Spectrum and SETI


The SETI project has been running for a few decades with a fairly consistent lack of signals from extraterrestrial life.  This has never been explained by any acceptably encompassing argument, with everything from Fermi’s paradox to Pascal’s wager stacked up against it – the latter of course cheekily. The more reasonable arguments have pointed at the distance signals would have to travel, the massive range of spectrum there is to monitor, the massive amount of sky there is to monitor, and the fact that we’ve only been scanning for a couple of decades. This yields us a six-dimensional subspace that we’ve successfully covered, and so far nothing.

(In case you lost count: Three dimensions of physical space, one spectrum dimension, one our-time dimension (i.e., the time we’ve been listening), and one their-time dimension (i.e., the time they’ve been broadcasting). There may be more dimensions of relevance, and the our-time and their-time dimensions do logically collapse onto each other, but for sake of argument I’ll leave it like this for now…)

Let’s assume for a second that extraterrestrial civilizations do exist and that they are avid users of electromagnetic radiation as a communications medium, like we are. As we know, the electromagnetic spectrum is not all equally useful for telecommunications, and some areas of it are better than others. Many areas of spectrum do not propagate well through our atmosphere, and different parcels of spectrum would behave differently in different types of atmosphere. Not only that, but by and large electromagnetic radiation needs to be moderately energetic to manage to propagate through the vacuum of space – low powered transmissions would hardly be noticable.

Now, our galactic neighbors, they being an advanced bunch, would also know this. And by virtue of having an expanding population thanks to similar industrial processes as led to our explosion in population, they have, much as we do, an expanding number of applications and peoples demanding access to spectrum in order to better communicate with one another over the surface of their planet, and perhaps beyond. Alongside this comes a greater awareness of issues such as privacy, communications security, and so on.

Faced with a similar situation ourselves, a rational approach that has been advocated for quite some time would be to make better use of existing technology and phase out technologies that rely on the high-powered spamming of huge chunks of the electromagnetic spectrum with analog messages. Instead, cognitive radios with smart processing capacities, similar to those used in modern WiFi chips, could make use of methods such as underweaving (passing messages under the DC noise level), cooperation gain (passing messages from one node to another) and processing gain (piecing together partially recieved messages with statistical inferrence). All of these technologies, if given large enough chunks of spectrum to reside in, would work to massively increase the available communications space to all of humanity – and similarly for our alien friends.

If we posit that any reasonable civilization would not let more than a century and a half pass between the discovery of methods to use the electromagnetic spectrum (i.e., Tesla and Marconi for us) to the point in time at which they have phased out awful spammy high powered EM communications (the next decade or two for us), then that means that any sensible civilization would more or less disappear off the perceivable spectrum after that time.

When merged with the fact that any reasonable civilization would undoubtedly start using compression algorithms and encryption algorithms as early as 40 years before that, as we have done for a lot of our communications already, this would make any signals contain the information equivalent of gibberish (technically, white or pink noise, depending of the nature of the transmission) to anybody who didn’t know what to expect. In the best case, the fact that it was in fact a signal might be given away by the spike in gain if they still engage in high powered communications.

For astronautical communications, there are multiple options to such a reasonable society. First off, lasers based communications are more secure than spammy wide-angle EM-based communications, and require a lot less power. Even if they aren’t advanced enough to do accurate tracking and pointing over long distances, they could use directional antennas to get their signal to and between space ships. Only if there’s planets, stars and such in the way do you really want to start using EM signals that can bounce around, but presumably any sufficiently advanced technology would have the ability to construct a network of relay stations, either terrestrially or in space.

All of this does not mean that we couldn’t detect them. Some low powered EM radiation from their surface would still possibly penetrate their atmospheres and leak out into space. This radiation, if they use the spectrum efficiently, would seem to us from afar like a minuscule uniform increase in the overall DC offset, possibly with some frequencies filtered out by the atmosphere. There would probably not be anything descernable as a signal, unless we had the good fortune of being able to make out start markers that could work as cribs to detect the beginnings of encrypted or compressed packet switched communications headers. And a lot of that is assuming we know things about the bitrate and so on.

All in all, we’d need a helluvalot more subtlety in our search for extraterrestrial intelligence than our current six-dimensional boundary conditions allow for. Unless we’re only interested in finding early industrial societies of course.

There’s a lot of hidden assumptions in the preceding paragraphs though. First, there’s an assumption of an industrial paradigm like the one we ourselves had. It is not entirely beyond the scope of imagination that a civilization may come up with a theory of information, a theory of mesh networking, and so on before developing the technology to make use of EM spectrum, and that they’d forgo our process of spammy analog communications entirely. It’s also possible that they figure out the next best thing, and surpass us entirely. But any questions of extraterrestrial life for us, having seen none, will always be predicated to some degree on what we know.

The less subtle assumption is that they are themselves not attempting to seek out new life and new civilizations, much like we are – actively engaging in listening for transmissions from far away worlds (and limited by similar six-dimensional boundng boxes as we are) as well as transmitting messages saying “Hello, is anybody out there?”

The question then becomes one of narrowing our scope. We know a lot about the EM field nowadays, we know a lot about how it works and how is best to use it. We also know quite a bit about math and chemistry and astrophysics and what not. We should be able to create a probabilistic model for which segments of the EM field are more likely than others to contain such messages.

We could also start doing more stuff with wide spectrum capture. Instead of tuning in to one frequency and listening really well, we could just capture chunks of spectral noise and start trying to find signs of advanced EM interactions. How do you spot an IPSEC packet from fifty light years away, anyway?

Of course, ideally, projects like SETI would get a lot more funding to cover more space. I’m actually starting to think of it as a more promising venture to expand the search for exoplanets and then focus SETI-style activities on those planets, but whatever we do, we sorely need to eliminate more of the six dimensional space. Economically it seems chaper to be able to eliminate portions of the space than to actually search through them intensively.

Perhaps some smart people have already thought of all of this. Sitting on a plane somewhere over the Atlantic when it came to mind, far away from any meshed communications networks available to public use, I didn’t have the ability to check. If it’s uninteresting or old, I apologise.

But here’s the real kicker for me: We need to be more like them. We’re being stupid and spammy about how we approach the use of the EM spectrum. If more spectrum was used to the amazingly dense degree that the 2.4 GHz band is, humanity would be having a whole of a lot more fun. We could scale up the Internet by lots and still have left over spectrum with which to fiddle around at sending out messages to our neighbors. Seriously folks, let’s get our act together. No more analog spamery. Spectrum to the people!