Физика]] | volume = 1 | issue = 3| pages = 195–200 | doi = 10.1103/PhysicsPhysiqueFizika.1.195 }}</ref> By 1935, it was already recognized that the predictions of quantum physics are [[probability|probabilistic]]. Einstein, Podolsky and Rosen presented a scenario that involves preparing a pair of particles such that the quantum state of the pair is [[quantum entanglement|entangled]], and then separating the particles to an arbitrarily large distance. The experimenter has a choice of possible measurements that can be performed on one of the particles. When they choose a measurement and obtain a result, the quantum state of the other particle apparently [[Wave function collapse|collapses]] instantaneously into a new state depending upon that result, no matter how far away the other particle is.  This suggests that either the measurement of the first particle somehow also influenced the second particle faster than the speed of light, ''or'' that the entangled particles had some unmeasured property which pre-determined their final quantum states before they were separated.  Therefore, assuming locality, quantum mechanics must be incomplete, as it cannot give a complete description of the particle's true physical characteristics. In other words, quantum particles, like [[electron]]s and [[photon]]s, must carry some property or attributes not included in quantum theory, and the uncertainties in quantum theory's predictions would then be due to ignorance or unknowability of these properties, later termed "hidden variables".

Bell carried the analysis of quantum entanglement much further. He deduced that if measurements are performed independently on the two separated particles of an entangled pair, then the assumption that the outcomes depend upon hidden variables within each half implies a mathematical constraint on how the outcomes on the two measurements are correlated. This constraint would later be named the ''Bell inequality''. Bell then showed that quantum physics predicts correlations that violate this inequality. Consequently, the only way that hidden variables could explain the predictions of quantum physics is if they are "nonlocal", which is to say that somehow the two particles can carry non-classical correlations no matter how widely they ever become separated.<ref name="C.B. Parker 1994 542">{{cite book | first = Sybil B. | last = Parker | title = McGraw-Hill Encyclopaedia of Physics | edition = 2nd | page = [https://archive.org/details/mcgrawhillencycl1993park/page/542 542] | date = 1994 | publisher = McGraw-Hill | isbn = 978-0-07-051400-3 | url = https://archive.org/details/mcgrawhillencycl1993park| url-access = registration }}</ref><ref name = "ND Mermin 1993-07">{{cite journal | last = Mermin |first = N. David |author-link=N. David Mermin |title = Hidden Variables and the Two Theorems of John Bell | journal = [[Reviews of Modern Physics]] | volume = 65 |pages = 803–15 | number = 3| date = July 1993  | url = http://cqi.inf.usi.ch/qic/Mermin1993.pdf |arxiv=1802.10119|doi = 10.1103/RevModPhys.65.803 |bibcode = 1993RvMP...65..803M |s2cid = 119546199 }}</ref>

Multiple variations on Bell's theorem were put forward in the following years, introducing other closely related conditions generally known as Bell (or "Bell-type") inequalities. The first rudimentary experiment designed to test Bell's theorem was performed in 1972 by [[John Clauser]] and [[Stuart Freedman]].<ref>{{cite press release |url=https://www.nobelprize.org/prizes/physics/2022/press-release/ |title=The Nobel Prize in Physics 2022 |date=October 4, 2022 |work=[[Nobel Prize]] |publisher=[[The Royal Swedish Academy of Sciences]] |access-date=6 October 2022}}</ref> More advanced experiments, known collectively as [[Bell test]]s, have been performed many times since. To date, Bell tests have consistently found that physical systems obey quantum mechanics and violate Bell inequalities; which is to say that the results of these experiments are incompatible with any local hidden variable theory.<ref name="NAT-20180509">{{cite journal |author=The BIG Bell Test Collaboration |title=Challenging local realism with human choices |date=9 May 2018 |journal=[[Nature (journal)|Nature]] |volume=557 |issue=7704 |pages=212–216 |doi=10.1038/s41586-018-0085-3 |pmid=29743691 |bibcode=2018Natur.557..212B |arxiv=1805.04431 |s2cid=13665914 }}</ref><ref>{{Cite web|url=https://www.quantamagazine.org/physicists-are-closing-the-bell-test-loophole-20170207/|title=Experiment Reaffirms Quantum Weirdness|last=Wolchover|first=Natalie|author-link=Natalie Wolchover|date=2017-02-07|work=[[Quanta Magazine]]|language=en-US|access-date=2020-02-08}}</ref>

