Since 1964, Penzias and Wilson, young engineers of Bell Telephone Company in the United States, have used this system to measure the background radio noise of the Milky Way. They jumped out of the box of early work, no longer turned a blind eye to these noises, but studied them carefully and deeply. They installed a low-temperature reference noise source and compared it with the noise from the sky. It is found that in the receiving system, the measured noise is always greater than the total noise calculated from any known noise source in the atmosphere and sky. In other words, they received noise from an unknown source with a wavelength of 7. 15 cm. The signal strength of this strange radio interference noise is the same in all directions, and it has not changed for several months.

At first, they thought it might be some other faults, but after months of careful observation and system improvement, they came to the conclusion that it was not caused by the fault of the receiving system or other reasons, but just a kind of radiation, the source of which they didn't know at that time. They also found that this radiation is isotropic, and the corresponding blackbody radiation temperature is 3.5kK. Later, at other wavelengths, through direct and indirect measurements, it was found that the radiation temperature was about 3 K.

The discovery of cosmic microwave background radiation opened up a new field of observing the universe, and also provided new observation constraints for various cosmic models, which was listed as one of the "Four Great Discoveries of Astronomy in 1960s".