Wheeler–Feynman absorber theory

A time-symmetric theory of classical electrodynamics in which charged particles interact directly across spacetime. It explains the observed direction of radiation through the response of the universe’s absorbers.

Fokker action: A relativistic action describing interactions between charged particles through terms coupling their positions at lightlike-separated events. It gives the theory’s direct particle-to-particle interaction without an independent electromagnetic field.
John Archibald Wheeler: An American theoretical physicist whose work ranged from nuclear physics and general relativity to quantum theory. He co-developed the absorber theory and supplied its physical framing.
Dirac equation for radiation reaction: A relativistic equation describing the self-force on a radiating point charge using retarded electromagnetic fields. It derives radiation reaction through a field-based prescription rather than a cosmic absorber response.
Arrow of time: The observed asymmetry between past and future in physical processes. The absorber theory aims to explain why radiation appears to propagate toward the future.
Advanced and retarded potentials: Solutions of electromagnetic field equations that propagate influence toward the future or toward the past, respectively. The theory uses both time directions before absorber response selects the observed radiation behavior.
Richard Feynman: An American theoretical physicist known for quantum electrodynamics, path integrals, and influential physics teaching. His early work with Wheeler developed the direct-action absorber account.
Causal structure: The pattern of which events can influence which others in a physical theory. The theory permits advanced as well as retarded contributions, challenging ordinary causal intuition.
Thermodynamic arrow of time: The direction in which entropy tends to increase in macroscopic systems. Its low-entropy cosmological boundary condition is often invoked to distinguish radiation’s arrow from thermodynamic irreversibility.
Radiation reaction: The force exerted on an accelerating charge by its own emitted electromagnetic radiation. The absorber account derives this familiar force from interactions with other charges.
Maxwell–Lorentz electrodynamics: Classical electrodynamics describing charged matter coupled to electric and magnetic fields governed by Maxwell’s equations. The absorber theory reformulates this framework’s radiation and interaction picture.

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