Interacting ems need not see exactly the same virtual environment. For example, each em might prefer to see a shared environment as decorated with their personal choices of colors or patterns. Ems might also prefer to overlay or augment their views of the virtual world with useful tags and statistics, or to see through virtual objects to see object components or to see what lies behind those objects. Virtual ems may have telescopic sight, allowing them to always vividly see anything anywhere they are allowed to view. However, overlays can impair perception, and so must be used carefully ( Sabelman and Lam 2015 ). To sensibly interact with others, ems usually want easy ways to quickly identify the aspects of their environments that they and their interaction partners see similarly. Some aspects of these worlds (such as where people are standing) are distinguished as shared by default, and interacting ems want standard ways to invite interaction partners to see some of their own less widely shared overlays and changes, and to accept such offers from others. At both work and play, many kinds of tasks require ems to manage physical systems. Such management often requires physical bodies (both immediate and extended) whose size, speed, shape, and materials sufficiently match those physical systems. It is also important for em minds to relate well to such bodies. But this seems feasible for a wide range of physical bodies. After all, people today interact with the world using a wide range of machines, such as vehicles and cranes, which they treat mentally as an extension of their bodies. For ems with task-matched physical bodies, the world they see and hear needn’t be an exact faithful representation of their physical world. For example, it might often be a sort of view like those in today’s head-up displays, overlaid with useful virtual annotations. But such overlays need to avoid overly obscuring important elements of that physical world. Because the feasibility, cost, and security of em interactions often depends on the physical and organizational locations of their brains and the brains of others, em virtual worlds may continually show such information about interaction partners. For example, ems often want to know when another em’s speed, period, phase, or distance makes direct fast interaction infeasible. So ems will need to share somewhat-realistic concepts of their locations in space and time.
Scale Symmetry and Friction