The galaxy is an immense and mysterious place
we may one day explore and settle, but for now, we have only one planet, and the galaxy holds
many dangers, so what can we do to defend Earth? One of the more fascinating things about
the Moon is all the craters[a] on it, some of which are the size of continents, but when
pondering those it does raise the worrisome issue that Earth has probably been hit just as hard and
often and probably by rocks even bigger than the one we tend to say got the dinosaurs. Indeed, the
Moon’s very existence is thought to be due to some small planet hitting proto-Earth and spewing
out a debris cloud from which the Moon formed. Needless to say, that’s not a survivable
strike, and indeed if we detected anything like that coming our way right now, or an alien
armada or any of a number of other potential astronomic catastrophes, our best strategy would
be to drop to our knees and pray. Should divine intercession not be forthcoming, it leaves you in
an excellent position to kiss your butt goodbye. There’s essentially no defense strategy available
to us if we haven’t got at least months to prepare right now, and against an alien armada or a
full-scale planet careening our way that wouldn’t be enough time either, outside of a Hollywood
movie. Indeed there’s not much you could do without centuries of advancement and forewarning
in those two cases, which you might actually have, and we’ll get to them later, but at the moment
even something a kilometer across would be something we’d need a large lead up time to
deploy against and deflect enough to not hit us. Thankfully, there are two important caveats
here even for those very large asteroids or alien invasion fleets. First, such catastrophic
astronomical natural events are rare enough that the odds of one getting us this next century
or so are pretty minimal, and lower the more severe the incident. We’ll talk about the odds of
asteroids by size and destructive capacity later but for things well below the dinosaur-killing
scale, if we can detect it a couple days out, even now we could mitigate damage, in the sense
human casualties, by calculating the strike location and evacuating that area and bringing in
personnel and resources to handle the aftermath. I doubt you could get everyone out of a major
metropolis in that time but you might be able to get most and from smaller cities, probably nearly
everyone, plus it is unlikely to impact on one. Second, we do have defensive strategies
we can prepare with time and resources, and those work best on the ones more likely to
occur, like a mile-wide asteroid heading our way rather than something like an ejected black hole
headed through our inner solar system. And even against such an overwhelming threat, we do have
options, even if we might need some centuries to be developed enough in space to manage them.
We also do know where most 1-mile wide asteroids near Earth are and none are plausible to hit
in the next century, so that mostly limits it to deep space or interstellar asteroids.
We are going to look through a number of threats today in increasing order of concern and
dwelling on those earlier and milder threats like asteroids, rogue spacecraft, orbital bombardments,
solar flares and coronal mass ejections, but we’ll move onto look at extreme scenarios
including supernovae and gamma ray burst defense, the asteroid being an entire planet instead,
an ejected black hole passing nearby, a von Neumann Swarm of alien or earthly origin,
or perhaps launched from an interstellar colony of ours that lost control of an experiment, or
deployed relativistic kill missiles our way, or even a Nicoll-Dyson Beam, before contemplating
what we do if an alien armada really does show up. The key defense against the milder scenarios
though is the successful development of cislunar space so you can get resources and equipment in
play, and so that you have a detection system that can give you the earliest warning. This is
why Defending Earth is one of the four pillars of the National Space Society along with last week's
topic of Clean Energy from Space, and those two along with Developing Space and Communities in
space were up on one of our audience image polls back in November and won, you voted for them,
and now we’re giving them each their own episode. You’re probably not creating vast power or
detection grids, or defenses to protect Earth, without developing space and creating those
communities up in orbit and connected to support from down here on the ground. Which
is why they are so important to the NSS, and for folks new to the show wondering who this
guy with the weird voice is, I am Isaac Arthur, host of this show, Science & Futurism, for
almost 10 years now, and president of the National Space Society for just over a year now.
I’m a theoretical physicist by training and a veteran of the US Army, and I’ve also had the
honor of guest lecturing at the US Air Force Academy and consulting for the Space Force back
when it was just starting. You have to rattle off the qualifications occasionally so folks assume
there’s a chance you know what you’re talking about rather than spouting crazy nonsense, though
as some folks often note, sanity is an optional trait for scientists and futurists anyway.
