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The incredibly slippery nature of superfluids

Slipperiness is a property that we often associate with everyday objects like ice, soap, and banana peels. However, there is a substance that is even more slippery than these: superfluids.

A normal liquid becomes a superfluid when it is cooled down below a certain temperature. This temperature is unique to all fluids, for example for helium it is 2.17 K. Below this temperature, the superfluid will behave in completely unique ways. For example, if a container of water at room temperature was spun, you’d expect the water to also spin around, creating a whirlpool. Whereas a superfluid in a spinning container doesn’t spin at all, until it reaches a certain speed!

 

The slippery property of a superfluid is caused by its ability to flow very easily. Usually it’s safe to leave a glass of water on a countertop (unless of course you’ve got a particularly excitable dog), but if you were to leave a glass of superfluid on a table, the liquid would creep out and escape. The tiny changes in temperature or pressure in the container cause it to flow, seemingly defying gravity. 

 

Unfortunately, superfluids cannot just be bought in the local supermarket! To produce a superfluid, devices known as cryostats can be used to cool a substance down to low temperatures. Using the ideal gas model, pressure, and volume can be related, so by reducing the pressure, the temperature of the device can also be decreased. The pressure is reduced using a vacuum pump, which works by removing particles from the cryostat.

 

The applications of superfluids are limited as, due to the typically very low temperatures needed for a normal fluid to transition to a superfluid, there is difficulty in producing superfluids. Currently, scientists are working on finding fluids that enter a stable superfluid state at room temperatures. 

 

However, superfluids are used within many fields of physics to explain certain phenomena. One theory is that the core of collapsed large stars (neutron stars) is a superfluid, despite the very hot temperatures. The idea is that below a certain temperature, it uses less energy for the core to behave like a superfluid which cools the star down at an increased rate. The superfluid theory of neutron stars is just a hypothesis, however hints at the role superfluids play in all areas of physics.



By Madeleine Hales



REFERENCES/ FURTHER READING:

https://www.aps.org/publications/apsnews/200601/history.cfm#:~:text=In%201927%20Willem%20Keesom%20and,helium%20I%20and%20helium%20II.

 

https://physicsworld.com/a/neutron-star-has-superfluid-core/

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