The exact nature of the assumptions required to prove a Bell-type constraint on correlations has been debated by physicists and by philosophers. While the significance of Bell's theorem is not in doubt, its full implications for the [[interpretation of quantum mechanics]] remain unresolved.

===Interpretations of quantum mechanics===
{{Main|Interpretation of quantum mechanics}}
In March 1927, working in [[Niels Bohr]]'s institute, [[Werner Heisenberg]] formulated the principle of uncertainty thereby laying the foundation of what became known as the [[Copenhagen interpretation]] of quantum mechanics. Heisenberg had been studying the papers of [[Paul Dirac]] and [[Pascual Jordan]].  He discovered a problem with measurement of basic variables in the equations. His analysis showed that uncertainties, or imprecisions, always turned up if one tried to measure the position and the momentum of a particle at the same time. Heisenberg concluded that these uncertainties or imprecisions in the measurements were not the fault of the experimenter, but fundamental in nature and are inherent mathematical properties of operators in quantum mechanics arising from definitions of these operators.<ref>Niels Bohr, ''Atomic Physics and Human Knowledge'', p. 38</ref>

The Copenhagen interpretation is somewhat loosely defined, as many physicists and philosophers of physics have advanced similar but not identical views of quantum mechanics. It is principally associated with Heisenberg and Bohr, despite their philosophical differences.<ref name="Faye-Stanford">{{Cite book|last=Faye|first=Jan|title=[[Stanford Encyclopedia of Philosophy]]|publisher=Metaphysics Research Lab, Stanford University|year=2019|editor-last=Zalta|editor-first=Edward N.|chapter=Copenhagen Interpretation of Quantum Mechanics|author-link=Jan Faye|chapter-url=https://plato.stanford.edu/entries/qm-copenhagen/}}</ref><ref name="camilleri2015">{{cite journal|first1=K. |last1=Camilleri |first2=M. |last2=Schlosshauer |title=Niels Bohr as Philosopher of Experiment: Does Decoherence Theory Challenge Bohr's Doctrine of Classical Concepts? |arxiv=1502.06547 |journal=Studies in History and Philosophy of Modern Physics |volume=49 |pages=73–83 |year=2015 |doi=10.1016/j.shpsb.2015.01.005|bibcode=2015SHPMP..49...73C |s2cid=27697360 }}</ref> Features common to Copenhagen-type interpretations include the idea that quantum mechanics is intrinsically indeterministic, with probabilities calculated using the [[Born rule]], and the principle of [[Complementarity (physics)|complementarity]], which states that objects have certain pairs of complementary properties that cannot all be observed or measured simultaneously.<ref>{{cite book|last=Omnès |first=Roland |author-link=Roland Omnès |chapter=The Copenhagen Interpretation |title=Understanding Quantum Mechanics |publisher=Princeton University Press |year=1999 |pages=41–54 |doi=10.2307/j.ctv173f2pm.9 |s2cid=203390914 |quote=Bohr, Heisenberg, and Pauli recognized its main difficulties and proposed a first essential answer. They often met in Copenhagen ... 'Copenhagen interpretation has not always meant the same thing to different authors. I will reserve it for the doctrine held with minor differences by Bohr, Heisenberg, and Pauli.}}</ref> Moreover, the act of "observing" or "measuring" an object is irreversible, and no truth can be attributed to an object, [[counterfactual definiteness|except according to the results of its measurement]]. Copenhagen-type interpretations hold that quantum descriptions are objective, in that they are independent of any arbitrary factors in the physicist's mind.<ref name="omnes">{{cite book|first=R. |last=Omnès |author-link=Roland Omnès |title=The Interpretation of Quantum Mechanics |publisher=Princeton University Press |year=1994 |isbn=978-0-691-03669-4 |oclc=439453957 }}</ref>{{Rp|85–90}}

