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Philosophy of physics

In philosophy, philosophy of physics deals with conceptual and interpretational issues in modern physics, many of which overlap with research done by certain kinds of theoretical physicists. Philosophy of physics can be broadly divided into three areas:

  • interpretations of quantum mechanics: mainly concerning issues with how to formulate an adequate response to the measurement problem and understand what the theory says about reality.
  • the nature of space and time: Are space and time substances, or purely relational? Is simultaneity conventional or only relative? Is temporal asymmetry purely reducible to thermodynamic asymmetry?
  • inter-theoretic relations: the relationship between various physical theories, such as thermodynamics and statistical mechanics. This overlaps with the issue of scientific reduction.

Philosophy of space and time edit

The existence and nature of space and time (or space-time) are central topics in the philosophy of physics.[1]

Time edit

 
Time, in many philosophies, is seen as change.

Time is often thought to be a fundamental quantity (that is, a quantity which cannot be defined in terms of other quantities), because time seems like a fundamentally basic concept, such that one cannot define it in terms of anything simpler. 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".[2] Time is defined 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 transition in the 133 caesium atom. (ISO 31-1). What time is and how it works 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 fields.

Both Newton and Galileo,[3] as well as most people up until the 20th century, thought that time was the same for everyone everywhere. The modern conception of time is based on Einstein's theory of relativity and 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 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.

Time travel edit

Some theories, most notably general relativity, suggest that suitable geometries of spacetime, or certain types of motion in space, may allow time travel into the past and future. Concepts that aid such understanding include the closed timelike curve.

Albert Einstein's special theory of relativity (and, by extension, the general theory) predicts time dilation that could be interpreted as time travel. The theory states that, relative to a stationary observer, time appears to pass more slowly for faster-moving bodies: for example, a moving clock will appear to run slow; as a clock approaches the speed of light its hands will appear to nearly stop moving. The effects of this sort of time dilation are discussed further in the popular "twin paradox". Although these results are experimentally observable, an intrinsic aspect of Einstein' theory is an equation applicable to the operation of GPS satellites and other high-tech systems used in daily life.

A second, similar type of time travel is permitted by general relativity. In this type a distant observer sees time passing more slowly for a clock at the bottom of a deep gravity well, and a clock lowered into a deep gravity well and pulled back up will indicate that less time has passed compared to a stationary clock that stayed with the distant observer.

Many in the scientific community believe that backward time travel is highly unlikely, because it violates causality[4] i.e. the logic of cause and effect. For example, what happens if you attempt to go back in time and kill yourself at an earlier stage in your life (or your grandfather, which leads to the grandfather paradox)? Stephen Hawking once suggested that the absence of tourists from the future constitutes a strong argument against the existence of time travel— a variant of the Fermi paradox, with time travelers instead of alien visitors.[4]

Space edit

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 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 coordinates 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 four spatial dimensions.

Philosophy of quantum mechanics edit

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:[5] 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 edit

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 notation, this limit is the evaluation of the 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 edit

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 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 physical fields cannot propagate faster than the speed of light. "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."[6]

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 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.[7][8] By 1935, it was already recognized that the predictions of quantum physics are probabilistic. Einstein, Podolsky and Rosen presented a scenario that involves preparing a pair of particles such that the quantum state of the pair is 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 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 interacted with the second particle at 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 electrons and photons, 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 are able to interact instantaneously no matter how widely they ever become separated.[9][10]

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.[11] More advanced experiments, known collectively as Bell tests, 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.[12][13]

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 edit

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.[14]

The term "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.[15][16] 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, which states that objects have certain pairs of complementary properties that cannot all be observed or measured simultaneously.[17] Moreover, the act of "observing" or "measuring" an object is irreversible, and no truth can be attributed to an object, 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.[18]: 85–90 

The Everett, or many-worlds interpretation of quantum mechanics 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 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,[19] 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.[20] Contemporary Everettians have argued that one can get an account of probability that follows the Born rule through certain decision-theoretic proofs,[21] but there is as yet no consensus about whether any of these proofs are successful.[22][23][24]

