  In this paper, we summarize the development of the concept of emergence in
physical science and propose key concepts of emergence in the form of
conjectures. Our conjectures are threefold: I. A system having a
broken-symmetry in membership relation with respect to micro and macro scales
can have emergent properties. II. Spontaneous symmetry-breaking is an example
of an emergent property. III. The phenomenon of hysteresis accompanies
spontaneous symmetry-breaking. We argue that these conjectures and their
relationship can illuminate the concept of emergence from the perspective of
symmetry breaking.
