Kvantna gravitacija

gravitational nor quantum effects can be ignored, such as in the vicinity of black holes or similar compact astrophysical objects, such as neutron stars as well as in the early stages of the universe moments after the Big Bang.

Three of the four fundamental forces of nature are described within the framework of quantum mechanics and quantum field theory: the electromagnetic interaction, the strong force, and the weak force; this leaves gravity as the only interaction that has not been fully accommodated. The current understanding of gravity is based on Albert Einstein's general theory of relativity, which incorporates his theory of special relativity and deeply modifies the understanding of concepts like time and space. Although general relativity is highly regarded for its elegance and accuracy it has limitations: the gravitational singularities inside of black holes, the ad hoc postulation of dark matter, as well as dark energy and its relation to the cosmological constant are among the current unsolved mysteries regarding gravity; all of which signal the collapse of the general theory of relativity at different scales and highlight the need for a gravitational theory that goes into the quantum realm. At distances close to the Planck length, like those near the center of the black hole, quantum fluctuations of spacetime are expected to play an important role. The breakdown of general relativity at galactic and cosmological scales also points out the necessity for a more robust theory. Finally the discrepancies between the predicted value for the vacuum energy and the observed values (which, depending on the considerations, can be of 60 or 120 orders of magnitude) highlight the necessity for a quantum theory of gravity.

The field of quantum gravity is actively developing, and theorists are exploring a variety of approaches to the problem of quantum gravity, the most popular being M-theory and loop quantum gravity. All of these approaches aim to describe the quantum behavior of the gravitational field, which does not necessarily include unifying all fundamental interactions into a single mathematical framework. However, many approaches to quantum gravity, such as string theory, try to develop a framework that describes all fundamental forces. Such a theory is often referred to as a theory of everything. Some of the approaches, such as loop quantum gravity, make no such attempt; instead, they make an effort to quantize the gravitational field while it is kept separate from the other forces. Other lesser-known but no less important theories include Causal dynamical triangulation, Noncommutative geometry, and Twistor theory.

One of the difficulties of formulating a quantum gravity theory is that direct observation of quantum gravitational effects is thought to only appear at length scales near the Planck scale, around 10⁻³⁵ meters, a scale far smaller, and hence only accessible with far higher energies, than those currently available in high energy particle accelerators. Therefore, physicists lack experimental data which could distinguish between the competing theories which have been proposed.

Thought experiment approaches have been suggested as a testing tool for quantum gravity theories. In the field of quantum gravity there are several open questions – e.g., it is not known how spin of elementary particles sources gravity, and thought experiments could provide a pathway to explore possible resolutions to these questions, even in the absence of lab experiments or physical observations.

In the early 21st century, new experiment designs and technologies have arisen which suggest that indirect approaches to testing quantum gravity may be feasible over the next few decades. This field of study is called phenomenological quantum gravity.

Literatura

• Green, M.B.; Schwarz, J.H.; Witten, E. (1987). Superstring theory. l. Cambridge University Press. ISBN 9781107029118. 
• Penrose, Roger (2004), The Road to Reality, A. A. Knopf, ISBN 978-0-679-45443-4 
• Ahluwalia, D. V. (2002). „Interface of Gravitational and Quantum Realms”. Modern Physics Letters A. 17 (15–17): 1135—1145. Bibcode:2002MPLA...17.1135A. S2CID 119358167. arXiv:gr-qc/0205121 . doi:10.1142/S021773230200765X. 
• Ashtekar, Abhay (2005). „The winding road to quantum gravity” (PDF). The Legacy of Albert Einstein. Current Science. 89. стр. 2064—2074. Bibcode:2007laec.book...69A. CiteSeerX 10.1.1.616.8952 . ISBN 978-981-270-049-0. doi:10.1142/9789812772718_0005. 
• Carlip, Steven (2001). „Quantum Gravity: a Progress Report”. Reports on Progress in Physics. 64 (8): 885—942. Bibcode:2001RPPh...64..885C. S2CID 118923209. arXiv:gr-qc/0108040 . doi:10.1088/0034-4885/64/8/301. 
• Hamber, Herbert W. (2009). Hamber, Herbert W., ур. Quantum Gravitation. Springer Nature. ISBN 978-3-540-85292-6. doi:10.1007/978-3-540-85293-3. hdl:11858/00-001M-0000-0013-471D-A. 
• Kiefer, Claus (2007). Quantum Gravity. Oxford University Press. ISBN 978-0-19-921252-1. 
• Kiefer, Claus (2005). „Quantum Gravity: General Introduction and Recent Developments”. Annalen der Physik. 15 (1): 129—148. Bibcode:2006AnP...518..129K. S2CID 12984346. arXiv:gr-qc/0508120 . doi:10.1002/andp.200510175. 
• Lämmerzahl, Claus, ур. (2003). Quantum Gravity: From Theory to Experimental Search. Lecture Notes in Physics. Springer. ISBN 978-3-540-40810-9. 
• Rovelli, Carlo (2004). Quantum Gravity. Cambridge University Press. ISBN 978-0-521-83733-0. 

Spoljašnje veze

• "Planck Era" and "Planck Time" Архивирано 2018-11-28 на сајту Wayback Machine (up to 10⁻⁴³ seconds after birth of Universe) (University of Oregon).
• "Quantum Gravity", BBC Radio 4 discussion with John Gribbin, Lee Smolin and Janna Levin (In Our Time, February 22, 2001)