According to an idea proposed in 1994 by a group of physicists at the University of Hawaii, Manoa, advanced civilizations could be transmitting bursts of neutrinos across the Galaxy as timing pulses.1 As a spokesman for the group pointed out:
Accurate synchronized clocks are needed for a wide range of scientific measurements, particularly in astronomy. But any advanced civilization is bound to require standards that are more exacting.
Without some system of synchronization, clocks at different locations in the Galaxy would gradually drift out of step because of a relativistic effect which causes time to flow more slowly where the local gravitational field is more intense. To bring widely dispersed clocks regularly back into line with an extremely accurate galactic standard would mean exchanging timing signals at the limits allowed by physics, which is where neutrinos might come in. The fastest known process in (terrestrial) physics is the decay of a subatomic particle known as the Zº boson into a neutrino and an antineutrino. It takes just 10-21 sec. Neutrinos also have the advantage that they are not blocked by material in space, such as cosmic dust, nor are they smeared out, or dispersed, by ionized gas. In addition, they can be produced with a higher luminosity than electromagnetic radiation can. The Hawaiian team suggested that neutrino pulses as narrow as 10-21 sec could be sent across many thousands of light-years and be generated by a giant particle accelerator, about the size of the Earth, in which electrons and positrons were collided head on. The Zº bosons produced by this device could be made in bursts synchronized by a master clock. If such interstellar neutrino signals are being transmitted, concluded the team, it might be possible to detect them using equipment such as DUMAND, the Deep Underwater Muon and Neutrino Detector, in the sea off Hawaii. Calculations showed that the detection of extraterrestrial neutrinos could be achieved with as little as a cubic kilometer of seawater if there is a transmitter within about 3,000 light-years. Any artificial signals should be quite distinctive since the neutrinos would come from a single direction in the sky and have a very well-defined energy.
1. Learned, J. G., Pakvasa, S., Simmons, W. A., and Tata, X. "Timing Data Communication with Neutrinos - A New Approach to SETI," Quarterly Journal of the Royal Astronomical Society, 35, 321 (1994).