Areas of Interest

##### My research interests include

*Foundations and Philosophy of Quantum Mechanics, Foundations and Philosophy of Space and Time, Quantum Information Theory and Computing.*##### Currently, my focus lies in formalising the inseparability of 'subject' and 'object' in physical theories, probing how this manifests itself as measurement uncertainty in classical mechanics, quantum mechanics, and intermediate theories like Spekkens' toy model. My interests include reconciling quantum features as aspects of limits on Nature's predictability as well as developing a better understanding of the nature of agency in physics.

Papers

#### Epistemic Horizons From Deterministic Laws: Lessons From a Nomic Toy Theory (2024)

with Tomáš Gonda and Gemma de les Coves.

doi.org/10.48550/arXiv.2406.17581

Quantum theory has an epistemic horizon, i.e. quantum states imply uncertainty for the outcomes of incompatible measurements. As shown by so-called Spekkens' toy theory, positing an epistemic horizon akin to Heisenberg's uncertainty principle in a classical mechanical setting also leads to a plethora of quantum phenomena. We describe a theory - nomic toy theory - in which information gathering agents are explicitly modelled as physical systems. While the physical state in principle determines the values of all observable of a system, we prove that precisely this epistemic horizon arises from deterministic interactions. Therefore, a physical system cannot be fully accessed, represented, and predicted. The result reconciles us to measurement uncertainty in quantum theory as aspects of the inseparability of subject and object. Significantly, the claims follow despite the theory being essentially classical. Hence, dynamical epistemic horizons may already exist in Newtonian physics.

#### The (un)detectability of Bohmian trajectories (2023)

forthcoming in Oldofredi, A., editor,

*100 Years of de Broglie-Bohm Theory: Where Do We Stand?*, Chapter 4. Oxford University Press, Oxford.Pilot wave theory endows particles with definite positions at all times governed by deterministic dynamics. However, individual particle trajectories are generically undetectable by experiment. This idea might seem to be contested in light of two proposals: (1) So-called `weak velocity measurements', allegedly detecting Bohmian trajectories by weakly probing a quantum system without essentially disturbing it, and (2) the so-called `surrealistic' trajectories experiment which supposedly establishes a conflict between the `actual' position of a particle and its position derived from pilot wave theory. Although both attempts shed light on the nature of Bohmian particles, neither constitute empirical or theoretical evidence in favour or against pilot wave theory. Both instances admit a straightforward standard quantum mechanical interpretation compatible with the predictions of Bohmian theories. It is concluded that the puzzles arise from the absence of a coherent account of what quantum mechanical measurements signify.

#### Epistemic Boundaries and Quantum Indeterminacy: What Local Observers Can (Not) Predict (2023)

doi.org/10.48550/arXiv.2310.09121

One of quantum theory's salient lessons is its inherent indeterminacy. That is, generic physical states imply uncertainty for the outcomes of measurements. We formally define and address whether quantum uncertainty could be fundamental or whether post-quantum theories can offer predictive advantage whilst conforming to the Born rule on average. We present a no-go claim combining three aspects: predictive advantage, signal-locality, and the epistemic relationship between quantum observers. The results of the analysis lead to the conclusion that there exists a fundamental limitation on genuine predictive advantage over standard quantum probabilities. However, we uncover a fascinating possibility: when the assumption of 'reliable intersubjectivity' between different observers is violated, subjective predictive advantage can, in principle, exist. This, in turn, entails an epistemic boundary between different observers of the same theory. The findings reconcile us to quantum uncertainty as an aspect of limits on Nature's predictability.

#### Quantum Predictive Advantage and Pilot Wave Theory (2023)

(in preparation)

How (not) to understand weak measurements of velocity (2020)

with Patrick M. Duerr. Studies in History and Philosophy of Modern Physics 85 (2021) 16–29

doi.org/10.1016/j.shpsa.2020.12.002

To-date, the most elaborated attempt to complete quantum mechanics by the addition of hidden variables is the de Broglie-Bohm (pilot wave) theory (dBBT). It endows particles with definite positions at all times. Their evolution is governed by a deterministic dynamics. By construction, however, the individual particle trajectories generically defy detectability in principle. Of late, this lore might seem to have been called into question in light of so-called weak measurements. Due to their characteristic weak coupling between the measurement device and the system under study, they permit the experimental probing of quantum systems without essentially disturbing them. It's natural therefore to think that weak measurements of velocity in particular offer to actually observe the particle trajectories. If true, such a claim would not only experimentally demonstrate the incompleteness of quantum mechanics: it would provide support of dBBT in its standard form, singling it out from an infinitude of empirically equivalent alternative choices for the particle dynamics. Here we examine this possibility. Our result is deflationary: weak velocity measurements constitute no new arguments, let alone empirical evidence, in favour of standard dBBT; One mustn't naïvely identify weak and actual positions. Weak velocity measurements admit of a straightforward standard quantum mechanical interpretation, independent of any commitment to particle trajectories and velocities. This is revealed by a careful reconstruction of the physical arguments on which the description of weak velocity measurements rests. It turns out that for weak velocity measurements to be reliable, one must already presuppose dBBT in its standard form: in this sense, they can provide no new argument, empirical or otherwise, for dBBT and its standard guidance equation.

