Kvantna mehanika – razlika između verzija

 

'''Kvantna mehanika''' je fundamentalna grana [[teorijska fizika|teorijske fizike]] kojom su zamenjene [[klasična mehanika]] i [[Elektromagnetizam|klasična elektrodinamika]] pri opisivanju atomskih i subatomskih pojava. Ona predstavlja teorijsku podlogu mnogih disciplina fizike i hemije kao što su [[fizika kondenzovane materije]], [[atomska fizika]], [[molekulska fizika]], [[fizička hemija]], [[kvantna hemija]], [[fizika čestica]] i [[nuklearna fizika]]. Zajedno sa [[Opšta teorija relativnosti|Opštom teorijom relativnosti]] Kvantna mehanika predstavlja jedan od stubova savremene fizike.

 

== Uvod ==

Izraz kvant (od latinskog quantum (množina quanta) = količina, mnoštvo, svota, iznos, deo) odnosi se na diskretne jedinice koje teorija pripisuje izvesnim fizičkim veličinama kao što su [[energija]] i [[moment impulsa]] (ugaoni moment) [[atom]]a kao što je pokazano na slici. Otkriće da talasi mogu da se prostiru kao čestice, u malim energijskim paketima koji se nazivaju kvanti dovelo je do pojave nove grane fizike koja se bavi atomskim i subatomskim sistemima a koju danas nazivamo Kvantna mehanika. Temelje kvantnoj mehanici položili su u prvoj polovini dvadesetog veka [[Verner Hajzenberg]], [[Maks Plank]], [[Luj de Brolj|Luj de Broj]], [[Nils Bor]], [[Ervin Šredinger]], [[Maks Born]], [[Džon fon Nojman]], [[Pol Dirak]], [[Albert Ajnštajn]], [[Volfgang Pauli]] i brojni drugi poznati fizičari 20. veka. Neki bazični aspekti kvantne mehanike još uvek se aktivno izučavaju.

 

 

Because everything is composed of quantum-mechanical particles, the laws of classical physics must approximate the laws of quantum mechanics in the appropriate limit. This is often expressed by saying that in case of large [[quantum number]]s quantum mechanics "reduces" to classical mechanics and classical electromagnetism. This requirement is called the [[correspondence principle|correspondence, or classical limit]].-->

 

== Teorija ==

Postoje brojne matematički ekvivalentne formulacije kvantne mehanike. Jedna od najstarijih i najčešće korišćenih je transformaciona teorija koju je predložio [[Pol Dirak]] a koja ujedinjuje i uopštava dve ranije formulacije, [[matrična mehanika|matričnu mehaniku]] (koju je uveo [[Verner Hajzenberg]]) <ref> Nakon što je 1932. godine Hajzenberg dobio Nobelovu nagradu za stvaranje kvantne mehanike uloga [[Maks Born|Maksa Borna]] u tome bila je umanjena. Biografija Maksa Borna iz 2005. detaljno opisuje njegovu ulogu u stvaranju matrične mehanike. To je i sam Hajzenberg priznao 1950. godine u radu posvećenom [[Maks Plank|Maksu Planku]]. Videti: Nancy Thorndike Greenspan, “The End of the Certain World: The Life and Science of Max Born (Basic Books, 2005), pp. 124 - 128, and 285 - 286. </ref> i [[talasna mehanika|talasnu mehaniku]] (koju je formulisao [[Ervin Šredinger]]).

 

 

The [[probability|probabilistic]] nature of quantum mechanics thus stems from the act of measurement. This is one of the most difficult aspects of quantum systems to understand. It was the central topic in the famous [[Bohr-Einstein debates]], in which the two scientists attempted to clarify these fundamental principles by way of thought experiments. In the decades after the formulation of quantum mechanics, the question of what constitutes a "measurement" has been extensively studied. [[Interpretation of quantum mechanics|Interpretations]] of quantum mechanics have been formulated to do away with the concept of "wavefunction collapse"; see, for example, the [[relative state interpretation]]. The basic idea is that when a quantum system interacts with a measuring apparatus, their respective wavefunctions become [[entangled]], so that the original quantum system ceases to exist as an independent entity. For details, see the article on [[measurement in quantum mechanics]].-->

 

=== Matematička formulacija ===

 

An alternative formulation of quantum mechanics is [[Feynman]]'s [[path integral formulation]], in which a quantum-mechanical amplitude is considered as a sum over histories between initial and final states; this is the quantum-mechanical counterpart of [[action principle]]s in classical mechanics.-->

 