And like a lot of you probably also have, I’ve spent a lot of time reading & watching science
fiction and pondering the threats presented in those and saying “Well if they’d just done X
instead…” or “Hey, that’s not how physics works!” I’ve consulted on a lot of science fiction
over the years, usually where the author or game developer wants to see if something is very
realistic, and while I always encourage that, it comes attached with the advice that you should
never let reality get in the way of a good story. I’m very fortunate to have a lot of friends
and colleagues who’ve also spent a lot of time seriously thinking and writing on these topics
that I can draw from. Also, I tend to take the reverse approach of what I recommend to sci-fi
authors by trying to figure out how to deal with over the top projects and threats, I figure out
what we want to do and then to see if reality permits it, even if only by extreme measures that
seem unbelievable to us now. Otherwise you can get lost in conventional wisdom and stuff everybody
knows, or everybody knows isn’t possible. And that’s a good place to segue into Asteroids,
because every so often I’ll hear someone saying you wouldn’t want to blow one up with a
big nuke or that wouldn’t work. And the answer is implied by one of our show’s favorite
mottos, “If Brute Force isn’t working, you just aren’t using enough of it”, which was also the
unofficial motto of my old artillery regiment. Nukes are a great solution to a lot of problems,
in accordance with the first Rule of Warfare, that there is no such thing as overkill,[b][c]
but they often are not going to be your easiest or best approach. You can’t just launch an ICBM
up into space, they don’t carry enough fuel to get into orbit let alone away from Earth. Nor
can we just slap an ICBM into a big rocket, get it into orbit then launch it from there at
an asteroid. Now the Department of Energy is responsible for our nuclear stockpile and I’m
glad to say they take planetary defense quite seriously, but our detection window is still small
and our ability to respond is very limited. We need a lot more development up there to pull off
the delivery of a nuke to a large asteroid far enough away to matter, and that same development
does offer some other solutions. On the plus side, Lawrence Livermore National Laboratory did some
modeling on nukes against asteroids recently and was pretty optimistic about their potential too.
I want to talk about some of the other approaches we’ll use on an asteroid, but I also want
to ask about what sort of infrastructure, capabilities, and development we need to pull
these off. Last week we spent a lot of time talking about power satellites and beaming
technology, for instance, to provide Earth with clean energy, and such platforms offer
us a couple ways to engage asteroids too. Now asteroids are going to be unlike
many of our other threats in that they tend to be pretty visible and give
you a lot of reaction time, compared to a Relativistic Kill Missile for instance,
which might be moving 10,000 times as fast, and perhaps a hundred-millionth the size of an
asteroid carrying the same damage potential. Meaning it needs to be 10,000 times closer
before you’d see it with the same detector and, since it is moving ten thousand times faster, will
give you a hundred-millionth of the reaction time. Asteroids also won’t generally be moving in
a straight line toward us, they’ll be on some elliptical orbital path of their own that happens
to intercept us and we may get decades of advance notice by spotting and calculating that in
a few more of its orbital cycles it’s going to cross our path too closely. It is generally
not hurtling in from deep space and if it were, it would probably have a nice ice shell that began
giving it a comet tail we could spot more easily. Instead your default asteroid is from the
various Near Earth Objects or asteroids, of which there’s many thousands, and after that
one of the many millions hanging around in the asteroid belt or the various loose families of
asteroids elsewhere in the system. Lots of those are the broken remnants of bigger asteroids that
collided with something in the past. And often some collision like that is what pushes them into
an orbit that’s going to eventually hit a planet, since otherwise their mass has been orbiting
the Sun just fine for billions of years and hundreds of millions of orbital cycles.
