Perhaps the most convincing evidence confirming the Big Bang theory is the cosmic microwave background radiation: the leftover energy from the hot, early universe that still fills space and permeates the cosmos in every direction. Scientists had predieted that such background radiation would indicate that the temperature of space would be several degrees above absolute zero. The detection of the background radiation showed that the temperature was very close to three degrees Kelvin—a spectacular success of the scientific method.
Three views of the universe from space observatories show the cosmic microwave background, objects in the early universe as they appear in infrared light, and stars and galaxies as they appear in visible light. This microwave background provides evidence of the Big Bang, according to astronomers. (NASA/JPL-Caltech/A. Kashlinsky)