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When a system is composed of many interacting components
new properties can emerge that are qualitatively different
from the properties of the individual components. Such emergent phenomena
lead to a stratification of reality and of scientific disciplines.
Emergence can be particularly striking and challenging to understand for
quantum matter, which is composed of macroscopic numbers
of particles that obey quantum statistics, such as electrons.
Emergent states of quantum matter have been the subject of
numerous Nobel Prizes including that for 2016.
Important examples include superfluidity, superconductivity, and the fractional quantum Hall effect. I will introduce some of the organising principles for describing
such phenomena: quasi-particles, spontaneously broken symmetry, and effective Hamiltonians. I may briefly describe how these ideas undergird
some of my own theoretical research on complex molecular materials such as
superconducting organic charge transfer salts, fluorescent proteins, and hydrogen bonded complexes. The interplay of emergence and reductionism raises issues in philosophy and as
to the best scientific strategy for describing complex systems. |