Short Wave — "The Trouble of Zero" (January 2, 2026, NPR)

Host: Regina Barber
Guest: Yasmin Saplakolu, Science Writer at Quanta Magazine

Episode Overview

This episode of Short Wave delves into the mystery, history, and neuroscience of zero—a number many take for granted but which is surprisingly complex both mathematically and cognitively. Host Regina Barber and guest Yasmin Saplakolu explore how zero was invented, why it’s challenging for the brain, and what cutting-edge research reveals about how we process "nothingness." Along the way, they sprinkle humor and relatable comparisons, making the science accessible and engaging.

Key Discussion Points & Insights

1. The History of Zero

• Origins as a Placeholder (00:54–01:25)

  • Zero first appeared about 2,500 years ago by Babylonian traders, used as a placeholder (not a true number).
    • "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." — Yasmin (01:09)
  • Other ancient civilizations, like the Maya, used similar placeholders.

• Becoming a Number (01:25–02:12)

  • True conceptualization of zero as a number happened in seventh-century India.
  • Spread through the Arab world; Fibonacci brought it to Europe in the 13th century, introducing base-10 arithmetic.

• Cultural Resistance (02:12–02:44)

  • Zero was unsettling in Medieval Europe; some associated it with chaos, disorder, even the devil.
    • "Some thought of it as like the devil's number." — Yasmin (02:18)
  • Florence, Italy, once banned the use of zero.
  • Zero's abstraction—representing 'nothing' rather than something tangible—made it hard to accept.

2. Why Zero Confuses Us (02:44–03:41)

• The brain struggles with zero because it represents absence, an extra level of abstraction compared to counting physical objects.
  • "It's like we're describing something that doesn't exist, right? ...But that is zero. That's an extra level of abstraction." — Yasmin (02:44)

3. The Neuroscience of Zero and Numbers

• Number Neurons (05:05–05:46)
  • The brain contains specialized neurons tuned to specific numbers (e.g., a neuron that "prefers" five will fire most strongly in response to groups of five).
  • "We have what are called number neurons in the brain ... they'll fire more if it sees five items on a table ... and then even less for three and seven." — Yasmin (05:05)
• Small v. Large Numbers (06:34–07:31)
  • The brain is precise with numbers up to four; above that, we shift from counting to roughly comparing.
    • "If you get above 4, you're not counting, you're actually comparing. And when you're below four, that's when ... your brain is counting." — Regina (06:34)
  • Possibly linked to working memory—humans can hold about four items in awareness, which may explain the cut-off.

4. Is Zero Processed Differently? (07:32–10:49)

• Recent Research:

  • Two main studies examined how the brain processes zero:
    • One used epilepsy patients with brain electrodes to look at individual neurons.
    • Another used magnetoencephalography (MEG) to see how groups of neurons respond.

• Numerical Distance Effect (08:44–09:11)

  • The brain easily distinguishes numbers that are farther apart (e.g., 7 vs. 10) but struggles with numbers close together (e.g., 7 vs. 8).
  • Researchers questioned whether zero is treated like other numbers in this context.

• Findings:

  • Group 1 (Larger Scale Study):
    • The brain positions zero at the start of the mental number line, just before one.
    • Shows the same numerical distance effect—suggesting our brain treats zero like any other number.
      • "Their conclusion was there's no difference in the way that the brain sees 0 than the other numbers ... in terms of both the digit 0 and 0 objects." — Yasmin (09:49)
  • Group 2 (Focused Neuron Study):
    • Subtle, notable difference: more neurons prefer zero than other small numbers, suggesting more accuracy or special status—but only for 'zero objects' (representing emptiness), not the digit.
      • "More neurons had zero as their preferred number than other small numbers. That suggested ... the brain might be representing ... this empty set with more accuracy." — Yasmin (10:19)

5. Complementary Findings & Future Research

• Both groups saw their findings as complementary, possibly due to differences in research scale.
• Next research frontiers:
  • Understanding how the brain comprehends absence itself (not just the concept of zero).
  • Comparing how the brain processes "zero," the digit "0," and the written word "zero."
  • Investigating unfamiliar or unusual numbers for unique neural representation.

6. Personal Reflections

• The episode ends with Yasmin reflecting on the astonishing complexity and adaptability of the human brain:
  • "I think my big takeaway is how incredible and complicated and big the brain is. ...we have neurons that are attuned to specific numbers ... and 0 especially is an abstraction and we somehow figured out a way to comprehend it, which is incredible to me." — Yasmin (12:40)

Notable Quotes & Memorable Moments

• "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." — Yasmin (02:18)
• "One city, Florence, Italy, actually banned the number zero altogether." — Regina (02:39)
• "We have what are called number neurons in the brain ... they'll fire more if it sees five items on a table." — Yasmin (05:05)
• "There's a weird boundary around the number four. ... The brain processes numbers that are smaller than four in a more precise way." — Yasmin (06:08)
• "If zero is special in math and history, maybe it's special in neuroscience. Maybe we think about it differently." — Regina (07:32)
• "For the digit 0, they did not find any difference. Like, the brain saw the digit 0 like it does the other digits." — Yasmin (10:26)
• "My mind is still blown that we have neurons that are attuned to specific numbers and ways to comprehend these abstract, you know, ideas." — Yasmin (12:40)

Timestamps for Key Segments

• 00:40 — Introduction to the theme of zero and its origins
• 01:09 — Zero as a placeholder in Babylonian and Mayan systems
• 01:39 — Indian mathematicians establish zero as a number
• 02:12 — European suspicion and bans concerning zero
• 02:44 — Discussion of zero’s abstract nature and cognitive challenges
• 05:05 — Neuroscience: number neurons and how brains process numbers
• 06:34 — The "magical number 4" boundary in counting and memory
• 07:32 — Is zero special in neuroscience? New research approaches
• 08:44 — The numerical distance effect and main study questions
• 09:49–10:49 — Study findings: zero as a number and neural uniqueness
• 12:40 — Yasmin’s reflections on abstraction and the human brain

Episode Takeaways

• Zero's journey from placeholder to number mirrors deep philosophical discomfort with "nothingness."
• The brain processes zero in intricate ways—sometimes just like other numbers, but sometimes with special precision.
• The mental handling of small numbers underlines links between math, cognition, and memory.
• Understanding how we process zero may provide broader insights into how the brain deals with abstraction.

For further listening on the cognitive challenges of numbers, Regina recommends the Short Wave episode How Big Numbers Break Our Brains.