—Consider a collision between two objects. What happens?
—One object hits another, and causes the other to accelerate.
—Why does the one object cause the other to accelerate?
—Because of the transfer of momentum.
—What does that mean? How does the momentum transfer?
—The short answer is that the electromagnetic force causes energy to move from one object to the other in the form of linear momentum and heat.
—So the electromagnetic force stops the first object, and starts the second object moving?
—Well, no, the electromagnetic force is just a name we give to observed rules of motion in interacting charged bodies.
—So, when we say "the electromagnetic force caused something", really we're just saying "the mechanics of the movement are described by these rules". I.e. we aren't actually specifying the agent that caused the motion. Is that right?
—Yes, I suppose that's right.
—So really the cause of the change is just the two objects, right?
—But that leaves the question unanswered. What caused the two objects to change in precisely this way? Why do they follow the rules of electromagnetism?
—Because they're made of charged particles.
—But aren't "charged particles" just defined as "things that are observed to follow the rules of electromagnetism"?
—Hmm, I suppose so.
—So why do these things follow those rules? I.e. why do they act as charged particles?
—Well, it's just their nature. It's what they are.
—But notice something: before the two objects collide, they're acting one way, and then during the collision they start acting differently. Is that right?
—Yes, that's right. During the collision, atomic interactions cause compression waves in both objects, possibly rearrange them, at least partially, and the various interactions cause some of the initial momentum to be converted into heat.
—Ok, so we've established that it's just in the nature of these objects to change as they do when they collide. But what makes them act in accord with that nature, instead of differently? Why don't the two objects just keep behaving the way they were, and pass right through each other?
—Well, they just don't. That's just the way things are.
—But scientifically, it seems like we have to be able to find some explanation, right? There has to be some basis for the particular rules of transformation that we've identified.
—Well, sure, but we don't have any material evidence about it, so science prefers not to speculate.
—Ok, fair enough. But it seems like in general science works this way: we observe an effect, and then we make an inference to the existence of the cause, even if we can't identify its exact nature. E.g. this was how the neutron was predicted, and the higgs boson, and so on.
—That's right. From an observed effect we make a guess about the existence of a cause, and then we try to draw further conclusions about the nature of that cause, which will allow us to make testable predictions.
—So, here we have an observed effect: the consistent, universal transformation of different substances in accord with observable "natures" or laws of nature. And we are looking for a cause: something which prompts this or that particular things to act and change in accord with these laws.
—Well, but hold on. Why do we assume that there is always going to be such a cause of change in the first place? Maybe it's just a fact that things change the way they do, and maybe there is no reason why. Maybe the universe is just a sort of ticker that follows observable patterns without there being an external "cause" that moves each thing to do whatever it does.
—Let me make sure I understand. Are you suggesting that maybe the whole idea that one thing causes another to move is questionable, and that there is no such thing as causation?
—Yes, I think so. Sort of like in a computer game, the way a space ship can "cause" an asteroid to blow up by firing lasers at it. In our heads we think "the space ship, i.e. this cluster of lighted pixels, caused the asteroid, i.e. that other cluster of lighted pixels, to explode, i.e. to change the way they are lit." But in reality the illumination of these portions of the screen in this way did not cause the other portions of the screen to change, since there was no direct interaction. The computer's video processor caused the whole thing.
—I see. But it's interesting, because in your analogy, the computer is still causing the screen to change according to certain rules. I.e. there is still an external cause of change. But I think you want to get away from that, is that right?
—Well, actually my idea is that the computer software executing the changes is like the laws of nature, and the objects on the screen are like material objects.
—Ok, I'll run with your analogy. It seems like my question still applies. Because even in your analogy, we can ask why the computer is running this particular software, with these rules, instead of some other software. And more compellingly, perhaps, we can ask why it is that the program is running at all. To translate these questions into our original discussion: why do things follow these laws of physics, and why are there any laws of physics at all?
