Big hiss missed by others
While the tools to find the echo of the Big Bang were known and could have been found by others, it is no big surprise that other researchers missed it. Theorists had been pursuing the cosmic microwave background (CMB), but most believed that it would be too faint to be detected.
Another factor that made the CMB difficult to find was that some theorists estimated a higher temperature for the CMB than was actually found. As discussed in the notes for the article "Murmur of a Bang", the spectrum of light of the CMB is that of a black-body. A black-body spectrum is characterized by the wavelength at which it peaks, corresponding to a characteristic temperature. Without knowing the characteristic temperature or the CMB, the signal CMB would be easy to miss.
Perhaps if Penzias and Wilson had not seen the paper by Dicke, they would have written the excess noise off to some "unattributable source", and continued with astronomical observations, oblivious to cosmological gem they had at their fingertips.
And as a side-note, a few other things in science that were discovered by accident include penicillin and gamma-ray bursts. It may be fun to have students find other examples.
The following web page has more detailed information:
- Cases of Accidental Scientific Discoveries at Trivia-Library.com