If ever there was a criminally underrated natural resource, it would have to be Helium. Though most commonly associated with party balloons and making one’s voice sound like a cartoon, Helium’s most important application is in cooling the magnets of Magnetic Resonance Imaging or MRI machines. While the finite and ever-dwindling global supply of this vitally important gas is a topic worthy of its own video, perhaps even more fascinating is just how bizarre an element Helium truly is. For if Helium is liquefied and cooled to a low enough temperature, it begins to behave like no other liquid on earth, seemingly violating the laws of gravity, thermodynamics, and even logic itself. This is the story of superfluid Helium II, the weirdest substance known to science. In order for Helium to be liquefied, it must be cooled to a temperature of -268.8 degrees Celsius or 4.2 Kelvin – that is, only 4.2 degrees above Absolute Zero, the coldest temperature theoretically possible. By contrast, Nitrogen liquefies at a relatively balmy 77 Kelvin, Oxygen at 54 Kelvin, and Hydrogen at 33 Kelvin. The reason Helium is so difficult to liquefy lies in its electron orbitals being completely filled, making it – like the other noble gases Neon, Argon, Krypton, Xenon, and Radon – electrically neutral and chemically inert. This means that the only force which can pull Helium atoms together is the so-called Van de Waals Force, which is caused by electrons shifting from one side of an atom to the other and creating a momentary electrostatic charge. This force is incredibly weak, meaning that Helium must be cooled to extremely low temperatures in order for the Van de Waals forces to overcome the energy of the moving atoms and pull them close enough together for the gas to liquefy. Solidifying Helium is even more difficult – so difficult, in fact, that it cannot be done at regular atmospheric pressures. Only at pressures of 25 atmospheres and above can solid Helium be created. Learn more about your ad choices. Visit megaphone.fm/adchoices