This is a good book for understanding where we are in terms of making some of science fiction's wildest technological advances into reality. It's a difficult read, but easy to get into because Kaku is obviously a science fiction buff who is very passionate and knowledgeable about his topic. I'm only giving it three stars, though, partly because so much of it is wildly speculative and therefore not very practical, and partly because Kaku, like so many other scientists along with him, sometimes pushes his own scientific ideas rather than being impartial and just relating the facts. Guessing about the future is ok, because he freely admits that he is just guessing, but at other times his biases are a lot more subtle. Take for example this passage:

"Although monopoles have never been conclusively seen experimentally, physicists widely believe that the universe once had an abundance of monopoles at the instant of the big bang...In fact, the lack of monopoles today was the key observation that led physicists to propose the inflationary universe idea. So the concept of relic monopoles is well established in physics."

Wow. That's just brilliant, Kaku. We can't show that monopoles actually exist, but we need them in order to construct the wildly unproven theory of inflation, which in turn is necessary to prop up holes in the (also unproven but "too big to fail") evolutionary argument. Is that really all it takes for something to be "well-established" in physics these days? Kaku also fails to mention in this book that he is co-founder of string theory, which he humbly claims to possibly be the crowning achievement of physics and consequently spends an inordinate amount of time writing about, considering no strong evidence for string theory has ever been found. No bias there at all, right? A few gripes aside, though, this is one well-written, informative, and interesting book.