Modern physics rests on two foundational frameworks that describe our universe at different scales. The first is General Relativity, Einstein’s theory of gravity, which describes gravity not as a force but as the curvature of spacetime itself. Massive objects bend the geometry of spacetime, and this curvature dictates how all massive objects move, from planets to black holes.
At the microscopic scale, we have quantum mechanics which describes the probabilistic nature of particles like electrons and photons. Quantum mechanics also laid the foundation for Quantum Field Theory where particles are no longer seen as standalone objects but as excitations of quantum fields that permeate spacetime. This is the formalism behind the Standard Model of particle physics, our best theory to date for describing the electromagnetic, weak, and strong nuclear forces.
Individually, both theories aren’t just theoretically robust but also experimentally validated. However, combining them isn’t as easy as it sounds. The mathematical frameworks of General Relativity and Quantum Field Theory are fundamentally incompatible. When we try to apply quantum principles to spacetime itself, like at the singularity of a black hole or during the earliest moments of the universe, the equations break down.
One of the most ambitious and mathematically rich attempts to reconcile these two frameworks is String Theory. In string theory, the point-like particles
of the Standard Model are replaced by tiny vibrating strings, and different vibrational modes correspond to different particles. Even though string theory comes with its own challenges, like the need to compactify extra dimensions, it remains one of the most compelling candidates for a unified theory of nature. One of its greatest successes lies in the discovery of dualities which connects seemingly unrelated theories. Among the most powerful of these is the AdS/CFT correspondence, or gauge/gravity duality, which proposes an equivalence between a theory of gravity in higher-dimensional spacetime and a quantum field theory without gravity on its lower-dimensional boundary.
Our guest today is Professor Andreas Karch, a theoretical physicist at the University of Texas at Austin, who has played a key role in shaping our understanding of gauge/gravity duality and has made significant contributions to string theory. If you’re someone curious about why we need to quantize gravity, eager to unpack the ideas behind string theory, or simply excited to explore the frontiers of fundamental physics — you’re in for a treat. Before we start the episode there’s something I'd like to mention. We went all the way from Houston to Austin to record this episode in his office, but because tech can be sneaky sometimes, we ended up losing our video footage — mine and Bhavay’s. Thankfully, Andreas’s camera kept rolling It was incredibly heartbreaking but we didn’t want to lose this episode so we got creative. If you're watching this on YouTube, the visuals you’ll see for the hosts are AI-generated avatars. The audio is 100 percent real. We have worked hard to create a compelling visual experience for you, we hope you like it. And like all our episodes, this conversation is raw, unedited, and without any cuts.
Andreas Karch is a professor of Physics at UT Austin, where he moved after being on the faculty for close to 20 years at the University of Washington in Seattle. He works on string theory and formal quantum field theory with an eye towards applications in other areas of physics. He did is undergraduate studies at the University of Wuerzburg in Germany, received an MA from UT Austin, his PhD from Humboldt University in Berlin, and did postdocs at MIT and Harvard. He is a fellow of the APS and a PI on the Simons Collaboration on Ultra Quantum Matter.
Check out his work here: https://scholar.google.com/citations?user=jO39jLYAAAAJ&hl=en
