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Thursday, March 30, 2006

car physics

In thinking about this question of whether accelerator physics is really physics, I think about the question of whether the problems facing car designers is physics. When you drive your car really fast, you want it to be a smooth ride. Is the systematic understanding of bumpiness in rapidly moving cars physics? Is it science?

I guess I would have to say the answer is maybe. The question is whether systematic approaches can be developed or not. That seems to be what we mean by science. The statistical mechanics of bumps in the road and the understanding of shock absorbers is applied physics. If one simply models the car in a really complex way, writing an elaborate computer program that simulates the effects of bumps, I would be more reluctant to call that physics. Coming up with simple models, finding what elements are essential and understanding that simplified model: that is what I would call physics.

The old joke about the physicists who starts out a calculation: "suppose the horse is a sphere..." that does seem to capture what we mean by physics in a way. It may be bad physics if one wants to understand how fast the horse can run, or how its surface to volume ratio relates to heat production, but the modeling aspect is physics.

Maybe physics has come to mean two distinct things. There is basic physics which relates to understanding of things in the extreme. Extreme simplicity, size- large and small, speed, complexity, etc. Then there is the process by which a system is replaced by a simplified model which is then analyzed. This is the sense in which accelerator physics is physics. I replace the complex of magnetic fields by a symplectic matrix. Quantum mechanics is ignored. The thoughts in the people nearby are ignored. The rising and setting sun is probably ignored.

Coming back to the car then, if you can think of it as a damped driven harmonic oscillator, then you are indeed doing physics. So I don't know how much interesting stuff has come out of car physics. But it does seem clearly meaningful to talk about car physics, even if the purpose is to design a better car.

What comes out of this definition of physics, however, seems to be that physics is not fundamental. It is an element of how we understand our world, a specific mode. It is not particularly descriptive. Listing the objects in a room is not physics, but it is a part of understanding the room. To take this a little further, one might say that physics is a language in which the world can be described. It asks the user to be very sparse in the number of elements of that description. One can use harmonic oscillators. One can use Hamiltonians. One can use random variables. One can use heat transfer and rigid bodies. From this language one will find that some things are quite difficult to describe.

You might argue that one always uses physics. If I say that there is a beer bottle and an apple core on my futon, you could ask: what do you mean by beer bottle and apple core? Don't you mean brown glass with colored labels and a spongy object which is a collection of cells and sugar molecules? The point is that I might not have these "scientific" descriptions at hand, yet I can still make myself understood by using the words "beer bottle" and "apple core". And beer bottle and apple core are really not words in the physics language.

Am I getting closer to understanding? I know one can go around and around in circles with these questions. But I do feel like this leaves me slightly closer to where I wanted to go.


Anonymous said...

Were you high when you wrote this?

Boaz said...

Ah, the joys of taking physics too seriously!
Nope, no illegal substances in my body.