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A Momentous Arrow of Time

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The Arrows of Time

Part of the book series: Fundamental Theories of Physics ((FTPH,volume 172))

Abstract

Quantum cosmology offers a unique stage to address questions of time related to its underlying (and perhaps truly quantum dynamical) meaning as well as its origin. Some of these issues can be analyzed with a general scheme of quantum cosmology, others are best seen in loop quantum cosmology. The latters status is still incomplete, and so no full scenario has yet emerged. Nevertheless, using properties that have a potential of pervading more complicated and realistic models, a vague picture shall be sketched here. It suggests the possibility of deriving a beginning within a beginningless theory, by applying cosmic forgetfulness to an early history of the universe.

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Notes

  1. 1.

    The laws are, of course, not completely time reflection symmetric, which might be exploited in the context discussed here [1].

  2. 2.

    It is interesting to note that the problem of time and motion becomes pressing when quantum gravity is considered. Quantum gravity is often tied to another expectation, that of discreteness or an atomic nature of space-time. Maybe solving the problem of time would lead us to establishing an atomic nature of time? If so, this would be reminiscent of a much older debate among pre-sokratic philosophers: Parmenides denied any reality to motion and change, which he logically argued to be pure illusion. His most basic statement was that nothingness does not exist, and so a body cannot move from where it is now to a place of empty space which was thought not to exist. The logical conflict was resolved by the atomists who accepted the notion of empty space and were led to the concept of material atoms.

  3. 3.

    A different perspective on the importance of gravitational degrees of freedom is discussed in [11].

  4. 4.

    In thermodynamics, coarse-graining plays an important role. Cosmic forgetfulness may be interpreted as forcing us to coarse-grain over many of the quantum variables. One should also note that cosmic forgetfulness is much stronger than decoherence (see e.g. [3]) since it appears even in exactly solvable models. It takes into account the specific dynamics of loop quantum cosmology, rather than being a generic property of quantum systems with many degrees of freedom.

  5. 5.

    Cosmic forgetfulness has been perceived as a challenge, heroically taken up in [55] by deriving bounds alternative to (11) for semiclassical states. However, those bounds are much weaker, allowing changes in the fluctuations by several orders of magnitude [56]. (Also this renewed challenge has been taken up in [57], though less heroically so.)

  6. 6.

    Numerical indications for a similarly sensitive behavior of inhomogeneities [62] already exist from Gowdy models with a loop-quantized homogeneous background [63].

  7. 7.

    James Joyce: Ulysses.

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Acknowledgements

This work was partially supported by NSF grant PHY0748336 and a grant from the Foundational Questions Institute (FQXi).

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  1. Institute for Gravitation and the Cosmos, The Pennsylvania State University, 104 Davey Lab, University Park, PA, 16802, USA

    Martin Bojowald

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Correspondence to Martin Bojowald .

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  1. Dept. Physics & Astronomy, University of North Carolina, Chapel Hill, 27599-3255, North Carolina, USA

    Laura Mersini-Houghton

  2. Posener Str. 85, Bietigheim-Bissingen, 74321, Germany

    Rudy Vaas

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Bojowald, M. (2012). A Momentous Arrow of Time. In: Mersini-Houghton, L., Vaas, R. (eds) The Arrows of Time. Fundamental Theories of Physics, vol 172. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-23259-6_9

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