Topics Science

Question Let's say that by positing the existence of some unobservable entities (e.g., strings), we can form theories which reliably predict observable behavior. Does the success of such theories provide evidence that the posited entities actually EXIST? Or is the significance of such entities merely heuristic?

Accepted:
February 20, 2008

Comments

Ian Hacking, in his very readable book Representing and Intervening, describes an experiment done by a friend which involved changing the electrical charge on a minuscule ball of niobium. And how was that done, he asked? His friend said "Well, we spray it with positrons to increase the charge or with electrons to decrease the charge". And Hacking comments "From that that day forth, I've been a scientific realist. So far as I'm concerned, if you can spray them then they are real."

Hacking's story remind us that many of our best theories about "unobservables" enable us to do a lot more than reliably predict observable behaviour in a hands-off, watching-from-the-sidelines, sort of way. They do more than merely tell us a story about a supposed hidden substructure of the world, something that we could perhaps treat as a "just so" story, a useful fiction, a "heuristic". Our theories guide us in causally manipulating unobservables, and in causally producing desired observable effects. We can reach in and tweak causal micro-processes, spraying electrons, cutting up DNA strands, and the like (or at least, that is how it is natural to describe what we are doing). How are we to understand what we are up if we suppose that such micro-processes and micro-objects are actually mere fictions?

Indeed, do we even understand what such a supposition really means? Imagine that Jack and Jill are engaged in the experiment Hacking mentions. Day in, day out, they improve the design of their experimental apparatus, improve their techniques for spraying very sparse streams of electron onto the niobium ball, and so forth. They talk in the laboratory incessantly of electrons, positrons, molecules and other other unobservables, and cheerfully use the relevant parts of the best going theories about such things, with great success. And now let's ask: what would really be at stake if one night Jack were to say in the pub afterwards, "But for all that, you know, I think electrons don't really EXIST"? (Shouting or thumping the table as he says it doesn't make what is at stake any clearer!)

In the laboratory Jack cheerfully talks about electrons, and works out how to spray them around with ever increasing accuracy. It isn't, we are supposing, that he has common-or-garden scientific reservations about what he is up to, any more than Jill has. So what could his purported philosophical reservations about some idea of capital-E existence really amount to? It isn't, to say the least, entirely clear, until we get a lot more explanation.

Now, of course, these quick remarks can only be the beginnings of a long and complex set of arguments about scientific realism. But perhaps they are just enough to suggest that the common-sensical realist view of at least some theories about unobservables (the theories that guide micro-technologies, for a start) has something going for it -- at least as a default starting point, pending some strong counter-arguments. (Philosophy being philosophy, there are of course those who try to offer such counter-arguments!)

The question of the status of string theory, however, is a whole different can of worms!