Mental Model from Newtonian Physics?

Physics to better understand investing.

I don’t think people really understand what a ‘mental model’ is; nor do I, for that matter. I suspect Munger preferred the concept to remain elusive. Intellectuals think they can cut down ideas into pieces and analyze these to find what they mean. But there are some that, once you do that, you lose their essence. I believe mental models fall into this category. Likewise for risk. And so does Pirsig’s Quality, which heavily influenced my thinking.

My intention here is to go over some of Newton’s ideas and my understanding thereof. With many of Darwin’s, I saw it much more clearly. With Newton, I’m partly guessing, and I’m dubious whether I’m getting the grasp of his texts. But perhaps some practical utility can be extracted from this.

Newtonian Physics

In essence, Newton created a System of the World. With observation, experimentation, and thinking, he came up with the fundamental laws underlying the motion of major objects. Thereupon, Isaac complemented these with his idea of gravity, which, as per a hypothesis, he realized it extends to celestial bodies, granting it the name of universal gravitation. Specifically, the pieces of the puzzle are:

• Law 1: Inertia, which posits that a body will remain in its state of rest or the rectilinear motion they’re in, unless a force is impressed upon it.

• Law 2: The change in a body’s motion is proportional to the force impressed upon it. The force will possess a linear given direction and will affect the body’s motion in that same direction.

• Law 3: To every action there is an equally opposed reaction.

• Gravity: The force by which bodies attract one another. It’s proportional to both of their masses and inversely proportional to the square of the distance between them.

  That is, F = m1 * m2 / distance^2. (The only math I understand)

With these simple fundamental inputs and their predictive behavior, Newton builds the system of the world. What I found curious is the diversity of natural phenomena he was able to explain with these elements. This triggers a more profound understanding of Buffett’s approach, or at least what he claims composes it.

At the moment, I don’t intend to go much farther and presume I know things I yet don’t. Nonetheless, my sense is that the corollaries and propositions Newton wrote follow some form of compounding of these forces. It’s very peculiar. This is an example that I think will help illustrate the idea.

Planetary Orbits

Astronomers had longly been dazzled by the behavior of celestial bodies, especially about planetary orbits. After Copernicus and Galileo, it became rather well known that planets orbit around the sun. However, what trajectory they followed was an unbelievably obscure question. Many suspected they drew circular or elliptical orbits, but no one could prove it. When the problem presented itself to Newton, he solved it with the combination of two of his fundamental ideas. Take a look at this figure for a second and follow along.

The planet starts at A. Inertia states that it will remain in its rectilinear motion, in this case going from A to B. But gravity states that bodies attract one another, the sun being the largest attractor due to its huge mass. So when the planet gets to B, the sun pulls it towards S, but it’s not such big a force as to change the planetary motion altogether. So it tilts it a bit and the planet continues moving straight, from B to C; then again the sun pulls it. And so on.

Final Remark

To me, this is a big deal. The explanatory power that can be drawn from the compounded effect of simple ideas is massive. My sense is that many more like this lie in the field of physics, some of which I’ll try to humbly bring to you. An expanded version of this, more comprehensive and including other disciplines, is what I wanted to base my book on. After the mental struggle, I suspect it will be more of a 10-year project than a 1-2 year one.

It’s beyond saying that this is my understanding of what Newton posits. I’ve no idea if it’s right or not, but logic and intuition tell me the concepts are at least roughly right. And that’s okay for me now.