Wednesday, December 01, 2004

Size Matters

As human beings, we all have a general sense of the physical rules of the universe. By this, I mean that we all understand gravity, the fact that objects have mass, and the repercussions of applied force. This is true even if we do not have a vocabulary to describe the phenomenon. When one drops a heavy weight, it is understood that it will fall to the ground and the word "gravity" never need be spoken. Moreover, we not only understand the existence of these rules but, more importantly, what these rules mean to us as we navigate our way through the universe. And because our experience on these matters is so consistent, we naturally believe that these rules, and the repercussions of them, are universal.

However, this is only true when you limit the conversation to humans. What about that fly walking across the ceiling right now? Assuming for the moment that communication with such a creature was possible, how would he respond to questions about the meaning of gravity? Well, most likely he would have no idea what you were talking about. His life is lived with little or no awareness of gravity, and therefore it would mean nothing to him. If asked what forces ruled his universe, he would describe the ever present reality of surface tension (the force that holds him to the ceiling).

Now, take a look around the room in which you are sitting. Notice how every object has a unique shape. This reality is so obvious you've probably never even thought to notice it. Of course different things have different shapes. It is one of the primary methods by which we identify objects. In fact, often times shape is the only characteristic that will differentiate objects from one another. Again, so ubiquitous is this reality in our world, we can hardly be faulted for again assuming that the differential shape of objects is universal.

Funny thing, though. Planet Earth is a sphere. Mercury, Venus, and Mars are also spherically shaped, as is every other planet in our solar system. This is also true of nearly every moon, the sun and, in fact, every star in the universe. In truth, spheres dominate existence. Deviation from a spherical shape is the exception, not the norm.

I present these examples to you for a very specific purpose. We have a reasonable tendency as human beings to assume universality of rules: gravity dominates the universe and shape is highly variable. However, as we have just seen, these supposedly universal rules are anything but. This raises an important question: what makes the rules change?


Gravity is irrelevant to a fly because its mass is incredibly small. The force gravity is able to exert on a fly, due to its negligible mass, is inconsequential when compared against the tensile strength of its exoskeleton. Conversely, surface tension is unrelated to mass and exerts a constant force that is quite substantial to such a tiny creature. At the other end of the scale, gravity becomes so powerful that it crushes everything above a certain mass into a sphere.

The lesson here is that size determines the rules. And, not only in the physical universe.

More on this soon.

Click here to read Part II
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