On this channel I often talk about the notion of detecting alien civilizations through SETI
and various efforts like looking for biosignatures.
So far, nothing convincing has come back, and the universe presents only the great silence
with only the occasional unverifiable blip that may suggest otherwise such as the Wow
signal.
But a lot of these kinds of efforts make a certain assumption, that aliens know about
us and wish to contact us or at least study us.
This is actually somewhat of a problem however, in that it may actually be extremely difficult
for them to know that we’re even here.
You see, not only is it harder than you might think to detect our technology, it’s actually
extremely difficult to even detect earth itself from a serious distance.
But that in itself makes a certain assumption.
Can intelligent aliens detect anything outside of their own world?
That’s not guaranteed.
We have always gazed at the heavens throughout our history and wondered what those tiny points
of light in the night sky are.
That question drove us to determine that they were stars, and now science works to gain
a complete understanding of them.
But would we have taken the same inquisitive route if we couldn’t see the stars?
What if the sky overhead at night were merely black, or obscured by an opaque atmosphere,
or permanent day from multiple suns?
Or worse, you live in an ocean permanently locked underneath a wall of ice, as perhaps
is the condition at Europa if there is life there.
Such an alien civilization may be intelligent, perhaps even more than we are, yet never know
or be motivated to ever explore space, or even realize that it’s there.
Pragmatic things like survival may occupy more of their time.
This was the case with us, for tens of thousands of years humans focused on day to day survival.
There was little time left for inventing smart phones 50,000 years ago, rather all time was
dedicated to survival, raising children, and continuing existence, along with time for
things like religion.
But a certain series of inventions, from tools to pottery to agriculture allowed us the time
to think about other things, and from that we built our civilization.
But that’s not guaranteed, if the wrong things happened, or indeed happen now, we
could get reset.
Maybe we are not the norm here and intelligent alien civilizations never have the time to
become a space faring civilization, or they get reset so much that they never become technological,
thus they never reach a stage to even know to look.
To ask a question, you must have a basis to formulate the question you want to answer.
If you never get there, then you never get an answer.
But once a civilization does get there, they enter a different boat.
That of the challenges of astronomy.
Detecting exoplanets is difficult.
Look at human history.
The first hominid that we can actually call Homo Sapiens like ourselves appears about
200,000 years ago.
Certainly they must have looked at the stars like we do and wondered, and that probably
even predates homo sapiens and extends to our progenitors.
Early humans saw the planets as well, and noticed that they moved, and so on, but how
long did it take for us to discover the first exoplanet?
It took until 1992, or approximately the entire 200,000 year history of our species.
And the discovery of exoplanets was a mere trickle since 1992 until we devised instruments
specifically intended to look for exoplanets.
And today, we know of thousands, and not a single one of them is a true twin of earth.
But that may not be a problem of there not being other earths, rather earth analogues
are extremely hard to see with the instruments we currently have.
This is getting better, we may be able to do things like characterize exoplanet atmospheres
now that we have the James Webb Space Telescope coming online.
But what if we hadn’t built it?
What if we didn’t have our global array of huge ground based telescopes?
What if we were just a little less curious, or occupied with other things?
The answer is that we’d not be studying exoplanets at all, which means that alien
civilizations may never find the time or resources to look into exoplanets.
Just because we currently do it, doesn’t guarantee that it would have been done under
other circumstances.
So we build ever larger and more capable telescopes, and aliens may never do that, but if they
do then they face the problem of detection.
Even if they had huge telescopes, much bigger than ours, then they’d need to know to even
look at us.
This is not as easy as it might seem.
First involves a bias.
Our sun is Type G.
But we also know that other types of main sequence stars could harbor life, specifically
the red and orange dwarfs, so maybe they have a bias and only look at those types of stars
for civilizations instead of our cranky and short-lived by comparison Type G sun?
But, then, what if they do realize Type G stars can host civilizations?
Well, to find us, you have to choose our sun to look at.
