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Cyan comments on Hypotheses For Dualism - Less Wrong
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Comments (32)
Ye olde rubber sheet analogy doesn't do it for you?
If someone pushes down in the middle of a sheet of rubber, it isn't mysterious to me why the rubber sheet gets distorted in other places.
Objecting to "non-physical" explanations means objecting to explanations that we don't understand. And yet huge swaths of science are things that we don't understand. Here's an example to distinguish between understanding and mere curve-fitting:
Thermodynamics: You say that heat is actually the kinetic energy of moving particles. Heat is communicated by particles bouncing off other particles and imparting momentum to them. Now you understand heat! You can use this understanding to construct equations that will let you predict how heat flows.
Gravity: You observe a lot of objects rising and falling. You observe the orbits of planets. You take all this data, and find some equations that fit it. You can now predict the influence of gravity. But you don't understand gravity.
In response to the comments in this thread that seem to argue that our understanding of gravity as just as good as our understanding of rubber deformation or in some way good enough, I would agree with the parent that our non-understanding of gravity is quite starkly different from our understanding of the deformation of rubber.
We really do understand the deformation of rubber in terms of local molecular interactions. Not in analogies but in actual detail of what the molecules are doing. The partial differential equations that give us the computational short-cut to solve the shape of the rubber can nevertheless be derived from first principles, and computed using local mechanisms that model exactly what the universe does.
In the case of gravity, we know the shape of the field, but we have no idea what local interactions are yielding them.
I don't see the differences between our understanding of either.
Yes, but what are molecules? Why do they exist and have the strong/weak/electric forces? And why do those forces ...?
No matter how many levels you go down and say, "Ah, X results from the effects of Y", you're still doing the exact same thing you (and PhilGoetz) claim is going on with gravity: you're "passing the buck" to another hypothetical entity.
I don't believe this distinction is useful. Rubber is no more explained when you know it's "really" just molecular forces writ large, than when you merely knew how it works.
The only way to have a terminating procedure to determine when you understand it is when you can predict your observations of it in a model that connects to your model for everything else. Positing the existence of molecules only helps you to the extent that helps generate such a model.
So, I think that both gravity and chemicals are equally well explained: we have a model that works for both.
Perhaps we have different underlying philosophies in what it means to understand something. I feel like I understand something when I know the mechanism for it. And then I can abstract that mechanism, so that I understand other systems that rely on that same mechanism.
For example, in the case of rubber deformation, once I understand the deformation of rubber, I understand the deformation of any elastic, non-compressible material. (Forgive me if I’m cloudy on the full number of necessary assumptions required – I’d have to pick up a textbook on this topic since it’s been a few years.) But I have a mental picture of a network of “molecules” connected by springs that deform and relay pressure. Thus I understand anything that works like this – regardless of what the “molecules” are.
But is this how gravity works? Not necessarily; many different mechanisms can result in the same pattern. Without knowing the mechanism for gravity, I can’t say I understand it.
But I have encountered persons who feel that prediction is understanding, which is what I meant by us possibly having different philosophies about understanding.
I don't disagree. That's why I put in this part:
That "connecting with the rest of your model" corresponds to what you might call "knowing the mechanism in such a way that it generalizes to other systems". For example, if your model uses the concept of a "floobel", then floobels must coherently and consistently fit in with explanations for other things.
So I agree that to understand something, you must not only be able to predict the observables, but do so using concepts that are common (causally connected) to the rest of the model and not just created ad-hoc for one specific problem. (If you could only do the former, that would certainly be a noteworthy success, but doesn't count as understanding. Rather, it's something like the guy in the Chinese room -- the person, of course, not the person+room+rulebook system!)
So I really overreached when I said:
And I apologize for that, because it glosses over what was really the crucial point of contention. I would say that the involvement of molecules can count as having more explanatory powers, so long as your suppositions about "molecules" have implications beyond just rubber stretching. (Which they do in standard scientific usage.) What I meant by the statement above is that if you invent something called molecules just for rubber stretching, your understanding hasn't increased. The understanding happens when you identify the general mechanism behind both molecules and other phenomena, and identify how the rubber properties fall out as an implication.
So let's look back at gravity now: does our understanding of its mechanism generalize beyond just gravity? I say it does, though I could be corrected on this since I'm no expert on relativity. Our description of gravity's behavior relies on concepts like mass, the speed of light, and wave propagation, which are extensively used, with the same values, in contexts where gravity is insignificant or ignored. So it does involve more general concepts and mechanisms.
Perhaps what you mean is that gravity generalizes to a much narrower area than quantum mechanics, making it appear ad hoc relative to quantum mechanics?
But rubber molecules don't actually have springs. It is a structural analogy. The same kind of structural analogy as comparing space-time to rubber. I do think these analogy are a little specious but they're ubiquitous.
Rubber molecules are springs, approximately, which can be verified experiments.
(Not 'spring' in the sense of a metal coil, but spring in the sense of Hooke's law.)
That is .... ideally. I guess if you examine the details, natural rubber isn't so accurately a Hookean material.
But the point isn't whether I'm an expert in the properties of real rubber (I'm not) but whether 'we' (modern science) understand the deformation of rubber, and we do, especially if we mean for some simplified, idealized concept of rubber. (You can google scholar 'rubber deformation', but already Wikipedia is convincing.) There are definitely boundaries to this understanding -- we don't understand everything about it, but it's much more than just understanding an analogy.
I see. I guess then my question is: why should we think that gravity needs more of an explanation? We can understand material elasticity in terms of their molecular bonding but why should we think there is an equivalent means of explanation for gravity? Maybe there is nothing left to reduce it to. If thats the case then I don't think it makes sense to say we don't understand enough about gravity- we'd understand all that anyone could.
Well said.
I (believe I) gained insight from reading your comment.
I don't think curve-fitting is quite the right idea in reference to general relativity -- the equivalence principle is parameter-free. But the principle does take the fact that masses attract as given, and the rubber sheet analogy doesn't help explain why it should be so. In the end, I think you're right (to the degree that you concur with byrnema's excellent comment).
Seems relevant: Feynman on understanding.
What do we mean by "understanding"? Things are always understood in terms of other things already familiar to you. Sometimes the distance between everyday experience and a given idea is too big for immediate explanations, but even otherwise grounding the idea in everyday experience may be cheating, since everyday experience may result from the phenomenon that you are trying to understand this way in the first place!
Gravity is the macro-scale effect of non-euclidean space Balls rolling in curves on rubber are the macro effect of the rubber not being flat.
Space has a tensor field of the locally correct lorentz transform. Rubber has a vector field of the local gradient. Both are derivatives; the fact they aren't constant implies non-eulcidean geometry
The laplacian (second derivative) of space appears made discontinuous only by mass-energy Ditto rubber.
If it isn't mysterious why rubber sheets get distorted, then it shouldn't be mysterious why space is distorted. Both are minimising the deviation of second derivative from a specified forcing, and have dynamics for the forcing over time. They are identical processes.