The purpose of a beacon or lighthouse is to show others the way in the darkness,
literally and metaphorically.
So there's some troubling implications when we regard the vast ocean of the night
and it appears nobody has lit one.
So today's topic is Interstellar Beacons, with a focus on Alien Beacons used to communicate
to new civilizations.
There's many good reasons to build a beacon loud enough to be easily heard at interstellar
distances, but one of those is to say hello to life in distant places.
One of the biggest open questions about our Universe is "where are all the other civilizations?"
In a place so enormously vast and ancient, we ought to detect plenty of other civilizations,
some of which should be vast and ancient and thus easy to spot.
Yet we don't, and we call this apparent contradiction between expecting to find alien
civilizations and their seeming absence, the Fermi Paradox.
I do not want to limit our discussion of Beacons today to only the Fermi Paradox, but it's
a major point so we'll give the paradox a major focus.
The purpose of a telescope is to see far away, that's the literal meaning, while beacon
is the opposite: a sign, signal, portent, or lighthouse, a thing meant to be seen far
away.
In combination, a decent telescope lets one civilization see the beacon of another civilization
much farther off.
However it only lets them do that if both the beacon and the telescope exist, and the
telescope is looking at the beacon.
Now 'see' is a relative term for telescopes these days, as a lot lot of our farthest seeing
ones don't detect visual light at all, but radio, infrared, and other wavelengths of
light not visible to the naked eye.
A lot of time with the Fermi Paradox, we emphasize radio communication because we're looking
for a signal, but as we've discussed before on this topic, that's likely a dead end
path.
The general notion most people are familiar with, and which makes sense on the surface,
is that since we broadcast by radio signals, odds are many other civilizations would too,
and we can listen in and learn about them.
But we are, and have been, all too aware that a signal broadcast on a planet and designed
for transmission to a regular antenna on that planet is practically impossible to hear thousands
of light years away.
We also have to assume anyone elsewhere making a beacon for us to detect knows that too.
Now there's a maximum range you can pick out a signal with a given setup.
Signals weaken with the inverse square of distance.
So if I have a transmitter that outputs a decent 1 megawatt signal as measured 1 meter
from the source, at 2 meters that signal strength will have decreased to only 250 kilowatts.
At 1 kilometer out, that decreases to only 1 Watt and the short hop to the moon at 384
thousand kilometers away, drops that signal to only 7 picowatts, which is tiny, and you
might be forgiven for assuming we could not detect this.
However, even with our current levels of technology, we can actually receive much fainter signals.
The Voyager probes are the farthest human made objects and they're still operating
out at the edge of the solar system.
Signals from them are being received at a power level of a 10 quadrillionths of a Watt,
that's 10 to the power -16 watts.
So while the signal strength is almost unfathomably tiny, we can still acquire the signal, so
don't underestimate the sensitivity we can achieve with a radio receiver.
I'd originally planned to examine megatelescopes and beacons in a single episode.
It soon became obvious, though, that was too much material to fit into one episode so we'll
visit it in a separate instalment in a couple of weeks.
These concepts are very related though.
We have lots of reasons to build enormous telescopes, but one is to hunt for life in
distant places.
As we'll see in Megatelescopes, we can also hugely boost our reception sensitivity.
Irrespective of the sensitivity of whatever massive telescopes we build, there is a hard
limit to what we can measure beyond what is called the Cosmological Event Horizon, many
billions of light years away.
The light and signals from those places will never reach us as space is expanding between
distant galaxies and the Cosmological Event Horizon is where that expansion rate reaches
the speed of light itself.
It's even a little closer than the Cosmological Event Horizon, because if you are looking
at some place where the light traveled 10 billion years to reach us, there's no realistic
chance for anyone to have existed back when those photons left and that's down to the
nature of the early universe.
Detection has another problem, though, because noise rises with distance too, as more things
can disrupt the signal or overlap it, but you can simply keep making your receiver bigger
and your computers scrubbing for noise bigger.
If you want to pick up a regular terrestrial signal a million light years away you'd
best be getting ready to build telescopes and attached computers that are ridiculously
huge even by the standards of this channel.
