The world that we know that we experience each day is what we call the classical world.

That is, the familiar laws of physics apply. The earth revolves around the sun because of gravity.

We can tell where a baseball is and measure how fast it's traveling.

A cup of hot coffee will eventually cool down.

Let's focus on that cup of coffee for a second.

It's cooling down because of what we call the second law of thermodynamics,

which states that in an isolated system, disorder will increase. This is why heat flows from a hotter area to a colder one.

It's a fundamentally classical idea, and it makes all the sense in the world.

As we've discussed on this podcast, and often in other stories in Quantum Magazine,

at the very smallest scales, the classical world we know and understand breaks down,

and the quantum world takes over.

It's a world where gravity has no obvious place, where we can't measure two properties at once,

where particles can be mysteriously connected with one another, where a system can be two things at once.

And maybe you saw this coming. Heat can flow from cold to hot.

Welcome to the Quanta podcast where we explore the frontiers of fundamental science and math.

I'm Samira Patel, editor-in-chief of Quantum Magazine.

Quantum physics is counterintuitive, but it's also correct, and it's incredibly useful.

Scientists are building their understanding of quantum systems every day in

ways that have all sorts of practical applications, from solar cells to MRI machines to

eventually quantum computers. And the quantum mechanical version of thermodynamics is no exception.

We recently explored quantum thermodynamics in a story

called a thermometer for measuring quantumness. The author of that story and frequent quantum

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