How will SETI claim to discover an advanced alien civilization? Will the discovery be opposed by some scientists as a mistake? Will some occultists claim to be in contact with the civilization by ESP? How long before ESP becomes acceptable as a means of contact? Or will one of these means become a cover, while ESP is the real method used?
Harvard dot edu presents a paper on non-radio methods of SETI:
Nonradio methods of SETI
The possibilities of exotic, nonradio methods of pursuing searches for extraterrestrial intelligence are discussed. Means of communication with extraterrestrial civilizations, other than radio means, include; (1) neutrino communication (neutrino beams are not affected by external perturbations and propagate with no losses in direction or intensity), (2) gravitational communication (gravitational waves may be focused in the gravitational fields of massive objects with spherical symmetry), (3) X-ray communication (X-ray pulses can be generated by hurling relatively small masses, say 10 to the 15th grams, onto the surfaces of neutron stars, and (4) star spectrum modification (generation of artificial spectral lines, e.g., of technetium).
Publication:Konferencja Naukowa CETI, 3rd, Katowice, Poland, Apr. 23, 1977. Postepy Astronautyki, vol. 10, no. 3, 1977, p. 39-67. In Polish.