SETI: Wild speculations time

Larry Klaes (
Tue, 27 Jul 1999 13:33:37 -0400

>From: "Clements, Robert" <>
>To: "'Larry Klaes'" <>
>Subject: SETI: Wild speculations time
>Date: Tue, 27 Jul 1999 11:03:19 +1000
>X-Mailer: Internet Mail Service (5.5.2448.0)
>This is wildly in the area of speculation; but could offer a method for
>detecting ETIs at distances beyond our current technology (effectively less
>than 100ly). I've be wondering along these lines for about a year ago; but
>some comments on another message board about interstellar travel brought the
>concept back into clear focus. If you think the speculations are worth
>considering, feel free to FWD to the SETI list; otherwise:....
>The method is designed to detect incidental noise (ie, not a designated SETI
>signal). It makes the following key assumption: that the ETI we're looking
>for is capable of interstellar travel (whether robotic or organic is
>irrelevant here); & that there are no transEinsteinian shortcuts being used.
>(Dangerous assumptions, of course; but you have to start somewhere)
>The simplest (& most fuel efficient) way to travel interstellar distances is
>to use beamed energy (as opposed to true solar) sails; where the beam has
>been concentrated from energy obtained directly from the system's star/s (a
>lens or a mirror, for eg). Unfortunately, sails like this are basically
>oneway thrusters (the star at the other end of the flight is unlikey to be
>able to completely decelerate the beam driven vehicle; unless its: a)
>hotter; or b) the sail can unfurl even further on arrival... both are
>entirely feasible; but place distinct limitations on the missions which can
>be flown); so regular interstellar flight seem to call for other
>technologies (such as antimatter drives)....
>... however: if you were able to build a second beam in the target system,
>you would create a beam of energy between the two systems to accelerate &
>deccelerate twoway traffic... in effect: you would have an interstellar
>river; along which starships can literally sail. Very appealing; & once the
>capital cost is met, the thing basically runs on maintainence (& debt
>servicing?). Perfect for robotic flight, of course; & if the beams were
>strong enough, organics could sail the stars as well... an idea well worth
>exploring if you're an ambitious, exploratory ETI....
>Assume that this reasoning is valid; & that these beams of energy actually
>exist... what would they look like from the outside? They'd be relatively
>bright but highly concentrated in space; so we may not be able to detect the
>beams themselves; but the spectrum of the star from which the beam emerges
>may very well be distorted by a pronounced spike in the direction of
>transmission; with the effect (possibly) most noticeable at some particular
>- & quite conceivably weird - wavelength (if the beam has been synchronised
>to maximise sail efficiency). Since the beamed acceleration to interstellar
>travel velocity is likely to take a year or more, these spike are likely to
>be longlived & possibly even permanent... they would also be highly
>directional (obviously); so would only vary as the angle of transmission
>shifts in relationship to Earth. Even better: the limit of detection would
>effectively be a far as a spectrum can be successfully obtained....
>This SETI (really OSETI) concept has the major advantage of not requiring
>designated technology to do it: i suspect a review of existing spectrodata
>would be enough to determine whether the idea is stupid; or worth exploring
>All the best,
>Robert Clements <>

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