Podcast Title: Unexplainable
Host/Authors: Noam Hassenfeld, Julia Longoria, Byrd Pinkerton, Meredith Hoddinott
Episode: We Don't Understand Yogurt
Release Date: June 11, 2025
Introduction to Soft Matter
In the June 11, 2025 episode of Unexplainable, host Bird Pinkerton delves into the enigmatic world of soft matter, a state of matter that defies the traditional classifications of solid, liquid, gas, and plasma. Inviting listeners to explore the peculiar properties and scientific mysteries surrounding everyday substances, Bird sets the stage for an engaging discussion with physicist Ray Robertson Anderson.
Bird Pinkerton introduces the concept by reminiscing about the classical states of matter:
“As a kid in school, I learned about four states of matter. Solid, liquid, gas, and then plasma. But recently I spoke to a physicist named Ray Robertson Anderson, and she told me that there is actually another state of matter out there.” [00:56]
Understanding Soft Matter
Ray Robertson Anderson explains that soft matter encompasses materials that are "bendy or squishy," exhibiting properties between solids and liquids. These materials include everyday items like yogurt, toothpaste, ketchup, and even biological substances such as our skin and saliva.
“Soft matter is basically stuff that is more bendy or squishy than a solid, but more able to hold its shape than a liquid can.” [01:41]
Unlike the well-understood behaviors of solids and liquids established centuries ago, soft matter operates under its own set of complex and not yet fully deciphered rules. Ray emphasizes the significance of understanding these materials as a stepping stone towards a unified model of the universe:
“We don't understand yogurt. So, like, we don't understand how these things, you know, for that we encounter every day, like toothpaste and shampoo and yogurt, like, we don't understand really how that works.” [02:04]
Everyday Examples of Soft Matter
To illustrate the peculiar behavior of soft matter, Bird and Ray discuss common examples that exhibit both solid-like and liquid-like properties depending on external stimuli.
Yogurt: A Classic Example
They examine yogurt's dual nature:
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Solid State: Upon opening a yogurt container, the product maintains its shape, allowing a spoonful to be scooped out effortlessly.
“You can scoop out an actual piece of the yogurt and it's solid.” [03:18]
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Liquid State: Stirring the yogurt alters its consistency, making it pourable.
“After you've stirred it, if you tilt it, you can actually pour it. It's become like a fluid.” [03:35]
Oobleck: The Non-Newtonian Fluid
Another fascinating example is Oobleck, a mixture of cornstarch and water that behaves differently under varying conditions:
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Solid Behavior: Punched or subjected to sudden force, Oobleck hardens, preventing penetration.
“If you punch [it] stiffens up and your hand cannot go through that fluid.” [04:24]
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Liquid Behavior: Slow insertion allows complete submersion without resistance.
“If you try to slowly put your hand into it, you can fully submerge it.” [04:24]
The Molecular Complexity of Soft Matter
Bird explains the molecular intricacies that make soft matter so challenging to study:
“In a material, you have 10 to the 23 spaghettis, that is 100 sextillion spaghettis that Ray is supposed to keep track of.” [07:09]
Ray elaborates using the metaphor of a bowl of spaghetti:
“Soft matter as a bowl of spaghetti. If I try to pull one strand out, it's hard; it might snap back. But poured altogether, it flows like a fluid.” [06:07]
This analogy underscores the difficulty in modeling soft matter due to the vast number of molecular interactions and the dynamic nature of these materials.
Implications for Biology and Engineering
Understanding soft matter extends beyond academic curiosity, impacting fields like biology and engineering.
Biological Significance
Ray highlights that human biology is fundamentally composed of soft matter:
“Life is made up of a whole bunch of squishy stuff, like our eyeballs and snot and saliva in our tongues and our skin.” [11:59]
On a cellular level, soft matter principles apply to the behavior of cells, which have molecular skeletons that can transition between rigid and fluid states to perform functions like division and movement.
“Cells can tense up and they can also fluidize to do things like divide and crawl and also like to form structures.” [12:05]
Future Engineering Applications
Ray envisions engineering breakthroughs inspired by soft matter, such as:
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Adaptive Bulletproof Vests: Vest materials that remain flexible under normal conditions but harden instantaneously upon high-speed impacts, mimicking Oobleck's behavior.
“If we figure out how all the molecules in something like Oobleck are coming together to do what they do, then maybe we could make a vest that was flowy and flexible under most conditions.” [13:19]
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Self-Healing Infrastructure: Bridges that automatically repair cracks by utilizing cell-inspired materials that fluidize to fill gaps and then solidify.
“She dreams of making a self healing bridge. So basically like a bridge where if it started to develop a crack of some kind, the cell inspired materials around that crack would react and become more fluid and basically fill in that crack.” [14:15]
Ongoing Research and Enthusiasm
Ray expresses her excitement and the endless array of puzzles soft matter presents:
“There's so many questions that we don't understand and that I would love to study.” [15:00]
Her enthusiasm is infectious, inspiring listeners to appreciate the hidden complexities in everyday substances.
Conclusion: Embracing the Mysteries of Soft Matter
Bird wraps up the episode by reflecting on the ubiquitous presence of soft matter and its myriad mysteries:
“Somehow looking at this bottle of ranch, it really hit me that the whole world is brimming over with mysteries, and even this ridiculous condiment contains riddles that we have not yet solved.” [16:55]
Listeners are encouraged to delve deeper into the subject through Ray's book, Biopolymer Networks, and her accessible content on TikTok (@physicsmama).
Credits:
- Produced by: Bird Pinkerton
- Edited by: Jorge Just
- Showrunner: Meredith Hoddinott
- Music: Noam Hassenfeld
- Mixing & Sound Design: Christian Ayala
- Fact-Checking: Melissa Hirsch
- Special Thanks: Brian Resnik, Colm Kelleher, Uri Bram
Additional Resources:
- Book: Biopolymer Networks by Ray Robertson Anderson
- TikTok: @physicsmama
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