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."[25]

Philosophy of thermal and statistical physics edit

The philosophy of thermal and statistical physics is that part of the philosophy of physics whose subject matter is an amalgam of classical thermodynamics, statistical mechanics, and related theories. Its central questions include: What is entropy, and what does the second law of thermodynamics say about it? What is the correct resolution of the Maxwell's demon paradox? Does either thermodynamics or statistical mechanics contain an element of time-irreversibility? If so, what does statistical mechanics tell us about the arrow of time? What is the nature of the probabilities that appear in statistical mechanics?[26]

History edit

Aristotelian physics edit

Aristotelian physics viewed the universe as a sphere with a center. Matter, composed of the 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 such as the Moon, the Sun, planets, or stars circled the center of the universe.[27] Movement is defined as change in place,[27] i.e. space.[28]

Newtonian physics edit

The implicit axioms of Aristotelian physics with respect to movement of matter in space were superseded in Newtonian physics by Newton's First Law of Motion.[29]

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.[30] Absolute space being three-dimensional Euclidean space, infinite and without a center.[30] Being "at rest" means being at the same place in absolute space over time.[31] The topology and affine structure of space must permit movement in a straight line at a uniform velocity; thus both space and time must have definite, stable dimensions.[32]

Leibniz edit

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 Newton. He devised a new theory of motion (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.[33]

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:[34] "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."[35]

