Searches for the role of spin and polarization in gravity

Understand

Spin is fundamental in physics.

• Gravitation is universal.
• Searches for the role of spin in gravitation dated before the firm establishment of the electron spin in 1925.
• Since mass and spin or helicity in the case of zero mass are the only invariants of the Poincare group and mass participates in universal gravitation, these searches are natural steps to pursue.