Physics Beyond the Multiverse - Naturalness and the Quest for a Fundamental Theory

TL;DR

This paper proposes a holistic, entanglement-based view of the universe as the fundamental quantum state, challenging traditional naturalness and finetuning concepts in physics, especially in light of multiverse theories and recent quantum gravity research.

Contribution

It introduces a new perspective that defines the universe as a zero-entropy entangled quantum state, shifting focus from subsystem-based theories to a universal quantum description.

Findings

Universe as a zero-entropy entangled quantum state

Subsystem finetuning is an artifact of non-fundamental theories

Quantum gravity research hints at a paradigm shift

Abstract

Finetuning and Naturalness are extra-empirical theory assessments that reflect our expectation how scientific theories should provide an intuitive understanding about the foundations underlying the observed phenomena. Recently, the absence of new physics at the LHC and the theoretical evidence for a multiverse of alternative physical realities, predicted by our best fundamental theories, have casted doubts about the validity of these concepts. In this essay we argue that the discussion about Finetuning should not predominantly concentrate on the desired features a fundamental theory is expected to have, but rather on the question what a theory needs to qualify as fundamental in the first place. By arguing that a fundamental description of the Universe should possess zero entropy, we develop a 'holistic' concept for the most fundamental layer of reality: The fundamental description of the Universe is the Universe itself, understood as an entangled quantum state. Adopting a universal applicability of quantum mechanics, in this framework the behavior of subsystems can be understood as the perspectival experience of an entangled quantum Universe perceived through the "lens of decoherence". In this picture the fundamental reality is non-local, and finetuned coincidences in effective theories may be understood in a way similar to EPR-correlations. This notion provides a fresh view on the topic of Naturalness and Finetuning since it suggests that Finetuning problems and hints for anthropic explanations are an artefact of theories building up on subsystems rather than on the fundamental description. Recent work in quantum gravity aiming at an understanding of spacetime geometry from entanglement entropy could be interpreted as a first sign of such a paradigm shift.