However, that isn't a concern if you're listening for an interstellar beacon, which
was the low-hanging fruit we hoped to find, not their terrestrial radio.
Keep in mind we confused the original pulsars we discovered with radio signals.
There was serious speculation they might be alien, and the nearest is nearly 300 light
years away, whereas the current furthest is 50 million.
I'm not sure how the notion got started that there was a hard limit on radio signal
distance but rather than going through the math and physics of that, I'll just point
out we use radio telescopes to get pictures of our universe well beyond a thousand light
years out.
If you can see a place well enough to make out patterns and details there is a capacity
to have sent a message by manipulating those.
On this channel we're no strangers to discussing stellar engineering or moving whole solar
systems if we need to, and while it might sound over the top to create an ultra-long
distance beacon by moving pulsars around to form a pattern, it is possible.
Picking up a star and picking up a terrestrial signal are two very different animals.
One is an immense natural phenomenon, and the other is artificial and designed to carry
as much data as possible.
Raw digital signals have a structure or pattern if you will, a noticeable, non-random sequence.
But compression schemes take advantage of that non-randomness to reduce the signal length
or pack in more data.
The compressed signal ends up looking much more random, what we often call pseudo-random,
which is difficult to distinguish from noise and susceptible to noise.
Compression also creates the additional puzzle of figuring out an alien compression protocol
so we can reverse it.
And this all assumes they aren't attempting to conceal or encrypt those transmissions.
So even detecting that there's actually a signal can be rather hard, even before we
get into deciphering and translating it.
However, keep in mind you need not crack a transmission to know there is one.
Someone might not be able to watch digital broadcast TV from Earth, but they can see
a spike in those wavelengths that doesn't match what they'd expect from natural sources.
As we discussed back in Cryptic Aliens, such a planet gives tons of clues off, like spikes
based on location and time of day.
This is the big difference between a beacon and data transmitter though, the data transmitter
sends specific information as fast as practical to a receiver looking for a signal in its
broadcast range.
The beacon is sending above all else only one message "Look at me", same as a lighthouse
or collision beacon on a tall tower.
You can then send something more complex on another frequency, say half or double your
beacon frequency, or maybe Pi times the beacon frequency if you're sending Pi, or pause
between repetitions to emit chunks of other messages.
We could send something more complex paragraph by paragraph, repeating once a day, but with
Pi between each paragraph or 128 characters.
Since the point is to talk to intelligent life, you can assume basic deductive reasoning
on their part.
Since the whole point of an interstellar beacon is to be discovered at interstellar distances,
you can expect those to be on the frequencies that come through best or which you'd expect
people to be watching.
The chief example of that is the Hydrogen Line at 1.4 GHz.
Except for that sharp hydrogen line, the spectrum band around that is fairly quiet, but much
of the Universe is made of hydrogen so our telescopes study that frequency a lot.
It's a safe bet any other young new civilization would too.
It's not enough to use the frequency people will look at but also to send something they
will easily recognize as artificial, again like the first 256 digits of Pi in binary
or prime numbers or perfect squares.
This is the key conceptual difference between a beacon and a regular signal, and why it
also circumvents common objections to us being able to find them.
We can make good educated guesses as to what kind of beacon they would expect aliens to
notice, but we do not understand what they might use for mundane communication among
themselves.
They might use something besides radio signals, which could include faster than light forms
of communication, like micro-wormholes that circumvent normal space entirely.
We would not send internet traffic to Mars from Earth by omnidirectional broadcast or
even a dish, we'd use a laser.
Those spread out over distance too but you can use a much weaker and concentrated signal
that way.
An alien civilization might use point-to-point beamed communication, beam cast rather than
broadcast, for the same reasons.
Which is another thing, we don't broadcast that loud.
We've worked hard at making better receivers for weaker transmitters since the dawn of
radio to save energy, something we still work hard at, so you'd expect signals to get
weaker as a civilization advanced.
You wouldn't expect any of that to apply to a beacon though, especially one meant for
alien civilizations.
Now, that's not the only reason to build a beacon.
Pulsars, natural radio beacons, can be used as a GPS to pinpoint your position and time
fairly accurately by triangulating several of them but they only offer so much accuracy.
An artificial network, a Galactic GPS if you would, can offer better if you're willing
to build one.
