Lee Smolin

"We show that some known classical results have particularly simple derivations within the Ashtekar formalism. These include Witten's positive energy theorem..."

"The positive energy theorem was for half a century or more an open challenge to relativists. Many attempts were made to prove flat spacetime was stable, but none completely succeeded completely until a majestic tour de force of geometric reasoning of Shoen and Yau. This was followed two years later by a proof of Witten, which was as elegant as it was short. It is this proof of Witten’s that we take as a template here for the quantum theory."

"The suggestion was that a positive energy proof for general relativity could be gotten by restricting supergravity to its bosonic sector, which is general relativity."

"Was ist Raum und Zeit? Darum geht es bei dem Problem der Quantengravitation. Mit der allgemeinen Relativitätstheorie gab Einstein uns nicht nur eine Theorie der Gravitation, sondern auch eine Theorie über das Wesen von Raum und Zeit, welche die vorausgegangene Konzeption Newtons erledigte. Die Schwierigkeit bei der Quantengravitation besteht darin, die aus der Relativitätstheorie gewonnenen Erkenntnisse über Raum und Zeit mit der Quantentheorie zu vereinbaren, die ebenfalls wesentliche, tiefgreifende Erklärungen über die Natur abgibt."