Of these, the specific characteristics of the asteroid matter, as a metallic one, is different
than one more composed of silicon or carbon, or ices for that matter. But I would say anything
over ten meters across has a non-zero chance of damaging something here on Earth, very non-zero
if it is made out of nickel or iron and is bigger, and even things as small as a millimeter across
can damage some spacecraft, station, or satellite in space. So your detection goal is to begin
by detecting anything threatening Earth, and the bigger the threat the bigger the asteroid, and
easier it is to spot, and gradually you get better at spotting and managing them till you are able
to protect even against small ones that threaten only your orbital infrastructure, not your planet.
By examining craters here, and on the Moon where they are easier to see, as well as the
composition of the asteroid belt, we know about how often bigger ones come, statistically
anyway. And frequency is essentially inverse with mass or inverse with the cube of diameter, as
mass rises with the cube of diameter. So, ten times the diameter, one thousand times the mass
and destructive potential, and we would expect them to show up about a thousandth as often.
We estimate an asteroid one kilometer across tends to hit Earth a couple times per million-year
period. Such an asteroid carries more kinetic energy in it than all the nuclear weapons
we’ve ever built combined but is arguably a smaller threat than them since we can target those
strategically to hit cities while an asteroid or volcano – which is in a similar energy scale – are
statistically unlikely to come down on any city, let alone break up to hit each one of them.
As such it could certainly wreak havoc on civilization but not in a civilization-ending
way, and it is something that has occurred repeatedly while humans have existed,
depending on where we want to place that cutoff in either what qualifies as human or
how big the asteroid needs to be to qualify. But I should note that even one just 10 meters
across is typically carrying as much energy as our earliest nuclear bombs and we typically get
one of these once a decade. These are as going to airburst, which makes them leave multiple
small craters if any, as opposed to a big one, and that further reduces their threat as
the atmosphere is soaking up most of their energy. We would generally expect anything
much under 40 meters across not to leave a single crater, even one made of iron.
This is one reason breaking an asteroid into pieces right before it hits us can be
a good thing, though it can also result in a shotgun blast style effect and one very likely
to set off a Kessler Syndrome Event in orbit, damaging or even ruining our orbital
infrastructure in the process. Which is why it's better to get them sooner.
Right now, if we had maybe a month’s warning, we could potentially get some nukes up into
higher orbit and on an orbital path that would take them near the asteroid as it came
by to be hit by some of that nuclear explosion, maybe even a close proximity strike would break
it apart. Whether or not you want to break an asteroid apart, especially that close, is very
debatable. So is where you should detonate a nuke for maximum effect, though I think the
strongest argument is for a short distance from it to spread the blast over its surface,
similar to when we contemplate using a nuke on the pusher plate of an Orion drive spacecraft.
Where, how, and when are tricky topics though, more modeling and experience is needed,
and depends on a lot of factors specific to the asteroid and intercept scenario.
We discussed the specifics more in our Asteroid Defense episode some years back.
But ultimately, the bigger our warning time, the better we can handle the problem.
That capacity to ensure a warning like that has slowly been growing and is nearly upon us,
and largely because of AI, which can scan a big cluster of data – such as telescope and radar data
– for something tiny like the sunlight or radar scatter off a rock a hundred million miles away,
pick it up a handful of times in a short interval, and automatically calculate its trajectory
to see if it’s in a threatening window, then forward those on to people at a big telescope
they can aim at it. Or a big gun for that matter. And that helps but honestly such a rock still has
a high probability of landing somewhere virtually uninhabited, and 70% chance of hitting the ocean,
and just doesn’t carry enough energy to cause a sweeping tsunami along a coastline. Over a certain
mass range it’s gonna hurt pretty much no matter where it lands, but most asteroids are smaller. In
sci-fi we always encounter one big enough to wreck a city or big enough to wreck a continent, and the
former are a million times more frequent and have way less than a one percent chance of landing
near any city, let alone a major metropolis. If you actually knew where the rock was going
to land and it wasn't catastrophically big, then in most cases you would rather let
it come in than have its blasted remains whacking through your orbital infrastructure.
