How device-independent approaches change the meaning of physical theory

TL;DR

This paper explores how device-independent approaches in physics shift the focus from physical entities to languages, challenging traditional notions of what physical theories describe, especially in the context of quantum correlations and causal structures.

Contribution

It introduces a novel perspective that physical theories may fundamentally be about languages rather than systems, expanding the conceptual framework of quantum foundations.

Findings

Device-independent models focus on correlations, not systems.

Physics can be interpreted as a language-based framework.

This approach offers new insights into quantum correlations and causal orders.

Abstract

Dirac sought an interpretation of mathematical formalism in terms of physical entities and Einstein insisted that physics should describe "the real states of the real systems". While Bell inequalities put into question the reality of states, modern device-independent approaches do away with the idea of entities: physical theory may contain no physical systems. Focusing on the correlations between operationally defined inputs and outputs, device-independent methods promote a view more distant from the conventional one than Einstein's 'principle theories' were from 'constructive theories'. On the examples of indefinite causal orders and almost quantum correlations, we ask a puzzling question: if physical theory is not about systems, then what is it about? The answer given by the device-independent models is that physics is about languages. In moving away from the information-theoretic reconstructions of quantum theory, this answer marks a new conceptual development in the foundations of physics.