See also edit

References edit

  1. ^ Maudlin, Tim (2012). Philosophy of Physics: Space and Time. Princeton University Press. p. xi. ISBN 978-0691143095. Retrieved 3 October 2017. ...the existence and nature of space and time (or space-time) is a central topic.
  2. ^ Rovelli, C. (2004). Quantum Gravity. Cambridge Monographs on Mathematical Physics. p. 71.
  3. ^ 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).
  4. ^ a b Bolonkin, Alexander (2011). Universe, Human mmortality and Future Human Evaluation. Elsevier. p. 32. ISBN 978-0-12-415810-8. Extract of page 32
  5. ^ BristolPhilosophy (19 February 2013). "Eleanor Knox (KCL) – The Curious Case of the Vanishing Spacetime". Archived from the original on 11 December 2021. Retrieved 7 April 2018 – via YouTube.
  6. ^ Bell, John S. (1987). Speakable and Unspeakable in Quantum Mechanics. Cambridge University Press. p. 65. ISBN 9780521368698. OCLC 15053677.
  7. ^ Einstein, A.; Podolsky, B.; Rosen, N. (15 May 1935). "Can Quantum-Mechanical Description of Physical Reality be Considered Complete?". Physical Review. 47 (10): 777–780. Bibcode:1935PhRv...47..777E. doi:10.1103/PhysRev.47.777.
  8. ^ Bell, J. S. (1964). "On the Einstein Podolsky Rosen Paradox" (PDF). Physics Physique Физика. 1 (3): 195–200. doi:10.1103/PhysicsPhysiqueFizika.1.195.
  9. ^ Parker, Sybil B. (1994). McGraw-Hill Encyclopaedia of Physics (2nd ed.). McGraw-Hill. p. 542. ISBN 978-0-07-051400-3.
  10. ^ Mermin, N. David (July 1993). "Hidden Variables and the Two Theorems of John Bell" (PDF). Reviews of Modern Physics. 65 (3): 803–15. arXiv:1802.10119. Bibcode:1993RvMP...65..803M. doi:10.1103/RevModPhys.65.803. S2CID 119546199.
  11. ^ "The Nobel Prize in Physics 2022". Nobel Prize (Press release). The Royal Swedish Academy of Sciences. 4 October 2022. Retrieved 6 October 2022.
  12. ^ The BIG Bell Test Collaboration (9 May 2018). "Challenging local realism with human choices". Nature. 557 (7704): 212–216. arXiv:1805.04431. Bibcode:2018Natur.557..212B. doi:10.1038/s41586-018-0085-3. PMID 29743691. S2CID 13665914.
  13. ^ Wolchover, Natalie (7 February 2017). "Experiment Reaffirms Quantum Weirdness". Quanta Magazine. Retrieved 8 February 2020.
  14. ^ Niels Bohr, Atomic Physics and Human Knowledge, p. 38
  15. ^ Faye, Jan (2019). "Copenhagen Interpretation of Quantum Mechanics". In Zalta, Edward N. (ed.). Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.
  16. ^ Camilleri, K.; Schlosshauer, M. (2015). "Niels Bohr as Philosopher of Experiment: Does Decoherence Theory Challenge Bohr's Doctrine of Classical Concepts?". Studies in History and Philosophy of Modern Physics. 49: 73–83. arXiv:1502.06547. Bibcode:2015SHPMP..49...73C. doi:10.1016/j.shpsb.2015.01.005. S2CID 27697360.
  17. ^ Omnès, Roland (1999). "The Copenhagen Interpretation". Understanding Quantum Mechanics. Princeton University Press. pp. 41–54. doi:10.2307/j.ctv173f2pm.9. S2CID 203390914. 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.
  18. ^ Omnès, R. (1994). The Interpretation of Quantum Mechanics. Princeton University Press. ISBN 978-0-691-03669-4. OCLC 439453957.
  19. ^ David Wallace, 'The Emergent Multiverse', pp. 1–10
  20. ^ David Wallace, 'The Emergent Multiverse', pp. 113–117
  21. ^ David Wallace, 'The Emergent Multiverse', pg. 157–189
  22. ^ Kent, Adrian (2010). "One world versus many: The inadequacy of Everettian accounts of evolution, probability, and scientific confirmation". In S. Saunders; J. Barrett; A. Kent; D. Wallace (eds.). Many Worlds? Everett, Quantum Theory and Reality. Oxford University Press. arXiv:0905.0624. Bibcode:2009arXiv0905.0624K.
  23. ^ Kent, Adrian (1990). "Against Many-Worlds Interpretations". International Journal of Modern Physics A. 5 (9): 1745–1762. arXiv:gr-qc/9703089. Bibcode:1990IJMPA...5.1745K. doi:10.1142/S0217751X90000805. S2CID 14523184.
  24. ^ Price, Huw (2010). "Decisions, Decisions, Decisions: Can Savage Salvage Everettian Probability?". In S. Saunders; J. Barrett; A. Kent; D. Wallace (eds.). Many Worlds? Everett, Quantum Theory and Reality. Oxford University Press. arXiv:0802.1390.
  25. ^ Omnès, Roland (2002). "11". Quantum philosophy : understanding and interpreting contemporary science (in French). Arturo Spangalli (transl.) (1st paperback ed.). Princeton: Princeton University Press. p. 213. ISBN 978-1400822867.
  26. ^ Frigg, Roman; Werndl, Charlotte (10 January 2023). "Philosophy of Statistical Mechanics". In Zalta, Edward N. (ed.). Stanford Encyclopedia of Philosophy.
  27. ^ a b 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."
  28. ^ 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."
  29. ^ 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."
  30. ^ a b 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.
  31. ^ 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 E3. 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."
  32. ^ 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.
  33. ^ Ariew and Garber 117, Loemker §46, W II.5. On Leibniz and physics, see the chapter by Garber in Jolley (1995) and Wilson (1989).
  34. ^ Rafael Ferraro (2007). Einstein's Space-Time: An Introduction to Special and General Relativity. Springer. p. 1. ISBN 978-0-387-69946-2.
  35. ^ See H. G. Alexander, ed., The Leibniz-Clarke Correspondence, Manchester: Manchester University Press, pp. 25–26.

