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On Causality and Predictivity

Damiano Anselmi

TL;DR

This paper challenges the view that causality is foundational in physics, especially for quantum gravity. It argues that microcausality and microscopic predictivity are not essential, using the fakeon framework to show how a renormalizable, unitary theory can coexist with short-scale causality violations up to $1/m_\chi$ and with controlled nonlocality. By introducing concepts such as disruptors and delayed prepostdictivity, the author argues that true predictions are not guaranteed, though retrospective verification remains possible, reframing causality as a statistical, emergent property rather than a fundamental law. The discussion situates nonlocality as a natural feature in gauge and gravity theories, suggesting that the path to predictive quantum gravity lies in embracing these extensions rather than clinging to an absolute causality principle.

Abstract

Certain approaches to quantum gravity, such as the one based on the concept of purely virtual particles (fakeons), sacrifice the cause-effect relation at very small scales to reconcile renormalizability with unitarity. Other developments have also urged caution regarding the idea of causality as a fundamental principle. In this paper, we examine the problem from multiple perspectives, including locality and predictivity, and extend the existing skepticism in several directions. Emphasizing the impact of unruly "disruptors", we point out that the illusory arrow of time associated with causality and predictivity is inherently statistical. This renders the cause-effect relation strained at the microscopic level. We also show that causation is a borderline concept that demands belief in entities which can act on nature without being part of it. Ultimately, not only is renouncing microcausality a reasonable price to pay for a consistent and predictive theory of quantum gravity (as is the one based on the fakeon idea), but the very notion of causality is misleading. Resting as it does on metaphysical assumptions, it should therefore be abandoned in fundamental physics.

On Causality and Predictivity

TL;DR

This paper challenges the view that causality is foundational in physics, especially for quantum gravity. It argues that microcausality and microscopic predictivity are not essential, using the fakeon framework to show how a renormalizable, unitary theory can coexist with short-scale causality violations up to and with controlled nonlocality. By introducing concepts such as disruptors and delayed prepostdictivity, the author argues that true predictions are not guaranteed, though retrospective verification remains possible, reframing causality as a statistical, emergent property rather than a fundamental law. The discussion situates nonlocality as a natural feature in gauge and gravity theories, suggesting that the path to predictive quantum gravity lies in embracing these extensions rather than clinging to an absolute causality principle.

Abstract

Certain approaches to quantum gravity, such as the one based on the concept of purely virtual particles (fakeons), sacrifice the cause-effect relation at very small scales to reconcile renormalizability with unitarity. Other developments have also urged caution regarding the idea of causality as a fundamental principle. In this paper, we examine the problem from multiple perspectives, including locality and predictivity, and extend the existing skepticism in several directions. Emphasizing the impact of unruly "disruptors", we point out that the illusory arrow of time associated with causality and predictivity is inherently statistical. This renders the cause-effect relation strained at the microscopic level. We also show that causation is a borderline concept that demands belief in entities which can act on nature without being part of it. Ultimately, not only is renouncing microcausality a reasonable price to pay for a consistent and predictive theory of quantum gravity (as is the one based on the fakeon idea), but the very notion of causality is misleading. Resting as it does on metaphysical assumptions, it should therefore be abandoned in fundamental physics.
Paper Structure (10 sections, 23 equations, 1 figure)

This paper contains 10 sections, 23 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Determinism and causality
  3. Causes as truly external entities
  4. Prepostdictivity
  5. Disruptors, incoming waves and statistics
  6. Remarks
  7. Delayed prepostdictivity
  8. Causality in quantum field theory
  9. Nonlocality in gauge theories, gravity and fakeon models
  10. Conclusions

Figures (1)

  • Figure 1: Prepostidictions