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 \textit{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 \textit{context}: where spacetime emerges from some `prior' non-spatiotemporal state (replacing the Big Bang), due to particular conditions in the early universe. 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. (shrink)

Scientific realists don’t standardly discriminate between, say, biology and fundamental physics when deciding whether the evidence and explanatory power warrant the inclusion of new entities in our ontology. As such, scientific realists are committed to a lush rainforest of special science kinds (Ross, 2000). Viruses certainly inhabit this rainforest – their explanatory power is overwhelming – but viruses’ properties can be explained from the bottom up: reductive explanations involving amino acids are generally available. However, reduction has often been taken to (...) lead to a metaphysical downgrading, so how can viruses keep their place in the rainforest? In this paper, we show how the inhabitants of the rainforest can be inoculated against the eliminative threat of reduction: by demonstrating that they are emergent. According to our account, emergence involves a screening off condition as well as novelty. We go on to demonstrate that this account of emergence, which is compatible with theoretical reducibility, satisfies common intuitions concerning what should and shouldn’t count as real: viruses are emergent, as are trout and turkeys, but philosophically gerrymandered objects like trout-turkeys do not qualify. (shrink)

Typically, a less fundamental theory, or structure, emerging from a more fundamental one is an example of synchronic emergence. A model emerging from a prior model upon which it nevertheless depends is an example of diachronic emergence. The case of spacetime emergent from quantum gravity and quantum cosmology challenges these two conceptions of emergence. Here, I propose two more-general conceptions of emergence, analogous to the synchronic and diachronic ones, but which are potentially applicable to the case of emergent spacetime: an (...) inter-level, hierarchical conception, and an intra-level, ‘flat’ conception. I then explore whether, and how, these ideas may be applicable in the case of several putative examples of relativistic spacetime emergent from the non-spatiotemporal structures described by different approaches to quantum gravity, and of spacetime emergent from a non-spatiotemporal ‘big bang’ state according to different examples of quantum cosmology. (shrink)

Effective quantum field theories are effective insofar as they apply within a prescribed range of length-scales, but within that range they predict and describe with extremely high accuracy and precision. The effectiveness of EFTs is explained by identifying the features—the scaling behaviour of the parameters—that lead to effectiveness. The explanation relies on distinguishing autonomy with respect to changes in microstates, from autonomy with respect to changes in microlaws, and relating these, respectively, to renormalizability and naturalness. It is claimed that the (...) effectiveness of EFTs is a consequence of each theory’s autonomyms rather than its autonomyml.1Introduction2Renormalizability2.1Explaining renormalizability3Naturalness3.1An unnatural but renormalizable theory4Two Kinds of Autonomy5The Effectiveness of Effective Quantum Field Theories6Conclusion. (shrink)

Relationships between current theories, and relationships between current theories and the sought theory of quantum gravity (QG), play an essential role in motivating the need for QG, aiding the search for QG, and defining what would count as QG. Correspondence is the broad class of inter-theory relationships intended to demonstrate the necessary compatibility of two theories whose domains of validity overlap, in the overlap regions. The variety of roles that correspondence plays in the search for QG are illustrated, using examples (...) from specific QG approaches. Reduction is argued to be a special case of correspondence, and to form part of the definition of QG. Finally, the appropriate account of emergence in the context of QG is presented, and compared to conceptions of emergence in the broader philosophy literature. It is argued that, while emergence is likely to hold between QG and general relativity, emergence is not part of the definition of QG, and nor can it serve usefully in the development and justification of the new theory. (shrink)

