Device-Independent Relativistic Quantum Bit Commitment

We examine the possibility of device-independent relativistic quantum bit commitment. We note the potential threat of {\it location attacks}, in which the behaviour of untrusted devices used in relativistic quantum cryptography depends on their space-time location. We describe relativistic quantum bit commitment schemes that are immune to these attacks, and show that these schemes offer device-independent security against hypothetical post-quantum adversaries subject only to the no-signalling principle. We compare a relativistic classical bit commitment scheme with similar features, and note some possible advantages of the quantum schemes

Disappearing Without a Trace: The Arrows of Time in Kent's Solution to the Lorentzian Quantum Reality Problem

Most existing proposals to explain the temporal asymmetries we see around us are sited within an approach to physics based on time evolution, and thus they typically put the asymmetry in at the beginning of time in the form of a special initial state. But there may be other possibilities for explaining temporal asymmetries if we don't presuppose the time evolution paradigm. In this article, we explore one such possibility, based on Kent's `final-measurement' interpretation of quantum mechanics. We argue that this approach potentially has the resources to explain the electromagnetic asymmetry, the thermodynamic asymmetry, the coarse-graining asymmetry, the fork asymmetry, the record asymmetry, and the cosmological asymmetry, and that the explanations it offers may potentially be better than explanations appealing to a special initial state. Our hope is that this example will encourage further exploration of novel approaches to temporal asymmetry outside of the time evolution paradigm.Comment: Forthcoming in BJP

Laws of Nature as Constraints

The laws of nature have come a long way since the time of Newton: quantum mechanics and relativity have given us good reasons to take seriously the possibility of laws which may be non-local, atemporal, ‘all-at-once,’ retrocausal, or in some other way not well-suited to the standard dynamical time evolution paradigm. Laws of this kind can be accommodated within a Humean approach to lawhood, but many extant non-Humean approaches face significant challenges when we try to apply them to laws outside the time evolution picture. Thus for proponents of non-Humean approaches to lawhood there is a clear need for a novel non-Humean account which is capable of accommodating these sorts of laws. In this paper we propose such an account, characterizing lawhood in terms of constraints, which are understood as a form of modal structure. We demonstrate that our proposed realist account can indeed accommodate a large variety of laws outside the time evolution paradigm, and describe some possible applications to important philosophical problems

Determinism Beyond Time Evolution

Physicists are increasingly beginning to take seriously the possibility of laws outside the traditional time-evolution paradigm; yet many popular definitions of determinism are still predicated on a time-evolution picture, making them manifestly unsuited to the diverse range of research programmes in modern physics. In this article, we use a constraint-based framework to set out a generalization of determinism which does not presuppose temporal evolution, distinguishing between strong, weak and delocalised holistic determinism. We discuss some interesting consequences of these generalized notions of determinism, and we show that this approach sheds new light on the long-standing debate surrounding the nature of objective chance

Are entropy bounds epistemic?

Entropy bounds have played an important role in the development of holography as an approach to quantum gravity, so in this article we seek to gain a better understanding of the covariant entropy bound. We observe that there is a possible way of thinking about the covariant entropy bound which would suggest that it encodes an epistemic limitation rather than an objective count of the true number of degrees of freedom on a light-sheet; thus we distinguish between ontological and epistemic interpretations of the covariant bound. We consider the consequences that these interpretations might have for physics and we discuss what each approach has to say about gravitational phenomena. Our aim is not to advocate for either the ontological or epistemic approach in particular, but rather to articulate both possibilities clearly and explore some arguments for and against them

Tabletop Experiments for Quantum Gravity Are Also Tests of the Interpretation of Quantum Mechanics

Recently there has been a great deal of interest in tabletop experiments intended to exhibit the quantum nature of gravity by demonstrating that it can induce entanglement. We argue that these experiments also provide new information about the interpretation of quantum mechanics: under appropriate assumptions, $\psi$-complete interpretations will generally predict that these experiments will have a positive result, $\psi$-nonphysical interpretations predict that these experiments will not have a positive result, and for $\psi$-supplemented models there may be arguments for either outcome. We suggest that a positive outcome to these experimenst would rule out a class of quantum gravity models that we refer to as $\psi$-incomplete quantum gravity (PIQG) - i.e. models of the interaction between quantum mechanics and gravity in which gravity is coupled to non-quantum beables rather than quantum beables. We review some existing PIQG models and consider what more needs to be done to make these sorts of approaches more appealing, and finally we discuss a cosmological phenomenon which could be regarded as providing evidence for PIQG models

Operational Theories as Structural Realism

We undertake a reconstruction of the epistemic significance of research on operational theories in quantum foundations. We suggest that the space of operational theories is analogous to the space of possible worlds employed in the possible world semantics for modal logic, so research of this sort can be understood as probing modal structure. Thus we argue that operational axiomatisations of quantum mechanics may be interpreted as a novel form of structural realism; we discuss the consequences of this interpretation for the philosophy of structural realism and the future of operational theories