Graviton — разлика између измена

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Ред 119: Ред 119:
|doi=10.1142/S0218271815440010
|doi=10.1142/S0218271815440010
|bibcode = 2015IJMPD..2444001D }}</ref>
|bibcode = 2015IJMPD..2444001D }}</ref>

== Energija i talasna dužina ==
{{rut}}
While gravitons are presumed to be [[massless particle|massless]], they would still carry [[energy]], as does any other quantum particle. [[Photon energy]] and [[gluon energy]] are also carried by massless particles. It is unclear which variables might determine graviton energy, the amount of energy carried by a single graviton.

Alternatively, [[massive gravity|if gravitons are massive at all]], the analysis of [[gravitational wave]]s yielded a new upper bound on the [[mass]] of gravitons. The graviton's [[Compton wavelength]] is at least {{val|1.6|e=16|u=[[metre|m]]}}, or about 1.6 [[light-year]]s, corresponding to a graviton mass of no more than {{val|7.7|e=-23|u=[[electronvolt|eV]]/[[speed of light|c]]<sup>2</sup>}}.<ref name="Abbott2017">{{cite journal|doi=10.1103/PhysRevLett.118.221101|title=GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2|journal=[[Physical Review Letters]]|date=1 June 2017|author=B. P. Abbott|display-authors=etal|collaboration=[[LIGO Scientific Collaboration]] and [[Virgo interferometer|Virgo Collaboration]]|volume=118|pages=221101|bibcode=2017PhRvL.118v1101A|arxiv=1706.01812}}</ref> This relation between wavelength and mass-energy is calculated with the [[Planck–Einstein relation]], the same formula that relates electromagnetic [[wavelength]] to [[photon energy]]. However, if gravitons are the quanta of gravitational waves, then the relation between wavelength and corresponding particle energy is fundamentally different for gravitons than for photons, since the Compton wavelength of the graviton is not equal to the gravitational-wave wavelength. Instead, the lower-bound graviton Compton wavelength is about {{val|9|e=9}} times greater than the gravitational wavelength for the [[GW170104]] event, which was ~ 1,700&nbsp;km. The report<ref name="Abbott2017" /> did not elaborate on the source of this ratio. It is possible that gravitons are not the quanta of gravitational waves, or that the two phenomena are related in a different way.

== Eksperimentalna opservacija ==

Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is impossible with any physically reasonable detector.<ref name="Rothman">
{{cite journal
|last=Rothman |first=T.
|last2=Boughn |first2=S.
|date=2006
|title=Can Gravitons be Detected?
|journal=[[Foundations of Physics]]
|volume=36 |issue=12 |pages=1801–1825
|arxiv=gr-qc/0601043
|bibcode=2006FoPh...36.1801R
|doi=10.1007/s10701-006-9081-9
}}</ref> The reason is the extremely low [[cross section (physics)|cross section]] for the interaction of gravitons with matter. For example, a detector with the mass of [[Jupiter]] and 100% efficiency, placed in close orbit around a [[neutron star]], would only be expected to observe one graviton every 10 years, even under the most favorable conditions. It would be impossible to discriminate these events from the background of [[neutrino]]s, since the dimensions of the required neutrino shield would ensure collapse into a [[black hole]].<ref name="Rothman" />

