Photons are available each wavelength you’ll be able to think about. However one specific quantum transition makes gentle at exactly 21 cm, and it’s magical.
In our Universe, quantum transitions are the governing rule behind each nuclear, atomic, and molecular phenomenon. In contrast to the planets in our Photo voltaic System, which might stably orbit the Solar at any distance in the event that they possessed the suitable pace, the protons, neutrons, and electrons that make up all the standard matter we all know of can solely bind collectively in a particular set of configurations. These potentialities, though quite a few, are finite in quantity, because the quantum guidelines that govern electromagnetism and the nuclear forces limit how atomic nuclei and the electrons that orbit them can organize themselves.
In all of the Universe, the most typical atom of all is hydrogen, with only one proton and one electron. Wherever new stars kind, hydrogen atoms change into ionized, turning into impartial once more if these free electrons can discover their method again to a free proton. Though the electrons will sometimes cascade down the allowed power ranges into the bottom state, that usually produces solely a particular set of infrared, seen, and ultraviolet gentle. However extra importantly, a particular transition happens in hydrogen that produces gentle of in regards to the…
