Brains Are Cool Enough to Be Quantum. Are They?

For decades, the stock answer to “quantum consciousness” was a scoff:

“The brain is too warm, wet, and noisy for fragile quantum states to survive.”

That objection sounded convincing in the late 20th century. Most quantum experiments then required cryogenic temperatures and ultra-clean isolation. But the science has moved on — and the brain deserves a fresh look.

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Biology Already Does Quantum at Body Temperature

Two discoveries blew up the old dogma:

• Photosynthesis (2007): Energy transfer in bacteria and plants isn’t a classical random walk. Excitons spread in quantum superposition, sampling multiple routes at once, for ~100–400 femtoseconds across ~5–7 nanometers — all at room temperature.
  • Engel et al., Nature: Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems
• Cryptochrome (2010s): Migratory birds navigate Earth’s weak magnetic field using a radical pair mechanism. Here, two electron spins remain in coherent superposition for microseconds at body temperature — seven orders of magnitude longer than photosynthesis.
  • Ritz et al., Nature: A model for photoreceptor-based magnetoreception in birds
  • Cai et al., Nature Physics: Quantum control and entanglement in radical pair systems

These aren’t fringe claims. They’re hard experimental facts: biology has evolved protein scaffolds that stabilize coherence in messy, warm, wet conditions.

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What That Means for the Brain

Does this prove the brain uses quantum coherence in thought? No.
But it does prove something equally important:

• The old objection is obsolete. Biology is not “too warm for quantum.” It can and does sustain quantum states.
• The scale gap isn’t infinite. Synaptic clefts are ~20–40 nm wide, neurotransmission unfolds in tens of microseconds. Cryptochrome already shows coherence lasting ~1 μs over ~1–2 nm. That’s within one or two orders of magnitude of the scales brains operate on.
• Evolution is clever. If quantum coherence offers any survival advantage in neurons, we can’t rule out that evolution found a way to use it.

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Updating Our Priors

The fair stance today is:

• ✅ Established: Biology uses quantum coherence functionally (photosynthesis, cryptochrome, enzyme tunneling).
• ❓ Open question: Does the brain harness it for cognition? We don’t know yet.
• 🚫 Outdated: The claim “brains are too messy for quantum” is 20th-century thinking.

So yes — brains are cool enough to be quantum.
The only live question is: are they?