The Atomic Hypothesis

In Section 3.3, we explored a model of two interacting atoms. If you were perceptive and curious, you may have clicked on the NetLogo Code button to try to figure out how the model works. We will use more models like this in the coming units and will explore more deeply how they work at that time. For now, all you need to know is that the model is based on a very simple idea - one that iconic physicist Richard Feynman thought was so important that he addressed it in his famous Lectures on Physics by posing the following opening question:

If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words?

It's certainly an interesting question, and here is Feynman’s own answer:

I believe it is the atomic hypothesis that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied. (Feynman, 1963)

This description should match what you experienced with the computational model on the previous page. In this chapter - and throughout the course - we will explore the power of the atomic hypothesis and use it to explore phenomena relevant to MSE. We'll see that there is indeed an enormous amount of information in that one sentence, but... let’s see if we can shorten Feynman's statement without losing anything. What if we just said:

All things are made of atoms — tiny entities that move around in perpetual motion.

Could we deduce from this short sentence that they attract each other when they are a little distance apart, but repel when squeezed into one another? From observations of the world around us, we can. If atoms never attracted one another, then solids and liquids would never form. On the other hand, if atoms didn’t repel one another when squeezed close enough together, then matter would collapse into a single point (Lesar 2013, Introduction).

So, we’ve kept the essential information and reduced the number of words to fourteen. Not bad! However, this statement has two major limitations:

  1. It doesn't explain why atoms behave that way. In the remainder of this chapter we will enhance our mental model to explain why atoms attract each other when they are a little distance apart and repel when squeezed into one another. Or put another way, why atoms bond.
  2. Our statement reflects an entirely qualitative mental model. It won’t let us make any predictions beyond what we’ve already stated: that solids and liquids (i.e., condensed matter) will form under some conditions, but matter won’t collapse into a singularity.

In the next chapter we will construct a quantitative model of the atomic hypothesis and see how it is useful in the field of MSE (this quantitative model is what underlies our simulation on the previous page). That is, what can we explain with this model, what can we predict with it, and what can we discover with it?