  How can we design safe reinforcement learning agents that avoid unnecessary
disruptions to their environment? We show that current approaches to penalizing
side effects can introduce bad incentives, e.g. to prevent any irreversible
changes in the environment, including the actions of other agents. To isolate
the source of such undesirable incentives, we break down side effects penalties
into two components: a baseline state and a measure of deviation from this
baseline state. We argue that some of these incentives arise from the choice of
baseline, and others arise from the choice of deviation measure. We introduce a
new variant of the stepwise inaction baseline and a new deviation measure based
on relative reachability of states. The combination of these design choices
avoids the given undesirable incentives, while simpler baselines and the
unreachability measure fail. We demonstrate this empirically by comparing
different combinations of baseline and deviation measure choices on a set of
gridworld experiments designed to illustrate possible bad incentives.