The [[many-worlds interpretation of quantum mechanics]] by [[Hugh Everett III]] claims that the wave-function of a quantum system is telling us claims about the reality of that physical system. It denies wavefunction collapse, and claims that [[superposition principle|superposition]] states should be interpreted literally as describing the reality of many-worlds where objects are located, and not simply indicating the indeterminacy of those variables. This is sometimes argued as a corollary of [[scientific realism]],<ref>David Wallace, 'The Emergent Multiverse', pp. 1–10</ref> which states that scientific theories aim to give us literally true descriptions of the world.

One issue for the Everett interpretation is the role that probability plays on this account. The Everettian account is completely deterministic, whereas probability seems to play an ineliminable role in quantum mechanics.<ref>David Wallace, 'The Emergent Multiverse', pp. 113–117</ref> Contemporary Everettians have argued that one can get an account of probability that follows the Born rule through certain decision-theoretic proofs,<ref>David Wallace, 'The Emergent Multiverse', pg. 157–189</ref> but there is as yet no consensus about whether any of these proofs are successful.<ref name=kent2009>{{Cite book|arxiv=0905.0624|last1=Kent|first1=Adrian|chapter=One world versus many: The inadequacy of Everettian accounts of evolution, probability, and scientific confirmation|title=Many Worlds? Everett, Quantum Theory and Reality |editor=S. Saunders |editor2=J. Barrett |editor3=A. Kent |editor4=D. Wallace |publisher=Oxford University Press|year=2010|bibcode=2009arXiv0905.0624K}}</ref><ref>{{cite journal | last1 = Kent | first1 = Adrian | year = 1990 | title = Against Many-Worlds Interpretations | arxiv = gr-qc/9703089 | journal = International Journal of Modern Physics A | volume = 5 | issue = 9| pages = 1745–1762 |bibcode = 1990IJMPA...5.1745K |doi = 10.1142/S0217751X90000805 | s2cid = 14523184 }}</ref><ref>{{Cite book| last1=Price |first1=Huw | chapter=Decisions, Decisions, Decisions: Can Savage Salvage Everettian Probability?|title=Many Worlds? Everett, Quantum Theory and Reality |editor=S. Saunders |editor2=J. Barrett |editor3=A. Kent |editor4=D. Wallace |publisher=Oxford University Press|year=2010|arxiv = 0802.1390}}</ref>

Physicist [[Roland Omnès]] noted that it is impossible to experimentally differentiate between Everett's view, which says that as the wave-function decoheres into distinct worlds, each of which exists equally, and the more traditional view that says that a decoherent wave-function leaves only one unique real result. Hence, the dispute between the two views represents a great "chasm". "Every characteristic of reality has reappeared in its reconstruction by our theoretical model; every feature except one: the uniqueness of facts."<ref>{{cite book|last1=Omnès|first1=Roland|title=Quantum philosophy : understanding and interpreting contemporary science|date=2002|publisher=Princeton University Press|location=Princeton|isbn=978-1400822867|page=213|edition=1st paperback |others=Arturo Spangalli (transl.)|language=fr|chapter=11}}</ref>

==Philosophy of thermal and statistical physics==
The philosophy of [[Thermal physics|thermal]] and [[Statistical mechanics|statistical physics]] is concerned with the foundational issues and conceptual implications of [[thermodynamics]] and [[statistical mechanics]]. These branches of physics deal with the macroscopic behavior of systems comprising a large number of microscopic entities, such as particles, and the nature of laws that emerge from these systems like [[Irreversible process|irreversibility]] and [[entropy]]. Interest of philosophers in [[statistical mechanics]] first arose from the observation of an apparent conflict between the [[T-symmetry|time-reversal symmetry]] of fundamental physical laws and the [[Irreversible process|irreversibility]] observed in thermodynamic processes, known as the [[arrow of time]] problem. Philosophers have sought to understand how the asymmetric behavior of macroscopic systems, such as the tendency of heat to flow from hot to cold bodies, can be reconciled with the time-symmetric laws governing the motion of individual particles.

