Summary
Overview
Michael Stevens and Hannah Fry embark on a fascinating journey to answer the question: what's the smallest thing you can feel? They systematically explore human sensory thresholds across taste, smell, hearing, touch, and sight, challenging poetic but unsourced claims found across the internet. Through scientific research and calculations, they progress from emotions requiring trillions of atoms down to the remarkable discovery that humans can detect single photons hitting their eyes, even if not consciously perceived.
The Challenge of Defining Sensory Thresholds
Michael begins by critiquing the ubiquitous but unsourced claims about human sensory thresholds found on Wikipedia and across the internet. These poetic descriptions—like hearing a watch tick 20 feet away or seeing a candle 30 miles away—lack scientific backing and don't provide concrete measurements in terms of atoms or molecules. The hosts establish their goal: to find the actual smallest amount of matter humans can detect across different senses, moving beyond vague descriptions to precise molecular counts.
- Wikipedia's human sensation chart has no reliable sourcing, with claims copied across the internet
- Poetic thresholds include: watch ticking 20 feet away (hearing), candle flame 30 miles away (vision), fly wing falling 7.6cm (touch)
- Scientific papers reveal there's no simple absolute threshold—it depends on the person, environment, mood, and what they've eaten
- The goal is to measure in actual molecules or atoms, not poetic descriptions
" I've been trying to learn an answer to this question for at least six years. My daughter was a little newborn baby when I first started trying to write a script about this. And I found a whole lot of answers with no source. "
" The actual scientific papers all said there is no simple, poetic, absolute threshold for the smallest thing we can sense in all these different modalities because it depends on the person. It depends on what they've been eating that day. "
Cancer Research UK: Understanding Cancer's Ancient Origins
This sponsored segment discusses how a 1.7 million year old foot bone containing a tumor reveals cancer's deep evolutionary roots. Cancer Research UK has doubled cancer survival rates over 50 years and continues developing treatments that minimize harsh side effects, including a breakthrough that nearly halved hearing loss in children receiving chemotherapy by administering a protective drug alongside treatment.
- A 1.7 million year old foot bone contains the oldest known example of cancer in people
- Cancer Research UK helped double UK cancer survival over the past 50 years
- A clinical trial showed giving another drug with chemotherapy nearly halved hearing loss in children
- The treatment combination is now used by doctors worldwide
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