k: the Boltzmann constant

• This might sound (and look) like sci-fi jargon, so let’s break this down a little bit. Cesium is a metal atom in the periodic table. Cesium-133 is its most common form, or isotope, containing a total of 133 protons and neutrons. • Like all atoms, cesium is orbited by electrons. The energy of cesium’s outermost electron can be controlled with microwave radiation. The frequency of microwave radiation that causes this electron to jump between two closely spaced low-energy states is known as the h...