=== Veza sa drugim naučnim teorijama ===

<!--The fundamental rules of quantum mechanics are very broad. They state that the state space of a system is a [[Hilbert space]] and the observables are [[Hermitian operators]] acting on that space, but do not tell us which Hilbert space or which operators. These must be chosen appropriately in order to obtain a quantitative description of a quantum system. An important guide for making these choices is the [[correspondence principle]], which states that the predictions of quantum mechanics reduce to those of classical physics when a system moves to higher energies or equivalently, larger quantum numbers. This "high energy" limit is known as the ''classical'' or ''correspondence limit''. One can therefore start from an established classical model of a particular system, and attempt to guess the underlying quantum model that gives rise to the classical model in the correspondence limit.

 

 

It has proven difficult to construct quantum models of [[gravity]], the remaining [[fundamental force]]. Semi-classical approximations are workable, and have led to predictions such as [[Hawking radiation]]. However, the formulation of a complete theory of [[quantum gravity]] is hindered by apparent incompatibilities between [[general relativity]], the most accurate theory of gravity currently known, and some of the fundamental assumptions of quantum theory. The resolution of these incompatibilities is an area of active research, and theories such as [[string theory]] are among the possible candidates for a future theory of quantum gravity.-->

 

== Primene ==

Kvantna mehanika uspeva izvanredno uspešno da objasni brojen fizičke pojave u prirodi. Na primer osobine [[Subatomske čestice|subatomskih čestica]] od kojih su sačinjeni svi oblici materije mogu biti potpuno objašnjene preko kvantne mehanike. Isto, kombinovanje atoma u stvaranju molekula i viših oblika organizacije materije može se dosledno objasniti primenom kvantne mehanike iz čega je izrasla [[kvantna hemija]], jedna od disciplina [[fizička hemija|fizičke hemije]]. Relativistička kvantna mehanika, u principu, može da objasni skoro celokupnu hemiju. Drugim rečima, nema pojave u hemiji koja ne može da bude objašnjena kvantnomehaničkom teorijom.

 

 

Researchers are currently seeking robust methods of directly manipulating quantum states. Efforts are being made to develop [[quantum cryptography]], which will allow guaranteed secure transmission of [[information]]. A more distant goal is the development of [[quantum computer]]s, which are expected to perform certain computational tasks exponentially faster than classical [[computer]]s. Another active research topic is [[quantum teleportation]], which deals with techniques to transmit quantum states over arbitrary distances.-->

 

== Filozofske posledice ==

 

The [[Everett many-worlds interpretation]], formulated in 1956, holds that all the possibilities described by quantum theory simultaneously occur in a "[[Multiverse (science)|multiverse]]" composed of mostly independent parallel universes. This is not accomplished by introducing some new axiom to quantum mechanics, but on the contrary by ''removing'' the axiom of the collapse of the wave packet: All the possible consistent states of the measured system and the measuring apparatus (including the observer) are present in a ''real'' physical (not just formally mathematical, as in other interpretations) [[quantum superposition]]. (Such a superposition of consistent state combinations of different systems is called an [[entangled state]].) While the multiverse is deterministic, we perceive non-deterministic behavior governed by probabilities, because we can observe only the universe, i.e. the consistent state contribution to the mentioned superposition, we inhabit. Everett's interpretation is perfectly consistent with [[John Stewart Bell|John Bell]]'s experiments and makes them intuitively understandable. However, according to the theory of [[quantum decoherence]], the parallel universes will never be accessible for us, making them physically meaningless. This inaccessiblity can be understood as follows: once a measurement is done, the measured system becomes [[entanglement|entangled]] with both the physicist who measured it and a huge number of other particles, some of which are [[photon]]s flying away towards the other end of the universe; in order to prove that the wave function did not collapse one would have to bring all these particles back and measure them again, together with the system that was measured originally. This is completely impractical, but even if one can theoretically do this, it would destroy any evidence that the original measurement took place (including the physicist's memory).-->

 

== Istorija ==

Da bi objasnio spektar zračenja koje emituje [[crno telo]] [[Maks Plank]] je 1900. godine uveo ideju o diskretnoj, dakle, kvantnoj prirodi energije. Da bi objasnio [[fotoelektrični efekat]] [[Albert Ajnštajn|Ajnštajn]] je postulirao da se svetlosna energija prenosi u kvantima koji se danas nazivaju [[foton]]ima. Ideja da se energija zračenja prenosi u porcijama (kvantima) predstavlja izvanerdno dostignuće jer je time Plankova formula zračenja crnog tela dobila konačno i svoje fizičko objašnjenje. Godine 1913. [[Nils Bor|Bor]] je objasnio [[spektar]] vodonikovog atoma, opet koristeći kvantizaciju ovog puta i ugaonog momenta. Na sličan način je [[Luj de Brolj|Luj de Broj]] 1924. godine izložio teoriju o talasima materije tvrdeći da čestice imaju talasnu prirodu, upotpunjujući Ajnštajnovu sliku o čestičnoj prirodi talasa.

