archive: Re: SETI Grav Lenses

Re: SETI Grav Lenses

Richard Burke-Ward ( richard@burke-ward.demon.co.uk )
Wed, 26 May 99 10:33:30 +0000

Dear All,

As well as using gravitational lensing as a way of amplifying at the
receiving end, might a civilisation not use it to amplify any signals it
wanted to transmit across interstellar distances? If so, there may be
frequency considerations to optimise the gain. Perhaps we should search
whatever frequencies are appropriate, as well as waterhole frequencies.

Another scenario suggested by the idea of using lensing to transmit is
this. If we ever send a probe to another star (IMHO, pretty much
inevitable one day, barring accidents to humanity), we might well want to
use lensing to relay data home. If another civilisation out there has
already done this, then they might well also use lensing to relay data.
This (admittedly speculative) scenario might suggest we stand a greater
chance of detecting signals transmitted via G-lens, becuase there will
only be one parent star, but potentially probes around several stars. And
while we're on the subject of probes... One of the stars which an ET
probe might arrive at is ours. Might there be a probe sitting out at 550
AU, using our own sun's len=sing effect to create a focussed long-range
beam.

Listening out for it wouldn't cost much. Scot Stride (erstwhile of this
list) has been looking into this, in dialogue with others. He sent me a
few references for those who might be interested, so they are enclosed
below.

Richard

1. Cohen, Nathan (1987). The Pro's and Con's of Gravitational Lenses in
CETI, Proceedings of the Bioastronomy Conference, Balatonfured, Hungary,
June 22-27, p. 395

2. Cohen, Nathan (1992). The Gravitational Lens as an Intergalactic
Communication Tool, Acta Astronautica, Vol. 26, No. 3-4, pp. 249-251

3. Drake, F. (1987). Stars as Gravitational Lenses, Proceedings of the
Bioastronomy Conference, Balatonfured, Hungary, June 22-27, pp. 391-394

4. Eshleman, Von, R. (1979). Gravitational Lens of the Sun: Its potential
for observations and communications over Interstellar Distances,
Science, Vol. 205, pp. 1133-1135

5. Kardashev, N. S., (1979). Optimal wavelength region for communication
with extraterrestrial intelligence: l=1.5mm, Nature, Vol. 278, pp.
28-30, March

6. Maccone, Claudio, (1994). Space Missions Outside the Solar System to
Exploit the Gravitational Lens of the Sun, Journal of the British
Interplanetary Society, Vol. 47, pp. 45-52

7. Maccone, Claudio, (1997). The Sun as a Gravitational Lens: Proposed
Space Missions, IPI Press, Colorado Springs, CO
http://www.ijvr.com/ipipress/maccone2.htm

8. Steffes, Paul. G. (1993). The Potential for Millimeter-Wave SETI,
Third Decennial US-USSR Conference on SETI, ASP Conference Series, Vol.
47, pp. 367-371, (G. Seth Shostak, ed.)