Caltech physicist Sean Carroll explains dimensions in ways that even a 5-year-old can understand.

One of my favorite books as a child was called Flatland: A Romance of Many Dimensions. Written by a grade-school teacher in 1884, it’s a novel narrated by a square who lives in a two-dimensional world, called Flatland, populated by lines and shapes. In the story, the square encounters a sphere from a three-dimensional universe called Spaceland, but he can only perceive this otherworldly visitor as a circle. It’s only once the square pays a visit to Spaceland that he begins to understand what it means to be three-dimensional.

Flatland is a great way to introduce kids to the concept of dimensions, a technical concept in physics and mathematics that defies our everyday notion of physical space. Indeed, the novel is arguably one of the best introductions to this heady subject—short of having Sean Carroll, a physicist at the California Institute of Technology, explain dimensions to you himself.

“The idea of dimension in pop culture is sometimes misunderstood like there’s a place you can go, a mystical dimension or something like that,” Carroll says. “To a physicist or mathematician, a dimension is just a direction.”

Most of us think in terms of three dimensions in our day-to-day lives. But physicists deal with several additional dimensions—10 or more if you’re a string theorist. Where are these dimensions hidden? It’s a question just as likely to perplex a child as a grown adult, so Carroll took WIRED up on the challenge of answering it at five levels of complexity.

Carroll starts by introducing the concept of multiple dimensions to a 9-year-old with Tinkertoys and builds upon these simple concepts until you’re convinced you might be able to build an interdimensional wormhole if you really wanted to. At the very least, by the end of WIRED’s latest “Five Levels” video, you’re guaranteed to know your De Sitter space from your p-branes, so you never embarrass yourself at a party again.

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Check it out. You can also watch the next two episodes (about Lasers and Sleep) now, on WIRED’s free app for Roku, Apple TV, Android TV, and Amazon Fire TV.