 

<!--Beginning in 1927, attempts were made to apply quantum mechanics to fields rather than single particles, resulting in what are known as [[Quantum field theory|quantum field theories]]. Early workers in this area included [[Paul Dirac|Dirac]], [[Wolfgang Pauli|Pauli]], [[Victor Weisskopf|Weisskopf]], and [[Pascual Jordan|Jordan]]. This area of research culminated in the formulation of [[quantum electrodynamics]] by [[Richard Feynman|Feynman]], [[Freeman Dyson|Dyson]], [[Julian Schwinger|Schwinger]], and [[Sin-Itiro Tomonaga|Tomonaga]] during the 1940s. Quantum electrodynamics is a quantum theory of [[electron]]s, [[positron]]s, and the [[electromagnetic field]], and served as a role model for subsequent quantum field theories.-->

<!--The theory of [[quantum chromodynamics]] was formulated beginning in the early 1960s. The theory as we know it today was formulated by [[H. David Politzer|Politzer]], [[David J. Gross|Gross]] and [[Frank Wilczek|Wilzcek]] in 1975. Building on pioneering work by [[Julian Schwinger|Schwinger]], [[Peter Higgs|Higgs]], [[Jeffrey Goldstone|Goldstone]], [[Sheldon Lee Glashow|Glashow]], [[Steven Weinberg|Weinberg]] and [[Abdus Salam|Salam]] independently showed how the weak nuclear force and quantum electrodynamics could be merged into a single [[electroweak force]].-->

 

=== Hronologija utemeljivačkih eksperimenata ===

<!--*[[The Pondicherry interpretation of quantum mechanics]]

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== Literatura ==

* Eric R. Scerri, The Periodic Table: Its Story and Its Significance, Oxford University Press, 2006. Considers the extent to which chemistry and especially the periodic system has been reduced to quantum mechanics. ISBN 0-19-530573-6

* Slobodan Macura, Jelena Radić-Perić, ATOMISTIKA, Fakultet za fizičku hemiju Univerziteta u Beogradu/Službeni list, Beograd, 2004. (stara kvantna teorija i većina utemeljivaćkih eksperimentata).

 

== Beleške ==

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'''Opšte:'''

* [http://www-history.mcs.st-andrews.ac.uk/history/HistTopics/The_Quantum_age_begins.html A history of quantum mechanics]

* [http://higgo.com/quantum/laymans.htm A Lazy Layman's Guide to Quantum Physics]

 

'''Materijal za kurs:'''

* [[MIT OpenCourseWare]]: [http://ocw.mit.edu/OcwWeb/Chemistry/index.htm Chemistry]. See [http://ocw.mit.edu/OcwWeb/Chemistry/5-61Fall-2004/CourseHome/index.htm 5.61], [http://ocw.mit.edu/OcwWeb/Chemistry/5-73Fall-2005/CourseHome/index.htm 5.73], and [http://ocw.mit.edu/OcwWeb/Chemistry/5-74Spring-2005/CourseHome/index.htm 5.74]

* MIT OpenCourseWare: [http://ocw.mit.edu/OcwWeb/Physics/index.htm Physics]. See [http://ocw.mit.edu/OcwWeb/Physics/8-04Quantum-Physics-ISpring2003/CourseHome/index.htm 8.04], [http://ocw.mit.edu/OcwWeb/Physics/8-05Fall-2004/CourseHome/index.htm 8.05], and [http://ocw.mit.edu/OcwWeb/Physics/8-06Spring-2005/CourseHome/index.htm 8.06].

 

'''Često postavljana pitanja:'''

* [http://www.hedweb.com/manworld.htm Many-worlds or relative-state interpretation]

* [http://www.mtnmath.com/faq/meas-qm.html Measurement in Quantum mechanics]

 

'''Filozofija:'''

* [http://plato.stanford.edu/entries/qm/ Quantum Mechanics (''Stanford Encyclopedia of Philosophy'')]

* [http://www.physicstoday.org/pt/vol-54/iss-2/p11.html David Mermin on the future directions of physics]

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