Best estimates right now is that the sun is one of a population of six billion type G
stars in the Milky Way Galaxy currently.
That’s a whole lot of sun analogues to look through to spot earth.
But say they looked at them all and decided to take a close look at the sun, would they
see earth?
Not without a huge telescope, bigger than anything we currently have, and that’s if
they’re close enough.
Spotting exoplanets is extremely difficult, though they might see earth transit the sun
directly … but only if our planet transits in their line of sight.
Spotting it directly is far less likely and much harder.
Otherwise the only thing they may know about earth is that it’s there through gravitationally
perturbing the sun and making it wobble.
And there is also the question of distance, the further you are from earth, the harder
it is to detect.
So while you might see it if you were close, you might also be halfway across the galaxy
and never know it was there.
It could be too distant to reasonably see.
As an aside though, even if close, they might not see a major feature of our planet.
The moon.
Exomoons are even harder to spot than earth-like planets, meaning that an alien civilization
studying us may never even know that we have a large moon.
But distance also makes us impossible to see as a civilization.
Our technological signals travel at the speed of light, and that means that our signals
can physically only be detected at a distance of currently about 100 light years.
But even then, the earliest signals humans have broadcast were very weak.
The 1936 Berlin Olympics television broadcast that’s popularly cited as the first thing
aliens might receive actually would not have made it out.
And it wasn’t the first television broadcast, and the radio at the time was many, many times
more powerful, as in half a million watts for some stations.
But at light years distant, not much of a chance to pick that up.
What they might pick up, and again this shrinks the radius in which this can currently be
detected, is our more powerful radar from World War II and later.
Even more visible would be things like the former Arecibo radio telescope radaring asteroids,
or sending out the famous arecibo message which would be very detectable …. if aliens
happen to be looking when it passes through.
But all of these are transient.
To pick any of it up aliens would have to be looking right at us at exactly the right
time, and even then if they have SETI protocols like our own, they will discard the detection
because none of them have repeated.
Make no mistake, we may well have detected alien radio signals and discarded them because
a one off detection isn’t enough to prove anything.
So how do they know when to look right at us?
Here, the playing field widens.
It’s earth’s biosphere that may tip them off to keep an eye on this world.
Whereas we’ve only been broadcasting for about a century, earth’s biosphere has been
broadcasting its existence for over two billion years.
Ever since the appearance of photosynthesis, our world has maintained an atmosphere that
is in chemical disequilibrium.
Oxygen occurs naturally without biology, but this much oxygen, currently about 21 percent
of the atmosphere, is pretty difficult to explain without biological processes creating
the pronounced disequilibrium.
Add in other biologically related gases such as methane and phosphine, and you have a growing
case for a biosphere being present at this world that any civilization in the galaxy
that has sufficient instrumentation to detect it, could very well know about this world
if they have surveyed the entire galaxy in detail.
Oddly, as an aside, Earth isn’t the only planet in the solar system that presents an
odd disequilibrium that of late has been getting increasingly difficult to explain.
It’s Venus, and it too shows a small unexplained chemical disequilibrium in its atmosphere,
far less than earth’s but adding another hint that there may be something microbial
going on in the atmosphere of that world.
We need much more data to determine that, but it’s interesting to say the least.
And then we come to another biosignature that could reveal something surprising in principle.
The idea is the vegetative red edge, where earth’s plants become highly reflective
in infrared, almost like mirrors, due to the structure of their cells.
This is something that scientists studying exoplanets will look for in the future, and
it’s something that in principle aliens might know about earth.
But here’s the oddity.
There’s one thing humans have done for far longer than radio that could possibly be detected,
though it’s very unlikely with earth.
But if an alien civilization were practicing very widescale agriculture, like covering
their planet in agricultural fields, it’s possible that signals within the red edge
might indicate widespread harvesting or manipulation of their biosphere by a pre-industrial civilization.
Given that humans have been practicing agriculture for at least ten thousand years, and recent
work suggests far longer than that, then it does seem to be a very long lived technosignature.