Taming the Delayed Choice Quantum Eraser (2019)

Quanta 2019; 8: 44-56

doi.org/10.12743/quanta.v8i1.88

I discuss the delayed choice quantum eraser experiment (DCQE) by drawing an analogy to a Bell-type measurement and giving a straightforward account in standard quantum mechanics. The delayed choice quantum eraser experiment turns out to resemble a Bell-type scenario in which the paradox's resolution is rather trivial, and so there really is no mystery. At first glance, the experiment suggests that measurements on one part of an entangled photon pair (the idler) can be employed to control whether the measurement outcome of the other part of the photon pair (the signal) produces interference fringes at a screen after being sent through a double slit. Significantly, the choice whether there is interference or not can be made long after the signal photon encounters the screen. The results of the experiment have been alleged to invoke some sort of 'backwards in time influence'. I argue that this issue can be eliminated by taking into proper account the role of the signal photon. Likewise, in the de Broglie-Bohm picture the particle's trajectories can be given a well-defined description at any instant of time during the experiment. Thus, it is again clear that there is no need to resort to any kind of 'backwards in time influence'.

Gravitational redshift revisited: inertia, geometry, and charge (2018)

with James Read. Studies in History and Philosophy of Science 108 (2024) 19-27

doi.org/10.1016/j.shpsa.2024.09.001

Gravitational redshift effects undoubtedly exist; moreover, the experimental setups which confirm the existence of these effects - the most famous of which being the Pound-Rebka experiment - are well-known. Nonetheless - and perhaps surprisingly - there remains a great deal of confusion in the literature regarding what these experiments really establish. Our goal in the present article is to clarify these issues, in three concrete ways. First, although (i) Brown and Read (2016) are correct to point out that, given their sensitivity, the outcomes of experimental setups such as the original Pound-Rebka configuration can be accounted for using solely the machinery of accelerating frames in special relativity (barring some subtleties due to the Rindler spacetime necessary to model the effects rigorously), nevertheless (ii) an explanation of the results of more sensitive gravitational redshift outcomes does in fact require more. Second, although typically this 'more' is understood as the invocation of spacetime curvature within the framework of general relativity, in light of the so-called 'geometric trinity' of gravitational theories, in fact curvature is not necessary to explain even these results. Thus (a) one can explain the results of these experiments using only the resources of special relativity, and (b) even when one cannot, one need not invoke spacetime curvature. And third: while one might think that the absence of gravitational redshift effects would imply that spacetime is flat, this can be called into question given the possibility of the 'shielding' of gravitational effects by charge. This argument is shown to be valid and both attractive forces as well as redshift effects can be effectively shielded (and even be repulsive or blueshifted) in the charged setting. Thus, it is not the case that the absence of gravitational effects implies a Minkowskian spacetime setting.

Is the World Just Wave Function? Determinism and the metaphysics of hidden variables in quantum mechanics. (2018)

*Master's thesis, ETH Zurich, Advisor: Renato Renner.*Observability and Predictability in Quantum and Post-Quantum Physics (2022)

*PhD thesis, University of Oxford, Advisors: Christopher G. Timpson, Owen J. E. Maroney.*available on

I introduce a framework to distinguish two domains of physics - the manifest (i.e. the directly observable empirical records in terms of manifest configurations) and the non-manifest domain of physics (i.e. the things that the manifest configurations signify according to a physical theory). I show that many quantum 'paradoxes' rest on ambiguous reasoning about the two domains. More concretely, I study so-called 'surrealistic' trajectories, the 'delayed choice quantum eraser', and 'weak measurements'. Finally, I show how the alleged puzzles resolve in the framework provided. I then formally define and address the question of whether quantum uncertainty could be fundamental or whether post-quantum theories could have predictive advantage whilst conforming to the Born rule on average. This notion of what I call 'empirical completeness' refers to actual prediction-making beyond the Born probabilities, and thus delineates the operational notion of predictability from a 'hidden variable' programme in quantum theory. I study how empirical completeness connects to signal-locality, and argue that a partial proof for the impossibility of predictive advantage can be established for bi-partite quantum systems. The relevant results demonstrate signal-locality as a sufficient principle that might explain the fundamental chanciness in present and future quantum theories and, in turn, reconciles us to many quantum features as aspects of limits on Nature's predictability.