1:51:54This Physicist May Have Just Solved Quantum Gravity
Neil Turok, the Higgs Chair at Edinburgh and former director of the Perimeter Institute, premieres a claim with host Curt Jaimungal that quantum gravity in four dimensions can be understood in a limit with no strings, no extra dimensions, and no multiverse. The vehicle is quadratic gravity, an old renormalizable and asymptotically free theory that was abandoned because of the Ostrogradsky instability and negative norm ghosts. Turok reinterprets the instability as ordinary cosmic expansion, and with his student Sam Bateman keeps the ghosts by working in a Krein space and slightly generalizing the Born rule so probabilities stay positive. The conversation extends to a composite Higgs and the hierarchy problem, the CPT symmetric universe, gravitational entropy and why the cosmos is smooth, the measure problem that Turok says condemns the multiverse, and a candid diagnosis of the health of theoretical physics. Turok adds his own caveat that this is a halfway result, not a finished theory of quantum gravity.