Short Wave - The trouble of zero

Episode Date: January 2, 2026

What better time to contemplate the conundrum that is zero than the start of a new year? Zero is a fairly new concept in human history and even more recent as a number. It wasn't until around the 7th century that zero was used as a number. That's when it showed up in the records of Indian mathematicians. Since then, zero has, at times, been met with some fear — at one point the city of Florence, Italy banned the number.Today, scientists seek to understand how much humans truly comprehend zero — and why it seems to be different from other numbers. That's how we ended up talking to science writer Yasemin Saplakoglu in this encore episode about the neuroscience of this number that means nothing.Read more of Yasemin's reporting on zero for Quanta Magazine. Plus, check out our episode on why big numbers break our brains.Interested in more math episodes? Let us know what kind of stories you want to hear from us in 2026 by emailing [e-mail]!Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, short wavers, it's Regina Barber. Happy New Year! The New Year is all about blank slates, new beginning, starting from scratch. And so we thought, what better time than now to focus on the number that signifies origin points, literally starting from nothing. Zero. So Zero was invented relatively late in history. It was first thought to be invented around like 2,500.

years ago by Babylonian traders in ancient Mesopotamia, actually. That's Yasmin Soplicolu. She's a science writer at Quantum Magazine. Back then, they used the symbol like two slanted wedges on clay tablets. But at the time, it wasn't a number yet. It was really used as a placeholder so that you can distinguish between different types of numbers like 20 or 250 or 205. And Yasmin says that this idea of a placeholder wasn't totally unique.

The ancient Maya, for example, had a little shell symbol that they used in a similar way. But zero didn't really become a number on its own until around the 7th century. There were Indian mathematicians who came up with a couple of ways to use zero as a number, and they were the kind of first to figure out that zero could be a digit, just like the other numbers, like one and two and three. after that, it kind of went out from India to the Arab world. And then, you know, in the 13th century, Feminacci actually picked up the idea during his travels in North Africa. And he brought it back to medieval Europe, you know, along with the base 10 number system.

But in medieval Europe, not everyone was thrilled about this concept of zero. People had difficulty with accepting it. It was kind of scary. People were confused by it. Some thought of it as like the devil's number that challenged like really deeply held ideas. And, you know, because of the influence of the church, like philosophers and theologians associated nothing with like chaos and disorder. One city, Florence, Italy, actually banned the number zero altogether. It's a weird concept if you even think too deeply about it.

It's like we're describing something that doesn't exist. Right? we like see three chairs or we see four birds and we can count those and they're, you know, physically there. But we don't see zero birds or zero chairs. We just know that they're absent. But that is zero. That's, you know, an extra level of abstraction from the other kinds of numbers that we see around us all the time.

And that abstraction actually makes it harder for our brains to process. So today on the show, The neuroscience of the number zero. How do humans think about the concept of nothing? How do we find out? And what does that mean for our brains? You're listening to Shortwave, the science podcast from NPR. Okay, Yasmin, before we get into the complexity of zero,

let's just start with like the neuroscience of numbers in general. You've done some writing about this, like how our brains comprehend small numbers differently than large numbers. Can you tell us more about that? Right. So this is actually kind of cool. We have what are called number neurons in the brain. So there are neurons that are tuned to specific numbers.

There are neurons that favor, for example, the number five. And there are other neurons that favor the number seven and so on. So that means that for the neurons that favor the number five, they'll fire more. Like if it sees five items on a table, it'll fire more than if it sees four or six. It'll still fire for four and six, but less. And then even less for, you know, three and seven. Yeah, so these neurons are specifically like four that number. They really like that number.

Yeah. Yeah, it's like kind of neat that we have all of these. And there's a lot of questions surrounding it still. Like, we don't know if there are neurons that fire for like a thousand, five hundred and five. That seems like there would be a lot of neurons in the brain then for the various numbers. I'm sure there's some other kind of mechanism. there. And yeah, there was this research recently that found that the brain actually

analyzes small numbers different than it does larger numbers. So there's a weird boundary around the number four. There seems to be some sort of double mechanism that's happening. So the brain processes numbers that are smaller than four in a more precise way than it does for numbers larger than four. Yeah, yeah, we did an episode about this like way back at the beginning of last year and like how if you get above four, you're not counting. You're actually comparing. And when you're below four, that's when you're literally like your brain is counting. Yeah. So you're not counting anymore past four. So interesting, right? It's like I think about this all the time where it's like, why is it four? Like, why not five? But it's four. Yeah. And when I reported that piece,

a couple of experts that were talking to me about how it's also, we're, related to working memory or awareness. So people can only really hold a certain number of objects in their awareness. And that's four. So they think that maybe there's some sort of connection there between, you know, how we're processing numbers and working memory. Yeah, it's like phone numbers, right? We're in chunks of three and four to like for us to remember.

