khoji parkDiscovery · Holmdel, New Jersey · 1964–1965
The Noise Came From the Universe
The unwanted part of the measurement was the important part.
Read in slides1. A sensitive antenna
Arno Penzias and Robert Wilson used a sensitive horn antenna at Bell Laboratories. Their measurements included microwave noise they could not immediately explain. A radio instrument can detect unwanted signals as well as intended ones. The researchers first needed to understand their own equipment.
The unwanted part of the measurement was the important part.
2. Start with the equipment
Before treating an unwanted radio signal as evidence about the universe, the researchers had to consider ordinary causes close to their instrument. That work was not a detour from discovery. Testing possible faults and interference made the remaining observation more useful, because the signal had survived attempts to explain it as something local.
The nuisance was becoming harder to blame on the antenna.
3. Removing explanations
They accounted for known sources, including the atmosphere and the equipment. A remaining signal still appeared in the data. Removing possible local causes was part of the investigation. The surviving signal could not be dismissed as a simple maintenance problem.
Cleaning up the measurement had not cleaned away the mystery.
4. A persistent background
The excess radiation did not behave like a single local transmitter. It suggested a background present across the sky. A persistent background required an explanation beyond a single component. The measurement became relevant to questions on a much larger scale.
The apparent interference had an extraordinarily large service area.
5. The cosmological connection
The result connected with predictions of radiation left from an early hot universe. Observations and theoretical work supplied complementary pieces of the explanation. Different researchers approached the problem through observation and theory. Connecting those approaches changed the interpretation of the troublesome signal.
The antenna had heard an ancient remainder.
6. A measurement meets a prediction
An observation can acquire new meaning when it is connected with a theoretical question being pursued elsewhere. The background signal did not announce its own cosmic history. The scientific achievement involved recognizing that the stubborn measurement and an account of the early universe could be examined together, each giving the other a more precise context.
The unwanted noise had found the right question.
7. The discovery
The findings, published in 1965, became evidence for cosmic microwave background radiation. An attempt to understand noise had changed cosmology. The evidence supported a physical account of the early universe. Its value depended on measurement rather than the drama of the discovery story.
Sometimes the signal is the part you tried to remove.