[[LIGO]] and [[Virgo interferometer|Virgo]] collaborations' observations have [[First observation of gravitational waves|directly detected]] [[gravitational waves]].<ref name="Abbot">{{cite journal |title=Observation of Gravitational Waves from a Binary Black Hole Merger| author=Abbott, B. P. et al. (LIGO Scientific Collaboration and Virgo Collaboration)| journal=Physical Review Letters| year=2016| volume=116|issue=6| doi=10.1103/PhysRevLett.116.061102|arxiv = 1602.03837 |bibcode = 2016PhRvL.116f1102A | pmid=26918975 | pages=061102}}</ref><ref name="Discovery 2016">{{cite journal |title=Einstein's gravitational waves found at last |journal=Nature News|date=February 11, 2016 |last=Castelvecchi |first=Davide |last2=Witze |first2=Witze |doi=10.1038/nature.2016.19361 }}</ref><ref name="NSF">{{cite web|title = Gravitational waves detected 100 years after Einstein's prediction {{!}} NSF - National Science Foundation|url = https://www.nsf.gov/news/news_summ.jsp?cntn_id=137628|website = www.nsf.gov|access-date = 2016-02-11}}</ref> Others have postulated that graviton scattering yields gravitational waves as particle interactions yield [[coherent state]]s.<ref>{{cite journal | last1 = Senatore | first1 = L. | last2 = Silverstein | first2 = E. | last3 = Zaldarriaga | first3 = M. | year = 2014 | title = New sources of gravitational waves during inflation | url = | journal = Journal of Cosmology and Astroparticle Physics | volume = 2014 | issue = 8| page = 016 | doi=10.1088/1475-7516/2014/08/016| arxiv = 1109.0542 | bibcode = 2014JCAP...08..016S }}</ref> Although these experiments cannot detect individual gravitons, they might provide information about certain properties of the graviton.<ref name="detecting graviton">{{cite journal|first=Freeman |last= Dyson|date=8 October 2013|journal=[[International Journal of Modern Physics A]]|volume=28|issue=25|pages=1330041–1–1330035–14|title=Is a Graviton Detectable?|doi=10.1142/S0217751X1330041X|bibcode = 2013IJMPA..2830041D }}</ref> For example, if gravitational waves were observed to propagate slower than ''c'' (the [[speed of light]] in a vacuum), that would imply that the graviton has mass (however, gravitational waves must propagate slower than ''c'' in a region with non-zero mass density if they are to be detectable).<ref>
{{cite journal
|last=Will |first=C. M.
|date=1998
|title=Bounding the mass of the graviton using gravitational-wave observations of inspiralling compact binaries
|journal=[[Physical Review D]]
|volume=57 |issue=4 |pages=2061–2068
|arxiv=gr-qc/9709011
|bibcode=1998PhRvD..57.2061W
|doi=10.1103/PhysRevD.57.2061
|url=http://cds.cern.ch/record/333219/files/9709011.pdf}}</ref> Recent observations of gravitational waves have put an upper bound of {{val|1.2|e=-22|u=eV/c2}} on the graviton's mass.<ref name="Abbot" /> Astronomical observations of the kinematics of galaxies, especially the [[galaxy rotation curve|galaxy rotation problem]] and [[modified Newtonian dynamics]], might point toward gravitons having non-zero mass.<ref>Trippe, S. (2013), "A Simplified Treatment of Gravitational Interaction on Galactic Scales", J. Kor. Astron. Soc. '''46''', 41. {{arxiv|1211.4692}}</ref>


== Vidi još ==
== Vidi još ==

Верзија на датум 5. новембар 2019. у 03:15

Graviton
KompozicijaElementarna čestica
StatistikeBoze-Ajnštajnova statistika
InterakcijeGravitacija
StatusHipotetičan
SimbolG[1]
AntičesticaSelf
Teorije1930-e[2]
Naziv se pripisuje Dmitriju Blokhintsevu i F. M. Galperinu u 1934. godini[3]
Masa0
Srednji poluživotStabilan
Naelektrisanjee
Spin2

U teorijama kvantne gravitacije, graviton je hipotetički kvant gravitacije, elementarna čestica koja posreduje gravitacionu silu. Ne postoji potpuna teorije kvantnog polja gravitona usled nerešenog matematičkog problema vezanog za renormalizaciju u opštoj teoriji relativnosti. U teoriji struna, za koju se smatra da je konzistentna teorija kvantne gravitacije, graviton je bezmaseno stanje fundamentalne strune.

Ako postoji, pretpostavlja se da je graviton bez mase, jer gravitacione sile deluju na veoma dugim opsezima i šire se brzinom svetlosti. Graviton mora biti spin-2 bozon, jer je izvor gravitacije energetsko-impulsni tenzor, tenzor drugog reda (u poređenju sa spin-1 fotonom elektromagnetizma, čiji izvor je četvorotočna struja, koja je tenzor prvog reda). Dodatno, može se pokazati da svako bezmaseno spin-2 polje može da proizvede silu koja se ne razlikuje od gravitacije, zato što bi se bezmaseno spin-2 polje spreglo sa energetsko-impulsnim tenzorom na isti način kao i gravitacione interakcije. Ovaj rezultat sugeriše da, ako se otkrije bezmasena spin-2 čestica, ona mora biti graviton.[4]