Unless it’s hitting something heavily populated you just evacuate all your people, pets,
and precious objects from the blast radius and rebuild afterward. But the smaller that
asteroid, the harder it’s going to be to see it and get a precise vector a long time out, and
the more likely it is to have fragmentation during atmospheric entry significantly alters its course.
Does that mean we should ignore this threat? No, though on the scale of thousands of years it’s
really more of a threat to our developed orbital space than a reason to develop that orbital
space to protect Earth from asteroids. Also a nice economic boon too, because an asteroid is
valuable raw materials entering Earth orbital space rather than one we have to mine from
a hundred million miles away. So your real aim is to capture it into a nice stable
orbit and without too much fragmentation. Aside from Nukes, there’s a few other mature
ideas on deflecting asteroids. You can Impact it with something, which we tried with
the Double Asteroid Redirection Test, or DART, a couple years back, and this might be
a series of collisions with multiple spacecraft or projectiles. There’s also the idea you could
paint the object, either dark or light, so that it reflected or absorbed sunlight which might
push it off course as it absorbs that momentum. But the method I tend to prefer is to just focus
an energy beam on the rock or iceball to ablate or vaporize some material off the rock as
a rocket stream that pushes it off course, and that will do, but I’d imagine in the more long
term you would expect a spacecraft to go to one, place a microwave receiver and engine on it,
and let an incoming energy beam power a more controlled thrust that efficiently and predictably
brings the rock into a new orbit of your choosing with little loss or fragmentation.
That’s the sort of exercise a good asteroid mining company will probably excel at
and which I would expect us to have a modestly robust supply of within a century or two, thus
I don’t really worry much about asteroids as a threat to Earth. Fist-sized rocks in orbit,
which are very common, are more of concern and only grow more so as we develop more things
in space, especially large cross-section satellites like solar power satellites. See
our recent episode on clearing space debris for more discussion of managing those though.
As mentioned, another option is to ram one with a high-speed and high-mass spacecraft, though
that’s likely to produce a lot of debris, as we discovered with DART about two years back. Also,
that high speed ramming craft option actually represents a bigger threat to us than those
asteroids and requires a better detection system. A Rogue Spaceship moving at interplanetary speeds
isn’t all that high-energy compared to an asteroid of the same size, it might be moving faster and
carrying an order of magnitude more kinetic energy per kilogram, but it is also mostly hollow. As
such it is easier to detect, pound-for-pound, so-to-speak. Unfortunately, it can also be aiming
itself rather precisely, letting it hit any given space station or space habitat, and it might have
atmospheric re-entry protection so as to allow it to come through intact to hit a major metropolis
right in downtown. It can also unpredictably change course. So it might only have the energy of
a rock 10 meters across but that’s still a small nuclear bomb, and one presumably any person with
access to a shuttle-sized spacecraft could hijack. This means you need monitoring and active defense
measures in place for handling such scenarios and that conveniently handles your smaller and more
frequent asteroids too, as they’re easier to spot, slower, and easier to target with longer
to work with. A bit like aircraft, scale is the biggest factor in damage so you
can escalate your security measures with scale in mind. This is also where regulation matters
earlier-on, as until we have enough assets in space to make such monitoring both necessary and
possible, we can mostly relax in the confidence of knowing that current spacecraft would need the
assistance of flight control to calculate such a suicide run so as to hit their desired target.
When you’re moving several kilometers per second you can’t really be placing yourself in
wherever you please using your mark-one eyeball. But as computers and AI get better
and more compact, and spacecraft more common, one Loonie with some skill or a terrorist cell
with some coordination might be able to pull this off. Or they might be a spacecraft owned by some
rogue state that’s going to have an ‘accident’. The good news is that for detection purposes
we don’t need more advanced science here, we just need more telescopes and detectors
aimed at space or up in space, and better AI and algorithms for helping on it. And this will
come organically in our continuing development of both astronomical and defense assets.
At some point we’ll probably need a formal grid up there. Things like the Space Fence system but
scaled up, and that’s going to be a non-trivial defense budget item and is more ideal for
something like the emerging Space Force as opposed to NASA and its cousin agencies around the world.
