I'm Steve Strogatz and this is The Joy of Why, a podcast from Quantum Magazine that takes you into some of the biggest unanswered questions in math and science today.

In this episode, we're going to ask, do we live in a multiverse?

We know that we all live in our own little bubbles, whether it be our family, our friends, our

hometown, even our workplace. And if you think about it, animals live in their own little

bubbles too. Fish live in certain parts of the ocean or different lakes or rivers. You won't find

them in ice with a microbe population or flying around in the sky with birds,

even though ice and water vapor in the sky are also forms of water.

Could the universe be the same way?

Maybe we're not alone, and what we can see with the help of telescopes and infrared cameras isn't all there is. Maybe space is infinite. Maybe there

are multiple universes beyond our own. Perhaps made up of some of the same components or possibly

even breaking the very laws of physics that allow us to call our universe home. It's a mind-blowing

concept, the idea that we could live in a multiverse.

And it's an idea that David Kaplan thinks could be possible.

Kaplan is a theoretical physicist at Johns Hopkins University in Baltimore.

He looks at the theoretical possibilities that apply to the standard model of particle physics and cosmology.

He also produced and appeared in the 2013 documentary Particle Fever about the first experiments at

the Large Hadron Collider.

David, thanks for joining us today.

My pleasure.

Well, this is great.

I'm very curious to hear your take on the multiverse.

Before we get to the multiverse, let's talk about the good old-fashioned universe. Sure. You know, I mean, I grew up hearing about the universe. That was sort of by definition, I think, all there is. Do I have that right? How would we define the universe before we define the multiverse? Wow. Well, I think to be a little bit more useful or practical or even

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