The universe is about 14 billion years old. Ever wondered—how do we even know the age of the universe? How can we look up at the sky and read time itself? We do this by studying the afterglow of the Big Bang, called the cosmic microwave background radiation (CMBR)—relic radiation from the very beginning of the universe. Physicists build ultra-cold microwave telescopes—cryogenic cameras with incredibly sensitive detectors—that can spot tiny temperature changes and faint polarization, and even see how gravity bends that light.
In this episode, Dr. Eve Vavagiakis, an experimental cosmologist at Duke University, takes us behind the scenes of how these instruments are designed, built, and calibrated across ACT, the Simons Observatory, CCAT-prime, and CMB-S4. Her expertise spans cryogenic instrumentation, superconducting detectors, and extracting meaningful physics from enormous datasets. She also writes children’s science books that turn big cosmic ideas into playful stories for young readers—bringing neutrinos, black holes, and photons to life. She believes kids should have access to—even if not a complete understanding of—the latest discoveries and complex ideas. If you wonder how we know the universe’s age—or you just like telescopes—you’re in for a delight.
About the guest
Dr. Eve Vavagiakis is an Assistant Professor of Physics at Duke University. She builds instruments and analyzes data for cosmology and astrophysics, and works with the ACT, CCAT-prime, Simons Observatory, and CMB-S4 collaborations. Her interests include cryogenic instrumentation, superconducting detectors, and cross-correlation studies that reveal the physics of galaxy clusters and the universe. Previously an NSF Astronomy & Astrophysics Postdoctoral Fellow at Cornell, she’s also the author of the Meet the Universe children’s book series from MIT Kids Press. Students excited about instrumentation or data analysis are welcome to reach out.
Website: https://evevavagiakis.com

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