  Virtual Reality (VR), Augmented Reality (AR), Mixed Reality (MR), digital
twin, Metaverse and other related digital technologies have attracted much
attention in recent years. These new emerging technologies are changing the
world significantly. This research introduces a fusion model, i.e. Fusion
Universe (FU), where the virtual, physical, and cognitive worlds are merged
together. Therefore, it is crucial to establish a set of principles for the
fusion model that is compatible with our physical universe laws and principles.
This paper investigates several aspects that could affect immersive and
interactive experience; and proposes the fundamental principles for Fusion
Universe that can integrate physical and virtual world seamlessly.