Further reading edit

External links edit

  • Stanford Encyclopedia of Philosophy:
    • "Absolute and Relational Theories of Space and Motion"—Nick Huggett and Carl Hoefer
    • "Being and Becoming in Modern Physics"—Steven Savitt
    • "Boltzmann's Work in Statistical Physics"—Jos Uffink
    • "Conventionality of Simultaneity"—Allen Janis
    • "Early Philosophical Interpretations of General Relativity"—Thomas A. Ryckman
    • "Everett's Relative-State Formulation of Quantum Mechanics"—Jeffrey A. Barrett
    • "Experiments in Physics"—Allan Franklin
    • "Holism and Nonseparability in Physics"—Richard Healey
    • "Intertheory Relations in Physics"—Robert Batterman
    • "Naturalism"—David Papineau
    • "Philosophy of Statistical Mechanics"—Lawrence Sklar
    • "Physicalism"—Daniel Sojkal
    • "Quantum Mechanics"—Jenann Ismael
    • "Reichenbach's Common Cause Principle"—Frank Artzenius
    • "Structural Realism"—James Ladyman
    • "Structuralism in Physics"—Heinz-Juergen Schmidt
    • "Supertasks"—JB Manchak and Bryan Roberts
    • "Symmetry and Symmetry Breaking"—Katherine Brading and Elena Castellani
    • "Thermodynamic Asymmetry in Time"—Craig Callender
    • "Time"—by Ned Markosian
    • "Time Machines" —John Earman, Chris Wüthrich, and JB Manchak
    • "Uncertainty principle"—Jan Hilgevoord and Jos Uffink
    • "The Unity of Science"—Jordi Cat

