Thanks, Bill, very interesting. This is something that's long puzzled me: Why should any theory of quantum gravity be based on an assumption that space is granular at the Planck length? I'm not suggesting that's it's assumed without reason - I just don't know what the reason is. Sure, we are reliably informed that directly measuring a smaller length would be impossible - but why should that impose a boundary on physical reality?

"Time is what prevents everything from happening at once" - John Wheeler