Kasutaja:Fatio de Duillier/Mehhaanilised gravitatsiooniteooriad

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Mall:Wikisourcecat Mehhaanilised gravitatsiooniteooriad (ehk kineetilised gravitatsiooniteooriad) on füüsikateooriad, mis püüavad selgitada gravitatsiooni toimet mehhaaniliste protsessidega nagu näiteks surve, mida põhjustavad tõuked, kasutamata seletuses kaugmõju. Sedalaadi teooriaid arendati 16.-19. sajandil koos eetriteooriatega. Tänapäeva teaduses taolisi mudeleid siiski enam usutavateks ei peeta ning standardmudel gravitatsiooni kaugmõjuta seletamiseks on üldrelatiivsusteooria. Ka kvantgravitatsiooni teooriad püüavad kirjeldada gravitatsiooni fundamentaalsemate protsesside kaudu nagu osakeste väljad, kuid need ei põhine klassikalisel mehhaanikal.

Varjestus[muuda | muuda lähteteksti]

Next.svg Pikemalt artiklis Le Sage'i gravitatsiooniteooria

See teooria on mehhaanilistest selgitustest ehk tuntuim[1]. Esimesena arendas selle välja Nicolas Fatio de Duillier 1690. aastal. Hiljem on varjestusteooria taasleiutanud näiteks Georges-Louis Le Sage (1748), Lord Kelvin (1872) ja Hendrik Lorentz (1900), seda on kritiseerinud James Clerk Maxwell (1875) ja Henri Poincaré (1908).

Varjestusteooria väidab, et gravitatsioonijõud on kogu universumis suurel kiirusel kõigis suundades liikuvate väikeste osakeste või lainetemõju tulemus. Osakestevoo intensiivsus on oletatavasti igas suunas sama, nii et eraldiseisvat objekti A mõjutatakse üleaegselt igast küljest, mille tulemus on vaid sissepoole suunatud surve, kuid lõppkokkuvõttes jääb keha paigale. Kui läheduses on aga teine objekt B, tõkestab see mõningaid osakesi, mis oleksid muidu A-d B suunast tabanud, nii et B varjab A-d, lastes oma suunalt A poole vähem osakesi kui tuleb vastassuunast. A ja B varjestavad teineteist ja sellest tuleneva jõudude tasakaalutuse tõttu tõugatakse mõlemat keha teineteise poole.

P5: Läbitavuse, nõrgenemise ja massi proportsionaalsus

Selline varjestus täidab pöördvõrdelise sõltuvuse seadust, kuna voo tasakaalutus kogu objekti ümbritseval sfäärilisel pinnal ei sõltu sfääri suurusest, samas kui sfääri pindala kasvab proportsionaalselt raadiuse ruuduga. Et saavutada massi proportsionaalsus, väidab teooria, et: a) mateeria algosakesed on sedavõrd väikesed, et makrotasandi tahked kehad koosnevad põhiliselt tühjast ruumist; b) osakesed on nii väikesed, et vaid väike osa neist jääb kinni tahketesse kehadesse. Selle tulemusena on iga keha "vari" proportsionaalne iga üksiku mateeriaosa pinnaga.

Kriitika[muuda | muuda lähteteksti]

Üks põhiargumente varjestusteooria vastu on termodünaamiline: selles mudelis tekib vari üksnes juhul, kui osakesed või lained absorbeeritakse vähemalt osaliselt tahketesse kehadesse, see aga peaks viima kehade järsku kuumenemiseni. Samuti on probleemiks takistus osakesevoogude liikumissuunas. Selle saaks lahendada valgusüleste kiirustega, kuid niisugune lahendus suurendaks soojenemisprobleeme veelgi ja oleks vastuolus erirelatiivsusteooriaga.[2]<ref>Maxwell 1875, "Atom"</ref>

Keerised[muuda | muuda lähteteksti]

Eetrikeerised taevakehade ümber

Ophilosophical beliefs, René Descartes proposed in 1644 that no empty space can exist and that space must consequently be filled with matter. The parts of this matter tend to move in straight paths, but because they lie close together, they can't move freely, which according to Descartes implies that every motion is circular, so the aether is filled with vortices. Descartes also distinguishes between different forms and sizes of matter in which rough matter resists the circular movement more strongly than fine matter. Due to centrifugal force, matter tends towards the outer edges of the vortex, which causes a condensation of this matter there. The rough matter cannot follow this movement due to its greater inertia—so due to the pressure of the condensed outer matter those parts will be pushed into the center of the vortex. According to Descartes, this inward pressure is nothing else than gravity. He compared this mechanism with the fact that if a rotating, liquid filled vessel is stopped, the liquid goes on to rotate. Now, if one drops small pieces of light matter (e.g. wood) into the vessel, the pieces move to the middle of the vessel.[3] [4] [5]

