Postgraduates work in progress

Speaker: Luke Kersten

Title: What does it take for a physical system to implement a computation?

Abstract: Traditionally, there have been two answers. One is to say that a system must have the right physical or causal structure, sometimes referred to as ‘physical/causal structure’ proposals. The other is to say that a physical system must manipulate representations, sometimes referred to as ‘semantic’ proposals or the ‘received’ view. More recently, some authors have turned to the concept of ‘mechanism’ to articulate an answer to the implementation question.

According to this view, computational implementation is best explicated within a mechanistic framework. Computational explanation is a species of mechanistic explanation, and computational mechanisms are a special type of functional mechanism, what is labelled here the ‘mechanistic approach to computation’ (MAC). The aim of this paper is to take up a recent challenge to MAC, what has been labelled ‘the abstraction problem’. The abstraction problem says that one of MAC’s central pillars – medium independence – is deeply confused when applied to the question of implementation. The concern is that while it makes sense to say that computational processes are abstract (i.e. medium independent), it makes considerably less sense to say that they are also concrete processes of a mechanism. After surveying existing responses and diagnosing their failures, I propose a solution to the abstraction problem based on Dennett’s illata-abstracta distinction. I argue that conceiving of computations as abstracta rather than illata provides a way to articulate a notion of medium independence that addresses the abstraction problem.