A closer look
Who needs a magnetic compass when your actual eyeballs are tangled up in quantum mechanics? Migratory birds like the European robin achieve their flawless global navigation using a protein in their retinas called cryptochrome. When a photon of blue light hits this protein, it knocks an electron out of place, creating a 'radical pair' of highly reactive molecules with quantum-entangled spins. The Earth's incredibly weak magnetic field is just strong enough to alter how these entangled electrons interact before they recombine. This bizarre quantum state effectively overlays a real-time, heads-up magnetic map directly onto the bird's visual field.