Following the basic premises of Descartes, Christiaan Huygens between 1669 and 1690 designed a much more exact vortex model. This model was the first theory of gravitation which was worked out mathematically. He assumed that the aether particles are moving in every direction, but were thrown back at the outer borders of the vortex and this causes (as in the case of Descartes) a greater concentration of fine matter at the outer borders. So also in his model the fine matter presses the rough matter into the center of the vortex. Huygens also found out that the centrifugal force is equal to the force, which acts in the direction of the center of the vortex (centripetal force). He also posited that bodies must consist mostly of empty space so that the aether can penetrate the bodies easily, which is necessary for mass proportionality. He further concluded that the aether moves much faster than the falling bodies. At this time, Newton developed his theory of gravitation which is based on attraction, and although Huygens agreed with the mathematical formalism, he said the model was insufficient due to the lack of a mechanical explanation of the force law. Newton's discovery that gravity obeys the inverse square law surprised Huygens and he tried to take this into account by assuming that the speed of the aether is smaller in greater distance.[5][6][7]

Criticism: Newton objected to the theory because drag must lead to noticeable deviations of the orbits which weren't observed.[8] Another problem was that moons often move in different directions, against the direction of the vortex motion. Also, Huygens' explanation of the inverse square law is circular, because this means that the aether obeys Kepler's third law. But a theory of gravitation has to explain those laws and must not presuppose them.[5][8]

Streams[muuda | muuda lähteteksti]

In a 1675 letter to Henry Oldenburg, and later to Robert Boyle, Newton wrote the following: [Gravity is the result of] “a condensation causing a flow of ether with a corresponding thinning of the ether density associated with the increased velocity of flow.” He also asserted that such a process was consistent with all his other work and Kepler's Laws of Motion.[9] Newtons' idea of a pressure drop associated with increased velocity of flow was mathematically formalised as Bernoulli's principle published in Daniel Bernoulli's book Hydrodynamica in 1738.

However, although he later proposed a second explanation (see section below), Newton's comments to that question remained ambiguous. In the third letter to Bentley in 1692 he wrote:[10]

It is inconceivable that inanimate brute matter should, without the mediation of something else which is not material, operate upon and affect other matter, without mutual contact, as it must do if gravitation in the sense of Epicurus be essential and inherent in it. And this is one reason why I desired you would not ascribe 'innate gravity' to me. That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance, through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it. Gravity must be caused by an agent acting constantly according to certain laws; but whether this agent be material or immaterial, I have left to the consideration of my readers.

On the other hand, Newton is also well known for the phrase Hypotheses non fingo, written in 1713:[11]

I have not as yet been able to discover the reason for these properties of gravity from phenomena, and I do not feign hypotheses. For whatever is not deduced from the phenomena must be called a hypothesis; and hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy. In this philosophy particular propositions are inferred from the phenomena, and afterwards rendered general by induction.

And according to the testimony of some of his friends, such as Nicolas Fatio de Duillier or David Gregory, Newton thought that gravitation is based directly on divine influence.[7]

Similar to Newton, but mathematically in greater detail, Bernhard Riemann assumed in 1853 that the gravitational aether is an incompressible fluid and normal matter represents sinks in this aether. So if the aether is destroyed or absorbed proportionally to the masses within the bodies, a stream arises and carries all surrounding bodies into the direction of the central mass. Riemann speculated that the absorbed aether is transferred into another world or dimension.[12]

Another attempt to solve the energy problem was made by Ivan Osipovich Yarkovsky in 1888. Based on his aether stream model, which was similar to that of Riemann, he argued that the absorbed aether might be converted into new matter, leading to a mass increase of the celestial bodies.[13]

Criticism: As in the case of Le Sage's theory, the disappearance of energy without explanation violates the energy conservation law. Also some drag must arise, and no process which leads to a creation of matter is known.

Static pressure[muuda | muuda lähteteksti]

Newton updated the second edition of Optics (1717) with another mechanical-ether theory of gravity. Unlike his first explanation (1675 - see Streams), he proposed a stationary aether which gets thinner and thinner nearby the celestial bodies. On the analogy of the lift (force), a force arises, which pushes all bodies to the central mass. He minimized drag by stating an extremely low density of the gravitational aether.

