The Search for Extraterrestrial intelligence as a human endeavor faces two serious challenges
when looking at radio signals from space.
The first is earth, we produce all manner of radio interference that can, and has, been
mistaken for potential alien signals.
That’s, of course, not surprising since they are transmissions from a technological
civilization, us.
The other problem is that space is chocked full of weird radio signals of natural origin.
I often wonder about the latter in a different way other than simply searching for alien
civilizations.
All of those signals that we disregard as of natural origin still could represent some
kind of odd astrophysical phenomenon that, eventually, will need to be studied though
it may well be centuries before we get to that state of hyper-focused radio astronomy.
And, of course, they could also represent lots of other things, such as equipment noise,
but one wonders what natural strangeness lies in the backlog of natural signals detected
by SETI.
Or, if you will, if the weirdest of these signals are not of alien origin, then what
are they?
I’ve covered a lot of these weird signals on this channel that satisfy the criteria
for being an alien signal but don’t repeat.
Some of these are famous, like the Wow!
Signal.
Some of them are more obscure such as a group of signals detected by a SETI search called
META, for Megachannel Extra Terrestrial Assay commencing in 1985.
At the time, META was well known.
It was partly funded by Stephen Spielberg and the Planetary Society and had the weight
of Carl Sagan behind it.
META’s successor programs continued for years until ultimately their radio telescope
collapsed in a storm.
Then the past projects faded from the public consciousness not having accomplished their
goal of detecting an alien signal, though successors to these efforts are still continuing
through the efforts of the Planetary Society.
But what’s not commonly known is that META did in fact detect anomalous signals that
passed all of the criteria of being of potential alien origin except that they didn’t repeat.
And they got quite a few of them, 32 in fact.
In a 1993 paper by Paul Horowitz and Carl Sagan, link in the description below they
detail 5 years of searching with META and the discovery of these candidates searching
near both the hydrogen line at 1420 megahertz, the frequency the Wow!
Signal was at, though Wow!
Is in a class of its own since it was extremely loud, but they also searched around 2840 megahertz.
They found candidates at both frequencies, and while none of these signals repeated,
which is really the gold standard for knowing if you have an alien civilization on your
hands or not, Horowitz and Sagan did notice one interesting thing about the signals as
a whole.
The majority of them originated from within the galactic plane.
Sagan and Horowitz further narrowed this crop of signals down to 11 particularly strong
ones.
Eight of those were on the galactic plane.
That doesn’t really mean much on its face, but if you think about it, if you’re detecting
alien civilizations it’s a fairly good bet that most of them will be on the galactic
plane where most of the stars in the galaxy appear.
But for Sagan, as he notes in his 1994 book Pale Blue Dot, this was suggestive that the
signals really were there and not artifacts of earth interference or equipment glitches.
Sagan advanced that maybe the reason that these signals do not appear to repeat is because
for some reason the interstellar medium itself might make them twinkle, so to speak, and
not be strong enough to be detectable all the time.
This possibility, though interesting, was eliminated in a 2002 paper by Lazio, Tarter
and Backus, link in the description below, for these candidates.
They simply did not repeat.
And haven’t since.
And that means that they can’t be verified.
Subsequent searches by the successors of META, such as META II, found even more non-repeating
signals.
A paper by F.R.
Colomb and colleagues from 1993 detail ten more such detections while searching the southern
skies.
Arguments could be made that aliens send out signals on very long cadences.
They may assume that other civilizations watch the entire sky on a constant basis for very
long periods of time, which is plausible for civilizations more advanced than us.
That could mean that signals like the Wow!
Signal or METI’s candidates do repeat, they just do it on a timeframe of years or centuries.
Since we don’t look at them constantly, we may be missing the repeats, especially
since the signals are of such short duration, Sagan notes that you can look and see a signal,
and then three minutes later it’s gone.
That may seem like an impossibly short time span for a meaningful alien signal to last.
But we don’t know what the rules for civilizations more advanced than our own actually are.
For really advanced equipment that monitors the sky continuously, a few second burst every
few years, or longer, may be all that’s needed.
And that leads to another video in this series that I’ll be making that takes on the question
of just how much information you could encode in a gamma ray burst.
It turns out that it’s quite a lot, but in the end the natural origin question is
left about these and subsequent discarded detections by SETI of signals that pass all
the criteria for artificial except non-repeatability.
Sagan asks it in the book, and it’s still relevant today in an adjusted form.
These days anomalous signals can often be traced to having originated from specific
star systems.
If these bizarrely narrowband signals that we pick up really are there, and can be narrowed
down to specific star systems or objects, and are of natural origin, then what astrophysical
process creates them?
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently worried that we’re
missing alien radio signals, perhaps the first alien signal we detect and decipher angrily
asks the question “why haven’t you called us back?” and be sure to check out my books
at your favorite online book retailer and subscribe to my channel for regular, in-depth
explorations into the interesting, weird and unknown aspects of this amazing universe in
which we live.