Kaku, a theoretical physicist, discusses various "science fiction" technologies and evaluates whether those actually would be possible to implement (once successfully invented, of course).
The repertoire of technologies is highly interesting, ranging from invisibility and teleportation to time travel and precognition.
The author categorizes the technologies, after assessment, into three categories: (1) those which are not possible today but do not violate any known physical laws, (2) those which probably don't violate physical laws but lay at the very edge of the current understanding of the human kind, and (3) those which violate laws of physics and hence are simply impossible (as we know physics today).
Quite interestingly, only two of the 15 technologies end up in the third class: perpetual motion machines and precognition. Thus, teleportation, invisibility and even time travel seem possible - yet quite difficult - to achieve.
Was it good?
The book is very good and engaging. The book could have been highly more condensed if for each technology there had been just a straightforward assessment and conclusion. Instead, Kaku has chosen to include a lengthy discussion about the history of pertinent physical laws and a discussion concerning current scientific understanding to ground his assessment. Unlike with most such "book-lengthening tactics", this works beautifully and adds significant value to the reading experience.
The main take-away for me?
On a meta level, the main take-away is that the laws of physics allow for quite outlandish phenomena such as time travel - though in many cases harnessing and controlling required amounts of energy may be practically impossible. Thus, like Tuomas Nevanlinna has aptly put it, modern-day physics tells a much more incredible story than any religion is capable of (dark matter, anti-universes, new baby universes created in laboratories by humans....).
Also, antimatter is quite an expensive substance (see chapter 10).
Who should read the book?
I think that the book can be enjoyed by anyone, and especially those who have and engineering mindset/training and/or are big fans of science fiction.
The book on Amazon.com: Physics of the Impossible