The Firefly and the Pulsar
We’ve now had humans in space for 25 continuous years, a feat that made the news last week and one that must have caused a few toasts to be made aboard the International Space Station. This is a marker of sorts, and we’ll have to see how long it will continue, but the notion of a human presence in orbit will gradually seem to be as normal as a permanent presence in, say, Antarctica. But what a short time 25 years is when weighed against our larger ambitions, which now take in Mars and will continue to expand as our technologies evolve.
We’ve yet to claim even a century of space exploration, what with Gagarin’s flight occurring only 65 years ago, and all of this calls to mind how cautiously we should frame our assumptions about civilizations that may be far older than ourselves. We don’t know how such species would develop, but it’s chastening to realize that when SETI began, it was utterly natural to look for radio signals, given how fast they travel and how ubiquitous they were on Earth.
Today, though, things have changed significantly since Frank Drake’s pioneering work at Green Bank. We’re putting out a lot less energy in the radio frequency bands, as technology gradually shifted toward cable television and Internet connectivity. The discovery paradigm needs to grow lest we become anthropocentric in our searches, and the hunt for technosignatures reflects the realization that we may not know what to expect from alien technologies, but if we see one in action, we may at least be able to realize that it is artificial.
And if we receive a message, what then? We’ve spent a lot of time working on how information in a SETI signal could be decoded, and have coded messages of our own, as for example the famous Hercules message of 1974. Sent from Arecibo, the message targeted the Hercules cluster some 25,000 light years away, and was obviously intended as a demonstration of what might later develop with nearby stars if we ever tried to communicate with them.
But whether we’re looking at data from radio telescopes, optical surveys of entire galaxies or even old photographic plates, that question of anthropocentrism still holds. Digging into it in a provocative way is a new paper from Cameron Brooks and Sara Walker (Arizona State) and colleagues. In a world awash with papers on SETI and Fermi and our failure to detect traces of ETI, it’s a bit of fresh air. Here the question becomes one of recognition, and whether or not we would identify a signal as alien if we saw it, putting aside the question of deciphering it. Interested in structure and syntax in non-human communication, the authors start here on Earth with the common firefly.
If that seems an odd choice, consider that this is a non-human entity that uses its own methods to communicate with its fellow creatures. The well studied firefly is known to produce its characteristic flashes in ways that depend upon its specific species. This turns out to be useful in mating season when there are two imperatives: 1) to find a mate of the same species in an environment containing other firefly species, and 2) to minimize the possibility of being identified by a predator. All this is necessary because according to one recent source, there are over 2600 species in the world, with more still being discovered. The need is to communicate against a very noisy background.
Image: Can the study of non-human communication help us design new SETI strategies? In this image, taken in the Great Smoky Mountains National Park, we see the flash pattern of Photinus carolinus, a sequence of five to eight distinct flashes, followed by an eight-second pause of darkness, before the cycle repeats. Initially, the flashing may appear random, but as more males join in, their rhythms align, creating a breathtaking display of pulsating light throughout the forest. Credit: National Park Service.
Fireflies use a form of signaling, one that is a recognized field of study within entomology, well analyzed and considered as a mode of communications between insects that enhances species reproduction as well as security. The evolution of these firefly flash sequences has been simulated over multiple generations. If fireflies can communicate against their local background using optical flashes, how would that communication be altered with an astrophysical background, and what can this tell us about structure and detectability?
Inspired by the example of the firefly, what Brooks and Walker are asking is whether we can identify structural properties within such signals without recourse to semantic content, mathematical symbols or other helpfully human triggers for comprehension. In the realm of optical SETI, for example, how much would an optical signal have to contrast with the background stars in its direction so that it becomes distinguishable as artificial?
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