The Scientist’s Essay for 5. Transformations
What’s important about transformations?
Change is so ubiquitious, in fact, that when we find something that doesn't change, there's a strong suspicion that it's telling us something important.
The cliché that change is the only constant is as true in the physical world as it is in human affairs. Change is so ubiquitious, in fact, that when we find something that doesn't change, there's a strong suspicion that it's telling us something important. Biologists look for aspects of life that are the same across species or that persist over millions of years of evolution. Anthropologists look for aspects of human society that are the same across disparate cultures and over hundreds or thousands of years. And physicists pay particular attention to quantities that remain constant even as a system undergoes (sometimes radical) transformations. These “invariants” or “conserved quantities” often carry deep implications for understanding, even if we're not always clever enough to figure them out right away. They also serve as valuable tools for predicting some aspects of a system's behavior even when the details are too complicated to figure out.
One of the reasons for looking at what happens when materials are cut, crushed, ground, or molded into different shapes is to focus attention on what doesn't change. Among the things that don't change under these sorts of transformations are the total weight and total volume of the material. But other things remain the same, too — is it still “the same stuff”? How can you tell?
Another goal of these transformations, though, is to provoke the imagination. Any real experiment eventually runs into practical limits — you just can't go any smaller, or any hotter, or any thinner, or whatever. But it's often instructive to ask: What if you could keep going? Would there eventually be a “smallest piece” that you couldn't divide any more? If so, would it still be “the same stuff”? How would you know? If not — if there's no limit to how small you can go — what would that imply about the nature of matter?
—Roger Tobin