Same with like, you know, social security number and stuff like that. Right. So fairly recently, these, like, two researchers were like, hey, if zero is special, like, in math and history, maybe, and this is what you were saying, maybe it's special in neuroscience. Maybe we think about it differently. One group looked at patients with epilepsy. They already had these, like, electrodes in their brain. So the researchers were able to see, like, how individual neurons were firing. Yeah.

And the other one? The other group looked more at populations of neurons. So it was kind of a larger scale. They used a magneto-enzo, I'm going to watch this. They used a magnetoencephalography scanner. That sounds right. That was impressive. Long word.

And basically, that means that, you know, as the neurons fire, they generate voltages, which creates magnetic fields that the machine can detect. And by analyzing the magnetic fields, the researchers were able to kind of probe what the neurons were doing when the participants were prompted to think about zero. That's so cool. Yeah. So these researchers, they're looking at neurons, either specifically or as a group, you know, firing. What did they find?

Was there like a new discovery on how we think about zero? So they actually, they were looking for something called the numerical distance effect, which is basically a phenomenon that occurs when the brain processes non-zero numbers. And it means that it can more easily distinguish numbers that are far apart from each other than those. that are close together. So the brain has a little bit more difficulty distinguishing between like seven and eight versus seven and ten, for example, or seven and eleven. Got it. Okay. So the idea for both these groups was that we should see if zero also is part of this numerical distance effect. Because if it is, then the brain might be seeing zero just as it does the other numbers. Just a normal number. Just a normal number. Yeah. Yeah. Probably not. Kind of. What happened? Yeah. So the first group, the one that looked at a bigger scale found that the brain processes zero similarly to other numbers. Basically, it puts zero at the start of a mental number line. Like, it's before one. It showed the numerical distance effect, which is what they were looking for. So their conclusion was there's no difference in the way that the brain sees zero than the other numbers. Zero in terms.

of both the digit zero and like zero objects. The second group also found that the brain puts zero before one on the mental number line, but they found subtle differences that still made zero special in the brain. Okay. So for example, they found that more neurons had zero as their preferred number than other small numbers that suggested to them that the brain might be representing you know, this empty set with more accuracy than it does for other small quantities. But this was only true for quantity zero.

For the digit zero, they did not find any difference. Like the brain saw the digit zero like it does the other digits, like one, two, three. So as you're doing this reporting, do you find that these like these conclusions are complementary? Do you think that they're like fighting each other? What do you think? Yeah, so I actually, it was funny because I had both groups kind of look at each other's results, and I was like, what's going on here? Like, why is this slightly different? And they both said that they think, you know, their results are complementary actually. And the reason for the discrepancy was most likely just scale. And, you know, they're hopeful that future experiments will be able to kind of tease apart, you know, what the nuances of this are. So like what other like research did they, did the researchers talk about like that they would like to do?

Yeah, I think that, I mean, there's a lot of directions you can go from here. Like it's how the brain comprehends zero. This was kind of the first step into that. And now, you know, one of the groups, actually, they're hoping to go more in the direction of understanding how the brain comprehends absence. because they think that if they can kind of compare how the brain is processing zero and processing absence, they might be able to see how, like, evolutionarily, how the steps toward understanding zero happened. And then the other group, they're more interested in the numbers aspect of things.

So they are hoping to look more into some of these maybe stranger numbers. But, for example, like no one looked at the written word, zero, which would be. be a really interesting thing to look at to, like, would that look different in the brain than the digit zero or then it would for empty sets? Right. What did you, like, take away from this reporting? Like, you're working on this, you know, you're learning about zero and the history. Like, what was your, like, big takeaway when you're talking to all, all of these researchers? I think my big takeaway is how incredible and complicated and big the brain is. I just, I think in my mind is still blown that we have neurons that are tuned to specific numbers and ways to comprehend

these abstract, you know, ideas. Because numbers, in zero especially, is an abstraction. And we somehow have figured out a way to comprehend it, which is incredible to me. Yeah. Yasmin, thank you so much for bringing us the story on zero. Of course. Thank you for being interested. It was super fun to report. So I'm glad I'm glad others. find it cool too. If you want to hear more about how numbers can be tricky for us to comprehend, that episode is called How Big Numbers Break Our Brains. We'll link to it in our show notes.

This episode was produced by Hannah Chin and edited by a showrunner Rebecca Ramirez. Tyler Jones checked the facts. Jimmy Keely was the audio engineer. Bet Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber. thank you for listening to Shorewave from NPR.