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byrnema comments on Hypotheses For Dualism - Less Wrong

1 Post author: byrnema 09 January 2010 08:05AM

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Comment author: byrnema 12 January 2010 07:48:59PM 1 point [-]

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.

Comment author: SilasBarta 13 January 2010 04:37:39AM 1 point [-]

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.

I don't disagree. That's why I put in this part:

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.

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:

Rubber is no more explained when you know it's "really" just molecular forces writ large, than when you merely knew how it works.

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?

Comment author: Jack 12 January 2010 09:19:32PM 1 point [-]

But I have a mental picture of a network of “molecules” connected by springs that deform and relay pressure.

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.

Comment author: byrnema 12 January 2010 09:53:48PM *  1 point [-]

But rubber molecules don't actually have springs

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.)

A rubber band behaves according to Hooke’s Law.

That is .... ideally. I guess if you examine the details, natural rubber isn't so accurately a Hookean material.

Rubber is generally regarded as a "non-hookean" material because its elasticity is stress dependent and sensitive to temperature and loading rate.

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.

Comment author: Jack 12 January 2010 10:16:23PM 2 points [-]

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.