  In this paper, we review the background of physical reality, virtual reality,
and some traditional mixed forms of them. Based on the current knowledge, we
propose a new unified concept called symmetrical reality to describe the
physical and virtual world in a unified perspective. Under the framework of
symmetrical reality, the traditional virtual reality, augmented reality,
inverse virtual reality, and inverse augmented reality can be interpreted using
a unified presentation. We analyze the characteristics of symmetrical reality
from two different observation locations (i.e., from the physical world and
from the virtual world), where all other forms of physical and virtual reality
can be treated as special cases of symmetrical reality.
