The biophysics of balanced living: a mechano-homeostasis paradigm for balancing in animals and robots

From birth until death animals resist gravity, effortfully asserting bodily form, animate behaviour, and postural balance. Most basic negentropic behaviours are understood as homeostasis (e.g. thermoregulation), but balance is taken to be an exception. Many studies have elucidated its sub-mechanisms, but the existence of goal-oriented homeostatic organisation remains an open question. The current theoretical paper reviews existing work to highlight and challenge the assumptions that belie a homeostatic model, arguing that balance is organised as one aspect of wider mechano-homeostasis, by a control loop organisationally akin to thermoregulation. The biophysical cost of maintaining an agent-medium density gradient defines the task, which is the regulation of mechanical force. Organism-level mechano-homeostasis must approximately maintain a certain mechanical force field at the surface of the organism (i.e. that which precisely cancels gravitational acceleration), or the organism will fall, dissipate and die. The argument specifies this fluid, dynamical force field of ‘balance’ for arbitrary morphologies and configurations, and describes how animals apprehend it developmentally for their own embodiment. I motivate and define this model, examine it against existing evidence, and discuss its implications, limitations and scope for understanding the embodied organisation of balance and spatiotemporal animacy in animals and robots.