Tuesday, 30 November 2010

What is Snow?

Dear Junior

On the morning after a night of snowfall, I took a morning walk to kindergarten with my two sons. The older of them (four years old, but soon five) asked:
"Why does snow glitter?"
Good question and I described how snow consist of snow flakes that are flat, and that it is the top-most layer of flakes that glitter - in the same way as the glitter palettes that you can glue onto paper. We discussed it a while, and he seemed to think that it made sense.
After some moments of silence came the next question:
"Why is snow soft and fluffy?"
Good question, and I described how the flakes fall on top of each other in loose layers. We discussed it a while, and he seemed to think that it made sense.
To no big surprise there came yet another question:
"Why are snow balls hard?"
Good question again, and I described how the loosely layered flakes are squeezed together and get stuck in each other - that is why the snowball does not fall apart. We discussed it a while, and he seemed to think that it made sense.

Now, is snow *really* snowflakes? Nahhh, snow is water that sticks together through covalent bindings that behaves in a certain way when the temperature drops so much that the kinetic energy of the molecules is so low that it make them bind to each other in certain geometric patterns.

But, you do not expect me to explain that to a four year old kid, I guess …

The snow flake metaphor is a model. It abstracts away a lot of really complex stuff to give us a way of explaining a limited set of phenomenons. Put another way, it answers some interesting questions.

As all models it has its limits. For example, had my son asked "How come that when snow melts, it become water, but when it freezes again it does not become snow, but ice?". Well, then the snow-flake model would not have helped much. It is just a model. It answers some questions in a way that makes sense, but not all questions.

However, the same goes for the "covalent binding" explanation. It is also just a model. It is not more or less "true" that the snowflake model. It is just capable of explaining another range of phenomena in a way that makes sense.

They are both useful models, and that is where they get their value. The interesting question is not whether the model is "true" or not, but whether the model is useful.

The "snow flake" model enables a father to give sensible answers to some questions a four year old boy might ask on the way to kindergarten on the morning after a night of soft snowfall.

From my point of view, that is a good model.