Top-down causation and quantum physics

Abstract

The nature of emergence of complexity out of the underlying physics is a key issue in understanding the world around us (1). Genuine emergence can be claimed (2⇓–4) to depend on top-down causation, which enables higher emergent levels to direct the outcomes of causation at lower levels to fulfill higher-level causal requirements; for example, the needs of heart physiology at the systems level determine gene expression at the cellular level via gene regulatory networks (5) (Fig. 1). However, the idea of top-down causation has been denied by a number of commentators (e.g., refs. 6 and 7). The paper by Aharonov et al. (8) makes a strong contribution to this debate by giving quantum physics examples where top-down causation manifestly occurs. This physics result has strong implications for the philosophical debate about whether strong emergence is possible. Indeed, it gives specific examples where it occurs in a remarkably strong form. Fig. 1. Bottom-up and top-down causation from the quantum level up to the organism level and down again. Adapted with permission of Royal Society, from ref. 5; permission conveyed through Copyright Clearance Center, Inc. Now, the word “causation” is regarded with suspicion by many philosophers of science, so to characterize what is happening one can perhaps rather use a number of different descriptions such as “whole–part constraint” or “top-down realization.” The key point remains the same, that higher levels can influence lower-level outcomes in many ways, and hence explain how strong emergence is possible. This occurs across science in general, and in physics in particular (3, 4). The latter point … [↵][1]1Email: george.ellis{at}uct.ac.za. [1]: #xref-corresp-1-1