Sep 6, 2026 · 57 min
One photon may be enough to trigger awareness
The Threshold of Human Sensation
The episode tests how biology, context, and physics set the limits of human perception—and whether consciousness begins with a single particle.
- 1Sensory thresholds vary with context, physiology, attention, and environment, making simple minimum-detection claims unreliable.
- 2Hearing, taste, smell, and touch require radically different physical signals, with smell proving exceptionally sensitive to individual molecules.
- 3The hosts conclude that one photon may be the smallest stimulus capable of producing conscious awareness, though emotion resists measurement.
Don't miss
Michael Stevens gives one photon as the smallest stimulus capable of producing detectable human awareness.
The brief
Michael Stevens and mathematician Hannah Mary Fry ask what the smallest thing a human can feel, expanding feeling beyond touch to sensation, perception, and awareness.
Popular claims about minimum thresholds quickly unravel: detection depends on context, environment, attention, biology, and physiological state rather than fixed numbers.
The tour moves across sound, taste, smell, and touch, from hydrogen ions and aspartame to odor molecules and nanoscale textures on optical discs.
Cosmic rays can produce flashes by passing through the brain, raising a boundary question: does a sensation count if it bypasses the ordinary sense organs?
The final answer is one photon, possibly enough to produce detectable awareness; the hosts distinguish consciously seeing it from merely sensing that something happened.
Featuring
Hannah Mary Fry
DVD
Lisa Feldman Barrett
CERNBooks & mentions
Listen to the full episode and explore every guest, topic, and moment on PodLume.