Space.com:  “A weird quantum effect that was predicted decades ago has finally been demonstrated — if you make a cloud of gas cold and dense enough, you can make it invisible. Scientists at the Massachusetts Institute of Technology (MIT) used lasers to squeeze and cool lithium gas to densities and temperatures low enough that it scattered less light. If they can cool the cloud even closer to absolute zero (minus 459.67 degrees Fahrenheit, or minus 273.15 degrees Celsius), they say it will become completely invisible.

“The bizarre effect is the first ever specific example of a quantum mechanical process called Pauli blocking. ‘What we’ve observed is one very special and simple form of Pauli blocking, which is that it prevents an atom from what all atoms would naturally do: scatter light,’ study senior author Wolfgang Ketterle, a professor of physics at MIT, said in a statement. ‘This is the first clear observation that this effect exists, and it shows a new phenomenon in physics.’

“The new technique could be used to develop light-suppressing materials to prevent information loss in quantum computers. Pauli blocking comes from the Pauli exclusion principle, first formulated by the famed Austrian physicist Wolfgang Pauli in 1925. Pauli posited that all so-called fermion particles — like protons, neutrons and electrons — with the same quantum state as each other cannot exist in the same space. Because at the spooky quantum level there only are a finite number of energy states, this forces electrons in atoms to stack themselves into shells of higher energy levels that orbit ever farther around atomic nuclei. It also keeps the electrons of separate atoms apart from each other because, according to a 1967 paper co-authored by the famed physicist Freeman Dyson, without the exclusion principle all atoms would collapse together while erupting in an enormous release of energy. These outcomes not only produce the startling variation of the elements of the periodic table but also prevent our feet, when planted on the dirt, from falling through the ground, taking us tumbling into the Earth’s center.”