A supercritical step for fundamental physics with green prospects

Solid, liquid, gas: the three states of matter…

Slg dmitry volkov. Getty
States of matter. Phase or state of matter and phase transition. Credit: Dmitry Vokov/Getty Images

Or maybe not. When matter is compressed or heated so much that it becomes “supercritical”, it’s actually hard to tell if it’s in a liquid or gas state as they behave pretty much the same.

Supercritical states are not just a weird or obscure idea in theoretical physics, they naturally exist on Earth (in the pressurised, boiling water from hydrothermal vents on the seafloor) and elsewhere in our solar system (such as in the hydrogen and helium atmospheres of Jupiter and Saturn).

They are also used as powerful cleaners and can destroy hazardous wastes which might otherwise need to be incinerated.

But until now, we haven’t really had a great grasp on exactly when these materials switch from being a liquid to a gas, nor the physics behind the process as a whole — believing it to be a complex and complicated area that isn’t yet able to be understood.

Supercritical water from a vent in the atlantic seafloor.
Hydrothermal Vent in the Atlantic. Credit: Ralph White/Getty Images

You could say that material scientists have been in a bit of a state about the whole thing.

It seems, however, the fog is lifting. (OK, I’ll stop…)

Looking at how materials absorbed and transferred heat, researchers at the Queen Mary University of London have investigated the point at which supercritical matter transitioned from liquid to gas.

Read More: How runny can a liquid get?

What they found really is a breath of fresh air for physics. (Sorry…)

The researchers discovered an “inversion point” — a singular point at which supercritical matter changes from having liquid-like properties to behaving like a gas — a first for physics.

In another exciting twist, the researchers found that this inversion point is incredibly close in all of the systems they studied. This suggests that there is a commonality and simplicity to how supercritical materials behave when changing state — which in itself was completely unexpected.

Understanding more about how materials behave under extreme conditions is not just important for fundamental physics and applications like understanding the properties of planetary atmospheres.

Engineers are keen to understand more about how supercritical matter behaves in order to better increase their efficiency in “green environmental applications and other areas”, says Kostya Trachenko, from Queen Mary University of London.

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