Teorija

Postoje hipoteze prema kojima su gravitacione interakcije posredovane sa jednom do sada neotkrivenom elementarnom česticom, nazvanom graviton. Tri druge poznate sile prirode su posredovane elementarnim česticama: elektromagnetizam fotonom, jaka interakcija gluonima, i slaba interakcija sa W i Z bozonima. Sve tri od ovih sila su precizno opisane pomoću standardnog modela fizike elementarnih čestica. Unutar klasičnih granica, uspešna teorija gravitona bi bila redukona na opštu relativnost, koja sama biva redukovana na Njutnov zakon gravitacije u granicama slabog polja.[5][6][7]

Termin graviton su originalno skovali 1934. godine sovjetski fizičari Dmitri Blokhintsev i F. Galperin.[3]

Gravitoni i renormalizacija

Pri opisivanju gravitonskih interakcija, klasična teorija Fejnmanovih dijagrama, i semiklasične korekcije kao što su dijagrami sa jednom petljom normalno se ponašaju. Međutim, Fejnmanovi dijagrami sa bar dve petlje dovode do ultraljubičaste divergencije. Ovi beskonačni rezultati se ne mogu ukloniti zato što kvantizovana generalna relativnost nije perturbativno renormalizabilna, za razliku od kvantno elektrodinamičkih modela kao što je Jang-Milsova teorija. Neiračunljivi odgovori se dobijaju iz perturbacionog metoda pomoću kojeg fizičari izračunavaju verovatnoću da čestica emituje ili apsorbuje gravitone, i konsekventno teorija gubi verodostojnost predviđanja. Ovi problemi i komplementarni aproksimacioni okvir su osnova da se pokaže da je teorija koja je u većoj meri ujedinjena nego kvantizovana generalna relativnost neophodna da se opiše ponašanje u blizini Plankove skale.

Upoređenje sa drigim silama

Poput nosilaca drugih sila (pogledajte naelektrisane crne rupe), gravitacija igra ulogu u opštoj relativnosti, u definisanju prostor-vremena u kome se događaji odvijaju. U pojedinim opisima energija modifikuje „oblik” samog prostora-vremena, i gravitacija je rezultat tog oblika, što je ideja koju je na prvi pogled teško uskladiti sa idejom sile koja deluje između dve čestice.[8] Difeomorfična invarijantnost teorije ne dozvoljava bilo kojoj prostorno-vremenskoj zaleđini da bude izdvojena kao „istinska” prostorno-vremenska zaleđina, te je stoga opšta relativnost nezavisna od pozadine. U kontrastu s tim standardni model nije nezavistan od pozadine, i Minkovskijev prostor ima specijalni status prostora-vremena sa fiksnom pozadinom.[9] Teorija kvantne gravitacije je neophodna da bi se pomirile razlike.[10] Otvoreno je pitanje da li ova teorija treba da bude nezavisna od zaleđine. Odgovor na to pitanje će odrediti naše razumevanje specifične uloge gravitacije u sudbini svemira.[11]

Gravitoni u spekulativnim teorijama

Teorija struna predviđa postojanje gravitona i njihove dobro definirane interakcije. Graviton u perturbativnoj teoriji struna je zatvorena struna u veoma specifičnom nisko-energijskom vibracionom stanju. Rasipanje gravitona u teoriji struna takođe se može izračunati iz korelacionih funkcija u teoriji konformalnog polja, kao što je diktirano AdS/CFT korespondencijom, ili iz teorije matrica.

Karakteristika gravitona u teoriji struna je da, kao zatvoreni nizovi bez krajnjih tačaka, oni nisu vezani za brane i mogu se slobodno kretati između njih. Ako živimo na brani (kao što je pretpostavljeno teorijama brane), ovo „curenje” gravitona iz brane u višedimenzionalni prostor moglo bi da objasni zašto je gravitacija tako slaba sila, a gravitoni iz drugih brana u blizini naše mogu pružiti potencijalno objašnjenje za tamnu materiju. Međutim, ako bi se gravitoni potpuno slobodno kretali između brana, došlo bi do prevelikog razblaženja gravitacije, što bi uzrokovalo kršenje Njutnovog zakona inverznih kvadrata. Da bi rešila taj problem, Liza Randal je postulirala da bi trostruka brana (poput naše) imala svoju gravitacionu silu, koja sprečava slobodno kretanje gravitona, što može da dovede do razređene gravitacije koju uočavamo, uz grubo održavanje Njutnovog zakona inverznih kvadrata.[12] Pogledajte bransku kosmologiju.

