Massive black holes drag and warp the spacetime around them in extreme ways. Observing these effects firsthand is practically impossible, so physicists look for laboratory-sized analogs that behave similarly. Fluids offer one such avenue, since fluid dynamics mimics gravity if the fluid viscosity is low enough. To chase that near-zero viscosity, experimentalists turned to superfluid helium, a version of liquid helium near absolute zero that flows with virtually no viscosity. At these temperatures, vorticity in the helium shows up as quantized vortices. Normally, these tiny individual vortices repel one another, but a spinning propeller — much like the blades of a blender — draws tens of thousands of these vortices together into a giant quantum vortex.
With that much concentrated vorticity, the team saw interactions between waves and the vortex surface that directly mirrored those seen in black holes. In particular, they detail bound states and black-hole-like ringdown phenomena. Now that the apparatus is up and running, they hope to delve deeper into the mechanics of their faux-black holes. (Image credit: L. Solidoro; research credit: P. Švančara et al.; via Physics World)
As a fluid dynamicist, a small mountain brook on a sunny day can be endlessly entertaining.
The shape of the water's surface is determined mostly the fluid's momentum and surface tension. You can see in this 1/2000 secs exposure the whimsical surface's shape, bubbles and capillary waves.
This fluid, seemingly at rest initially, turns out to be convecting as revealed by a #timelapse movie. #Evaporation cools the fluid at the surface, which makes it a bit heavier than the fluid below, thus #convection ensues, very slowly!
This fluid is #rheoscopic, easy to make at home using shaving cream.
That word theory gets thrown around a lot. Some of my colleagues hold it to a really high bar whereas others use it pretty interchangably with hypothesis testing.
There’s an early phase of research that I’m not sure how to label. It’s not so much about levels, but something else. Here’s an example: what would you call the contribution of Copernicus to planetary motion? Ptolomy had these elaborate descriptions of everything revolving around the earth as cycles and epicycles to make up for wonky trajectories, and Copernicus came along and demonstrated that it all becomes a lot simpler if it’s all revolving around the sun. “Theories” of why the planets revolve as they do (Newton’s gravity and Einstein’s bending space time) came later.
Was Copernicus’s contribution a theory, replotting the data in a more sensible way, or something in between? Whatever it was, it was important, and it led to all that followed. But what do we call it (aka how do we regard it)?
Would you be interested in writing about a 'new' compression algorithm for Aerodynamic effects, which regards the moving Aerofoil as an ENERGY DISTRIBUTOR...?
This 'theory' would logically form a shorter algorithm than 'proxy' analyses built around an assumption of 'Airflow', which is really the 'reverse model' found
A non-Newtonian fluid is a fluid that does not follow Newton's law of viscosity, that is, it has variable viscosity dependent on stress. In non-Newtonian fluids, viscosity can change when under force to either more liquid or more solid.