Life in a Vortex
Frodo Baggins and Gandalf take a moment to relax and contemplate Frodo’s birthday. They take turns blowing smoke rings in this scene from Jackson’s movie adaptation of Tolkein’s The Fellowship of the Ring.
Do we need magic to make a smoke ring? Bilbo doesn’t, and neither do we. We just need to mix two fluid, and give one a push. Here is a great mini-documentary on how one researcher made “vortex guns” that work in air and water.
The vortex is ubiquitous: if you are in a fluid, and you move, you will make a vortex. Vortex motion is one of the fundamental modes of motion for a fluid. There is a connection between vortex formation and generating lift. John Anderson’s textbook, The Fundamentals of Aerodyanmics, shows us how lift is not possible without a vortex. Birds, dragonflies, maple seeds, Boeing 747s, all of these object create lift by generating vortices. Here’s a jellyfish creating vortices to swim.
What is going on here, that fluids flowing around objects or around one another make vortex rings? Of course, one of the best places to start on this topic is the Wikipedia article on the mechanics of the vortex ring. I am certain there are hundreds if not thousands of great research papers on the mechanics behind vortex rings. One that I find intriguing is from Caltech and NASA Ames on the timescale associated with vortex ring formation. As we press forward with creating the DOORSTEP software, we will ensure it has the hooks in place to generate vortex ring simulation.
But the nature of those hooks will take some investigation. Certainly, the dark matter flowing through the Earth acts as a fluid. But the fluids we see rings in have motion that responds to viscosity (or variants of viscosity). And the relative motion between the fluids and/or bodies is small.
The required drag-like force could be caused by dynamic friction. The role of dynamic friction in the mechanics of dark matter near the Earth is a phenomenon targeted by the DOORSTEP simulation. This will be the topic of future papers, videos and blogs.
An open question is: at what level would vortex ring formation occur? Would the rings form at the atomic level? Or at the macroscopic level, as the dark matter fluid encounters changes in the density of the Earth at different depths? I have studied how the Earth’s density, as it changes with depth, can change the dynamics of Earth bound dark matter. We should visit that topic another time.
Meanwhile, consider: we live inside a dark matter fluid. And certainly we move within it. What vortices are we making? Feel free to contribute your thoughts about vortex rings and dark matter here.