4 Cherenkov Telescopes for Optical SETI
23
Although both scientists were over optimistic in guessing the flux of potential
high-energy sources, their vision somehow started the effort to build gamma-ray
detectors and a new branch of astronomy.
4.1.2 Searching for Interstellar Communications
In parallel to their seminal papers on the foundation of high-energy astrophysics,
Cocconi and Morrison in 1959 published an equally important paper [6] where they
discuss the best strategy to search for a signal from an alien civilization. Decades
before the discovery of the first extrasolar planet, these two visionary scientists
reviewed the knowledge of the time and concluded that the most promising wavelengths to use is the 21 cm hydrogen line which is not absorbed by the interstellar
matter nor by our own atmosphere. To maximize the chances of a detection they
suggest that the search should be directed towards nearby stars similar to our sun.
Although, very honestly, they admit that it is very hard to quantify the chances of
finding a signal, their conclusion is unescapable: “if we never search, the chance of
success is zero” [6].
This paper inspired Frank Drake to start the first targeted search of a 21 cm radio
signal from nearby stars from the Green Bank radio observatory and this later evolved
into the SETI program.
Meanwhile the discovery of the laser prompted Schwartz and Townes [7] to reevaluate the potential of searching interstellar signals at other wavelengths. In a
review paper [8] written two decades after [7], Townes concludes that “the infrared
is as good as, and may be a more favorable region for SETI than, the microwave
region… However, it does not indicate that we should search only in the infrared
or even search at all in this wavelength region with present technology. There is
considerable uncertainty as to what design parameters would be considered most
critical for interstellar communication by an extraterrestrial civilization. …But I
believe the above discussion does show that we have no assurance the microwave
region is the one of choice for a civilization trying to communicate with us. This
may affect the scale and style with which SETI is carried out on Earth even in the
immediate future”.
4.2 The Current Situation
After the common start, SETI and gamma-ray astronomy proceeded independently
for more than half a century. While SETI, after the enthusiastic beginning, faced
difficulties, now partly solved owing to the Breakthrough initiatives [9], gamma-ray
astronomy blossomed first in space and more recently on the ground [5] through a
number of successful projects based on the simultaneous use of several Cherenkov
Telescopes.
23
Although both scientists were over optimistic in guessing the flux of potential
high-energy sources, their vision somehow started the effort to build gamma-ray
detectors and a new branch of astronomy.
4.1.2 Searching for Interstellar Communications
In parallel to their seminal papers on the foundation of high-energy astrophysics,
Cocconi and Morrison in 1959 published an equally important paper [6] where they
discuss the best strategy to search for a signal from an alien civilization. Decades
before the discovery of the first extrasolar planet, these two visionary scientists
reviewed the knowledge of the time and concluded that the most promising wavelengths to use is the 21 cm hydrogen line which is not absorbed by the interstellar
matter nor by our own atmosphere. To maximize the chances of a detection they
suggest that the search should be directed towards nearby stars similar to our sun.
Although, very honestly, they admit that it is very hard to quantify the chances of
finding a signal, their conclusion is unescapable: “if we never search, the chance of
success is zero” [6].
This paper inspired Frank Drake to start the first targeted search of a 21 cm radio
signal from nearby stars from the Green Bank radio observatory and this later evolved
into the SETI program.
Meanwhile the discovery of the laser prompted Schwartz and Townes [7] to reevaluate the potential of searching interstellar signals at other wavelengths. In a
review paper [8] written two decades after [7], Townes concludes that “the infrared
is as good as, and may be a more favorable region for SETI than, the microwave
region… However, it does not indicate that we should search only in the infrared
or even search at all in this wavelength region with present technology. There is
considerable uncertainty as to what design parameters would be considered most
critical for interstellar communication by an extraterrestrial civilization. …But I
believe the above discussion does show that we have no assurance the microwave
region is the one of choice for a civilization trying to communicate with us. This
may affect the scale and style with which SETI is carried out on Earth even in the
immediate future”.
4.2 The Current Situation
After the common start, SETI and gamma-ray astronomy proceeded independently
for more than half a century. While SETI, after the enthusiastic beginning, faced
difficulties, now partly solved owing to the Breakthrough initiatives [9], gamma-ray
astronomy blossomed first in space and more recently on the ground [5] through a
number of successful projects based on the simultaneous use of several Cherenkov
Telescopes.