I would also tend to assume the US wouldn’t be the only folks working on that, but while we might
see NATO or allied nations developing one used together, I would not expect global participation
on that, and exactly because the bigger threat is manmade objects which a rogue agency might deploy.
Of course a nation state might be the secret backers of such a rogue agency, but they also
might consider full scale orbital bombardment this way rather than some singular strike,
and in a case like this the full-escalation scenario probably involves seeking to cripple
the detection grid and orbital defense grid first. This escalation is likely to come with
some advanced warning. Generally speaking, wars rarely start without advanced warning. When
they do, they tend to either start small, or start barely coordinated, or both. There’s a lot of
logistics involved in a major operation like that and trying to keep any whiff of it from getting
out in advance tends to be nigh-impossible, and comes with a tradeoff between a decent chance
of secrecy at the cost of lots of unprepared or underprepared errors. Need to know operations
tend not to scale well and start forgetting to include important folks in the planning.
You show up for the invasion and half your troops are missing or half asleep and logistics
wasn’t told to move spare fuel into the area. You are also not likely to have all your orbital
detection and defense system in orbit themselves, with a lot inside nicely shielded groundside
bunkers, and anybody who starts enthusiastically blowing orbital infrastructure up is doing
so with the full knowledge that it is an open declaration of war on everybody else with
assets up there, since all that space debris is likely to damage things indiscriminately. See our
orbital bombardment episode for more on the types of weapons those can entail, both near-term
and higher tech, as well as the groundside defense strategies you can employ, which can
also entail mobile and stealthy submarines as opposed to bunkers in the actual ground.
Generally speaking space itself doesn’t allow a lot of options for stealth, beyond the
sheer speed and enormity of things making it hard to spot and react to things in time,
especially as that speed lets them be relatively small objects for their damage potential.
Some things also move a lot faster than even spacecraft and asteroids. Solar Flares
& Coronal Mass Ejections thankfully take some time to develop where we can spot them, and they
are pretty visible, but they move fast. Solar wind in general moves a couple orders of magnitude
faster than orbital spacecraft, and while it isn’t subtle, you can’t defend against that by blowing
up the individual particles, since in this case they are indeed individual particles at the atomic
scale, not millimeters to kilometers across. This is another example of where prediction
and early detection are vital, but here we have options like placing a big solar deflector at
our L1 LaGrange point, much as we discuss using to help protect a possible future Martian atmosphere
in our episode on giving Mars a Magnetosphere. We discussed these more in our January episodes on
Statites & Lagites and Lagrange Point Settlement, but short form, while Earth's Magnetosphere is
huge and powerful, deflection in space is just as easy to achieve with an early and small push as
a late and powerful one, much like with asteroids. Our L1 Lagrange point is four times further from
us than our Moon is and is always between us and the Sun, and is 200 times further from Earth’s
center than Earth’s own surface is, let alone that big spinning ball of molten metal in
our core. As such, it needs only give a fractionally smaller magnetic nudge to incoming
ionized particles as they approach from the sun to scatter them away from our planet and its
vulnerable infrastructure on Earth and in orbit. Indeed with Lagites we can put it even closer,
and the sort of huge power collector running a massive electromagnet is exactly the sort
of device that works well as a Statite or Lagite. Or perhaps a swarm of such devices at
a smaller scale but operating in tandem. Nor are we contemplating massive objects for this
purpose, merely large but thin solar collectors running fairly simple electromagnets and at power
levels we already generate here on Earth. This, incidentally, would also work against something
like a shockwave coming off the galactic core, though would need to be lined up in that
direction and keeping things between us and other stars is a bit trickier than with our own Sun.
But speaking of giant explosions and other stars, while the danger of Supernovae and Gamma Ray
Bursts to Earth tends to be somewhat exaggerated, it is a possibility. A key point today is that we
are most threatened by other intelligences rather than natural catastrophes. We can hardly
ignore the latter as they’re quite real, but we principally need to prepare ourselves
against man-made, or AI or Alien made attacks, not just natural disasters. However the devices
built to protect against intelligent actors will often work for natural disasters too, and often
more easily. A Supernova scatters an intense blast of radiation and high-energy particles in a wide
omnidirectional blast and thus loses potency with distance. And while they are insanely powerful,
they generally would leave planets behind even in their own solar system, especially gas giants.
