In the strange world of low-temperature physics, few more unusual phenomena have been discovered than monatomic hydrogen gas. According to a recent report (New Scientist, Jan. 1981, p. 204), hydrogen atoms do not tend to pair up to form molecules under special low-temperature-cryogenic experimental conditions. The reasons for the existence of atomic hydrogen gas at ultra-low temperature, and for its implications, lie in an understanding of its almost pure quantum mechanical properties. Practical uses of atomic hydrogen will await more knowledge of its properties, but right now, if available in sufficient abundance, atomic hydrogen could be used in maser clocks because it emits highly defined frequencies of microwave radiation at room temperature, and atomic hydrogen gas could be used as an energy conservative fuel, as it recombines to the diatomic molecule. For every recombination between two hydrogen atoms, 4.5 eV of energy are released, which calculates to be over 1 million watts of power per second for 10 grams of atomic hydrogen recombined. The large impulse relative to its light mass could be significant in applications of atomic hydrogen as a rocket fuel. Practical applications aside, the main interest in atomic hydrogen at this moment is in the insight into quantum mechanics that study of its properties may provide. Atomic hydrogen atoms ‘abound throughout the universe,’ even though not on Earth, and thus quantum effects in space, and the hydrogen-rich planets as well, may be elucidated by results of these studies.