power of gravitational lensing could also be used to receive radio transmissions from the target solar system that would otherwise be too faint to detect. This is especially interesting because the maximum range the Arecibo radio telescope would be able to detect our own radio transmissions is one light-year. This isn’t enough range to hear anything, so only much more powerful transmissions, probably deliberately sent to us, are detectable by SETI. The same sort of telescope at the gravitational lensing distance would have much greater range and sensitivity.
The same technology used to receive transmissions from aliens could also be used to create information links between human colonies. Although theoretically these telescopes, in this case also equipped with radio or laser transceivers, could be used to link opposing points in the Oort cloud, their primary usage will likely be for interstellar communication. Any probe sent to, say, Alpha Centauri would have a much easier time transmitting and receiving information if the transmissions were magnified by gravitational lensing. A pair of transceivers, one beyond the gravitational lensing point of the Sun, one aligned with it beyond the gravitational lensing point of Alpha Centauri, could use gravitational lensing to communicate with each other without needing extremely powerful transmitters or having to hope that less-powerful transmissions don’t get lost in the interstellar noise. These transceivers, in turn, could use more ordinary methods to relay the interstellar transmissions to and from the inner parts of each solar system.
Although transmissions to even the nearest star, Alpha Centauri, would still take over four years to travel one-way, these relays in the “telescope cloud regions” do seem to be by far the most effective way of transmitting between star systems. The same transceivers used by probes can also be used by future human colonies, theoretically even to the point of maintaining an interstellar internet of sorts, though with years of lag time it would necessarily be more like transmitting an internet archive with “messages in a bottle” between systems every so often than any remotely real-time communication. Pairs of transceivers can be set up in other solar systems as well, thus forming a network connecting all the nearby stars.
The amount of amplification that can be achieved is quite large; as this New Yorker article points out, one particular frequency that SETI has identified as interesting could be enhanced by a factor of up to 1.3 quadrillion using gravitational lensing. This is powerful enough to open up the possibility of detecting signals across intergalactic distances. Of course, any radio transmission would be distorted, and an alien transmission would be much harder to reconstruct than a message from one of our own transceivers we know the position of (and thus can calculate precisely how to adjust for the distortion), but the idea that such a feat may be possible with near-future technology is certainly quite interesting.
Indeed, after considering all these possibilities, the sun’s gravitational lensing effect appears to be one of the greatest natural endowments of our solar system as far as human use is concerned. Any alien civilization in any star system would have the same advantage, and the same techniques discussed here for human use in the future may already be in use by any aliens that may be out there. Aliens might be sending transmissions to other solar systems (including our own) that are designed to be receive using gravitational lensing, perhaps intended for only a more advanced civilization to receive, or because they assume anyone they would want to talk to would be using it, or because of convenience for them if they already have such transceivers or telescopes.
The many possibilities of using gravitational lensing for astronomical observation and transmitting information, along with the implications for human scientific discovery and even space colonization, is an area that to my knowledge is hardly ever explored in science fi