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Tuesday, July 01, 2003
Void
I have an interest in the history of science, although I wouldn't claim to know a great deal of that history. There are multiple reasons for this interest, I suppose. One is that I just enjoy watching science in its amateur days. Also, I have found that I understand the theories of science when I can trace them from their origins. Science education usually proceeds by presenting the student with theory and a few observations, either observations that can be replicated in a school lab or key observations in the field. When observation and theory are given as a package, it is difficult to separate one from the other. It is only when there are competing theories that it becomes clear what the actual evidence is, prior to its interpretation.
Unfortunately, my tracing of the history of the science has not made it very far or been very thorough, so I'm not much better off grasping contemporary theories than anyone else. In fact, it is even worse than that, because sometimes I find myself drawn to older theories that have long been left in the proverbial dustbin. For example, I find myself to be a fan of the ether, whatever the Michelson-Morley experiment might have shown. And over the past month, I've found myself increasingly sympathetic to Descartes' conception of matter and critical of the Newtonian concept of mass.
Descartes said that matter was simply extension, i.e., substance that fills a certain volume. By effectively equating matter with volume, Descartes was ruling out the notion of mass, which suggests that a given volume can hold different amounts of matter. The greater the amount of matter relative to a given volume, the greater the mass.
The notion of mass seems to fit with our common experience. If something is hard, we imagine that there is more matter there to resist what is moving against it, while the soft gives way. And although the concept of mass is not identical to the concept of weight, it makes sense that harder things are generally heavier than softer things: the harder things have more matter, and thus more attraction to the earth.
And yet, as I was trying to imagine how Descartes was seeing the world, the concept of mass became more fuzzy for me. Let me explain why and hopefully some of you who have actually studied science into the 21st century can help me out.
Imagine raking leaves and putting them into a bag. As we all know, at some point you press down on the leaves in the bag to make them more compact so that you can fit more leaves in. As you do so, you often can feel the air that is being pushed out as you push down. Let us imagine that we have done this a couple of times and now have a fairly heavy bag full of leaves. Let us also imagine that we have not actually stretched the bag in the process, i.e., the volume of the bag has remained constant.
This process of putting more leaves into the bag seems to accord with the notion of increasing mass. I am taking a given volume and adding more matter to it. And, as expected, the bag becomes harder and heavier. It looks like Descartes loses.
But think about this. As I push down the leaves, a volume of air rushes out of the bag. If I fill the bag with leaves up to the point it was at before I pushed it down, I can see that I have displaced a certain volume of one material (air) with another (leaves). In fact, given that the bag volume is a constant, I can safely say that the total volume of leaves + air in the bag is a constant as well. Every cubic inch of leaves displaces an identical cubic inch of air.
If I am displacing equal volumes of material, why should we think that there is more material when we add leaves at the expense of the air? The explanation that comes to mind for me is this: it is because the leaves themselves have more mass than the air. The problem, however, is that this appears to me to just be pushing the problem back a step. If mass is akin to stuffing more matter into a given volume, then it would seem that we should be able to explain it on the level of the leaves and the air. If I start to talk about the mass of the leaves, however, I have just created a new volume to stuff matter into. And won't I end up with the same question?
To see this more clearly, let's just think about the mass of leaves. Presumably some leaves have greater mass than other leaves. If we were to somehow increase the mass of a given leaf, wouldn't we again be displacing one material with another, each of equal volume? To explain this, are we going to make the same assertion as before, that the leaf with more mass has more mass because its parts have more mass? Where does it end?
This looks like a Chinese box to me. Help me out.
Eddie 1:48 AM
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