Tuesday, 5 February 2013


Think of a fluid with no viscosity.  In other words it is perfectly runny and if you stir it to start it rotating in a beaker it will spin for ever.  Literally for ever! 

This same magical fluid can also climb up the walls of the beaker containing it, run over the top and down the outside, to drip off the bottom.  And to cap it all, it transfers heat perfectly well too.

Surely this fluid doesn't exist.

Well, surprisingly it does!  It was well studied by Jack Allen at The University of St Andrews.  It is called a 'superfluid' and the best known example of it is liquid helium (specifically helium 4 rather than the lighter isotope, helium 3).  'Normal' liquid helium has a boiling point 4.2 degrees above absolute zero, or as we describe that temperature on the kelvin scale it is at 4.2K.

However, if you cool this liquid to below 2.2K it changes into a new form.  It still looks like an ordinary colourless liquid (and yes it really is possible to photograph things that are this cold if you do it carefully)  but it now has the amazing properties described above.  The embedded video shows you enough that you might want to investigate the subject further.  I hope you will.

Thank goodness water doesn't have these properties.  Imagine if your nice hot cup of tea could escape from its cup and drip onto your legs.  Ouch!

Small note:  In memory of my friend Bob Mitchell who died last year.  Bob was a key member of the team of cryogenic experts who first filmed the effects of superfluidity for Jack Allen, at St Andrews University.  He also inspired the first part of my career, working with superconducting magnets and cryostats, and as luck would have it, he was the customer on my first cryogenic system installation .

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