| We have conducted an experiment to search for an advanced component of electromagnetic radiation, as suggested by the time symmetry of Maxwell's equations. A dipole transmitting antenna was driven periodically with 10.2 GHz microwave pulses of 12 ns duration and 4 watt instantaneous power. A receiving dipole antenna at a distance r = 10m away was instrumented to search for power above noise received in a time gate at a time r/c prior to transmission of each pulse. Data were integrated over 10('7) pulses. The experiment was performed at Lick Observatory, atop Mt. Hamilton, CA, to enable placement of the antennas so that a line connecting them, when extended to infinity in both directions, encounters no local complete absorber. Defining R to be the ratio of signal power in the "advanced" time gate to power received in a corresponding "retarded" gate at time r/c after pulse transmission, we obtain a limit: R < 10('-11.5) (90% confidence). Runs were also made using dielectric microwave lenses placed to focus an advanced radiation component, yielding a more theory-dependent result: R < 10('-14.0). These results have cosmological implications within the Wheeler-Feynman absorber theory of radiation. |
