How I made a slime mould the protagonist of my new sci-fi novel

What if a slime mould was a graduate student?

Henri Koskinen / Alamy

I never start writing a science fiction book without first asking scientists a lot of extremely strange questions. My next novel – A Wall Is Also a Road, which comes out on 6 October – was a particularly tough case. I decided that my main character would be a cellular slime mould who is also a graduate student. Why not? I certainly spent most of graduate school feeling like an amoeba.

Gardenpath, the slime mould in question, is studying environmental science at a university that floats high above our galactic plane in a gaseous region known as the circumgalactic medium. You may not have heard of it, but this roughly spherical space is where the Magellanic clouds orbit – two dwarf galaxies near the Milky Way – along with rogue stars, planets and other chunks of random crap squirted out by Sagittarius A*, the black hole at the centre of our own galaxy. It’s full of all kinds of stuff that could support an advanced civilisation, from metals to water.

Before I could even begin to imagine what Gardenpath looked like, I needed to understand where they live. So I called up Molly Peeples at the Space Telescope Science Institute in Maryland, whose lab made stunning simulations of the circumgalactic medium (you can see them on the web at foggie.science). She gave me a tour of this distant region, which is full of spots where the swirling gas is warmer or colder, almost like weather.

I decided that the slime moulds would experience the circumgalactic medium the way humans experience the atmosphere on Earth. Their single-celled bodies could be absolutely enormous in this low-pressure environment full of diffuse gases. Living in this region of space would affect the slime moulds’ understanding of what is scientifically possible, too. That’s why Gardenpath’s fellow scholars think the galactic plane – where we live – is utterly lifeless and uninhabitable. Who could possibly survive in that radiation-saturated gravity well?

Gardenpath literally fumes when their professors scoff at their proposed area of study: a little planet inside one of the Milky Way’s spiral arms. But they don’t express rage by emitting sound waves that agitate molecules in a soupy, thick atmosphere like we do. Instead, they spurt electrons, hormones and other chemicals, opening receptors in their membrane to receive answers. On Earth, we call this cellular signalling. To Gardenpath, it’s just talking.

Wesley Swingley, a molecular biologist at Northern Illinois University, spent a long afternoon with me on a video call brainstorming about what kind of culture would develop among polymorphous people who communicate by swapping smells through apertures in their skin. A diffuser would be like a megaphone, I suggested, and a specific gas like methane could serve as a question mark. Swingley added that the slimes would need an organelle for storing memories, which I dubbed a gnosome. Because their membranes are permeable, Gardenpath’s professors can actually reach inside their body to probe their gnosomes during a test, which is just as creepy as it sounds.

Cells have many single-purpose receptors, which led us to think about something I called an “oath receptor”. Think of it as a biological friendship ring. When Gardenpath’s classmate Oriel wants to become BFFs forever, the two of them reach inside each other to create special receptors that can only receive their friend’s signals. It would be as if your bestie gave you a set of custom ears that can only hear their voice.

What else do slime mould graduate students need? A way to publish their findings, of course. The slimes store data inside fungi, so their libraries look like nurseries packed with containers of mushrooms. Want to send some data over the network? Plug your fungus notebook into a vent and release a bunch of spores that will bring your information to its destination.

I also created slime mould body language. These blobby little guys get bumpy when they are nervous and stretch up tall to laugh. They sprout more eyestalks when something intrigues them and dangle an extra-long arm to add a sarcastic edge to whatever they are emitting.

This makes things especially weird for Gardenpath on Earth, because humans look like people who are laughing sarcastically while paying very little attention to anything with their paltry two eyes. Still, they manage to find a friend among these weird creatures, a woman named Murtis who lives in a city called Pompeii, at the foot of a very intriguing volcano.

Don’t worry – I talked to a lot of archaeologists to get ancient Roman culture just right. Thankfully, Pompeii expert Eric Poehler at the University of Massachusetts Amherst walked me through Pompeiian plumbing and told me about the famous “prosciutto sundial” discovered in Herculaneum, a site nearby. If you want to know how that fits into the story, you’ll have to read it!