In this document, scientist Bernard M. Oliver, a scientist and founder of Hewlett-Packard company, motivates the need for international preservation and protection of what he perceived to be the optimal window from which we may receive signals from extraterrestrial intelligence, namely the “Water Hole.” Among his many contributions to the fields of radio and electronics, he also had an interest in the Search for Extraterrestrial Intelligence (SETI). Prior to 1979, previous studies had already shown that the region bounded by the spin-flip transition of Hydrogran at 1.42GHz and the hydroxyl line at 1.66MHz was a prime region of frequency space to search for pulsed signals. At the time, several navigational satellites had been planned who would operate within these frequencies and disrupt such a search. Therefore, as a prophylactic measure, Oliver suggested a re-examination of the merits of the water hole and of the radio search in general.
He presents a case for electromagnetic radiation being the medium through which an advanced intelligent society would aim to transmit their communications and beckons to lower societies based on its satisfaction of multiple criteria. Important among these criteria are the need for the signal to be of low power, to not be absorbed or deflected as it passes through interstellar media and their corresponding electromagnetic fields, travel very quickly, and exceed the background levels. These criteria mostly preclude massive particles and favors low energy electromagnetic radiation, hence lending support to the idea of interstellar radio communications. He also presents a case that the water hole is the best window into the microwave and radio based on the low amounts of background contamination from contributions to the spectral noise power density like synchrotron radiation (which dominates below 1GHz) and quantum spontaneous emission (dominating above 60GHz). From free space, the case could be made for the frequency space between these upper and lower limits, however, when moved to the terrestrial frame, it becomes clear that significant portions of window are obscured by atmospheric molecular absorption. He also takes into consideration the motion of the Earth and the resultant Doppler drift, which increases the noise by a factor ^1/2, which dramatically builds the case for the hydrogen-hydroxyl water hole.
^1/2, which dramatically builds the case for the hydrogen-hydroxyl water hole.He admits to the romanticism and chauvinism of holding such a perspective, that water-based lifeforms would convergently arrive at such a bandpass for their communications. He acknowledges these shortcomings but insists that water is likely to be a common solvent for biochemistry to take place in throughout the universe, and contends that romanticism may be an inherent feature of highly evolved, sentient beings akin to humans.
