Cosmic Microwave Background Radiation (CMB) was discovered in 1965 when physicists Arno Penzias and Robert Wilson detected a faint, uniform microwave “hiss” coming from every direction in space. At first, they thought it was interference from their equipment—even cleaning out pigeon droppings from their antenna—but the signal wouldn’t go away. Around the same time, other scientists had predicted that if the universe began in a hot, dense state, it should still be filled with cooled-down radiatio