In a paper entitled INTERSTELLAR PROBES: A NEW APPROACH TO SETI, published by the Journal of the British Interplanetary Society, Vol. 33, pp. 95-100, 1980, Robert A. Freitas Jr. raised the following idea:
Interstellar transmissions via energy-markers (photons) or matter-markers (probes) appear to be energetically indistinguishable alternatives for advanced technical societies. Since only Type II and Type III civilizations realistically can afford beacons or starprobe technology, alternative distinguishability criteria suggest the possible superiority of intelligent artifacts for contact and communication missions among extraterrestrial cultures. A balanced, more cost-effective Search for Extraterrestrial Intelligence (SETI) strategy is proposed.
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