Debate on causation in physics between Kevin Sloway and Richard Healey taken from the Reasoning Show podcast.
Kevin: Okay. Let's say we have an object A. It could be a chair. Now, there's something else that is necessary for its existence. And that's something other than itself. We have a duality. So, we have a thing A, and a thing that is not-A.
Richard: What is the "not-A" ?
Kevin: It could be its environment. It's something that is not the chair. It's everything that is not the chair. So you could say that there's an interdependence between the two, where they cause each other. Not in time, but where each is dependent upon the other.
Richard: I'm not sure I'd want to call that a causal relationship. It's an interesting dependence relationship. Let me give you an example of something else that looks like that kind of dependence relationship. Suppose somebody makes a statue out of a lump of clay. They say, "It's necessary for the existence of that statue, that it be constituted of clay." There's a necessary connection, they might allege, between the existence of the statue, and the existence of something, without which it could not exist, namely, the lump of clay which constitutes it. I take it that that's the sort of thing you are talking about, but I would not call that a causal relationship at all but a relation of constitution, whatever that comes to.
David: If you define "cause" as something that is necessary for something else to exist, then the clay would be a necessary cause of the statue, because without the clay, there would be no statue.
Richard: How about this:- I don't think you're going to like this one, but tell me why not.....Isn't the statue also necessary for the existence of the statue, so that it is the cause of itself?
David: That would seem very technical to me, that one.
Richard: You don't like it, so there has to be another condition than merely "be necessary for the existence of something".
David: I don't think it means anything. If we define a cause as something that is necessary for something else to exist, then the statue causing itself doesn't fall into that definition.
Richard: Because the word "else" got in there. Good. I admire it, but it's not going to get you everywhere you need, because you need to explain to me what "necessary" means.
David: Without the clay, the statue couldn't possibly exist. It's necessary to its existence.
Richard: Now "possibility" got stuck in there, and that's as bad as "necessity". Philosophers typically distinguish different grades of "necessity", and a correlative grade of "possibility". They talk about logical necessity, metaphysical necessity, physical necessity, and so on. What kind of necessity did you have in mind?
David: Absolute necessity. For example, a car cannot exist without its parts: the engine and its wheels.... If you take all those things away, there would be no car. So there's a necessary connection there. And the same with space, time, molecules.....
Richard: That's not sounding like the kind of necessity that's discussed in the context of causal relations between events. That's to say, my dropping something and its landing on the floor: someone might say, "It had to land on the floor, given you dropped it and there was nothing in the way. So, necessarily it landed on the floor." That's not the kind of necessity you're talking about?
David: No, there's no certainty there, between linkages of events, but nevertheless you still need a floor for something to hit the floor, so there's a necessary connection there.
Richard: I'm still not quite sure what concept of "necessity" you're playing with. But I can see why you'd think that such a grade of necessity is not likely to be challenged by developments in empirical science.
David: Even empirically, I can't see how any observation or test by science can actually prove or disprove causality.
Richard: Yes, but you used that word "causality": is that simply the claim that nothing pops into existence without cause?
Richard: When you think of the causal relation, what do you think it relates? Do you think it relates things or do you think it relates events?
David: I don't make any distinction between things and events.
Richard: I think you need to. Suppose I say, "My mother is necessary for my existence," I think you'd agree that in some sense that's got to be true. There, what seems important is "my mother" and the event of "my coming into existence", and indeed, not just anything about my mother, but my mother had to be in certain states, and there had to be various events involving my mother. So that's what the causal relation really relates: those states and events involving my mother, and the event of my being born and continuing to exist afterwards.
David: I agree with that, but obviously it's not just your mother. Your mother was only one of countless other things, for instance, oxygen, space, the evolution of the species, etc. All these things are contributing causes. And they've all been necessary, because if they were absent then you wouldn't exist. So, your mother is just one of an infinite number of necessary causes.
Richard: Are they all necessary, though? Couldn't I have existed without a few of them? Given the way I actually came into existence, there were various events that preceded my coming into existence. Well: they could have been a bit different, and yet I'd still have been me.