Another key issue is the [[Probability interpretations|interpretation of probability]] in [[statistical mechanics]], which is primarily concerned with the question of whether probabilities in statistical mechanics are [[Epistemology|epistemic]], reflecting our lack of knowledge about the precise microstate of a system, or [[Ontology|ontic]], representing an objective feature of the physical world. The epistemic interpretation, also known as the subjective or [[Bayesian]] view, holds that [[Probability|probabilities]] in [[statistical mechanics]] are a measure of our ignorance about the exact state of a system. According to this view, we resort to probabilistic descriptions only due to the practical impossibility of knowing the precise properties of all its micro-constituents, like the positions and momenta of particles. As such, the [[probabilities]] are not objective features of the world but rather arise from our ignorance. In contrast, the [[Ontology|ontic]] interpretation, also called the objective or [[Frequentist probability|frequentist]] view, asserts that probabilities in statistical mechanics are real, physical properties of the system itself. Proponents of this view argue that the probabilistic nature of statistical mechanics is not merely a reflection of our ignorance but an intrinsic feature of the physical world, and that even if we had complete knowledge of the microstate of a system, the macroscopic behavior would still be best described by probabilistic laws.

==History==
===Aristotelian physics===
{{Disputed section|date=September 2022}}
[[Aristotelian physics]] viewed the universe as a [[Sublunary sphere|sphere]] with a center. Matter, composed of the [[classical element#Greece|classical elements]]: earth, water, air, and fire; sought to go down towards the center of the universe, the center of the Earth, or up, away from it. Things in the [[Aether (classical element)|aether]] such as the Moon, the Sun, planets, or stars circled the center of the universe.<ref name = MaudlinPPST3 >[[Tim Maudlin]] (2012-07-22). ''Philosophy of Physics: Space and Time: Space and Time'' (Princeton Foundations of Contemporary Philosophy) (p. 3). Princeton University Press. Kindle Edition. "Because it is a sphere, Aristotle's universe contains a geometrically privileged center, and Aristotle makes reference to that center in characterizing the natural motions of different sorts of matter. 'Upward', 'downward', and 'uniform circular motion' all are defined in terms of the center of the universe."</ref> Movement is defined as change in place,<ref name = MaudlinPPST3 /> i.e. space.<ref name = MaudlinPPST4 >[[Tim Maudlin]] (2012-07-22). ''Philosophy of Physics: Space and Time: Space and Time'' (Princeton Foundations of Contemporary Philosophy) (p. 4). Princeton University Press. Kindle Edition.  "Aristotle adopts the concept of space, and the correlative concept of motion, that we all intuitively employ."</ref>

