I have been reading the 2008 book by Dr Michio Kaku, the well known physicist. (click here.) The book is titled "Physics of the Impossible: A Scientific Exploration of the World of Phasers, Force Fields, Teleportation and Time travel." The book was published by Allen Lane. London. ISBN 978-0-713-99992-1. (Click here.)
The work is divided into three parts, class I, class II and class III impossibilities. He defines these as:
Class I - "These are technologies that are impossible today but that do not violate the known laws of physics, so they might be possible in this century, or perhaps the next, in modified form..."
Class II - "These are technologies that sit at the very edge of our understanding of the physical world. If they are possible at all, they might be realized on a scale of millenia to millions of years in the future..."
Class III - "These are technologies that violate the known laws of physics...If they do turn out to be possible, they would represent a fundamental shift in our understanding of physics..." (pp.xvii)
It was therefor surprising that in part 1, class I impossibilities, that there is a chapter titled "Extraterrestrial UFOs."
Kaku covers the search for extraterrestrial life, SETI, where are they? Plus information on extra-solar planets, before touching on the topic of UAP.
"Some people claim that extraterrestrials have already visited the Earth in the form of UFOs. Scientists usually roll their eyes when they hear about UFOs and dismiss the possibility because the distances between stars are vast. But regardless of scientists' reactions, persistent reports of UFOs have not diminished over the years." (p.147.)
Kaku then notes that "UFO sightings actually date back to the beginning of recorded history." (p.141) citing biblical and other sources. Mention is made of Project Blue Book and the 2007 release of French government files (click here.)
As to the cause of the majority of reports, Kaku lists Venus, swamp gas, meteors, atmospheric anomalies, radar echoes, weather and research balloons, aircraft and deliberate hoaxes. "At least 95 percent of sightings can be dismissed as one of the above." (p.150.)
"But thus still leaves open the question of the remaining few percent of unexplained cases." (p.150.) He cites as examples, the 1986 JAL flight 1628 case; (click here) the 1976 Tehran aircraft encounter (click here) and the 1989-1990 Belgium wave.
However, "What is frustrating to scientists is that, of the thousands of recorded sightings, none has produced hard physical evidence that can lead to reproducible results in the laboratory. No alien DNA, alien computer chip or physical evidence of an alien landing has ever been retrieved." (p.150.)
"Allowing for the moment that such UFOs might be real spacecraft.." (p.150) Kaku poses the question what propulsion system could they use?
Using the reported characteristics of unexplained cases he postulates "...a vehicle propelled by magnetism " (p.151) and goes on to examine potential nanotechnology.
This section concludes with "Given the rapid advance in SETI and discovering extra-solar planets, contact with extraterrestrial life, assuming it exists in our vicinity, may occur within this century..." (p.153.)
It was interesting to find this piece in such a work. Unfortunately, it is a cursory overview, but at least if doesn't totally dismiss the topic out of hand, even noting that there remain unexplained cases.
I looked up the biography to see what books on UAP, that Kaku had referenced as the source(s) of his information. There aren't any. There are also no footnote references to the topic.