National University of Singapore

Mile Gu

Nanyang Technological University, Singapore

Co-Investigators

Vlatko Vedral, National University of Singapore

Project Title

Observer-dependent complexity: The quantum-classical divergence over 'what is complex?'

Project Summary

The most interesting phenomena are complex, lying at the border between order and chaos. Complex systems exhibit rich behaviour, from emergence and self-organization to the ability to perform universal computation. Understanding complexity is thus considered essential to describe nearly all non-trivial phenomena around us, from phase transitions in the physical sciences to life itself. A fundamental concern in complexity science is to formalize our intuition of ‚"what is complex?", into quantifiable values. Statistical complexity achieves this by asking "How much memory must an observer maintain to understand a process?",It has been recently established that the answer to this depends not only on the complex system itself, but also on properties of the observer, who judges the system -- especially if one observer has access to the power of quantum information. This could herald entirely new ways for complexity to behave, opening a new paradigm where "what is complex?", fundamentally depends on the physics of the observer. Our project establishes this by providing a formal framework for the physics of the observer. We examine the extent to which observers can disagree about complexity, and ascertain the consequences of their disagreement, including both in their thermal behaviour and impact on causality.

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