Silvano P Colombano, a computer scientist at Nasa Ames Research Centre and a professor says Earth may have already been visited by Aliens, but humans may not have noticed.
He suggests in a research paper that aliens may look vastly different than the expectations that humans have of them such as being carbon-based organisms which would allow them to remain undetected.
In the paper, he wrote, “I want to point out the fact that the intelligence we might find and that might choose to find us (if it hasn’t already) might not be at all produced by carbon-based organisms like us.”
According to him, “The size of the ‘explorer’ might be that of an extremely tiny super-intelligent entity, If we adopt a new set of assumptions about what forms of higher intelligence and technology we might find, some of those phenomena might fit specific hypotheses, and we could start some serious enquiry.”
He suggests the reasons UFO phenomena may have gone unnoticed or overlooked are because, in addition to assuming a low likelihood of Aliens travel and a high likelihood of hoaxes, the subject is generally avoided by the scientific community.