===Newtonian physics===
The implicit axioms of Aristotelian physics with respect to movement of matter in space were superseded in [[Classical mechanics|Newtonian physics]] by [[Isaac Newton|Newton's]] [[Newton's laws of motion#Newton's first law|first law of motion]].<ref name = MaudlinPPST3-4 >[[Tim Maudlin]] (2012-07-22). ''Philosophy of Physics: Space and Time: Space and Time'' (Princeton Foundations of Contemporary Philosophy) (pp. 4–5). Princeton University Press. Kindle Edition. "Newtonian physics is implicit in his First Law of Motion: Law I : Every body perseveres in its state either of rest or of uniform motion in a straight line, except insofar as it is compelled to change its state by impressed forces. 1 This single law smashes the Aristotelian universe to smithereens."</ref>{{cquote|Every body perseveres in its state either of rest or of uniform motion in a straight line, except insofar as it is compelled to change its state by impressed forces.}}
"Every body" includes the Moon, and an apple; and includes all types of matter, air as well as water, stones, or even a flame. Nothing has a natural or inherent motion.<ref name = MaudlinPPST5>[[Tim Maudlin]] (2012-07-22). ''Philosophy of Physics: Space and Time: Space and Time'' (Princeton Foundations of Contemporary Philosophy) (pp. 5). Princeton University Press. Kindle Edition.</ref> [[Absolute time and space|Absolute space]] being [[three-dimensional space|three-dimensional]] [[Euclidean space]], infinite and without a center.<ref name = MaudlinPPST5 /> Being "at rest" means being at the same place in absolute space over time.<ref name = MaudlinPPST9-10  >[[Tim Maudlin]] (2012-07-22). ''Philosophy of Physics: Space and Time: Space and Time'' (Princeton Foundations of Contemporary Philosophy) (pp. 9–10). Princeton University Press. Kindle Edition. "Newton believed in the existence of a spatial arena with the geometrical structure of E{{smallsup|3}}. He believed that this infinite three-dimensional space exists at every moment of time. And he also believed something much more subtle and controversial, namely, that identically the same points of space persist through time."</ref> The [[topology]] and [[Affine space|affine structure]] of space must permit movement in a [[Line (geometry)|straight line]] at a uniform velocity; thus both space and time must have [[Absolute time and space|definite, stable dimensions]].<ref name = Maudlin12 >[[Tim Maudlin]] (2012-07-22). ''Philosophy of Physics: Space and Time: Space and Time'' (Princeton Foundations of Contemporary Philosophy) (p. 12). Princeton University Press. Kindle Edition. "...space must have a topology, an affine structure, and a metric; time must be one-dimensional with a topology and a metric; and, most importantly, the individual parts of space must persist through time.</ref>

===Leibniz===
[[Gottfried Wilhelm Leibniz]], 1646–1716, was a contemporary of Newton. He contributed a fair amount to the statics and dynamics emerging around him, often disagreeing with [[Descartes]] and [[Isaac Newton|Newton]]. He devised a new theory of [[Motion (physics)|motion]] ([[Dynamics (mechanics)|dynamics]]) based on [[kinetic energy]] and [[potential energy]], which posited space as relative, whereas Newton was thoroughly convinced that space was absolute. An important example of Leibniz's mature physical thinking is his ''Specimen Dynamicum'' of 1695.<ref>Ariew and Garber 117, Loemker §46, W II.5. On Leibniz and physics, see the chapter by Garber in Jolley (1995) and Wilson (1989).</ref>

Until the discovery of subatomic particles and the [[quantum mechanics]] governing them, many of Leibniz's speculative ideas about aspects of nature not reducible to statics and dynamics made little sense.

He anticipated Albert Einstein by arguing, against Newton, that [[space]], [[time]] and motion are relative, not absolute:<ref name=Ferraro>{{cite book |title =Einstein's Space-Time: An Introduction to Special and General Relativity|page= 1| url=https://books.google.com/books?id=wa3CskhHaIgC&q=time+%22absolute+space%22&pg=PA1|author=Rafael Ferraro |isbn=978-0-387-69946-2 |publisher=Springer |year=2007}}</ref> "As for my own opinion, I have said more than once, that I hold space to be something merely relative, as time is, that I hold it to be an order of coexistences, as time is an order of successions."<ref>See H. G. Alexander, ed., ''The [[Leibniz-Clarke Correspondence]]'', Manchester: Manchester University Press, pp. 25–26.</ref>

