In our discussions about UFOs and in browsing the web, UFOS encounters, again and again, the same fallacious lines of reasoning being used to justify a belief that aliens are visiting the Earth. In this column I will discuss the errors in these arguments. "Aliens are too smart to leave evidence lying around" Mainstream UFOlogy in North America holds to the ET hypothesis - that the small residual of UFO sightings that cannot be explained are of extra-terrestrial craft. And yet, even the most ardent of believers in the ET hypothesis will admit that there is no physical evidence available that proves that aliens are visiting the Earth. In spite of all the supposed crashes of alien space ships, all of the close encounters, all of the abductions, cattle mutilations and crop circles, all of the archaeological investigations of supposedly alien feats of ancient engineering, not one scrap of physical evidence - nothing ALIEN - has been presented to the scientific community for study. If such evidence were available, there would be no debate about the true nature of UFOs and no room for skepticism about the ET hypothesis.

There are basically two schools of thought within UFOlogy about the absence of physical evidence. One asserts that there is a global conspiracy that descends instantly upon any evidence anywhere in the world, concealing the evidence and silencing its discoverers, in order to prevent the panic that would supposedly result from the certain knowledge that aliens are visiting this Earth. Because this conspiracy requires the collusion of all the world's governments, the cold war, in fact all of recorded human history, must therefore be a sham, because no verifiably alien artifact has EVER been made public. A somewhat less paranoid explanation for the absence of evidence is that the aliens are just too smart to get caught. The chain of reasoning goes as follows: 1.

Aliens are visiting the Earth, aliens who are a lot smarter than humans, because they can travel between the stars. 2. Being smarter than us, we can expect them to be able to out-fox our attempts at detecting their presence, and to clean up behind themselves so that no alien artifacts will be left lying around. But this chain of reasoning, which purports to explain the lack of physical evidence, is nothing more than smoke and mirrors. Firstly, it says that if aliens are visiting the Earth, they cannot be detected. In other words, because this version of the ET hypothesis is true, no evidence can be found to support it.

Furthermore, it cannot be shown to be false either, because the prediction it makes, that no evidence will be found, is indistinguishable from that of the null hypothesis, "aliens are not visiting the Earth." Secondly, in order for the first part of this version of the ET hypothesis to be shown to be true, the second part has to be false.