The Elegant Universe
really is one of the better summaries of the field - Greene is a pretty good writer and advocate, and you don't have to deal directly with Calabi-Yau space mathematics to get there.
(I'm just trying to imagine what would happen if he wrote the book like Roger Penrose did Road to Reality
: don't know tensor calculus? Well, tough luck!)
I would also recommend Lee Smolin's The Trouble With Physics
in which Smolin actually paints a fairly sympathetic view of the field and what promises it held and holds. The conclusion to that book was anti-String Theory, but more in the sense that we have no backup plan should it prove wrong and that it is so far entirely lacking in lab corroboration - no denying the promise or 'beauty' of String Theory.
And, since a Borromean Ring construct is so stable, perhaps that's why no one has ever seen a proton decay.
I'm also curious as to why protons do not decay, but I am unsure as to whether a Borromean Ring would be the answer. Protons are uud
and never decay; neutrons are udd
and decay with a half-life of fifteen minutes, at least when they are unbound.
The only three-quark systems with the same quarks are notoriously unstable: the Δ++
and the Δ-
have lifetimes in the 6 x 10-24
There no harm in trying to e-mail him - I know I've been surprised at responses I get from people that I was sure would not answer - although should he not respond, it may be from being overwhelmed with e-mail rather than any personal opprobium :)