On land or underwater, sand dunes usually appear in large groups. But even when these natural formations are in close contact with their neighbors, they still need personal space from time to time.
When two identical dunes migrate long distances, these structures will suddenly change their pace, so they will end up evenly distributed, which is suggestive of how these mounds of sand might 'communicate'.
“They're definitely communicating,” physicist Natalie Vrind of Cambridge University told The Washington Post.
“If I push my neighbor in front of me, I know why. But we are not talking about people with brains, we are talking about sand dunes that communicate – inanimate objects that transmit information. '
Obviously, the sand dunes cannot talk to each other. But the researchers argue that the influence of the dunes on their driving forces changes the influence of the forces on the surrounding dunes, forcing these physical structures to 'communicate' their position.
This contradicts what many theoretical models have assumed for dune migration, which occurs so slowly and at such great distances that it is extremely difficult to study.
Typically, these structures are seen as self-propelled autonomous agents that can sometimes collide and absorb each other, but not necessarily cooperate.
'Another theory is that dunes can collide and exchange momentum, like billiard balls bouncing off each other, until they are the same size and move at the same speed,' explains theoretical physicist Karol Bachik from University of Cambridge.
Both of these explanations seem to be inadequate. Small sand dunes are known to move faster and large sand dunes more slowly, suggesting that dunes of similar size will move at the same speed; but new results show that this is not always the case.
Instead, two sand dunes of equal volume and shape can speed up or slow down to move further apart, all without exchanging much of the mass in the process.
“We discovered physics that was not part of the model before,” says Vrind.
This repulsion from nearby sand dunes has been seen in satellite imagery before, but the forces behind it have not been studied.
This can be incredibly important in preparing for climate change. Over the years, global warming has intensified dune movement in parts of the world, including the United States and Africa.
Figuring out where these massive sand structures are headed – and how they move – could enable us to prepare the infrastructure for the coming collision.
The study was published in Physical Review Letters.
