SJ has hit the nail on the head, it's not even theoretical. It's an idea someone had and has written convincingly about.
But it is s a hell of a theory. Ballsy doesn't even cover it. For it to work you need not only four new dimensions above the usual three and time, you also need two new fundamental forces.
Hell you even need "Graviphotons" so you can "couple together gravity and electromagnetism and allow the conversion of electromagnetic energy into gravitational and vice-versa."
Still the
New Scientist has me convinced that it's at least worth looking at. There's something there, his theory is at least self consistent and his predictions match up.
Not that I think it's likely but it's 'Blue Sky' research, the same approach that gave us blue lasers (DVDs) and radar.
This may not work, hell it may be utter rubbish, but that's no reason not to do it.