The Horizon Effect, also known as the horizon problem, is caused by the depth limitation of the search algorithm.

• Because only a partial game tree has been analyzed, it will appear to the system that an event can be avoided when in fact this is not the case.
• Besides obligatory Quiescence search, Extensions, especially Check Extensions are designed to reduce horizon effects.

When evaluating a large game tree using techniques such as Minimax with Alpha-Beta pruning, search depth is limited for feasibility reasons.

• However, evaluating a partial tree may give a misleading result.
• When a significant change exists just over the horizon of the search depth, the computational device falls victim to the horizon effect.

Horizon Effect