The greatest challenge for physics is to combine its two most successful theories: general relativity and quantum mechanics. The resulting quantum theory of gravity would explain the universe across all scales. Much has been said about the approach based on string theory. Here, Jim Baggott describes...

The greatest challenge for physics is to combine its two most successful theories: general relativity and quantum mechanics. The resulting quantum theory of gravity would explain the universe across all scales. Much has been said about the approach based on string theory. Here, Jim Baggott describes its powerful rival: Loop Quantum Gravity.