One of the most persistent questions within SETI is the notion of whether aliens might
use communications systems other than radio that we either are only just now able to detect,
or still outright aren’t even aware of.
Does radio at some point become obsolete, or alternatively does it follow our current
trend of getting quieter as we advance further.
This is problematic however, in that there really doesn’t seem to be anything better
than radio for certain tasks, such as radar mapping asteroids.
You don’t need to spend hundreds of millions of dollars in resources to do some novel form
of mapping, when a simple, energy cheap radio pulse will do.
Or if you will, if you want to melt a candle, you can do it by tossing it in a campfire
but you could also do it with a hydrogen bomb.
But there may be other ways of communicating that could be cheap, in principle, and we
just don’t know how to harness them yet.
This ranges from questions about spooky action at a distance, where instantaneous connection
of some sort seems to happen between entangled particles, but that we can currently think
of no way to send useful information using the effect.
This is in itself strange.
The universe seems to have governors on it that prevent certain things from happening.
There are quite a few of these in physics, why does time move forward instead of backward,
why do a number of parameters have to be just so in order for matter to exist and so on.
But here the big prohibition is faster than light communications.
The universe does not like this, and you could characterize the speed of light as not only
that, but also the speed of time, and ultimately the fastest speed at which propagation of
information can occur within the universe.
Without it, paradoxes form, but if you remove that keyword, information, from the equation,
the speed of light rule steps aside and spooky action at a distance can happen because no
useful information is being transferred.
The universe’s overall strangeness aside, ever since the 2017 Nobel prize winning confirmation
of the existence of gravitational waves there have been suggestions that gravitational waves
might be the preferred way for aliens to communicate over long distances.
We have since detected many natural gravitational waves sources with detectors like LIGO that
open up the possibility for SETI to search gravitational waves for signs of alien communication.
There’s an interesting aspect here, using gravitational waves over radio might serve
as a communications filter.
Small scale up and coming less than Kardashev type I civilization such as ourselves may
use radio, and at our level of technological development we may not be that interesting
to talk to by a galaxy spanning Kardashev type III civilization.
Firstly though, it must be noted that now that we have something around 100 detections
of gravitational waves, they’ve all been from predicted sources.
Black hole and neutron star mergers.
We haven’t yet seen anything unexplained.
There is not yet a wow!
Signal in the field of gravitational waves.
But there’s also the question of sensitivity.
Our gravitational wave detectors are not that sensitive yet, and indeed they’re relative
newcomers to the game and future instrumentation will likely be more precise.
As a result, the signals that might come from aliens are still lost in the noise so to speak.
This works the same way in radio astronomy, many natural radio signals, and indeed the
first ones we picked up in the early days of radio were very powerful.
Those huge natural signals were the low hanging fruit.
But as our radio telescopes got better and more sensitive, we now see a much more nuanced,
detailed view of the radio sky.
We still don’t unambiguously see aliens, but we do see all manner of interesting natural
signals, some very weak.
No doubt this will be the case for gravitational waves, but there is a problem here, there
really isn’t an easy way to create them without titanic engineering projects.
Some serious energy is needed here.
In a paper by Marek Abrahmowicz and colleagues, link to all papers in the description below.
They detail that there is a kind of sign post in our galaxy that anyone doing astronomy
is going to know about.
There are a number of these, but this one is dramatic.
It’s Sagittarius A star, the supermassive black hole at the center of the milky way.
Now if it’s not spooky enough that we have a supermassive black hole lurking at the center
of our galaxy silently accredting material, it may also be a natural place for a highly
advanced alien civilization, far more advanced than we are, to move to.
The obvious reason to do this is energy extraction, and for that matter scientific probing of
a supermassive black hole, but what of communication?
This is spooky not for the implications of the paper, but what can be sci fi speculated
about it.
More on that in a minute.
But the idea is that if you really want to use a black hole, you’ll need to build massive
structures around it.
Build a Jupiter’s mass worth of structures, and the motion of that should create a signature
in a gravitational wave signal that might be detectable.
It may even be arranged to be a method of internal communications, so you can communicate
over long periods and distances, but still at the speed of light, with the rest of your
civilization.
There are a few things about this however that need to be addressed.
This really gives you a starting point to look for a supercivilization in the milky
way.
The center of the galaxy is a highly radioactive environment with stars packed closely together.
It’s unlikely that life could ever gain much of a foothold in that environment without
technology, so the center of the galaxy lies outside the standard view of the galactic
habitable zone.
Too harsh for any kind of life we can envision.
Which means that if it is inhabited, someone technological moved there.
Crossing the vast distances of interstellar space to probe into the center of the galaxy
would require a supercivilization.