It's the same basic concept, some transmitter yells over and over again "I am transmitter
42, the time is 11:08 AM".
Though in point of fact they mostly don't say the time, they transmit a pseudo-random
code, which would make them harder to recognize if you don't know what they are.
Nonetheless, it's quite likely any civilization that does a lot of interstellar travel has
giant transmitters set up with each bellowing the time, and time lag on communication is
irrelevant in this context since you are specifically trying to tell people the time the transmission
left at, so they can calculate the distance to it, and its siblings, and triangulate their
precise location.
So odds are good the first signal we'd pick up from an alien civilization would be, "I
am transmitter 42, the time is 11:08 AM, I am transmitter 42, the time is 11:08 AM and
4 seconds", and so on.
Another good candidate would be "3.14159" or rather its binary form, "11.00100 10000"
possibly with some strung out explanation of how to build a hyperspace transmitter in
between repetitions.
Motives for sending the latter could vary a lot, and include pure friendly curiosity,
or if humanity is any guide, that message might be "See attached blueprint to make
your planet's own hyperspace communicator, and use Promo Code 'Vega' to get 1000
FREE galactic credits to the iGalaxy app store".
And if Nature is any guide, the beacon might just be repeating "This beacon is in our
territory, stay out, stay away, mine, keep out, trespassers will be disintegrated".
As we discussed in the episode Hidden Aliens, there's lots of reasons to talk to people,
even if you're xenophobic.
Hiding is practically impossible or at least a huge hassle so if you want to be left alone,
it's easier to say "Leave us alone."
We expect that most starfaring species will be curious by nature, or else they wouldn't
have advanced in science and technology.
Curious species are likely to send probes and scouts and send even more if one inexplicably
disappears.
Since controlled aggression is also likely to be a common trait among intelligent civilizations,
it also prevents the likely probability of them sending an armada to say a special hello
in person after you blew up their scouts without provocation.
It's unlikely any species that's curious by nature will consider "accidentally and
unknowingly walked into your territory, which you in no way identified as yours or told
people to stay away from," a legitimate excuse to blow someone up.
As always, we can't know the minds and behaviors of aliens but we can draw probable inferences
from traits we'd expect to be common.
If we see it a lot in nature, and it makes sense why it evolved, or the same for civilizations
as they progressed, then odds are good it's common throughout the Universe if not universal.
Curiosity is one of those, a desire for survival and security should be another.
What kind of beacons a civilization might build all depends on how much energy they
have and how cheap it is.
I'll go ahead and say no civilization will worry much about one-millionth of their energy
being used to maintain a beacon or positioning clock.
I will use a simple real case to create an example.
Now I mentioned the Voyager probe earlier, which is 20 billion kilometers away and transmits
at 20 watts.
That is probably at the outer limits of our present ability to reasonably detect such
a signal, so let's run with that signal strength to detect a beacon.
Extrapolating a 20 watt transmitter on Voyager at 20 billion kilometers, we will detect a
signal at a trillion kilometers out if we use something like the WJR 760 AM 50,000 watt
transmitter across the lake from me in Detroit, which is 2500 times louder than Voyager.
That's a distance of a tenth of a light year.
Ramp it up further by making it 100 times louder, 5 megawatts, and you can pick it up
1 light year away.
This would be louder than any radio tower now in service, our most powerful coming in
at about 2 megawatts.
To make it as easy to hear a thousand light years away would mean jumping up a million
fold on power, up to 5 terawatts.
And to receive it 100,000 light years away, across the galaxy, would mean boosting all
the way up to 50 petawatts, a bit less than a quarter of all the energy hitting our planet,
but almost nothing compared to the output of our Sun.
Now at this point most reasonable folks would say Voyager is hard to detect, not something
you can pick up on your car radio, and nobody will broadcast at 50 petawatts.
However, we said we could reasonably expect a civilization not to mind spending one millionth
of their energy budget on a beacon and for a Kardashev 2 civilization, a Dyson Sphere
or Swarm, 50 petawatts is not a millionth of their power budget, it's about a billionth.
It's the equivalent of the US maintaining a beacon that cost about $20,000 a year to
run.
