Double copy and the double Poisson bracket

We derive first-order and second-order field equations from ambitwistor spaces as phase spaces of massless particles. In particular, the second-order field equations of Yang-Mills theory and general relativity are formulated in a unified form $\{\{H,H\}\}_\nabla = 0$, whose left-hand side describes a doubling of Poisson bracket in a covariant sense. This structure originates from a one-loop diagram encoded in gauge-covariant, associative operator products on the ambitwistor worldlines. A conjecture arises that the kinematic algebra might manifest as the Poisson algebra of ambitwistor space.