Like Newton, Leonhard Euler presupposed in 1760 that the gravitational aether loses density in accordance with the inverse square law. Similarly to others, Euler also assumed that to maintain mass proportionality, matter consists mostly of empty space.[14]

Criticism: Both Newton and Euler gave no reason why the density of that static aether should change. Furthermore, James Clerk Maxwell pointed out that in this "hydrostatic" model "the state of stress... which we must suppose to exist in the invisible medium, is 3000 times greater than that which the strongest steel could support".<ref name=maxwell>Maxwell (1875, Attraction), Secondary sources</ref>

Waves[muuda | muuda lähteteksti]

Robert Hooke speculated in 1671 that gravitation is the result of all bodies emitting waves in all directions through the aether. Other bodies, which interchange with these waves, move in the direction of the source of the waves. Hooke saw an analogy to the fact that small objects on a disturbed surface of water move to the center of the disturbance.[15]

A similar theory was worked out mathematically by James Challis from 1859 to 1876. He calculated that the case of attraction occurs if the wavelength is large in comparison with the distance between the gravitating bodies. If the wavelength is small, the bodies repel each other. By a combination of these effects, he also tried to explain all other forces.[16]

Criticism: Maxwell objected that this theory requires a steady production of waves, which must be accompanied by an infinite consumption of energy.<ref name=maxwell>Maxwell (1875), Secondary sources</ref> Challis himself admitted, that he hadn't reached a definite result due to the complexity of the processes.[15]

Pulsation[muuda | muuda lähteteksti]

Lord Kelvin (1871) and Carl Anton Bjerknes (1871) assumed that all bodies pulsate in the aether. This was in analogy to the fact that, if the pulsation of two spheres in a fluid is in phase, they will attract each other; and if the pulsation of two spheres is not in phase, they will repel each other. This mechanism was also used for explaining the nature of electric charges. Among others, this hypothesis has also been examined by George Gabriel Stokes and Woldemar Voigt.[17]

Criticism : To explain universal gravitation, one is forced to assume that all pulsations in the universe are in phase—which appears very implausible. In addition, the aether should be incompressible to ensure that attraction also arises at greater distances.[17] And Maxwell argued that this process must be accompanied by a permanent new production and destruction of aether.<ref name=maxwell />

Other historical speculations[muuda | muuda lähteteksti]

In 1690 Pierre Varignon assumed that all bodies are exposed to pushes by aether particles from all directions, and that there is some sort of limitation at a certain distance from the Earth's surface which cannot be passed by the particles. He assumed that if a body is closer to the Earth than to the limitation boundary, then the body would experience a greater push from above than from below, causing it to fall toward the Earth.[18]

In 1748 Mikhail Lomonosov assumed that the effect of the aether is proportional to the complete surface of the elementary components of which matter consists (similar to Huygens and Fatio before him). He also assumed an enormous penetrability of the bodies. However, no clear description was given by him as to how exactly the aether interchanges with matter so that the law of gravitation arises.[19]

In 1821 John Herapath tried to apply his co-developed model of the kinetic theory of gases on gravitation. He assumed that the aether is heated by the bodies and loses density so that other bodies are pushed to these regions of lower density.[20] However, it was shown by Taylor that the decreased density due to thermal expansion is compensated for by the increased speed of the heated particles, therefore no attraction arises.[15]

Uuemad teooriad[muuda | muuda lähteteksti]

Mehhaanilised gravitatsiooniteooriad ei saavutanud kunagi laialdast tunnustust, ehkki füüsikud kaalusid taolisi ideid aeg-ajalt kuni 20. sajandi alguseni. Tollest ajast saati peetakse neid teaduslikult ümberlükatuteks. Siiski leidub väljaspool teaduse põhivoolu tänini uurijaid, kes püüavad taoliste teooriate järelmeid välja selgitada.

