To most people helium might be little more than a fun, if not a little adrenaline-inducing, gas to fool around with. But there is much more to this little molecule than making you sound like Spongebob Squarepants. For one, it might help answer some of the biggest questions in physics today. The Student contacted Prof. Adrian Del Maestro, a professor at the University of Vermont, who was part of the team that just discovered helium can behave like a black hole.
He wrote, “Understanding how to control the entanglement in superfluid helium (by changing the pressure) may allow for future ideas on how it could be extracted and transferred to a device that can do quantum information processing.” But more on that later.
Helium makes up 24% of universal mass, and is the second most bountiful element (proceeded only by hydrogen). And there is a good reason for this. Without hydrogen none of the other elements would even exist. Main sequence stars, whether low or high mass, start off by fusing hydrogen into helium. This process releases immense amounts of energy which is what “powers” our sun today. Helium has thus been around since the early universe, however, it was only discovered in 1868 by Jules Janssen, when he noted its unique spectrum while monitoring a solar eclipse. His observation was reinforced that same year by Norman Lockyer who found similar results. He inferred they had discovered a new element, which he called helios, meaning Sun.
Helium is one of the noble gases, and as such is inert. It is so unreactive, in fact, that there are no natural compounds containing helium. When it is cooled down to below -150 degrees Celsius it exhibits cryogenic behavior, characterized by an almost complete stop to molecular motion. This property has been harnessed by the medical community for freezing biological material, such as organs. Its low density and low solubility in the blood has been utilized in diving. Where a mix of oxygen and helium are used for breathing, replacing much of the nitrogen normally found in the air. Nitrogen, becomes increasingly soluble in the blood at high pressures, and thus builds up during dives. However, once resurfaced the nitrogen loses this property forming air bubbles- leading to a potentially deadly condition called, the bends. Helium, on the other hand is less soluble, and thus reduces this risk.
There are many applications when it comes to helium, however, del Maestro’s discovery might just be the most fascinating. In 1972 Jacob Berkenstein and Stephen Hawking established that contrary to what one might think the entropy of a black hole is dependent on its surface area, and not its volume – this observation is now known as the “area law” of physics. It turns out superfluid helium exhibits a similar behavior, in a phenomena called “entanglement area law.” When asked about the implications of this find del Maestro said, “The “area law” we have discovered appears to be quite universal, i.e. it shows up in all kinds of different places and at different scales. This points to it being fundamental in nature.” It turns out the team chose helium for a unique reason, del Maestro explains, “The isotope helium-4 is a boson as it has an integer spin quantum number. This means that a macroscopic number of helium-4 atoms can share the same ground state, something not possible for fermions, which have half-integer spin and are subject to the Pauli exclusion principle.” This ultimately means two bosons can occupy the same space, whilst two fermions cannot.
Helium’s role in history has been one of fundamental importance. Not only could we not exist, but it turns out it may just be the missing link needed to tie in gravity with quantum mechanics.