On the Equivalence of Physical Theories

This chapter argues against formal accounts of theoretical equivalence in physics. It defends the importance of a theory’s picture of the world and its explanations of the phenomena, drawing on examples from classical physics, Newtonian gravitation, classical electromagnetism, special relativity, and quantum mechanics. The discussion draws a distinction between metaphysical equivalence and informational equivalence and argues that these are equally important to the equivalence of physical theories. The chapter concludes that there are fewer cases of wholly equivalent theories in physics than usually thought. However, this is not a problem, for it is still possible to talk about the various respects in which physical theories are, or are not, equivalent to one another.