Hello everyone, welcome to the Mindscape Podcast. I'm your host, Sean Carroll. We've all heard of the clockwork universe, right?

This is the idea that came into physics, post-Isak Newton, and Pierre Simone Laplace. The idea if you knew everything was going on in the universe,

you could predict exactly what would happen next. Of course, the clockwork universe isn't the current paradigm for thinking about physics.

Because of quantum mechanics, which came about in the early 20th century, we know that the world as we observe it is not deterministic. There is unpredictable quantum randomness in the world.

But that quantum randomness is not the first time that randomness or probability popped up in the history of physics.

There's also famously in the late 19th century the advent of statistical mechanics.

We had thermodynamics, we were inventing in the 19th century, putting together the theory of thermodynamics, the science of heat, and how different kinds of fluids and gases pushed on each other and did work and dissipated entropy and all that stuff.

And then Maxwell and Boltzmann and their collaborators figured out that you could understand thermodynamics if you believed in atoms and molecules.

If you believed that things you thought of as a fluid or a solid are actually many, many, little particles, and these particles were more likely to behave in some ways than others.

So probability came in. The fact that entropy increases over time is not an airtight rule in Boltzmann's way of thinking about it. It's just very, very, very likely.

People didn't like this at the time. There were strong, strong objections, but now it's the accepted law.

So you might think that statistical mechanics, which involves probability and quantum mechanics, which involves probability, would be close bedfellows, right?

They would be natural partners and you would think about quantum statistical mechanics and its implications for either pure science or for technology or what have you.

Well, they are natural fellow travelers, but it's taken a long time for scientists to really dig into the essence of quantum statistical mechanics.

How do you combine together the idea of quantum mechanics, replacing particles and fields with wave functions and observations with probability outcomes with statistical mechanics?

The idea that you don't know exactly what the system is doing, you can only make probabilistic assertions about what's going to happen next.

Today's guest, Nicole Younger-Helpern, is a leading expert of a young person, but nevertheless leading in the dawning science of quantum statistical mechanics and thermodynamics and its relationship to things like information theory, how much do you know about a system?

And the fact that it combines crazy radical ideas with potentially real world experimental implications has inspired Nicole to name her own field quantum steampunk.

And she has a new book out called Quantum Steampunk, all about this revolution that's been going on for no more than 20 or 30 years, I would say, in physics, where we're really understanding the frontier of statistical mechanics with quantum at the heart of it.

And so again, it has both implications for how we think about the fundamental nature of reality, right, because that's what quantum mechanics is.

And maybe implications for things like how biophysics works, right, how DNA works, or maybe for nanotechnology, for building little machines at these tiny scales.

Thermodynamics and statistical mechanics were driven by the urge to understand steam engines, at some sense, in some way, quantum thermodynamics is going to be building steam engines at the molecular scale.

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