Hart: There is no ETI therefore there should be no SETI

Hart (1975) is about asserting why the author believes that there are no other intelligent civilizations in our galaxy. That essentially makes this paper about addressing the Fermi Paradox.

The entire article is written about refuting different explanations for the fact that “there are no intelligent beings from outer space on Earth now”, which he puts into four categories: physical, sociological, and temporal as well as those that say that we have been visited, but the visitors are no longer here.

The paper makes its case by attacking each type of explanation individually. Physical explanations are refuted by providing some examples of future possibilities for long distance space travel and saying a sufficiently advanced civilization could figure it out. Sociological explanations aren’t valid unless they apply to all civilizations for the entirety of their existences. Temporal explanations are addressed by stating that it would be a mighty coincidence that a galaxy colonizing civilization evolved less than a million years ago (<0.1% of our galaxy’s age). The last category is address with a mixture of arguments from the temporal and sociological section.

Finally, anyone saying that the main fact is actually false and that aliens are here is wrong because few astronomers believe that. This point is added on at the end and I find it childish. I don’t really see the point of bringing up the possibility of the main fact being wrong if it is not going to be properly addressed.

This paper is interesting because it is the first paper that is openly against spending resources on SETI.

I feel like the paper takes a lot of logical liberties in order to make its point. Importantly, his conclusion is that there are no intelligent civilizations in our galaxy, and I think he means currently. When he makes his arguments against sociological explanations, he talks about how cultures change over millennia, so any intelligent civilization would eventually start venturing out to find us, but a critical point he never mentions (at any point in the paper) is that we don’t know how long intelligent civilizations last. A lot of his arguments (eventually their technology will advance, their cultures will change, their colonization borders will grow) fall apart when dealing with technological civilizations that only last a thousand years or so.

The Origin of Bracewell Probes

Bracewell (1960) asks the following question: How will civilizations of equal or greater intelligence try to initiate communication with nearby, unknown civilizations. He mostly elaborates on this by following semi-informal chains of thought. He argues that it is unlikely that they are running megawatt level transmitters pointed towards every nearby star that could possibly be hosting (or nurturing future) intelligent life. He instead argues that it is more feasible to search for life by sending out a swarm of armored, radio-transmitting probes to rapidly explore the nearby stellar neighborhood and a selection of further, promising target stars.

I think some of his reasoning is flawed here as one of his arguments against the interstellar transmitters is that they have a “dependence on our ingenuity in selecting the right star and the right wavelength”. It seems like he is suggesting that his probe swarm is a better idea than using a single transmitter. I would agree, but I think the swarm would be more comparable to using a network of many transmitters. Maybe the cost of building and maintaining thousands of transmitters continuously pointed at all of the targets is significant, but I would imagine the cost of launching thousands of autonomous probes would be pretty high as well.

He postulates that if there are already several advanced civilizations that know about each other, they will be connected and communicating, so we would only find evidence of the nearest community that is looking for us.

It is noted that by looking for probes within our own solar system we are in a way looking for signs that there are any advanced civilizations capable of reaching us. A cool idea. The probe within our solar system might only be a listener that reports back to home base via a star to star relay system.

This paper seems to have significance due to its documentation of several novel communication ideas and its introduction of extraterrestrial civilization network ideas.