philosophy, physics, this, article, possibly, contains, original, research, please, improve, verifying, claims, made, adding, inline, citations, statements, consisting, only, original, research, should, removed, september, 2017, learn, when, remove, this, temp. This article possibly contains original research Please improve it by verifying the claims made and adding inline citations Statements consisting only of original research should be removed September 2017 Learn how and when to remove this template message In philosophy philosophy of physics deals with conceptual and interpretational issues in modern physics many of which overlap with research done by certain kinds of theoretical physicists Philosophy of physics can be broadly divided into three areas interpretations of quantum mechanics mainly concerning issues with how to formulate an adequate response to the measurement problem and understand what the theory says about reality the nature of space and time Are space and time substances or purely relational Is simultaneity conventional or only relative Is temporal asymmetry purely reducible to thermodynamic asymmetry inter theoretic relations the relationship between various physical theories such as thermodynamics and statistical mechanics This overlaps with the issue of scientific reduction Contents 1 Philosophy of space and time 1 1 Time 1 2 Time travel 1 3 Space 2 Philosophy of quantum mechanics 2 1 Uncertainty principle 2 2 Locality and hidden variables 2 3 Interpretations of quantum mechanics 3 Philosophy of thermal and statistical physics 4 History 4 1 Aristotelian physics 4 2 Newtonian physics 4 3 Leibniz 5 See also 6 References 7 Further reading 8 External linksPhilosophy of space and time editMain article Philosophy of space and time The existence and nature of space and time or space time are central topics in the philosophy of physics 1 Time edit Main article Time in physics nbsp Time in many philosophies is seen as change Time is often thought to be a fundamental quantity that is a quantity which cannot be defined in terms of other quantities because time seems like a fundamentally basic concept such that one cannot define it in terms of anything simpler 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 2 Time is defined 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 transition in the 133 caesium atom ISO 31 1 What time is and how it works 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 fields Both Newton and Galileo 3 as well as most people up until the 20th century thought that time was the same for everyone everywhere The modern conception of time is based on Einstein s theory of relativity and 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 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 Time travel edit Main article Time travel Some theories most notably general relativity suggest that suitable geometries of spacetime or certain types of motion in space may allow time travel into the past and future Concepts that aid such understanding include the closed timelike curve Albert Einstein s special theory of relativity and by extension the general theory predicts time dilation that could be interpreted as time travel The theory states that relative to a stationary observer time appears to pass more slowly for faster moving bodies for example a moving clock will appear to run slow as a clock approaches the speed of light its hands will appear to nearly stop moving The effects of this sort of time dilation are discussed further in the popular twin paradox Although these results are experimentally observable an intrinsic aspect of Einstein theory is an equation applicable to the operation of GPS satellites and other high tech systems used in daily life A second similar type of time travel is permitted by general relativity In this type a distant observer sees time passing more slowly for a clock at the bottom of a deep gravity well and a clock lowered into a deep gravity well and pulled back up will indicate that less time has passed compared to a stationary clock that stayed with the distant observer Many in the scientific community believe that backward time travel is highly unlikely because it violates causality 4 i e the logic of cause and effect For example what happens if you attempt to go back in time and kill yourself at an earlier stage in your life or your grandfather which leads to the grandfather paradox Stephen Hawking once suggested that the absence of tourists from the future constitutes a strong argument against the existence of time travel a variant of the Fermi paradox with time travelers instead of alien visitors 4 Space edit Main article 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 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 coordinates 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 four spatial dimensions Philosophy of quantum mechanics editMain article 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 5 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 edit Main article 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 notation this limit is the evaluation of the 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 edit Main articles EPR paradox and 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 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 physical fields cannot propagate faster than the speed of light 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 6 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 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 7 8 By 1935 it was already recognized that the predictions of quantum physics are probabilistic Einstein Podolsky and Rosen presented a scenario that involves preparing a pair of particles such that the quantum state of the pair is 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 