Author Archives: rojefferson

Hilbert space factorization and quantum gravity

There’s a fundamental problem in gauge theory known as Hilbert space factorization. This has its roots in the issue of how local quantities (e.g., operators) are defined in quantum field theory, and has consequences for everything from entanglement and holographic … Continue reading

Posted in Physics | Leave a comment

Quantum 101

Reference: John Preskill’s notes on Quantum Information and Computation. In quantum mechanics, a state is a complete description of a physical system. Mathematically, it is given by a ray (an equivalence class of vectors) in Hilbert space, , which is … Continue reading

Posted in Physics | Leave a comment

Generalized gravitational entropy

The derivation of Ryu-Takayanagi (RT) put forward by Lewkowycz and Maldacena (LM) is essentially an extension of the (boundary) replica trick into the bulk. The basic idea of the replica trick is that entanglement entropy is generally hard to calculate, … Continue reading

Posted in Physics | 1 Comment

Hawking pairs and ontic toys

The most widely known picture of Hawking radiation involves the creation of a particle-antiparticle pair at the horizon. At face value, this seems natural enough: we know from QFT that the vacuum is hardly vacuum at all, but instead a … Continue reading

Posted in Philosophy, Physics | 1 Comment

Action integrals and partition functions

There’s a marvelous — and by now quite well-known — paper (paywalled) by Gibbons and Hawking, in which they compute the entropy of black holes from what is essentially a purely geometrical argument. This relies on the fact that the … Continue reading

Posted in Physics | 4 Comments