Nav: Home

Celestial bodies born like cracking paint

March 01, 2016

DURHAM, N.C. -- A Duke theorist says there's a very good reason why objects in the universe come in a wide variety of sizes, from the largest stars to the smallest dust motes -- and it has a lot to do with how paint cracks when it dries.

In a paper published March 1 in the Journal of Applied Physics, Adrian Bejan, the J.A. Jones Professor of Mechanical Engineering at Duke University, explains how the need to release internal tension shaped the universe as we see it.

Though unknowably large and spread out, the very early universe can be thought of as a finite volume of suspended particles. And because every object in the universe exerts a gravitational force on every other object in the universe, this volume was in internal tension.

It was only a matter of time before particles began coming together to form larger objects. But why did they come together to form objects in such a wide variety of sizes, rather than in a uniform manner?

"We know from common experiences that things in volumetric tension crack, and they crack instantly everywhere," said Bejan. "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."

According to Bejan, this pattern of relief follows the constructal law, which he penned in 1996. The constructal law states that any flowing system allowed to change freely over time will trend toward an easier flowing architecture. For rivers, roots and vascular systems, this means a few large channels carry massive flows to numerous smaller branches for evacuation. For a young universe with particles pulling every which way, this means its internal tension released in the fastest way possible.

In a series of thought experiments and simple physics equations, Bejan's paper shows that the fastest way for the tension to be released was through the formation of bodies in a hierarchy. That is, he demonstrates that if all bodies formed were of the same size, the tension would not be released as affectively as when a few large bodies were formed along with many smaller bodies.

Just like the cracks in the paint.

"All volumetric cracking is hierarchical. You never see uniform cracking or shattering," said Bejan. "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."
"The physics origin of the hierarchy of bodies in space." A. Bejan and R.W. Wagstaff. Journal of Applied Physics, 2016. DOI: 10.1063/1.4941986

Duke University

Related Gravity Articles:

Einstein's description of gravity just got much harder to beat
Astrophysicists put general relativity to a new test with black hole images.
MUSC researchers test brain stimulation in zero gravity
How does zero gravity affect astronauts' brains? MUSC scientists took to the skies as they try to figure that out.
Gravity causes homogeneity of the universe
Gravity can accelerate the homogenization of space-time as the universe evolves.
Gravity wave insights from internet-beaming balloons
A better understanding of how gravity waves in the upper atmosphere interact with the jet stream, polar vortex and other phenomena could be key to improved weather predictions and climate models.
A stepping stone for measuring quantum gravity
A group of theoretical physicists, including two physicists from the University of Groningen, have proposed a 'table-top' device that could measure gravity waves.
Surface tension, not gravity, drives viscous bubble collapse
By demonstrating that surface tension -- not gravity -- drives the collapse of surface bubbles in viscous liquids, a new study flips the previous understanding of how viscous bubbles pop on its head.
How earthquakes deform gravity
Researchers at the German Research Centre for Geosciences GFZ in Potsdam have developed an algorithm that for the first time can describe a gravitational signal caused by earthquakes with high accuracy.
Physicists mash quantum and gravity and find time, but not as we know it
A University of Queensland-led international team of researchers say they have discovered ''a new kind of quantum time order''.
Quantum gravity's tangled time
The theories of quantum mechanics and gravity are notorious for being incompatible, despite the efforts of scores of physicists over the past fifty years.
When plant roots learned to follow gravity
Highly developed seed plants evolved deep root systems that are able to sense Earth's gravity.
More Gravity News and Gravity Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Warped Reality
False information on the internet makes it harder and harder to know what's true, and the consequences have been devastating. This hour, TED speakers explore ideas around technology and deception. Guests include law professor Danielle Citron, journalist Andrew Marantz, and computer scientist Joy Buolamwini.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

How to Win Friends and Influence Baboons
Baboon troops. We all know they're hierarchical. There's the big brutish alpha male who rules with a hairy iron fist, and then there's everybody else. Which is what Meg Crofoot thought too, before she used GPS collars to track the movements of a troop of baboons for a whole month. What she and her team learned from this data gave them a whole new understanding of baboon troop dynamics, and, moment to moment, who really has the power.  This episode was reported and produced by Annie McEwen. Support Radiolab by becoming a member today at