Such a transmitter could be a statite, basically a glorified solar sail composed of tissue
paper thin mesh several thousand kilometers a side that uses the light pressure and solar
wind to stay in position.
We could set it to transmit an AU above its Sun's north pole for instance; big but thin,
not a hard device to construct in any K2 civilization.
That's not ideal for being heard by 20th century civilizations across the galaxy, but
we could be confident they'd eventually point their telescopes in the right direction
and hear our signal, and you might say that's quite enough.
The signals already take thousands of years to arrive, and an equal time for a return
hello, so you might be fine with using one weak enough it might take them a couple centuries
of radio astronomy before they've got telescopes big enough to see it and continue surveying
long enough to spot it.
But I think not because if you are doing an intentional beacon to newly emerging civilizations
there's a good chance you don't only want to say hello but give some friendly advice
too.
If you're worried about potential new friends blowing themselves up when they figure out
nukes or how to bulk manufacture anti-matter, you want that warning delivered prior to them
having those options.
A century or two on the whole means nothing to you, but that specific century or two when
they first hear it does, so louder is better, something they can't possibly miss.
If they were going for a millionth of their energy budget, that would be, for our sun
specifically, a transmitter blowing away at 400 billion gigawatts.
That's assuming a steady output too rather than pulsing it louder.
And mind you, that's just a Kardashev 2 civilization.
An interstellar empire controlling a bubble of a thousand or so light years around their
home-world could easily spare an entire star to fuel such a beacon.
At this point you are outshining pulsars, and can intentionally mimic them but introduce
an artificial pattern, and be confident someone will notice that.
You don't even have to do radio.
At the K2+ scale where you've enveloped your entire star for power, you can simply
have your mirrors, panels, or radiating fins flicker simultaneous patterns in the visible
or infrared spectrum, or use modified Shkadov Thruster or Star lifting technology to do
the same, turning a whole sun into a literal lighthouse or semaphore.
This you probably would not do though as these are white light sources and you can transmit
much louder on a single frequency with the same total power instead.
The other thing is that on this kind of scale, you need not do an omnidirectional broadcast,
or even in a rotating cone, but could send out narrow beams aimed at every single star
instead, or every one you thought had a non-infinitesimal chance of having technological life.
A narrow spotlight the size of that star's habitable zone, a weaker and modified form
of the Nicoll-Dyson Beam we've discussed using for pushing spaceships up to speed or
blowing up planets.
That's handy too since it gives you something to do with such beams when not pushing spaceships
or blowing up planets.
Okay, so that's the basics of a beacon, let's ask why you'd build one.
Or rather, since there don't appear to be any, why someone might not.
We already mentioned one obvious motive, simple curiosity and a desire to say hello, but that
is a lot of energy to spend for a very long time, and someone is bound to point out they
could run one, say, a tenth as strong for a tenth the price and be confident a new civilization
would find it as they improved their own telescopes and continued their own surveys.
After all, those signals may have to travel many thousands of light years, and thus be
thousands of years old, before anyone hears them, and just as long back to respond.
If you know you can be spotted by a 22nd century civilization with a specific wattage, and
a 21st century civilization for ten times as much power, but that the message will still
take 5000 years to reach you, that extra investment so you can get a hello back in the year 7018
instead of 7118 might seem a bit pointless.
We mentioned another motivation too, the territorial markers.
But the point of a territorial marker is to keep people away from your territory, so the
goal is for them to see it at your border.
Now in spaceship terms this is a little different, because an interstellar ship is committed
to a journey once it finishes its initial acceleration, they can't stop when they cross
your border so you need to warn them well in advance.
Preferably before they leave but at least soon enough so they can find some place you
don't claim or plan to claim to either colonize or refuel at.
However you can also rely on them sending unmanned probes first to do flybys and training
their telescopes on a prospective colony planet before committing to a mission.
So your target broadcast strength for a territorial marker is loud enough they can't miss it
if they are doing common sense preliminary homework, scouting out planets and mapping
the places out.
Whenever you're discussing an alien civilization, you are automatically discussing several of
them, because if there's one near us then there's probably several more inside a sphere
of space not much bigger, and likely some them are ancient and not prone to massive
expansion.