==See also==
{{Portal|Philosophy|Physics}}
{{Div col|colwidth=23em}}
* [[Anthropic principle]]
* [[Arrow of time]]
* [[Causality (physics)]]
* [[Causal closure]]
* [[Determinism]]
* [[Digital physics]]
* [[Mind-body dualism]]
* [[Functional decomposition]]
* [[Holism]]
* [[Instrumentalism]]
* [[Laws of thermodynamics]]
* [[Modal realism]]
* [[Monism]]
* [[Physical ontology]]
* [[Naturalism (philosophy)|Naturalism]]:
** [[Metaphysical naturalism|Metaphysical]]
** [[Methodological naturalism|Methodological]]
* [[Operationalism]]
** [[Phenomenology (particle physics)]]
* [[Philosophy of science|Philosophy of]]:
** [[Philosophical interpretation of classical physics|Classical physics]]
** [[Philosophy of space and time|Space and time]]
** [[Philosophy of thermal and statistical physics|Thermodynamics and statistical mechanics]]
**[[Philosophy of motion|Motion]]
* Physical
** [[Physical bodies|Bodies]]
** [[Physical law|Law]]
** [[Physical system|System]]
* [[Physicalism]]
* [[Physics]]
** [[Physics (Aristotle)|Aristotle]]
* [[Physics envy]]
* [[Quantum mechanics|Quantum theory]]:
** [[Bohr-Einstein debates]]
** [[Einstein's thought experiments]]
** [[EPR paradox]]
** [[Interpretation of quantum mechanics|Interpretations of]]
** [[Quantum metaphysics|Metaphysics]]
** [[Quantum mysticism|Mysticism]]
* [[Reductionism]]
* [[Theory of relativity|Relativity]]:
** [[Introduction to general relativity|General]]
** [[Special relativity|Special]]
* [[Space]]
** [[Absolute theory]]
** [[Container space]]
** [[Free space]]
** [[Relational space]]
** [[Relational theory]]
** [[Spacetime]]
* [[Supervenience]]
* [[Symmetry in physics]]
* [[Theophysics]]
* [[Time in physics]]
{{Div col end}}

==References==
{{Reflist}}

== Further reading ==
* [[David Albert]], 1994. ''Quantum Mechanics and Experience''. Harvard Univ. Press.
* [[John D. Barrow]] and [[Frank J. Tipler]], 1986. ''[[Anthropic principle|The Cosmological Anthropic Principle]]''. Oxford Univ. Press.
* Beisbart, C. and S. Hartmann, eds., 2011. "Probabilities in Physics". Oxford Univ. Press.
* [[John S. Bell]], 2004 (1987), ''Speakable and Unspeakable in Quantum Mechanics''. Cambridge Univ. Press.
* [[David Bohm]], 1980. ''[[Wholeness and the Implicate Order]]''. Routledge.
* [[Nick Bostrom]], 2002. ''[https://web.archive.org/web/20060826121429/http://www.anthropic-principle.com/book/ Anthropic Bias: Observation Selection Effects in Science and Philosophy]''. Routledge.
* Thomas Brody, 1993, Ed. by [[Luis de la Peña]] and [[Peter E. Hodgson]] ''The Philosophy Behind Physics'' Springer {{ISBN|3-540-55914-0}}
* [[Harvey Brown (philosopher)|Harvey Brown]], 2005. ''Physical Relativity. Space-time structure from a dynamical perspective''. Oxford Univ. Press.
* Butterfield, J., and [[John Earman]], eds., 2007. ''Philosophy of Physics, Parts A and B''. Elsevier.
* [[Craig Callender]] and Nick Huggett, 2001. ''Physics Meets Philosophy at the [[Planck Scale]]''. Cambridge Univ. Press.
* [[David Deutsch]], 1997. ''[[The Fabric of Reality]]''. London: The Penguin Press.
* [[Bernard d'Espagnat]], 1989. ''Reality and the Physicist''. Cambridge Univ. Press. Trans. of ''Une incertaine réalité; le monde quantique, la connaissance et la durée''.
* --------, 1995. ''Veiled Reality''. Addison-Wesley.
* --------, 2006. ''On Physics and Philosophy''. Princeton Univ. Press.
* [[Roland Omnès]], 1994. ''The Interpretation of Quantum Mechanics''. Princeton Univ. Press.
* --------, 1999. ''[[Quantum Philosophy]]''. Princeton Univ. Press.
* Huw Price, 1996. ''Time's Arrow and Archimedes's Point''. Oxford Univ. Press.
* Lawrence Sklar, 1992. ''Philosophy of Physics''. Westview Press. {{ISBN|0-8133-0625-6}}, {{ISBN|978-0-8133-0625-4}}
* [[Victor Stenger]], 2000. ''Timeless Reality''. Prometheus Books.
* [[Carl Friedrich von Weizsäcker]], 1980. ''The Unity of Nature''. Farrar Straus & Giroux.
* [[Werner Heisenberg]], 1971. ''Physics and Beyond: Encounters and Conversations''. Harper & Row (''World Perspectives'' series), 1971.
* [[William Berkson]], 1974. ''Fields of Force''. Routledge and Kegan Paul, London. {{ISBN|0-7100-7626-6}}
* [http://www.britannica.com/topic/philosophy-of-physics Encyclopædia Britannica, Philosophy of Physics, David Z. Albert]