But once they got there, they would have access to an extremely useful supermassive black
hole and as much raw materials as they could possibly want.
Everything’s concentrated there.
But it’s also a somewhat radio loud area, and not really an area well searched by SETI.
Even still, if you want to look for a supercivilization in the Milky Way, Sagittarius A star would
be a prime candidate.
For our purposes as primitive humans, we’d want to look to see if there’s any weirdness
or anomalies in gravitational waves coming from the vicinity of this supermassive black
hole.
But there’s a problem.
There’s no shortage of lower mass black holes in the galaxy, but there’s really
only one black hole on this level.
That goes for most galaxies actually,
Unique real estate in the galaxy as far as competing alien civilizations is not good.
It means that there lies in our galaxy a potential holy grail that all civilizations within it
are eventually going to want control of.
This is bad.
If the supermassive black hole Sagittarius A star indeed holds properties that would
be of great value to any civilization of sufficient technological prowess, then that’s where
you might look for interstellar wars.
A potential focus for such things.
And given where it’s located, there’s no guarantee that we’d have any method within
radio SETI in which to clearly see such a war.
Wrong area of the galaxy for that.
But it may be preemptive, in that the reason behind any kind of zoo hypothesis scenario
is not the usual things I talk about on this channel in this regard, such as stopping the
development of generalized artificial intelligence or dangerous nanotechnology but rather access
to the supermassive black hole at the center of the galaxy.
So how do we probe just what might be going on at the center of the galaxy?
The best bet may be gravitational waves.
But we don’t really yet have a plan for a really sensitive gravitational wave detector
suited for this purpose.
At least until now.
In a paper by Karan Jani and Avi Loeb the authors advance the idea of a gravitational
wave detector, across the gravitational wave spectrum, that could be implemented by the
new NASA Artemis Launch System.
The idea is that a lunar based gravitational wave observatory could be ideal for looking
at certain frequencies of gravitational waves in an ideal way.
This is interesting, because it’s been known for a long time that in radio astronomy a
radio telescope on the far side of the moon would be extremely useful, especially in SETI
where the moon would block most of earth’s radio interference and get cleaner signals
than the huge interference mess we have now.
This is interesting because it could allow for a detection of a gravitational wave on
the level with an asteroid hitting a planet, like what killed the dinosaurs as opposed
to the enormously gravity loud neutron star mergers we can detect now.
Better resolution at least at certain frequencies.
Though, you’d need to be doing this a lot as an alien civilization for us to see it.
Earth doesn’t get hit by such asteroids very often, but if you’re doing it intentionally
as a kind of orchestrated shooting gallery then that might be a techno signature.
But there is another option.
In a paper by Luke Sellers and colleagues they show that even before getting into future
gravitational wave detectors, it’s possible that LIGO, which already exists, could be
useful in SETI searches.
Here we deal with just how big of a spacecraft an alien civilization wants to accelerate.
We don’t know what aliens do, but if they had a spacecraft the size of Jupiter, we might
actually be able to see such a spacecraft being accelerated.
They term it a RAMAcraft and LIGO might actually see one of Jupiter Mass being accelerated
to a significant fraction of the speed of light.
Searching for and studying gravitational waves are the wave of the future for us now that
we’ve actually detected them, something Albert Einstein once wrote a paper that suggested
that they didn’t exist even though they were a prediction of relativity.
In the future, NASA and ESA are planning a gravitational wave observatory into space
called LISA, or Laser Interferometer Space Antenna.
How this works is that you have three spacecraft widely separated that shoot lasers at each
other and detect minute variations in distance as gravitational waves distort everything
as they move through.
This is how LIGO works but on a smaller scale.
These detectors literally look for distortions in the fabric of spacetime caused by gravitational
waves.
This is where you could detect oddities going on with Sagittarius A star.
And even messages.
And there is an advantage for doing it this way.
At the right frequencies, nothing can block such a message.
Electromagnetic waves can be obscured and blocked by interstellar dust and gas, and
earth’s atmosphere, but not this.
We truly are entering a new phase of SETI, and for those that make the entirely valid
argument that maybe we don’t know how to look for aliens, at least we’re getting
better.
Thanks for listening!
I am futurist and science fiction author John Michael Godier not at all happy with the center
of the galaxy.
We’re out in the backwater just outside some spiral arm, but the real action seems
to be in there.
What if it’s like a club where you have to reach the civilization equivalent of 21
years old to get into, say 21,000 years of high technology, only to find out it’s not
really that great.
Such are the worries of an adolescent technological civilization and be sure to check out my books
at your favorite online book retailer and subscribe to my channels for regular, in-depth
explorations into the interesting, weird and unknown aspects of this amazing universe in
which we live.