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 interacted with the second particle at 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 electrons and photons 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 are able to interact instantaneously no matter how widely they ever become separated 9 10 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 11 More advanced experiments known collectively as Bell tests 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 12 13 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 edit Main article 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 14 The term 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 15 16 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 which states that objects have certain pairs of complementary properties that cannot all be observed or measured simultaneously 17 Moreover the act of observing or measuring an object is irreversible and no truth can be attributed to an object 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 18 85 90 The Everett or many worlds interpretation of quantum mechanics 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 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 19 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 20 Contemporary Everettians have argued that one can get an account of probability that follows the Born rule through certain decision theoretic proofs 21 but there is as yet no consensus about whether any of these proofs are successful 22 23 24 Physicist Roland Omnes 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 25 Philosophy of thermal and statistical physics editThe philosophy of thermal and statistical physics is that part of the philosophy of physics whose subject matter is an amalgam of classical thermodynamics statistical mechanics and related theories Its central questions include What is entropy and what does the second law of thermodynamics say about it What is the correct resolution of the Maxwell s demon paradox Does either thermodynamics or statistical mechanics contain an element of time irreversibility If so what does statistical mechanics tell us about the arrow of time What is the nature of the probabilities that appear in statistical mechanics 26 History editAristotelian physics edit This section s factual accuracy is disputed Relevant discussion may be found on Talk Philosophy of physics Please help to ensure that disputed statements are reliably sourced September 2022 Learn how and when to remove this template message Aristotelian physics viewed the universe as a sphere with a center Matter composed of the 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 such as the Moon the Sun planets or stars circled the center of the universe 27 Movement is defined as change in place 27 i e space 28 Newtonian physics editThe implicit axioms of Aristotelian physics with respect to movement of matter in space were superseded in Newtonian physics by Newton s First Law of Motion 29 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 30 Absolute space being three dimensional Euclidean space infinite and without a center 30 Being at rest means being at the same place in absolute space over time 31 The topology and affine structure of space must permit movement in a straight line at a uniform velocity thus both space and time must have definite stable dimensions 32 Leibniz edit 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 Newton He devised a new theory of motion 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 33 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 34 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 35 See also edit nbsp Philosophy portal nbsp Physics portalAnthropic principle Arrow of time Causality physics Causal closure Constructor theory Determinism Digital physics Mind body dualism Field physics Functional decomposition Fundamental interaction Holism Instrumentalism Laws of thermodynamics Macroscopic Mesoscopic scale Modal realism Monism Pluralism Physical ontology Naturalism Metaphysical Methodological Operationalism Phenomenology Phenomenology particle physics Philosophy of Classical physics Space and time Thermodynamics and statistical mechanics Motion Physical Bodies Law System Physicalism Physics Aristotle Physics envy Quantum theory Bohr Einstein debates Einstein s thought experiments EPR paradox Interpretations of Metaphysics Mysticism Reductionism Relativity General Special Space Absolute theory Container space Free space Relational space Relational theory Spacetime Supervenience Symmetry in physics Theophysics Time in physicsReferences edit Maudlin Tim 2012 Philosophy of Physics Space and Time Princeton University Press p xi ISBN 978 0691143095 Retrieved 3 October 2017 the existence and nature of space and time or space time is a central topic Rovelli C 2004 Quantum Gravity Cambridge Monographs on Mathematical Physics p 71 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 a b Bolonkin Alexander 2011 Universe Human mmortality and Future Human Evaluation Elsevier p 32 ISBN 978 0 12 415810 8 Extract of page 32 BristolPhilosophy 19 February 2013 Eleanor Knox KCL The Curious Case of the Vanishing Spacetime Archived from the original on 11 December 2021 Retrieved 7 April 2018 via YouTube Bell John S 1987 Speakable and Unspeakable in Quantum Mechanics Cambridge University Press p 65 ISBN 9780521368698 OCLC 15053677 Einstein A Podolsky B Rosen N 15 May 1935 Can Quantum Mechanical Description of Physical Reality be Considered Complete Physical Review 47 10 777 780 Bibcode 1935PhRv 47 777E doi 10 1103 PhysRev 47 777 Bell J S 1964 On the Einstein Podolsky Rosen Paradox PDF Physics Physique Fizika 1 3 195 200 doi 10 1103 PhysicsPhysiqueFizika 1 195 Parker Sybil B 1994 McGraw Hill Encyclopaedia of Physics 2nd ed McGraw Hill p 542 ISBN 978 0 07 051400 3 