Otago research helping to unlock superfluid mysteries

University of Otago physicist Dr Ashton Bradley reflects on the behaviour of very chilly...
University of Otago physicist Dr Ashton Bradley reflects on the behaviour of very chilly superfluids. Photo by Linda Robertson.

One of the most surprising things about exotic superfluids, fluids that form at extremely low temperatures, is just how unsurprising some of their behaviour may be.

These superfluids form in the laboratory, within about two degrees of absolute zero, which is minus 273.15degC.

If you look at many streams, you can see how turbulent eddies - the swirling of a liquid and resulting reverse currents - occur downstream, after flowing water encounters a sizeable rock.

University of Otago physicist Dr Ashton Bradley holds a prestigious Rutherford Discovery Fellowship and leads a research group which is investigating some of the tantalising secrets of superfluids, exotic fluids with no friction or viscosity.

Viscosity is the measure of a fluid's resistance to flow. Honey, for example, has a high viscosity.

Dr Bradley said his theoretical research led him to the view that ''turbulence in these exotic superfluids behaves, to a remarkable degree, just like the normal fluids familiar from everyday life''.

And he believes superfluids will also surprisingly display that stream-like turbulence if they encounter what he terms a ''quantum rock'', an obstruction simulated by a laser.

The eddy-like response would arise from ''the chaotic motion of many tiny quantum vortices - microscopic tornadoes of superfluid''.

These research findings have been published by the US-based journal Physical Review Letters this week.

The Otago work was at the cutting edge of superfluid turbulence research and ''it's an exciting time'', Dr Bradley said.

Most of the project's ''hard work'' had been done by his PhD student, Matt Reeves.

Dr Bradley said fluids were so common in everyday life that people hardly noticed their ''peculiar behaviour''.

''Stir a cup of coffee while adding milk, and watch the way the fluids mix - how does this complex process work?

''The truth is nobody knows, and unlocking the mysteries of fluid turbulence is one of the grand challenges of modern physics,'' he said.

Since the 19th century, a mathematical construct called a Reynolds number had been used to measure fluid turbulence.

But the simpler response of a superfluid - without friction or viscosity - could lead to further insights into the nature of all fluid turbulence, and could eventually produce ''a simpler picture'' that might replace our current models.

Such research could eventually unlock the ''mysteries of turbulent motion'' in many fluids, including the blood in your veins and the swirling contents of your latest coffee, he said.


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