In this context you're entering a diplomatic realm where the notion of 'due diligence'
will apply.
So you can justify your actions to other civilizations even if you don't have to justify them to
your own people, which you probably will.
You and whoever sent such a mission are both playing with blindfolds on so you want to
ensure you've gone far enough they can't have missed your territorial beacon unless
they were being far more negligent than you were.
Regardless, this means your territorial beacons are pretty loud, but not designed to be easily
noticed by casual inspection thousands of light years away by a species that is not
yet advanced enough to even send an interstellar probe, let alone a colony ship.
So we've got two reasons to build one, both of which can be argued to be stuff we'd
miss now.
Ironically, though our half-humorous remark earlier about them sending instructions and
some free credits to access the iGalaxy app store provides a better one.
Everyone who wants to talk to another civilization has some sort of motive to do so.
Maybe you want to be friends, maybe you're warning them off your turf, maybe you want
to sell them stuff, maybe you want them to join your religion or accept your political
or economic ideologies.
No matter how you cut that, time is a factor.
Not just because sooner is better, but because sooner is easier.
It's a lot easier to convince a civilization to be your friends if you phone them with
an awesome new technology to solve their problems rather than waiting till they've discovered
those or accidentally destroyed themselves.
"Here's a device that produces clean, cheap, abundant energy" is a pretty nice
housewarming gift for those entering the galactic neighborhood.
A xenophobic alien race will find it a lot easier to convince a civilization to stay
away from its territory when they are a tiny single planet only dreaming of colonizing
the stars rather than one that's already got fleets out doing so.
It's also a lot easier to convince a commercial civilization to buy your products or subscribe
to your services when its way better than anything they've got and nobody else is
sending them invites.
It's certainly easier to convince folks to join your religion or ideology when you
can present yourselves as vastly older and wiser too, and can answer any regular questions
or doubts before they've even thought of them, let alone locked into an opinion on
them.
Now the problem here is that while that gives you a great motivation to broadcast very loudly,
it might make even more sense to just travel there until we remember the kinds of energies
it takes to move a single large spaceship around the galaxy; they are a lot higher than
what it would take to send a targeted radio beam at one planet for even millions of years.
Similarly sending out a wave of ships to do that to every possible inhabited world is
like an omnidirectional broadcast, and more expensive.
Also, while we can't be sure there are no alien beacons out there yet, we can be pretty
sure no one is doing open contact missions with Earth right now.
A lot of folks think there are little green men running around the planet, but even if
they are right, that would seem to imply a different operational profile and motivation
from an Alien Beacon, as they are at most likely secretly chatting with our governments,
not landing mother ships at the UN and rolling out banners.
So this is a tricky one, because it would seem to make sense to have loud beacons, enough
that we'd expect many civilizations to choose to do so, and as always with the Fermi Paradox,
it's not about why some civilization would not, or even why most would not, but rather
if no one would.
I don't think you can make a strong case that nobody does this, not when there appear
many good reasons to do so, and the only bad reason is worrying that it tells people where
you live, which as we discussed in Hidden Aliens and will look at more in Megatelescopes,
isn't a good reason at all.
On the other hand, there doesn't seem to be a super-strong case for broadcasting so
loud we couldn't possibly miss the signal nowadays.
It's a weak case, especially in the context of all the other Fermi Paradox issues we've
raised in other episodes, but not so weak we can just rule it out entirely.
That there may be beacons but folks tend to limit their strength to a level they figure
no one can detect before they'd be casual spacefarers too.
And so while I'd say it isn't likely, there's still a chance we might find some
beacons in the next couple centuries as our off-planet infrastructure and technology improve.
We can start mass producing the kinds of giant telescopes that might hear another planet's
regular radio and we'll look at those in two weeks in Mega-Telescopes.
However before we discuss that, we'll be looking at the kinds of civilizations that
can afford to produce truly enormous telescopes and many other things we discuss on this channel,
with an expanded examination of Post Scarcity Civilizations.
We'll be covering that for multiple episodes, and trying to look at some problems civilizations
like these might face despite having a seeming abundance of everything.
For alerts when those and other episodes come out, make sure to subscribe to the channel.
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Until next time, thanks for watching, and have a great week!
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