==External links==
{{Commons category}}
* [http://plato.stanford.edu/ Stanford Encyclopedia of Philosophy]:
** "[http://plato.stanford.edu/entries/spacetime-theories/ Absolute and Relational Theories of Space and Motion]"—Nick Huggett and Carl Hoefer
** "[http://plato.stanford.edu/entries/spacetime-bebecome/ Being and Becoming in Modern Physics]"—Steven Savitt
** "[http://plato.stanford.edu/entries/statphys-Boltzmann/ Boltzmann's Work in Statistical Physics]"—Jos Uffink
** "[http://plato.stanford.edu/entries/spacetime-convensimul/ Conventionality of Simultaneity]"—Allen Janis
** "[http://plato.stanford.edu/entries/genrel-early/ Early Philosophical Interpretations of General Relativity]"—Thomas A. Ryckman
** "[http://plato.stanford.edu/entries/qm-everett/ Everett's Relative-State Formulation of Quantum Mechanics]"—Jeffrey A. Barrett 
** "[http://plato.stanford.edu/entries/physics-experiment/ Experiments in Physics]"—Allan Franklin
** "[http://plato.stanford.edu/entries/physics-holism/ Holism and Nonseparability in Physics]"—Richard Healey
** "[http://plato.stanford.edu/entries/physics-interrelate/ Intertheory Relations in Physics]"—Robert Batterman
** "[http://plato.stanford.edu/entries/naturalism/ Naturalism]"—David Papineau
** "[http://plato.stanford.edu/entries/statphys-statmech/ Philosophy of Statistical Mechanics]"—Lawrence Sklar
** "[http://plato.stanford.edu/entries/physicalism/ Physicalism]"—Daniel Sojkal
** "[http://plato.stanford.edu/entries/qm/ Quantum Mechanics]"—Jenann Ismael
** "[http://plato.stanford.edu/entries/physics-Rpcc/ Reichenbach's Common Cause Principle]"—Frank Artzenius
** "[http://plato.stanford.edu/entries/structural-realism/ Structural Realism]"—James Ladyman
** "[http://plato.stanford.edu/entries/physics-structuralism/ Structuralism in Physics]"—Heinz-Juergen Schmidt
** "[https://plato.stanford.edu/entries/spacetime-supertasks/ Supertasks]"—JB Manchak and Bryan Roberts
** "[http://plato.stanford.edu/entries/symmetry-breaking/ Symmetry and Symmetry Breaking]"—[[Katherine Brading]] and Elena Castellani
** "[http://plato.stanford.edu/entries/time-thermo/ Thermodynamic Asymmetry in Time]"—Craig Callender
** "[http://plato.stanford.edu/entries/time/ Time]"—by [[Ned Markosian]]
** "[https://plato.stanford.edu/entries/time-machine/ Time Machines]" —John Earman, Chris Wüthrich, and JB Manchak
** "[http://plato.stanford.edu/entries/qt-uncertainty/ Uncertainty principle]"—Jan Hilgevoord and Jos Uffink
** "[http://plato.stanford.edu/entries/scientific-unity/ The Unity of Science]"—Jordi Cat

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