Figure 53
The Chirality Chain
How the universe's handedness reaches biology
A proposed cascade [Inference]: one leading hypothesis among competing accounts.
Particle
Physics
Physics
Weak Force Parity Violation
W bosons couple only to left-handed particles — the first handedness, baked into the Standard Model since the electroweak phase transition
may contribute to
Astrophysics
Circularly Polarized UV Light
Neutron stars and star-forming regions emit light that spirals preferentially. Several mechanisms generate it, including dust scattering and aligned grains; one proposed contribution traces the asymmetry to parity violation in the weak force
preferentially destroys
Photochemistry
Selective Destruction of D-Precursors
One enantiomer absorbs circularly polarized UV more readily, degrades faster — the mirror image survives in slight excess
accumulates in
Solar
System
System
L-Excess in Meteorites
Murchison meteorite: ~18.5% L-isovaline excess — a chiral bias arriving from space, free of terrestrial contamination
delivers to
Planetary
Seeding of Prebiotic Chemistry
Meteorite bombardment delivers chiral bias to young planets — a slight thumb on the scale of molecular competition
locks in as
Biology
Life's Homochirality
All L-amino acids, all D-sugars — universal across all known life, irreversible once chosen, maintained by continuous energy expenditure
The universe chose a hand. It shakes with it across 13.8 billion years, and the handshake propagates.