Can gravity behave as fluid to cause turbulence?

You must have seen a serene, cool journey across spacetime in sci-fi movies without turbulence but in reality, the ride is full of bumps and swirls.

Debunking earlier thoughts that spacetime cannot become turbulent, new research shows that gravitational fields around black holes may disturb the flying experience.

The researchers followed the line of thought that gravity can behave as a fluid.

One of the characteristic behaviours of fluids is turbulence - that is, under certain conditions, they do not move smoothly but are edgy and swirl.

Can gravity do that too?

"Gravity can be described as a field theory. It is a two-step dance: gravity equals field theory, and field theory equals fluids, so gravity equals fields equals fluids. That's called the gravity/fluids duality," explained Luis Lehner from Perimeter Institute for Theoretical Physics, an independent research centre in Ontario, Canada.

For many years, the folklore among physicists was that gravity could not be turbulent.

To clear their doubts, the team decided to study fast-spinning black holes, because a fluid-dynamics description of such holes hints that the spacetime around them is less viscous than the spacetime around other kinds of black holes.

Low viscosity increases the chance of turbulence - think of the way water is more swirly than molasses.

The team also decided to study non-linear perturbations of the black holes.

Gravitational systems are rarely analysed at this level of detail, as the equations are very complex.

They were stunned when their analysis showed that spacetime did become turbulent.

"I was quite surprised. I never believed in turbulent behaviour in space," said Huan Yang from Perimeter and Institute for Quantum Computing.

The most exciting consequences of this research relates not to gravity but to ordinary, earth-bound turbulence.

From hurricanes to cream stirred into coffee, from the bumblebee's impossible flight to the vortices shearing off the end of airplane wings, turbulence is all around us.

This research strengthens the idea that gravity can be treated as a fluid - which also means that fluids can be treated gravitationally, the study concluded.