Quantum physics governs the world of the very small and that of the very cold. Your dog cannot quantum-tunnel her way through the fence, nor will you see your cat exhibit wave-like properties. But physics is funny, and it is continually surprising us. Quantum physics is starting to show up in unexpected places. Indeed, it is at work in animals, plants, and our own bodies.
We once thought that biological systems are too warm, too wet, and too chaotic for quantum physics to play any part in how they work. But it now seems that life is employing feats of quantum physics every day in messy, real-world systems, including quantum tunneling, wave-particle duality, and even entanglement. To see how it all works, we can start by looking right inside our own noses.
The human nose can distinguish over one trillion smells. But how exactly the sense of smell works is still a mystery. When a molecule referred to as an odorant enters our nose, it binds to receptors. Initially, the prevailing theory held that these receptors used the shape of the odorants to differentiate smells. The so-called lock and key model suggests that when an odorant finds the right receptor, it fits into it and triggers a specific smell. But the lock and key model ran into trouble when tested. Subjects were able to tell two scents apart, even when the odorant molecules were identical in shape. Some other process must be at work.
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