Spinning water droplets behave like black holes
WHAT does a drop of water have in common with a black hole and an atom? Well, levitating water droplets can now simulate the dynamics of both cosmological and subatomic objects.
Richard Hill and Laurence Eaves at the University of Nottingham, UK, turned to water droplets because the surface tension that holds the drops together can be used to model other forces. For example, the event horizon of a black hole is sometimes thought of as a "stretched" membrane with a surface tension. Similar forces also prevent atoms from flying apart.
The team levitated the droplets using an effect called diamagnetism: when an external magnetic field was applied to the droplets, they created their own opposing magnetic field, initiating a repulsive force strong enough to counteract gravity. To set the droplets spinning, they implanted two tiny electrodes, which generated an electric field.
They found that once a droplet with a diameter of 1 centimetre reached about 3 revolutions per second, its shape, when viewed from above, became triangular, an effect never seen before in the lab (Physical Review Letters, DOI: 10.1103/PhysRevLett.101.234501).
"The breakthrough in this work is the ability to reproduce, in a simple table-top experiment, 100 years of theoretical work in fluid dynamics," says Vitor Cardoso of the University of Mississippi.