Perhaps this does not exist, thought I'd ask:
Asked DD6, if she could learn about anything what would it be. She answered, "portals." (from an elf movie she saw; I told her portals actually may exist.)

Does anyone know of a physics (how stuff works for 6 year old) book that explains relativity, string theory, portals, etc.?

Just looking for a fun book that illustrates basic physics principals, Newtonian, quantum, some of the weird stuff in comics that she would find interesting, introduces concepts, but isn't over a 6 year old's head.

Am I asking for a unicorn here?

There should be plenty of those types of books at your local library. My DS-at-the-time-6 loved a comic-book-style series that detailed out some of those principles (force and motion, etc.).

As for relativity, there's a good new Cosmos episode about it that my DS was able to digest. YMMV.

I think the Stephen Hawking series of books for kids would be right up your alley. They are very popular.

http://www.amazon.com/Georges-Secre...7108607&sr=8-10&keywords=hawking

Max axiom has some basic physics topics, but they may be too simple for your purposes, as DS loved them at 3 (and still does at 4).

How about "Q is for Quark" by David M Schwarz

All excellent responses and exactly what I was seeking. Thank you all!