Group Field Theory and Its Cosmology in a Matter Reference Frame
While the equations of general relativity take the same form in any coordinate system, choosing a suitable set of coordinates is essential in any practical application. This poses a challenge in background-independent quantum gravity, where coordinates are not a priori available and need to be recon...
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| Format: | Article |
| Language: | English |
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MDPI AG
2018-10-01
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| Series: | Universe |
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| Online Access: | http://www.mdpi.com/2218-1997/4/10/103 |
| _version_ | 1811278099235471360 |
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| author | Steffen Gielen |
| author_facet | Steffen Gielen |
| author_sort | Steffen Gielen |
| collection | DOAJ |
| description | While the equations of general relativity take the same form in any coordinate system, choosing a suitable set of coordinates is essential in any practical application. This poses a challenge in background-independent quantum gravity, where coordinates are not a priori available and need to be reconstructed from physical degrees of freedom. We review the general idea of coupling free scalar fields to gravity and using these scalars as a “matter reference frame”. The resulting coordinate system is harmonic, i.e., it satisfies the harmonic (de Donder) gauge. We then show how to introduce such matter reference frames in the group field theory approach to quantum gravity, where spacetime is emergent from a “condensate” of fundamental quantum degrees of freedom of geometry, and how to use matter coordinates to extract physics. We review recent results in homogeneous and inhomogeneous cosmology, and give a new application to the case of spherical symmetry. We find tentative evidence that spherically-symmetric group field theory condensates defined in this setting can reproduce the near-horizon geometry of a Schwarzschild black hole. |
| first_indexed | 2024-04-13T00:28:34Z |
| format | Article |
| id | doaj.art-2b0a4b913b8345359867d41a21e0721e |
| institution | Directory Open Access Journal |
| issn | 2218-1997 |
| language | English |
| last_indexed | 2024-04-13T00:28:34Z |
| publishDate | 2018-10-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Universe |
| spelling | doaj.art-2b0a4b913b8345359867d41a21e0721e2022-12-22T03:10:31ZengMDPI AGUniverse2218-19972018-10-0141010310.3390/universe4100103universe4100103Group Field Theory and Its Cosmology in a Matter Reference FrameSteffen Gielen0School of Mathematical Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UKWhile the equations of general relativity take the same form in any coordinate system, choosing a suitable set of coordinates is essential in any practical application. This poses a challenge in background-independent quantum gravity, where coordinates are not a priori available and need to be reconstructed from physical degrees of freedom. We review the general idea of coupling free scalar fields to gravity and using these scalars as a “matter reference frame”. The resulting coordinate system is harmonic, i.e., it satisfies the harmonic (de Donder) gauge. We then show how to introduce such matter reference frames in the group field theory approach to quantum gravity, where spacetime is emergent from a “condensate” of fundamental quantum degrees of freedom of geometry, and how to use matter coordinates to extract physics. We review recent results in homogeneous and inhomogeneous cosmology, and give a new application to the case of spherical symmetry. We find tentative evidence that spherically-symmetric group field theory condensates defined in this setting can reproduce the near-horizon geometry of a Schwarzschild black hole.http://www.mdpi.com/2218-1997/4/10/103quantum gravitygroup field theoryharmonic coordinatesspherical symmetry |
| spellingShingle | Steffen Gielen Group Field Theory and Its Cosmology in a Matter Reference Frame Universe quantum gravity group field theory harmonic coordinates spherical symmetry |
| title | Group Field Theory and Its Cosmology in a Matter Reference Frame |
| title_full | Group Field Theory and Its Cosmology in a Matter Reference Frame |
| title_fullStr | Group Field Theory and Its Cosmology in a Matter Reference Frame |
| title_full_unstemmed | Group Field Theory and Its Cosmology in a Matter Reference Frame |
| title_short | Group Field Theory and Its Cosmology in a Matter Reference Frame |
| title_sort | group field theory and its cosmology in a matter reference frame |
| topic | quantum gravity group field theory harmonic coordinates spherical symmetry |
| url | http://www.mdpi.com/2218-1997/4/10/103 |
| work_keys_str_mv | AT steffengielen groupfieldtheoryanditscosmologyinamatterreferenceframe |