Planets, stars and dust all come in different sizes. Now, a Duke theorist has claimed that has a lot to do with how paint cracks when it dries.
In this latest study, a scientist looked at why objects in space tend to be different sizes. More specifically, he's explained at how the need to release internal tension may have shaped the universe as we know it.
The very early universe can be thought of as a finite volume of suspended particles. Because every object in the universe exerts a gravitational force on every other object in the universe, this volume was in internal tension. This means that it was only a matter of time before particles began to come together to form larger objects. But why did they come together to form larger objects in such a wide variety of sizes instead of in a uniform matter?
"We know from common experiences that things in volumetric tension crack, and they crack instantly everywhere," said Adrian Bejan, the J.A. Jones Professior of Mechanical Engineering at Duke University. "The easiest example is paint drying on a wall. As it dries, it shrinks, putting the entire system in tension. Then boom, it suddenly cracks overnight, relieving the tension. And the design responsible for that relief is hierarchical, meaning few large and many small."
This pattern of relief follows the constructal law, which states that any flowing system allowed to change freely over time will trend toward an easier flowing structure. This holds true for rivers, roots, vascular systems and, apparently, the young universe.
In fact, researchers found that the fastest way for tension to be released in the early universe was through the formation of bodies in a hierarchy in this latest study. More specifically, if all bodies formed were of the same size, the tension would not be released as effectively as when a few large bodies were formed along with many smaller bodies.
"All volumetric cracking is hierarchical," said Bejan. "You never see uniform cracking or shattering. In celestial mechanics, there is this very old idea that bodies coalesce and grow due to gravity, which is of course correct. Growth is one thing, but growing hierarchically rather than all in the same size is another, which is called nature."
