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5 min readThe Threshold of Human Sensation
Michael Stevens has been trying to answer a single question for six years: what is the smallest thing a human can feel? Not emotionally feel, but physically detect through any of the senses. The problem, he explains, is that most popular answers to this question are essentially made up. The Wikipedia page for "sense" includes an unsourced chart claiming that the quietest sound we can hear is a watch ticking twenty feet away, that we can see a single candle flame from thirty miles on a clear night, and that the lightest touch we can detect is a fly's wing falling on our cheek from three inches. "These sound too poetic," Stevens says. And when he tried to find scientific backing, he discovered that no simple, universal threshold exists for any sense—it depends on the person, what they've eaten, the room they're in, even their mood.
The Scale Problem: From Trillions Down to Millions
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What you'll learn
- 1 (00:00) **Episode Introduction and Setup** - Michael Stevens and Hannah Fry introduce the question: what is the smallest thing a human can feel?
- 2 (04:52) **Debunking the Wikipedia "Absolute Thresholds"** - Michael reads the famous unsourced thresholds and begins questioning their validity.
- 3 (08:21) **Defining the Goal: Smallest Amount of Matter** - Michael reframes the question: not poetic descriptions, but the actual number of molecules or atoms needed to sense something.
- 4 (12:42) **Hearing: The Need for Trillions** - Michael explains why hearing requires the most matter of any major sense.
- 5 (16:26) **Taste: From Quadrillions to Billions** - Michael investigates the molecular threshold for taste, starting with sourness and moving to artificial sweeteners.
- 6 (21:47) **Smell: The Nose's Direct Line to the Brain** - Michael explains why smell is more sensitive than taste, down to millions of molecules.
- 7 (33:01) **Touch: Feeling 70,000 Atoms** - Michael examines the static indentation threshold for touch.
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Guests on this episode
Show Notes
What is the smallest thing you can possibly feel?
Michael Stevens and Professor Hannah Fry journey through varying levels of perception, from the faintest touch on skin to the faintest trace of flavour and odour, and on to the remarkable question of whether the eye can register a single particle of light.
This is an exploration of human senses at their most sensitive, blending physics and neuroscience with everyday experience to reveal where our biology draws the line between nothing and something, and what about emotion... how do we feel those?
What is the smallest thing you can possibly feel?
Michael Stevens and Professor Hannah Fry journey through varying levels of perception, from the faintest touch on skin to the faintest trace of flavour and odour, and on to the remarkable question of whether the eye can register a single particle of light.
This is an exploration of human senses at their most sensitive, blending physics and neuroscience with everyday experience to reveal where our biology draws the line between nothing and something, and what about emotion... how do we feel those?
Darwin's The Expression Of The Emotions In Man And Animals.
Lisa Feldman Barrett - How Emotions Are Made: The Secret Life of the Brain.
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