Invited Commentary: Hypothetical Interventions to Define Causal Effects—Afterthought or Prerequisite?

Abstract

“It is philosophy, not science.” Physicists are familiar with this criticism of string theory, a theory that provides a unified description of all forces operating in the universe (1). Unlike philosophical arguments, scientific theories or their predictions need to be confirmed empirically. String theory involves an elegant set of mathematical equations; unfortunately, it is unclear whether its predictions are, or will be, testable—not a small obstacle for a “theory of everything.”