[Paper Review] Temporal relationalism

Lee Smolin|arXiv (Cornell University)|May 31, 2018

Quantum Mechanics and Applications4 citations

TL;DR

This paper proposes temporal relationalism, a realist framework in which time, causality, energy, and momentum are fundamental, while space, spacetime, and quantum mechanics are emergent. By modeling the universe as an energetic causal set that evolves via a principle of maximal variety, the theory reproduces general relativity in the thermodynamic limit and provides a relational, time-as-fundamental foundation for quantum gravity and quantum foundations.

ABSTRACT

Because of the non-locality of quantum entanglement, realist approaches to completing quantum mechanics have implications for our conception of space. Quantum gravity also is expected to predict phenomena in which the locality of classical spacetime is modified or disordered. It is then possible that the right quantum theory of gravity will also be a completion of quantum mechanics in which the foundational puzzles in both are addressed together. I review here the results of a program, developed with Roberto Mangabeira Unger, Marina Cortes and other collaborators, which aims to do just that. The results so far include energetic causal set models, time asymmetric extensions of general relativity and relational hidden variables theories, including real ensemble approaches to quantum mechanics. These models share two assumptions: that physics is relational and that time and causality are fundamental.

Motivation & Objective

• To resolve foundational issues in quantum mechanics and quantum gravity by unifying them under a single relational framework.
• To establish time and causality as fundamental, rejecting the idea that time emerges from a timeless theory.
• To derive quantum mechanics and general relativity as emergent phenomena from a deeper, more fundamental dynamics.
• To address the measurement problem and non-locality in quantum mechanics through relational hidden variables and ensemble theories.
• To show that spacetime geometry and Einstein's equations emerge from the thermodynamic limit of energetic causal sets.

Proposed method

• Model the universe as an energetic causal set where events are related by causal order and carry energy, forming a network of causal relations.
• Apply the principle of maximal variety to select the most diverse configuration of relations, which governs the dynamics of the causal set.
• Use Jacobson-Padmanabhan-style thermodynamic reasoning to derive the Einstein equations from the entropy and energy structure of the causal set.
• Introduce relational hidden variables via real ensemble approaches, where each system's behavior is influenced by all similar systems across the universe.
• Construct a causal theory of views, where each event's 'view' is defined by its causal neighborhood and the similarity of views determines effective locality.
• Explore evolving laws via cosmological natural selection and the principle of precedence, allowing laws to change over time in a meta-theory of dynamics.

Experimental results

Research questions

• RQ1 Can a theory be constructed in which time is fundamental, and space and spacetime are emergent?
• RQ2 How can quantum mechanics be completed in a realist framework that resolves non-locality and the measurement problem?
• RQ3 Can general relativity emerge from a discrete, causal, energetic structure without assuming spacetime a priori?
• RQ4 What is the role of energy and momentum in a fundamental theory where they are not derived from symmetries?
• RQ5 How does the principle of maximal variety lead to the emergence of quantum behavior and relativistic spacetime?

Key findings

• The Einstein equations can be derived from the thermodynamic limit of an energetic causal set model under four specific principles, including the requirement that quantum spacetime be described by such a model.
• The principle of maximal variety—extremizing the diversity of views among similar systems—leads to a structure closely related to the Bohmian quantum potential, suggesting a dynamical origin for quantum effects.
• Relational hidden variables, defined as shared properties between particle pairs, can be constructed and studied within the framework, offering a realist alternative to standard quantum mechanics.
• The theory realizes a time-as-fundamental perspective, where the present is a thick, growing domain of causally connected events, resolving the conflict with special relativity through the emergence of Lorentz invariance.
• Evolving laws are modeled via cosmological natural selection and the principle of precedence, offering a solution to the meta-law dilemma of how laws themselves might evolve.
• A causal theory of views emerges from combining real ensemble quantum mechanics with energetic causal sets, where the beables are the causal perspectives of individual events.