The Cosmic Background Radiation
Discovery Supporting Big Bang Theory for the Origin of the Universe
Penzias and Wilson accidentally discovered the 3K cosmic microwave background radiation, which provided strong evidence supporting the big bang theory.
TV Static and the Universe
Disconnect your TV from any cable connection. Tune it to a channel with no station in your area. Not picking up any signal, you will see a fuzzy nonpicture that we commonly call static or snow. The technical term for this static is noise.
Now imagine attaching your TV to an antenna large enough to pick out even the weakest signals from all that noise. To further enhance your ability to pick up weak signals, you would need to eliminate all sources of noise. So, imagine systematically identifying and then eliminating all possible sources of noise. In the early 1960s, Arno Penzias and Robert Wilson did just that.
OK! They weren't really using their TV. They did however have a microwave receiver (about the same wavelength as TV signals) attached to a large horn shaped antenna. Penzias and Wilson were trying to build a microwave receiver sensitive enough to pick up weak signals emitted by celestial sources in our Milky Way galaxy.
They were working for Bell labs, so their employers may have had the ulterior motive of using the microwave receivers they developed for long distance communication. Basic research problems in science nearly always have very practical applications or lead to the development of technology with practical applications.
To pick up the weak celestial signals, Penzias and Wilson worked to eliminate all the noise from their antenna and receiver. The last stubborn little bit of noise would not go away no matter what they tried. They even crawled into the antenna, chased away the pigeons setting up housekeeping there, and removed the nest and what they called a "white dielectric film" left by the pigeons. All to no avail! The noise was not pigeons or their droppings. It was still there. It was something bigger.
Perhaps the microwave noise somehow came from nearby New York City. Pointing the antenna towards the big apple didn't change the noise level. New York was not awash in microwaves. It was something bigger than the big apple.
As the Earth turned, their antenna pointed to different parts of the solar system. If the source of these mysterious microwaves were in the solar system, the strength of this noise should vary as the Earth turned on its axis. For example if the microwaves somehow originated in the Sun, the noise level would be higher in the daytime than at night. It wasn't. The noise did not originate in the solar system. It was something bigger.
The Earth continued its annual journey around the Sun. If the microwaves originated from a distinct location in our galaxy, the galaxy itself, or perhaps another galaxy, then the noise level should increase when Earth was on the same side of the Sun as the source of microwaves. The noise level didn't change, as the Earth orbited the Sun. It was something still bigger.
Big Bang Theory
Not many things are bigger than a galaxy. Penzias and Wilson were puzzled. At the nearby Institute for Advanced Study, in Princeton New Jersey, Robert Dicke and his colleagues had recently concluded that if the big bang theory for the origin of the universe were correct, the entire universe should be awash in a faint microwave glow.
They were even starting to try finding this radiation when they learned that Penzias and Wilson had scooped them. The microwaves turned out to be what is left, after 10 to 20 billion years, of the heat from the big bang. Penzias and Wilson had inadvertently discovered the big bang. Their mysterious microwaves were not pigeons, New York, the Sun, the Milky Way, or another galaxy. They were the universe! There isn't something bigger.
Further Reading
Barrow, J.H. and Silk, J., The Left Hand of Creation, Oxford, 1983.
Silk, J., The Big Bang, Times Books, 2000.
