of radio waves such as quasars and radio-emitting galaxies.
radio waves: Waves in the electromagnetic field that are like waves of visible light, but have much longer wavelengths, of the order of meters rather than centimeters.
radioactivity: The spontaneous breakdown of one type of atomic nucleus into another.
red shift: The reddening of light from a star that is moving away from us, due to the Doppler effect.
second law of thermodynamics: A law that says that the amount of disorder, or entropy, in the universe increases with time. It is different from other laws in that it is not always true, but only nearly always, and it depends on the universe's starting out in