Le Sage'i teooriat uurisid Radzievskii ja Kagalnikova (1960),[21] Shneiderov (1961),[22] Buonomano and Engels (1976),[23] Adamut (1982),[24] Jaakkola (1996),[25] Tom Van Flandern (1999),[26] ja Edwards (2007).[27] Le Sage'i mudeli mitmesuguseid variante ja muid nendega seotud teemasid on käsitletud teoses: Edwardsi jt 2002. aasta teoses "Pushing Gravity".[28]

Teisesed allikad[muuda | muuda lähteteksti]

  • Van Lunteren, F., kirjapandud Montreal, Edwards, M.R., toim., Pushing Gravity: New Perspectives on Le Sage's Theory of Gravitation 
  • Zehe, Horst, kirjapandud Hildesheim, Die Gravitationstheorie des Nicolas Fatio de Duillier, ISBN 3-8067-0862-2 

Esmased allikad[muuda | muuda lähteteksti]

  1. Taylor (1876), Peck (1903)
  2. Poincaré (1908)
  3. Descartes, R., Les principes de la philosophie (1644), http://gallica.bnf.fr/document?O=N094260 
  4. Descartes, 1644; Zehe, 1980, pp. 65–70; Van Lunteren, p. 47
  5. 5,0 5,1 5,2 Zehe (1980), Secondary sources
  6. Huygens, C., Discours de la Cause de la Pesanteur (1690), http://gallica.bnf.fr/ark:/12148/bpt6k77870g/f451.table 
  7. 7,0 7,1 Van Lunteren (2002), Secondary sources
  8. 8,0 8,1 Newton, I., Newton's Principia : the mathematical principles of natural philosophy (1687), http://www.archive.org/details/newtonspmathema00newtrich 
  9. I. Newton, letters quoted in detail in The Metaphysical Foundations of Modern Physical Science by Edwin Arthur Burtt, Double day Anchor Books.
  10. Newton, 1692, 3rd letter to Bentley
  11. Isaac Newton (1726). Philosophiae Naturalis Principia Mathematica, General Scholium. Third edition, page 943 of I. Bernard Cohen and Anne Whitman's 1999 translation, University of California Press ISBN 0-520-08817-4, 974 pages.
  12. Riemann, B., Neue mathematische Prinzipien der Naturphilosophie 
  13. Yarkovsky, I. O., Hypothese cinetique de la Gravitation universelle et connexion avec la formation des elements chimiques 
  14. Euler, L., Briefe an eine deutsche Prinzessin, Nr. 50, 30. August 1760, http://books.google.at/books?id=FaMAAAAAMAAJ&pg=PA1#PPA173,M1 
  15. 15,0 15,1 15,2 Taylor (1876), Secondary sources
  16. Challis, J., Notes of the Principles of Pure and Applied Calculation, http://www.archive.org/details/notesonprinciple00chalrich 
  17. 17,0 17,1 Zenneck (1903), Secondary sources
  18. Varignon, P., Nouvelles conjectures sur la Pesanteur, http://gallica.bnf.fr/ark:/12148/bpt6k74179x 
  19. Lomonosow, M., On the Relation of the Amount of Material and Weight (1758), http://www.archive.org/details/mikhailvasilevic017733mbp 
  20. Herapath, J., On the Causes, Laws and Phenomena of Heat, Gases, Gravitation, http://books.google.at/books?id=nCsAAAAAMAAJ&pg=RA1-PA273 
  21. Radzievskii, V.V. and Kagalnikova, I.I., The nature of gravitation  Ingliskeelne toortõlge nende artiklist ilmus USA riiklikus tehnilises raportis: FTD TT64 323; TT 64 11801 (1964), Foreign Tech. Div., Air Force Systems Command, Wright-Patterson AFB, Ohio (taastrükk: Pushing Gravity)
  22. Shneiderov, A. J., On the internal temperature of the earth 
  23. Buonomano, V. & Engel, E., Some speculations on a causal unification of relativity, gravitation, and quantum mechanics, doi:10.1007/BF01807095, Bibcode1976IJTP...15..231B 
  24. Adamut, I. A., The screen effect of the earth in the TETG. Theory of a screening experiment of a sample body at the equator using the earth as a screen, doi:10.1007/BF02509010, Bibcode1982NCimC...5..189A 
  25. Jaakkola, T., Action-at-a-distance and local action in gravitation: discussion and possible solution of the dilemma, http://redshift.vif.com/JournalFiles/Pre2001/V03NO3PDF/V03N3JAA.PDF 
  26. Van Flandern, T., Dark Matter, Missing Planets and New Comets 
  27. Edwards, M .R., Photon-Graviton Recycling as Cause of Gravitation, http://redshift.vif.com/JournalFiles/V14NO3PDF/V14N3EDW.PDF 
  28. Edwards, M. R., toim., Pushing Gravity: New Perspectives on Le Sage's Theory of Gravitation 

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