Science and philosophy have always been woven together. Some of history’s greatest minds—Aristotle, Galileo, Aryabhata and even Einstein—were as much philosophers as they were scientists.

This has also been true for ancient Indian civilization, where science and philosophy were explored with extraordinary depth, not as separate pursuits, but as complementary paths to knowledge.

These insights were preserved in Sanskrit, a language whose precision allowed complex ideas to be recorded with remarkable clarity. But centuries
of invasions and nearly a thousand years of foreign rule made this knowledge less accessible, and its nuance steadily eroded.

Much of it was collapsed into the broad label of “spirituality”—a word that has itself lost the rigor and depth it once carried. The central dogma of these ancient Indian texts was an uncompromising commitment to curiosity
and questioning.

Our guest today, Dr. Ramakrishnan Hosur, apart from being a renowned figure in science, has embarked on the journey of demystifying these texts with that same uncompromising commitment. He believes in building upon that curiosity and using it as an anchor for scientific progress. In his book, Where Science Meets Spirituality, he explores precisely this intersection.

Dr. Hosur is a distinguished biophysicist and his remarkable career spans pioneering developments in nuclear magnetic resonance (NMR) spectroscopy, structural biology, and protein folding. His work earned him India’s fourth-highest
civilian honour, the Padma Shri, in 2014. He has spent decades at the Tata Institute of Fundamental Research in Mumbai, where he also headed the National Facility for High-Field NMR. And now, he has been inspiring a whole new way of looking at knowledge by demystifying ancient Indian texts and showing how curiosity can bridge science and spirituality.

So if you’re someone who finds inspiration at the crossroads of science, philosophy and spirituality, or simply someone who’s just curious, you’re in for a treat. So let's go.

His wikipedia page: https://en.wikipedia.org/wiki/Ramakrishna_V._Hosur

Imagine walking deep into a dense forest without a map or GPS. Initially, you kind of know where you started. But as you wander further, eventually, it's impossible to tell where you came from — every direction looks the same. That's thermalization.

The initial state's details get scrambled across all degrees of freedom and as a result local observables settle into a stable, time-independent state called the equilibrium state. The fact that macroscopic objects equilibrate with their environments is such a ubiquitous experience that understanding it doesn't seem very interesting. Although it's absolutely non-trivial. At Equilibrium these local observables are represented by their thermal expectation values.

So if one had access to a map or perhaps a GPS which just means keeping track of those initial details such as any non-local correlations or even the entire state, locally thermalization would still occur, but one could easily backtrack to the initial state. In physics it is quite surprising how systems behave collectively, when compared to the behavior of its components. This is known as emergent behavior.

We've been taught that evolution of any system should entirely depend on initial conditions but we see that a lack of initial state dependence is what actually gives a consistent behavior macroscopically.

For an isolated quantum many-body system, this becomes even more fascinating because even though the full evolution, is unitary and reversible--which means backtracking is guaranteed-- locally, memory seems to be lost.

Then how does this classical behaviour emerge from Quantum mechanics?

A key idea is the Eigenstate Thermalization Hypothesis (ETH): each non-degenerate energy eigenstate itself can be considered “thermal”.

Their expectation values fluctuate little between nearby eigenstates, provided the local operator acts on few degrees of freedom.

Intuitively, a small subsystem of an isolated quantum system acts as if it's in contact with a thermal bath—the rest of the system. So in large, non-integrable systems, thermal behavior emerges without needing a microcanonical average—a single eigenstate often suffices.

If ETH is true then if the initial state dependent coefficients are concentrated around some single energy then our TEV will give the desired microcanonical and canonical averages.

Our guest today is Pavan Hosur, a theoretical physicist in the Department of Physics and the Texas Center for Superconductivity at the University of Houston. His research focuses on understanding topological phases of matter, exotic broken symmetry phases, and how to detect them experimentally. He also explores quantum ergodicity, quantum chaos, and more broadly, how concepts from classical statistical mechanics extend into the quantum realm. We’re recording this episode in his lovely office, discussing how our complex yet elegant macroscopic world emerges from the quantum laws that govern the microscopic one. So let’s get started.

His website is here: https://sites.google.com/nsm.uh.edu/qmb/home

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