Out of a Silent Planet
Fine Tuning the Drake Equation with the Rezabek Ratio
After the 2013 Icarus Interstellar Starship Congress a number of those of us who participated continued to correspond about interesting ideas that came out of the conversations, and one of these ideas was that of the Rezabek Ratio. During a discussion of METI (active messaging of extraterrestrial intelligence) by Jim Benson, Heath Rezabek suggested that someone opposed to unregulated METI could broadcast a static or random signal as a masking counter-signal to a METI signal and essentially silence the outbound METI signal. Formally, this can be expressed such that the factors of the Drake equation, which terminates with the number of communicative civilizations (which Carl Sagan would have identified with the number of civilizations in possession of large radio telescopes), could be supplemented by another factor that represents the number of communicating civilizations the signals of which are electronically suppressed. We came to call this factor the Rezabek Ratio after Heath. (You can read the document in which we discussed this.)
A recent article in Science has made me realize that a distinction needs to be made between civilizations in which METI signals are intentionally suppressed, transforming them into non-communicative civilizations even if they are in possession of large radio telescopes, and civilizations in which radio signals are unintentionally suppressed, also transforming them into non-communicative civilizations, though as a matter of historical accident, not a matter of purposeful suppression of METI signals.
The article in question was Starlink already threatens optical astronomy. Now, radio astronomers are worried by Daniel Clery, which discusses the impact that the Starlink satellite constellation, intended to provide internet access anywhere on Earth, could have on radio astronomy. These concerns were prompted by a report from the Square Kilometer Array (SKA), SKAO Needs Corrective Measures From Satellite ‘Mega-Constellation’ Operators To Minimise Impact On Its Telescopes, which stated, “…our study demonstrated even with the current smaller constellation sizes (of 6,400 satellites), there is likely to be a continuous loss of sensitivity impacting all astronomical observations in Band 5b within the frequency range of the satellite’s transmissions unless mitigating actions are implemented.”
The concern at present is for radio astronomy, but radio astronomy includes SETI and METI. It seems more likely that any feeble SETI signals that we might possible receive would be more vulnerable to disruption than METI transmissions, but I include the METI scenario here as it is an interesting idea, and is endangered by the same technology. Just as a Kessler syndrome could accidentally be triggered by too many satellites in orbit, so too the suppression of outward bound METI messaging (as well as inbound SETI messaging) could accidentally obtain as a result of too many communications satellites. If, as a result of building a constellation of internet-enabling satellites, radio telescopy is compromised, future build-outs of additional internet infrastructure in space will further compromise radio telescopy. If this process is iterated, the construction of internet-enabling satellite constellations could eventually converge upon near total yet unintentionally implemented silencing of Earth, as well as silencing any SETI messages intended for Earth.
A satellite constellation such as those now under construction could compromise radio telescopy (thus SETI and METI) simply operating as intended, but if a satellite constellation were specifically engineered to disrupt radio telescopy, utilizing an array constructed for this purpose, the intentional silencing of SETI and METI could in principle be sufficiently effective to rule out any possibility of SETI or METI. The extent to which this suppression effect could be scaled up is not clear, but if the suppression effect is indefinitely scalable, the eerie silence — i.e., the fact that SETI searches have turned up nothing so far — might not be an accident of nature, but could be the engineered result of a silenced cosmos.
The scaling up of the unintentional suppression effect could come about by a relatively straight-forward build-out of communications throughout the solar system. SpaceX’s Starlink satellite constellation is well within the orbit of the moon, so that the far side of the moon still represents a pristine place for radio astronomy, and therefore also a pristine location for SETI and METI efforts. This will remain true for some time, but it will not necessarily remain true in perpetuity. If a human presence in space expands to the moon and the Lagrange points, we would expect that internet infrastructure would expand proportionally, and at this point the far side of the moon would lose its pristine character unless protected (Claudio Maccone has advocated for the protection of the far side of the moon as a pristine location for radio astronomy).
However, even with a build-out of internet radio infrastructure in the inner solar system, and the consequent loss of the far side of the moon as a location for radio astronomy, the outer solar system would remain a refuge for radio telescopy and SETI/METI. This leap-frogging process could continue, so that a human presence pervasive within the solar system would drive radio telescopy and SETI/METI outside the solar system.
A solar system-wide civilization with a robust internet connecting everything within the solar system would likely be a radio-loud phenomenon, and such a system-wide network would be an appropriate target for SETI searches. Because this scale of radio technology would be relatively obvious, it would also be an obvious target for intentional suppression. Transmission and suppression might also alternatively leap-frog each other, so that, say, the technology of transmission pulls ahead, and this is a spur for suppression efforts, which would then pull ahead. The resulting signals in historical time would then be spaced in pulses with strong signals originating from period when transmission technology was in the ascendancy, followed by weak or non-existent signals during a period when suppression technologies were in the ascendancy. These pulsed signals would be a distinctive technosignature for a civilization in conflict over SETI and METI.