Mermin N David July 1993 Hidden Variables and the Two Theorems of John Bell PDF Reviews of Modern Physics 65 3 803 15 arXiv 1802 10119 Bibcode 1993RvMP 65 803M doi 10 1103 RevModPhys 65 803 S2CID 119546199 The Nobel Prize in Physics 2022 Nobel Prize Press release The Royal Swedish Academy of Sciences 4 October 2022 Retrieved 6 October 2022 The BIG Bell Test Collaboration 9 May 2018 Challenging local realism with human choices Nature 557 7704 212 216 arXiv 1805 04431 Bibcode 2018Natur 557 212B doi 10 1038 s41586 018 0085 3 PMID 29743691 S2CID 13665914 Wolchover Natalie 7 February 2017 Experiment Reaffirms Quantum Weirdness Quanta Magazine Retrieved 8 February 2020 Niels Bohr Atomic Physics and Human Knowledge p 38 Faye Jan 2019 Copenhagen Interpretation of Quantum Mechanics In Zalta Edward N ed Stanford Encyclopedia of Philosophy Metaphysics Research Lab Stanford University Camilleri K Schlosshauer M 2015 Niels Bohr as Philosopher of Experiment Does Decoherence Theory Challenge Bohr s Doctrine of Classical Concepts Studies in History and Philosophy of Modern Physics 49 73 83 arXiv 1502 06547 Bibcode 2015SHPMP 49 73C doi 10 1016 j shpsb 2015 01 005 S2CID 27697360 Omnes Roland 1999 The Copenhagen Interpretation Understanding Quantum Mechanics Princeton University Press pp 41 54 doi 10 2307 j ctv173f2pm 9 S2CID 203390914 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 Omnes R 1994 The Interpretation of Quantum Mechanics Princeton University Press ISBN 978 0 691 03669 4 OCLC 439453957 David Wallace The Emergent Multiverse pp 1 10 David Wallace The Emergent Multiverse pp 113 117 David Wallace The Emergent Multiverse pg 157 189 Kent Adrian 2010 One world versus many The inadequacy of Everettian accounts of evolution probability and scientific confirmation In S Saunders J Barrett A Kent D Wallace eds Many Worlds Everett Quantum Theory and Reality Oxford University Press arXiv 0905 0624 Bibcode 2009arXiv0905 0624K Kent Adrian 1990 Against Many Worlds Interpretations International Journal of Modern Physics A 5 9 1745 1762 arXiv gr qc 9703089 Bibcode 1990IJMPA 5 1745K doi 10 1142 S0217751X90000805 S2CID 14523184 Price Huw 2010 Decisions Decisions Decisions Can Savage Salvage Everettian Probability In S Saunders J Barrett A Kent D Wallace eds Many Worlds Everett Quantum Theory and Reality Oxford University Press arXiv 0802 1390 Omnes Roland 2002 11 Quantum philosophy understanding and interpreting contemporary science in French Arturo Spangalli transl 1st paperback ed Princeton Princeton University Press p 213 ISBN 978 1400822867 Frigg Roman Werndl Charlotte 10 January 2023 Philosophy of Statistical Mechanics In Zalta Edward N ed Stanford Encyclopedia of Philosophy a b 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 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 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 a b 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 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 E3 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 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 Ariew and Garber 117 Loemker 46 W II 5 On Leibniz and physics see the chapter by Garber in Jolley 1995 and Wilson 1989 Rafael Ferraro 2007 Einstein s Space Time An Introduction to Special and General Relativity Springer p 1 ISBN 978 0 387 69946 2 See H G Alexander ed The Leibniz Clarke Correspondence Manchester Manchester University Press pp 25 26 Further reading editDavid Albert 1994 Quantum Mechanics and Experience Harvard Univ Press John D Barrow and Frank J Tipler 1986 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 Anthropic Bias Observation Selection Effects in Science and Philosophy Routledge Thomas Brody 1993 Ed by Luis de la Pena and Peter E Hodgson The Philosophy Behind Physics Springer ISBN 3 540 55914 0 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 realite le monde quantique la connaissance et la duree 1995 Veiled Reality Addison Wesley 2006 On Physics and Philosophy Princeton Univ Press Roland Omnes 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 Weizsacker 1980 The Unity of Nature Farrar Straus amp Giroux Werner Heisenberg 1971 Physics and Beyond Encounters and Conversations Harper amp Row World Perspectives series 1971 William Berkson 1974 Fields of Force Routledge and Kegan Paul London ISBN 0 7100 7626 6 Encyclopaedia Britannica Philosophy of Physics David Z AlbertExternal links edit nbsp Wikimedia Commons has media related to Philosophy of physics Stanford Encyclopedia of Philosophy Absolute and Relational Theories of Space and Motion Nick Huggett and Carl Hoefer Being and Becoming in Modern Physics Steven Savitt Boltzmann s Work in Statistical Physics Jos Uffink Conventionality of Simultaneity Allen Janis Early Philosophical Interpretations of General Relativity Thomas A Ryckman Everett s Relative State Formulation of Quantum Mechanics Jeffrey A Barrett Experiments in Physics Allan Franklin Holism and Nonseparability in Physics Richard Healey Intertheory Relations in Physics Robert Batterman Naturalism David Papineau Philosophy of Statistical Mechanics Lawrence Sklar Physicalism Daniel Sojkal Quantum Mechanics Jenann Ismael Reichenbach s Common Cause Principle Frank Artzenius Structural Realism James Ladyman Structuralism in Physics Heinz Juergen Schmidt Supertasks JB Manchak and Bryan Roberts Symmetry and Symmetry Breaking Katherine Brading and Elena Castellani Thermodynamic Asymmetry in Time Craig Callender Time by Ned Markosian Time Machines John Earman Chris Wuthrich and JB Manchak Uncertainty principle Jan Hilgevoord and Jos Uffink The Unity of Science Jordi Cat Retrieved from https en wikipedia org w index php title Philosophy of physics amp oldid 1179310827 Philosophy of quantum mechanics, wikipedia, wiki, book, books, library,

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