—Hmm. I'm starting to see your point, but let me try one other dodge. Let's just suppose that this particular "program" or "set of laws" is one facet of a single unchanging super-program, i.e. the multiverse, and that our particular way things work is just one of an infinitely large number of variations on the same rules. The multiverse isn't really a cause in the way you want there to be a cause, it's just the totality of which our natural world forms a part.
—Hmm, well at this point your dodge seems to have landed you into some seriously speculative hypotheses about the nature of the universe. I'm not sure that qualifies as what you want to call "science."
—Sure, but it's still an alternative to the sort of cause you seem to want to hypothesize.
—Is it? Well, let's suppose there is a multiverse, and it's infinite, and it includes every possible set of physical laws. It seems like we still end up with the same problem.
—Well, we can ask, why is it that this multiverse exists instead of a different one, e.g. a finite one, or one with just our universe? Actually you've just shifted the problem back a level. It's exactly the same. The multiverse has particular rules and properties, and changes in particular ways, in its various parts, and it could be different. Why is it the way it is, and why does it behave the way it does?
—Well, we don't have any data yet. Perhaps some day we can scientifically investigate those questions.
—Ah, but that's just a cop out. In fact we do have a ton of data. All the data ever collected conclusively shows that things act and change in accord with fixed laws, and that these laws are different depending on the kind of objects under examination and the way they are interacting. Whether the reason for this set of natural laws is immediately available or mediated through a multiverse, or through a super-multiverse, or through however many layers you want, it's good science to assume that if there is an observed effect there must be a causal principle behind it. We notice that things change in a certain way, so we should be willing to hypothesize that there is a thing (not a rule) that moves them to change the way they do.
—But we've already named those things. They're just bosons, i.e. force carrying particles. And if you posit the existence of something else on top of them, you're doing double-duty explanation-wise.
—Force carrying particles are just another part of the explanation, though. They themselves change depending on the circumstances. They have natures, they interact in certain ways, etc. What causes the causes to cause change the way they do? It doesn't seem that there's an answer.
—Well, fine, let's suppose there's another kind of particle or force field or something that causes those changes. Is that satisfactory?
—But if that cause is itself something that changes in accord with laws of nature, we have to ask the same question for it.
—So, the conclusion is that eventually, either there's just a bare unexplained fact "hey the universe is just like this, and there's no reason why", or there's got to be some thing, which causes other things to change, to follow the laws of nature, to act however they do, but never changes itself, and has no random properties that we can ask "why is it this way?" about.
—Hmm. But such a thing would have to be unobservable.
—Yes, that's right.
—But that's a problem for science, because if we make a theory that predicts the existence of a particular kind of thing, we need to be able to make testable hypotheses about the effects of that thing.
—Well, but notice that this hypothesis is pretty singular. The thing being hypothesized is different from any other thing that physics describes. It's not a particular kind of object that interacts with other objects in an observable way. It's the cause of all the regular phenomena of nature.
—Yes, I see. Ok, but one more thing: why do we need this sort of explanation at all? Isn't it enough to just say "hey, sooner or later this is just the way things are"?
—You could, but the problem with that is that it seems to undercut the explanatory power of science. Instead of being someone who reliably traces events to their underlying causes, the scientist becomes someone who just says "hey, a correlation!" and leaves it there. Causation vanishes.
—Hmm, and you want to say that science necessarily makes claims about causation?
—Yeah, I think it does. To be sure, you could surrender the principle that changes are caused, but it seems like once you resort to "that's just how things are" you've given up real science.
—But how does your proposed super-cause not fall victim to the same criticism? Why is there this super-cause and not another?
—Well, that line of questioning just clarifies what the super-cause, as you call it, must have to be like. And whether we can frame a coherent account of the nature of that cause is a different problem. But if you accept that there must be such a super-cause if we are to preserve the idea of an ordered and intelligible (i.e. investigable, science-friendly) universe, then it seems that we have gotten to the existence of that being which most people refer to as "God".