The world-renowned physicist, Freeman Dyson of Princeton's Advanced Institute of Study (Einstein's former home), wrote that "Life may succeed against all odds in molding the Universe to its own purposes. And the design of the inanimate Universe may not be as detached from the potentialities of life and intelligence as scientists of the 20th century have tended to suppose."
The underlying assumption of Dyson's statement is his belief that in a universe some 14 billion years old that their are advanced technological civilizations in existence far more ancient than our 4.5 billion year-old Earth who are capable of feats of "macro-engineering" that we can hardly imagine.
Following Dyson's lead, Milan Cirkovic of the Astronomical Observatory of Belgrade believes that rather than searching for radio or optical laser signals, the search for should seek out artifacts of cosmic macro-engineering, which might include Dyson Spheres -an artificial cluster of rotating objects the size of a planetary orbit that would collect almost all the solar energy available and create a vast habitat for life.
In a recent paper Cirkovic wrote that this approach makes far more sense to detect a civilization immensely older and more advanced than us: "It seems preposterous even to contemplate any possibility of communication between us and billion-year old super civilizations."
Cirkovic calls his recommendation the "Dysonian Approach": "Even," he continues,"if they are not actively communicating with us, that does not mean that we cannot detect them and their astro-engineering activities. Their detection signatures may be much older than their communication signatures. Unless they have taken great lengths to hide or disguise their detection signatures, the terrestrial observer should still be able to observe them at those wavelengths and those should be distinguishable from normal stellar spectra."
Echoing Cirkovic and Dyson is Luc Arnold (Observatoire de Haute-Provence, France), who suggests that the same methods could be employed to find artificial planet-sized objects in orbit around stars. Arnold belives that transits of multiple objects could be used to emit signals that might be detected by other civilizations.
The light-curves of objects from spheres to triangles and even more exotic shapes will have their own distinctive signature, even as multiple objects could send a ‘message’ whose timing and number would announce the willingness of their makers to communicate.
Upcoming missions like Kepler and the European Corot, according the Centauri Dreams blog, may be able to detect such objects as they look for planetary transits.
Source: Cirkovic, "Macro-Engineering in the Galactic Context: A New Agenda for Astrobiology."