Teorija koju su formulisali Ahmed Farag Ali i Saurja Das dodaje kvantno mehaničke korekcije (koristeći Bemove trajektorije) u generalnu relativističku geodeziju. Ako se gravitonima da mala nenulta masa, to može da objasni kosmološku konstantu bez potrebe za tamnom energijom i da reši problem kosmološke konstante.[13] Ova teorija je dobila počasno priznanje na konkursu za eseje 2014. godine Fondacije za istraživanje gravitacije zbog objašnjenje male veličine kosmološke konstante.[14] Isto tako, teorija je dobila počasno priznanje na konkursu za eseje 2015. godine Fondacije za istraživanje gravitacije zbog prirodnog objašnjavanja homogenosti velikih dimenzija i izotropije univerzuma pomoću predloženih kvantnih korekcija.[15]

Energija i talasna dužina

While gravitons are presumed to be massless, they would still carry energy, as does any other quantum particle. Photon energy and gluon energy are also carried by massless particles. It is unclear which variables might determine graviton energy, the amount of energy carried by a single graviton.

Alternatively, if gravitons are massive at all, the analysis of gravitational waves yielded a new upper bound on the mass of gravitons. The graviton's Compton wavelength is at least 1,6×1016 m, or about 1.6 light-years, corresponding to a graviton mass of no more than 7,7×10−23 eV/c2.[16] This relation between wavelength and mass-energy is calculated with the Planck–Einstein relation, the same formula that relates electromagnetic wavelength to photon energy. However, if gravitons are the quanta of gravitational waves, then the relation between wavelength and corresponding particle energy is fundamentally different for gravitons than for photons, since the Compton wavelength of the graviton is not equal to the gravitational-wave wavelength. Instead, the lower-bound graviton Compton wavelength is about 9×109 times greater than the gravitational wavelength for the GW170104 event, which was ~ 1,700 km. The report[16] did not elaborate on the source of this ratio. It is possible that gravitons are not the quanta of gravitational waves, or that the two phenomena are related in a different way.

Eksperimentalna opservacija

Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is impossible with any physically reasonable detector.[17] The reason is the extremely low cross section for the interaction of gravitons with matter. For example, a detector with the mass of Jupiter and 100% efficiency, placed in close orbit around a neutron star, would only be expected to observe one graviton every 10 years, even under the most favorable conditions. It would be impossible to discriminate these events from the background of neutrinos, since the dimensions of the required neutrino shield would ensure collapse into a black hole.[17]

LIGO and Virgo collaborations' observations have directly detected gravitational waves.[18][19][20] Others have postulated that graviton scattering yields gravitational waves as particle interactions yield coherent states.[21] Although these experiments cannot detect individual gravitons, they might provide information about certain properties of the graviton.[22] For example, if gravitational waves were observed to propagate slower than c (the speed of light in a vacuum), that would imply that the graviton has mass (however, gravitational waves must propagate slower than c in a region with non-zero mass density if they are to be detectable).[23] Recent observations of gravitational waves have put an upper bound of 1,2×10−22 eV/c2 on the graviton's mass.[18] Astronomical observations of the kinematics of galaxies, especially the galaxy rotation problem and modified Newtonian dynamics, might point toward gravitons having non-zero mass.[24]