Nobody living on their surface or in orbit of them is surviving of course, even stuff
living in ultra-deep underwater trenches, which would be boiling their way off into space
with the blast. But planetary distance is on an order of ten to a hundred thousand times smaller
than distance to the neighboring solar system and because it falls off inverse square, those
energies are falling off on an order of hundreds of millions to billions of times weaker. Such
explosions are visible at the moment they strike, both moving at or near light-speed,
so there’s not much immediate warning. But there’s no supernova candidates close enough
to Earth to cause any serious damage to us at the moment and such stars are always going to be
easily naked-eye visible to us if they’re in range, so they don’t sneak up on you. Here you
could employ a large thin metal shield that was literally hanging between us and that star and
was paper thin, and which you would need to use some fairly coordinated energy beaming and station
keeping to remain at that spot or moving window, probably way out in a Trans-Neptunian orbit or
even further. We can’t determine exactly when a supernova is going to occur down to a precise
moment yet but our observations of supernovae are mostly after-the-fact so we don’t know
if there’s very obvious pre-detonation signs. At a minimum you should get a few hours advance
notice if you have decent neutrino detectors and then you could have some big guns packed with
shells full of folded up shielding that could fire them in that star direction and which
could then pop off and expand to form a cloud of shielding the supernova particle wave would
run into. Indeed you might use a whole ton of big inflatables full of gas to help absorb the
energy and re-emit in less harmful frequencies. It is an awful lot of energy, even a few dozen
light years off a Type 1a supernova might whack Earth with as much radiation as the Sun gives us
over many hours and not in benign wavelengths. But if some shield or cloud absorbs the energy
coming toward Earth and is vaporized by it, that gas is emitting what it absorbs
omnidirectionally now and in low energy photons. Based on the star or stellar remnant in
question you will know how much its blast will produce and can prepare to put the right amount of
matter to absorb the blast in between you and it, but you could easily have several million
joules impact per square meter so this is not a case where your shield is tissue paper thick
the way our statites we discuss normally are, but you don’t need a planet sized
slab of metal meters thick either. For a type II supernova anyway, that’s a big
star exploding and you will be expecting that event and build such detectors and defenses
if you have such a star in threat range or migrating into threat range or age. Centuries of
advance notice are implied there at a minimum. Type Ia supernovae, which is when a white
dwarf absorbs enough matter to detonate, do not give that specific core collapse warning
that big stars when fusing and imploding on their iron core do. However that amount of mass is
fairly precise, the Chandrasekhar limit of 1.4 Solar masses, and we are likely to get even
more accurate with that, and also unlikely to miss any white dwarf in that mass range with
our modern capabilities, especially as it is likely to have a binary partner donating mass.
Same basic defense applies. Gamma Ray Burst are less well understood at this time and also
directional, so they can be dangerous from thousands of light years away, not dozens, and
this is exactly where more knowledge and better observations are vital and the cornerstone
of defense. Knowing is half the battle, or maybe more, and the same sort of defense work.
When it comes to truly large objects like Rogue Planets, that knowledge is even more important
because unlike stars, or even dead stars like white dwarfs, they don’t emit much radiation of
their own for us to detect. Neither do asteroids but distance is a big deal here. The amount
of sunlight bouncing off an object is inverse square to its distance, and the amount of light we
need to see an object by follows this same ratio, so an object ten times further from us and the
Sun is giving off a hundredth the light and only a hundredth of that light reaches us, so its ten
thousand times harder to see. This is why Mercury and Mars are visible to our eyes but Pluto
requires a decent telescope to spot. A rogue planet entering our solar system that’s just
a sixth of light year away, just a few percent of the distance to the nearest star, is 10,000
AU, