The Hart (1975) is a complete rejection of SETI studies. The problem the paper is trying to address is that the whether we are the only intelligent life in our galaxy. The author supports this point by disproving three alternative hypotheses that could lead to the fact that we have not detected or encountered any other alien intelligent life. The first one is the technology argument that it could be very energy and time consuming to do interstellar travel. However, the author argues that the lifespan and form of technology might be completely different from human so there could be alien civilizations that can perform long distance interstellar travel. The second alternative argument is that the alien civilizations have cultures that prevent them from visiting Earth or they might have destroyed themselves quickly through nuclear wars. The author argues that these hypotheses are simply inadequate since the culture for an alien civilization could change over time and we are assuming they could destroy themselves based on our own current global situation. The third alternative argument is the alien civilizations have not reached Earth yet. The author counters this argument by saying it would only take 2 million years to explore the whole galaxy so the chances that alien missed us is very small. The fourth and final argument is that alien might have visited Earth before. The authors counters this argument by questioning why the alien civilizations have stopped visiting us and we could not provide sufficient answers to this question.
By countering all the alternative explanations that might explain why we have not encountered any aliens so far, the author concludes that we are the only intelligent civilization in the galaxy. However, I think the author missed one important point that even alien does not exist now. It does not mean it did not exist before. I could reference the video called “HALO” that there existed a life form called the swarm that depended on other form of life in the universe. Maybe the aliens in our galaxy were almost all killed by the swarm and we are one of the few civilizations that survived. The other possibility is that instead of Earth as a zoo, the whole galaxy, even the whole universe is a zoo, specifically created for human. Finally, maybe the advanced civilizations in our galaxy have cloaking devices that hide them from the rest of the galaxy for safety purposes and that is the reason we have not detected any of them. It could be very dangerous to send our location information out into the universe.