This book is the closest I’ve seen to ELI5ing general relativity

https://www.amazon.co.uk/Why-Does-mc2-Should-Care/dp/0306819...

And it makes it obvious why FTL travel implies time travel

It’s chock-full of a-ha moments and is a pleasure to read

http://www.amazon.co.uk/Why-Does-mc2-Brian-Cox/dp/0306819112

Chances are FTL communication is not possible.

http://curious.astro.cornell.edu/question.php?number=612

http://en.wikipedia.org/wiki/Superluminal_communication

The book, "Why E=mc^2" is an exceptional read. If I recall correctly, it explains why light-speed is a universal limit:

http://www.amazon.co.uk/Why-Does-mc2-Brian-Cox/dp/0306819112