This paper is about the searching strategy for alien civilizations and the actual experiment associated with it. In this sense, the paper addressed two questions 1) what kind of signal we should be looking for 2) how we would conduct our experiment to search for this signal. The paper suggested three ways we could look for SETI signal 1) “searching for radiation that other civilizations are using for their own purposes” 2) searching for radiation at 1420 MHz 3) “a passive observation with a very large telescope” to search all kinds of signals.
Then the author described the effort at Green Bank Observatory to look for signals at the nearest stars such as Tau Ceti and Epsilon Eridani. Two horns and two channels were used for this experiment. One horn was used for detecting SETI signals and the other horn was for detecting background noise. The detector they were using had one narrow band channel and one broadband channel, similar to the two horns would separate the real SETI signal from the background as the signal for SETI would be stronger in the narrow band compared to the broad band. The author also mentioned the use of Dicke radiometer and superheterodyne receiver to maintain the narrow band observations with bandwidth of 100 Hz.
I think the reason this paper was assigned is because project OZMA marks one of the earliest experimental efforts to search for SETI signal. There is one obvious error in the paper such as the age of our galaxy. The author assumed it to be 25 billion years. However, we know now the age of the universe is even smaller than this number. This could be due to the fact the Hubble constant was not refined at 1960s. Although almost 60 years have passed, we still have not detected any unequivocal signal which is definitely coming from alien civilizations. That could imply maybe the advanced alien civilizations might live further than we thought before. We should also consider looking for other frequencies. In this paper, the author observed the 21cm line because it was important to us. However, whether this frequency was important for alien civilizations is not clear. This is a circular problem because we do not know what the typical frequencies advanced civilizations might emit. The type of technology developed could be significantly different.