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Spacetime Emergence: Collapsing the Distinction Between Content and Context?

Part of the The Frontiers Collection book series (FRONTCOLL)

Abstract

Several approaches to developing a theory of quantum gravity suggest that spacetime—as described by general relativity—is not fundamental. Instead, spacetime is supposed to be explained by reference to the relations between more fundamental entities, analogous to ‘atoms’ of spacetime, which themselves are not (fully) spatiotemporal. Such a case may be understood as emergence of content: a ‘hierarchical’ case of emergence, where spacetime emerges at a ‘higher’, or less-fundamental, level than its ‘lower-level’ non-spatiotempral basis. But quantum gravity cosmology also presents us with the possibility of emergence of context: where spacetime emerges from some ‘prior’ non-spatiotemporal state (replacing the Big Bang). I present a general conception of emergence which is plausibly able to accommodate both pictures. This is a positive conception that does not rely on a failure of reduction or explanation in any sense (indeed, reduction is a necessary feature of quantum gravity, and is useful in understanding emergence in this case). I also consider the possibility that the distinction between content- and context- based explanations is blurred, or usefully ‘collapsed’, in the case of spacetime emergence.

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Fig. 1
Fig. 2
Fig. 3

Figure adapted from Guay and Sartenaer (2016)

Fig. 4
Fig. 5
Fig. 6
Fig. 7

Figure adapted from Markopoulou (2009)

Notes

  1. 1.

    See, e.g., Butterfield and Isham (1999, 2001), Crowther (2016), Huggett and Wüthrich (2013), Oriti (Forthcoming), Wüthrich (2017, 2019).

  2. 2.

    See, e.g., Brahma (2020), Crowther (2020), Huggett and Wüthrich (2018).

  3. 3.

    For more on LQG, see Rovelli (2004), Rovelli and Vidotto (2014). Note that this latter reference is much more up-to-date than the brief sketch of the kinematic aspect of the theory that I present here; in particular, it has much more detail on the dynamics of the theory, using the covariant approach to LQG.

  4. 4.

    These are semiclassical states; i.e., states in which the quantum fluctuations are minimal and the gravitational field behaves almost classically.

  5. 5.

    The analogy comes from Ashtekar et al. (1992).

  6. 6.

    The following discussion is based on Crowther (2018a), although the definition of relative fundamentality differs here in that I include two conditions, while Crowther (2018a) requires only one.

  7. 7.

    While QG must be more fundamental than GR, QG need not be a fundamental theory; i.e., it is not necessary to include the criterion of (absolute) fundamentality in the definition of QG (Crowther & Linnemann, 2019). For other ideas of fundamentality in physics and metaphysics, see Morganti (2020a, 2020b).

  8. 8.

    Penrose explores this second possibility, see e.g. Penrose (1999, 2002).

  9. 9.

    Correspondence takes various forms and plays many important roles in theory development and assessment; see, e.g, Crowther (2018b), Hartmann (2002), Post (1971), Radder (1991).

  10. 10.

    The discussion in this section is based on Crowther (2020).

  11. 11.

    This is largely due to Butterfield and Isham (1999, 2001), Butterfield (2011a, 2011b).

  12. 12.

    See Batterman (2000, 2002, 2018), Crowther (2015), Franklin (2018a) for more on autonomy, universality, and multiple-realisability, particularly as related to emergence in effective field theory.

  13. 13.

    Actually, the dynamics can be thought of as not simply a ‘quantum version’ of GR, as this characterisation suggests, but a more radically different theory; see Oriti (2014, 2018) for more on this aspect.

  14. 14.

    Although these notions may have non-spatiotemporal analogues, e.g., causation without time (Baron & Miller, 2014, 2015; Tallant, 2019).

  15. 15.

    Note that the “Big Bang" strictly refers to the GR singularity, whereas in QG cosmology, this state may not be singular.

  16. 16.

    Shech (2019) also suggests weakening the novelty condition along these lines.

  17. 17.

    In other LQC models, however, the ‘Big Bounce’ picture is arguably better-supported.

  18. 18.

    Under these conditions, the system has a fractal structure, not changing as we view it at smaller length scales. In this example of the second order phase transition between liquid and vapour, as we look at smaller scales we would see liquid water droplets containing bubbles of steam, within which float even tinier liquid droplets, and so on... until we reach the scale of atoms.

  19. 19.

    See Batterman (2005, 2011), Bain (2013), Franklin (2018b), Rivat and Grinbaum (2020) for more on this.

  20. 20.

    Cf. Footnote 14.

  21. 21.

    For details: Konopka et al. (2008), Markopoulou (2009). Another active approach to geometrogenesis is in group field theory, see Oriti (2009, 2014).

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Acknowledgements

Thanks to Sebastiano Orioli for help with the figures.

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Correspondence to Karen Crowther .

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Crowther, K. (2022). Spacetime Emergence: Collapsing the Distinction Between Content and Context?. In: Wuppuluri, S., Stewart, I. (eds) From Electrons to Elephants and Elections. The Frontiers Collection. Springer, Cham. https://doi.org/10.1007/978-3-030-92192-7_22

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