That’s if it could actually be gleaned out of any red edge measurements, which may prove
a step too far.
To detect such a thing with earth would require the alien civilization to be very close.
And this comes up against a statistical problem.
Take proxima centauri, the closest star system to the sun, that also has at least two planets
orbiting it.
If one of those planets has a civilization on one that happens to exist right at the
same time we do, then that would imply that there are alien civilizations literally everywhere.
After all, what are the chances that the closest star system to you also has a civilization?
At that point, any habitable star system could have one.
If that were the case, then we should readily see evidence of a plethora of civilizations
and we simply don’t.
Extending the sphere out to about 100 light years, as SETI currently favors, and we still
so far haven’t seen any close aliens.
But that doesn’t mean that there haven’t been close aliens in the past.
The galaxy is a tumultuous place, with stars constantly in motion.
In the 4.6 billion year history of our solar system the sun has passed closeby to countless
other stars, most of which we cannot reconstruct or even know about these long past encounters.
We do however know of more recent ones, and it could be that at some point in the past
the sun passed close to an inhabited system.
If that’s the case, then close alien encounters become more plausible and any civilization
advanced enough to cross a few light-years may have deposited probes in our system and
studied earth in the past, and possibly even continue to do so.
This concept is known as a Benford probe, and presents one of the possible ways an alien
civilization may study earth close up, just by the sheer luck of passing by.
It also opens up the even greater possibility that a passing inhabited star system encountering
us further out might have studied earth with their telescopes, but were too distant to
feasibly visit.
Perhaps they still watch us today.
But say this was happening now, and there is another civilization within, say, 50 light
years.
Here is where we become significantly more visible.
Not just in our radar, but something that can be detected much more distantly.
The signatures of chemicals in our atmosphere such as CFCs that do not easily occur in nature,
if at all.
But there is one final way where aliens actually could easily know about us.
That’s if they have colonized the galaxy in some form or another.
This is the famous idea of self replicating self repairing probes that spread across the
galaxy creating copies of themselves like a virus.
In which case, in a few million years a civilization could have a probe stationed in every star
system in the galaxy.
In this one situation, we would be known about and watched, and indeed all civilizations
in the galaxy would be watched by these probes.
There are two forms of this idea, active and passive probes.
With passive probes, they are simply watchers that allow civilizations to develop on their
own, and they simply observe for the sake of science and learning.
With active ones, they may intervene for some reason and make direct contact.
It may function as a 3d printer, and create subordinate probes to explore the solar system,
and perhaps even dip into earth’s atmosphere.
Imagine if someone saw it.
It’s worth mentioning here as well that there has been one other form of communication
that we’ve tried.
Actual physical evidence of us in the form of our space probes bearing gold records and
plaques.
It’s marginally possible, but extremely highly unlikely that anyone will ever find
those.
They are far beyond needles in haystacks, but rather needles in haybales the size of
Jupiter or more.
Right now some of them weakly transmit towards earth, but in a few years they will run out
of energy and just drift as incredibly tiny flotsam in the interstellar medium and will
almost certainly never be found.
So the solution to the Fermi Paradox here is quite simply that aliens can’t see us,
and don’t until we do something so huge in the far future that we become visble, such
as encasing the sun in a dyson swarm, or build a huge radio beacon.
Maybe no one ever does that, and it could also be that we simply lack the instrumentation
and ability to see the aliens and that the whole detection of other civilizations is
far more difficult than was previously imagined.
So much so, they very well may not know of us.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently concerned about the
first radio broadcast aliens might pick up.
The Berlin olympics were probably too weak, but later transmissions just a few years later
were far more powerful.
So what happens if the aliens pick up Orson Welles’ production of War of the Worlds
and think we’re under attack.
They might show up with battlestars ready for a fight only to find that we cried wolf.
Very disturbing.
And also, anyone that wants to hear me get interviewed for a change should check out
a recent 3 hour conversation I had with Carson Ness, link in the description below 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 liiiiiive.