Vidi još

Reference

  1. ^ G is used to avoid confusion with gluons (symbol g)
  2. ^ Rovelli, C. (2001). „Notes for a brief history of quantum gravity”. arXiv:gr-qc/0006061Слободан приступ. 
  3. ^ а б Blokhintsev, D. I.; Gal'perin, F. M. (1934). „Гипотеза нейтрино и закон сохранения энергии” [Neutrino hypothesis and conservation of energy]. Pod Znamenem Marxisma (на језику: руски). 6: 147—157. 
  4. ^ For a comparison of the geometric derivation and the (non-geometric) spin-2 field derivation of general relativity, refer to box 18.1 (and also 17.2.5) of Misner, C. W.; Thorne, K. S.; Wheeler, J. A. (1973). Gravitation. W. H. Freeman. ISBN 978-0-7167-0344-0. 
  5. ^ Feynman, R. P.; Morinigo, F. B.; Wagner, W. G.; Hatfield, B. (1995). Feynman Lectures on Gravitation. Addison-Wesley. ISBN 978-0-201-62734-3. 
  6. ^ Zee, A. (2003). Quantum Field Theory in a Nutshell. Princeton University Press. ISBN 978-0-691-01019-9. 
  7. ^ Randall, L. (2005). Warped Passages: Unraveling the Universe's Hidden Dimensions. Ecco Press. ISBN 978-0-06-053108-9. 
  8. ^ See the other articles on General relativity, Gravitational field, Gravitational wave, etc
  9. ^ Colosi, D.; et al. (2005). „Background independence in a nutshell: The dynamics of a tetrahedron”. Classical and Quantum Gravity. 22 (14): 2971—2989. Bibcode:2005CQGra..22.2971C. arXiv:gr-qc/0408079Слободан приступ. doi:10.1088/0264-9381/22/14/008. 
  10. ^ Witten, E. (1993). „Quantum Background Independence In String Theory”. arXiv:hep-th/9306122Слободан приступ. 
  11. ^ Smolin, L. (2005). „The case for background independence”. arXiv:hep-th/0507235Слободан приступ. 
  12. ^ Kaku, Michio Parallel Worlds – The science of alternative universes and our future in the Cosmos. Doubleday. 2006. ISBN 978-0385509862. стр. 218-221.
  13. ^ Ali, Ahmed Farag (2014). „Cosmology from quantum potential”. Physics Letters B. 741: 276—279. Bibcode:2015PhLB..741..276F. arXiv:1404.3093v3Слободан приступ. doi:10.1016/j.physletb.2014.12.057. 
  14. ^ Das, Saurya (2014). „Cosmic coincidence or graviton mass?”. International Journal of Modern Physics D. 23 (12): 1442017. Bibcode:2014IJMPD..2342017D. arXiv:1405.4011Слободан приступ. doi:10.1142/S0218271814420176. 
  15. ^ Das, Saurya (2015). „Bose–Einstein condensation as an alternative to inflation”. International Journal of Modern Physics D. 24 (12): 1544001—219. Bibcode:2015IJMPD..2444001D. arXiv:1509.02658Слободан приступ. doi:10.1142/S0218271815440010. 
  16. ^ а б B. P. Abbott; et al. (LIGO Scientific Collaboration and Virgo Collaboration) (1. 6. 2017). „GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2”. Physical Review Letters. 118: 221101. Bibcode:2017PhRvL.118v1101A. arXiv:1706.01812Слободан приступ. doi:10.1103/PhysRevLett.118.221101. 
  17. ^ а б Rothman, T.; Boughn, S. (2006). „Can Gravitons be Detected?”. Foundations of Physics. 36 (12): 1801—1825. Bibcode:2006FoPh...36.1801R. arXiv:gr-qc/0601043Слободан приступ. doi:10.1007/s10701-006-9081-9. 
  18. ^ а б Abbott, B. P. et al. (LIGO Scientific Collaboration and Virgo Collaboration) (2016). „Observation of Gravitational Waves from a Binary Black Hole Merger”. Physical Review Letters. 116 (6): 061102. Bibcode:2016PhRvL.116f1102A. PMID 26918975. arXiv:1602.03837Слободан приступ. doi:10.1103/PhysRevLett.116.061102. 
  19. ^ Castelvecchi, Davide; Witze, Witze (11. 2. 2016). „Einstein's gravitational waves found at last”. Nature News. doi:10.1038/nature.2016.19361. 
  20. ^ „Gravitational waves detected 100 years after Einstein's prediction | NSF - National Science Foundation”. www.nsf.gov. Приступљено 2016-02-11. 
  21. ^ Senatore, L.; Silverstein, E.; Zaldarriaga, M. (2014). „New sources of gravitational waves during inflation”. Journal of Cosmology and Astroparticle Physics. 2014 (8): 016. Bibcode:2014JCAP...08..016S. arXiv:1109.0542Слободан приступ. doi:10.1088/1475-7516/2014/08/016. 
  22. ^ Dyson, Freeman (8. 10. 2013). „Is a Graviton Detectable?”. International Journal of Modern Physics A. 28 (25): 1330041—1—1330035—14. Bibcode:2013IJMPA..2830041D. doi:10.1142/S0217751X1330041X. 
  23. ^ Will, C. M. (1998). „Bounding the mass of the graviton using gravitational-wave observations of inspiralling compact binaries” (PDF). Physical Review D. 57 (4): 2061—2068. Bibcode:1998PhRvD..57.2061W. arXiv:gr-qc/9709011Слободан приступ. doi:10.1103/PhysRevD.57.2061. 
  24. ^ Trippe, S. (2013), "A Simplified Treatment of Gravitational Interaction on Galactic Scales", J. Kor. Astron. Soc. 46, 41. arXiv:1211.4692

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