Finished (Audiobook) - "Physics of the Impossible: A Scientific Exploration into the World of Phasers, Force Fields, Teleportation, and Time Travel" - Michio Kaku

Kaku's "Physics of the Impossible" is a great read.  It covers all the key sci-fi topics, such as force fields, time travel, teleportation and ESP.

The great thing about the book is that Kaku treats the topics as serious, and worthy of scientific analysis.  He defines different levels of "impossible", the most "possible" being topics where we have the ability to execute the task, but it would be costly or difficult (e.g. travel to other planets does not require any breakthroughs in physics, or any major new understanding of science, just efficient application of known science and engineering).  A more "impossible" level requires extensions of what we currently can do, but don't require significant re-imagining of physical laws - things like advanced spacecraft for interstellar travel, or the carbon nano-fibre space elevator (both require engineering beyond what we currently have, but not significant breakthroughs in theory).

I did have a little disagreement with Kaku's envisioning of time travel, when he was setting the stage for the range of possibilities for explaining why time travel doesn't appear to have happened (e.g. why aren't there any time tourists coming from the future).  There was nothing "wrong" with his discussion, it just seemed to miss a few things that I'd consider reasonable;

My take:  There may be no evidence of time travellers because....

1. time travel is not possible;
2. time travel requires equipment at both ends of the path, so it hasn't been invented yet, so they can't travel this far back (e.g. like travelling between telephone handsets);
3. time travel causes splinter universes - "our" timeline doesn't have visitors, and any that travel back cause a new timeline to exist (this is how comics handle time travel)
4. time travel is like the uncertainty principle - any attempts to go back are unstable, and only exist until some perturbation in actions ripple into a future that would cause you not to go back (e..g. the "kill your grandfather" paradox).  Virtually any action from viewing to interacting may be enough to cause a decoherence that negates that timeline
5. Perhaps our species does not survive long enough to engineer time travel (e.g. go extinct, world war...).  If we don't survive in a progressive way for a 100 years or so, we might not have time to invent time travel;
6. perhaps time travellers are here - as long as they don't "announce" themselves, they may seem to be "regular people".  Maybe Newtons, Hitlers, Einsteins and Hawkings are really time travellers coming back at critical periods to make history "flow".

I experienced Kaku's book as an audiobook, which was an excellent way to pass time in the car.  The topics were invariably interesting, and none of the topics were overly long - both perfect for interrupted listening in the car.