Temporal Interaction

Abstract

In which we learn that when you are code you are never alone. That the universe evolves in time and software execution requires temporal interaction between many parts.

Code executes in time. The universe evolves through time. We might not understand what that means, but the implications for the nature of code we write are strong. In particular, a pure function is timeless and an interactive program has irreversible side effects. Once the paper is printed, it can’t be unprinted.

Edsger Dijkstra refers to it as the problem of the mosquito and the elephant. If you start with two tiny programs and let them interact you can find you have an enormous and complex beast on your hands.

But this is the nature of any program that must interact with the universe, and there are many nice solutions to various problems that involve multiple programs running at the same time.

The technicalities of the distinction between multi-programming, multithreading, parallel programming, multi-tasking, and other similar terms and concepts are not the issue here. The question is simply, what happens when two programs interact? Or a program interacts with the outside universe?