In this paper I develop a framework for relating dualities and emergence: two notions that are close to each other but also exclude one another. I adopt the conception of duality as 'isomorphism', from the physics literature, cashing it out in terms of three conditions. These three conditions prompt two conceptually different ways in which a duality can be modified to make room for emergence; and I argue that this exhausts the possibilities for combining dualities and emergence. I apply this (...) framework to gauge/gravity dualities, considering in detail three examples: AdS/CFT, Verlinde's scheme, and black holes. My main point about gauge/gravity dualities is that the theories involved, qua theories of gravity, must be background-independent. I distinguish two senses of background-independence: minimalistic and extended. I argue that the former is sufficiently strong to allow for a consistent theory of quantum gravity; and that AdS/CFT is background-independent on this account; while Verlinde's scheme best fits the extended sense of background-independence. I argue that this extended sense should be applied with some caution: on pain of throwing the baby out with the bath-water. Nevertheless, it is an interesting and potentially fruitful heuristic principle for quantum gravity theory construction. It suggests some directions for possible generalisations of gauge/gravity dualities. The interpretation of dualities is discussed; and the so-called 'internal' vs. 'external' viewpoints are articulated in terms of: epistemic and metaphysical commitments; parts vs. wholes. I then analyse the emergence of gravity in gauge/gravity dualities in terms of the two available conceptualisations of emergence; and I show how emergence in AdS/CFT and in Verlinde's scenario differ from each other. Finally, I give a novel derivation of the Bekenstein-Hawking black hole entropy formula based on Verlinde's scheme; the derivation sheds light on several aspects of Verlinde's scheme and how it compares to Bekenstein's original calculation. (shrink)

Within physics there are two ways of establishing the relative fundamentality of one theory compared to another, via two senses of reduction: "inter-level" and "intra-level" (Crowther, 2018). The former is standardly recognised as roughly correlating with the chain of ontological dependence (i.e., the phenomena described by theories of macro-physics are typically supposed to be ontologically dependent on the entities/behaviour described by theories of micro-physics), and thus has been of interest to naturalised metaphysics. The latter, though, has not been considered interesting (...) for metaphysics, because it is not thought to correlate either with ontological dependence, nor causal or dynamical dependence. I argue, however, that this is a mistake, and that actually, the intra-level relation does reflect ontological dependence (in the same sense as the inter-level relation) and thus should not be neglected by metaphysics of physics. This argument further supports the assertion that the same notion of fundamentality underlies both the inter- and intra-level claims of fundamentality in physics, and that this notion of relative fundamentality in physics correlates with that of metaphysics. (shrink)

Although the interest about emergence has grown during the last years, there does not seem to be consensus on whether it is a non-trivial and interesting notion and whether the concept of reduction is relevant to its characterization. Another key issue is whether emergence should be understood as an epistemic notion or if there is a plausible ontological concept of emergence. The aim of this work is to propose an epistemic notion of contextual emergence on the basis of which one (...) may tackle those issues. Resumen Aunque el interés en torno a la emergencia ha crecido durante los últimos años, no parece haber un consenso sobre si es una noción no trivial e interesante ni sobre si el concepto de reducción es relevante para su caracterización. Otra cuestión clave es si la emergencia debería ser entendida como una noción epistémica o si hay un concepto ontológico plausible de emergencia. El objetivo de este trabajo es proponer una noción epistémica de emergencia contextual sobre cuya base uno podría abordar estos problemas. (shrink)

Naturalness, as a guiding principle for effective field theories, requires that there be no sensitive correlations between phenomena at low- and high-energy scales. This essay considers four reasons to adopt this principle: natural EFTs exhibit modest empirical success; unnatural EFTs are improbable; naturalness underwrites what Williams calls a “central dogma” of EFTs; namely, that phenomena at widely separated scales should decouple; and naturalness underwrites a non-trivial notion of emergence. I argue that the first three are not compelling reasons, whereas the (...) fourth is. (shrink)

Although general relativity is a predictively successful theory, it treats matter as classical rather than as quantum. For this reason, it will have to be replaced by a more fundamental quantum theory of gravity. Attempts to formulate a quantum theory of gravity suggest that such a theory may have radical consequences for the nature, and indeed the fate, of spacetime. The present article articulates what this problem of spacetime is and traces it three approaches to quantum gravity taking general relativity (...) as their vantage point: semi-classical gravity, causal set theory, and loop quantum gravity. (shrink)