Quantum cosmology
The quantum cosmology is a theoretical approach to physics that attempts to be a quantum theory of the universe to develop.
The quantum cosmology approach is primarily about clarifying open questions of classical cosmology that concern the initial phases of the universe. Classical cosmology is based on Albert Einstein's general theory of relativity . It describes the development of the universe very well, as long as one does not come too close in time to the initial state of the cosmos, the phase of the so-called Planck time . Here the theory of relativity fails and there is hope that quantum theory will continue to answer open questions. This requires a theory that brings together the theory of relativity and quantum theory, such an approach is tried, for example, with loop quantum gravity, another approach with string theory .
Tasks of quantum cosmology
If you get closer and closer to the Big Bang according to the big bang model of classical cosmology, the universe becomes denser and denser until you reach a point where the density and gravity should be infinitely large, the singularity. Mathematically, it cannot be calculated, the limit of effectiveness of the theory of relativity has been reached. This makes it clear that the general theory of relativity is incomplete, since it cannot describe the Big Bang.
Among other things, the initial singularity , the initial conditions after the Big Bang and the determination of the ground state energy for the universe after the Planck time must be clarified .
In addition, questions about the cause of the direction of time , the development of large-scale structures from quantum fluctuations, and dark matter and dark energy should also be better clarified.
Theoretical approaches
Quantum cosmology tries with the help of quantum theory to avoid the occurrence of a singularity in the description of the early days of our universe. According to her, singularities are not necessary, the big bang does not develop from a singularity, but from a quantum fluctuation. In Bojowald's view, the universe can only assume discrete sizes; since there cannot be a value zero, something must also have existed before the big bang.
Loop quantum gravity
In loop quantum cosmology, the singularity is skipped over, so to speak. This could possibly be caused by a big bounce caused by the collapse of another universe, but which is not causally related to our universe. The classical evolution is replaced by a wave function in the loop quantum cosmology. This should make it possible to expand quantum spacetime to include classical singularities and to understand the structure of the geometry around them. The new structure of space-time that results from it should also provide new insights into the nature of time.
String theory
In string theory, the connection between general relativity and quantum mechanics is established through the spatial expansion of strings. This spatial expansion of the strings also implies an interesting effect on spacetime . While cracks and holes are not possible in space-time, which is assumed to be smooth and continuous, due to the general theory of relativity, they are entirely conceivable due to string theory. Cracks and holes are therefore enclosed by strings. Wormholes and time travel cannot be excluded within this theory.
From universe to multiverse
The quantum theoretical view of the universe allows the assumption that our universe is not isolated, but a small part of a multiverse . According to this, there are many universes that constantly arise or fade away and develop completely differently from our universe. Similar to virtual particles, even virtual universes are conceivable.
As early as 1957, Hugh Everett tried to explain paradoxes of the quantum theoretical consideration of the universe with the many-worlds interpretation . String theory also allows the assumption that there can be innumerable other universes. Some of them may be similar to ours, but most of them are very different. In addition, the universes - according to string theory - are constantly connected to one another via various parameters (so-called landscape = cosmological landscape).
literature
- Martin Bojowald : Quantum Cosmology. A Fundamental Description of the Universe. (= Lecture Notes in Physics. Vol. 835). Springer, 2011, ISBN 978-1-4419-8276-6 .
- JJ Halliwell: Introductory Lectures on Quantum Cosmology (1990) . In: arXiv . General Relativity and Quantum Cosmology . September 14, 2009, arxiv : 0909.2566 .
- Claus Kiefer : The quantum cosmos . S. Fischer, 2008, ISBN 978-3-10-039506-1 .
Web links
- Before the Big Bang 1 - Loop Quantum Cosmology Explained on YouTube (conversations with two scientists)
Individual evidence
- ^ Klebanov, Igor and Maldacena, Juan: Solving Quantum Field Theories via Curved Spacetimes . In: Physics Today . Vol. 62, 2009, pp. 28 , doi : 10.1063 / 1.3074260 , bibcode : 2009PhT .... 62a..28K ( ias.edu [PDF; accessed on February 14, 2015]). Solving Quantum Field Theories via Curved Spacetimes ( Memento of the original from July 2, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Hans-Joachim Blome: The scope of physical cosmology . In: Sabina Jeschke, Eva-Maria Jakobs, Alicia Dröge (eds.): Exploring Uncertainty . Springer, 2013, ISBN 978-3-658-00897-0 , pp. 105–151.
- ↑ a b Claus Kiefer: The quantum cosmos. From the timeless world to the expanding universe ( memento of the original from December 19, 2014 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Lecture from February 17, 2011
- ↑ Martin Bojowald : Back to the Big Bang. The whole history of the universe. S. Fischer, Frankfurt am Main 2009 ISBN 978-3-10-003910-1 .
- ↑ Martin Bojowald: Loop Quantum Cosmology . ( Memento of the original from March 3, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Living Reviews in Relativity ISSN 1433-8351 , 2008. p. 1.
- ↑ Edward Witten: Space-Time Transitions in String Theory , 1993 on archive.org
- ↑ Research Report 2012 - Max Planck Institute for Gravitational Physics: Inflation and Cycles in the Multiverse
- ^ Bryce S. DeWitt, R. Neill Graham (Eds.): The Many Worlds Interpretation of Quantum Mechanics . Princeton University Press, 1973
- ^ Leonard Susskind: The Anthropic landscape of string theory , In: Universe or multiverse? 247-266; Carr, B. (Ed.); Cambridge University Press (2007)
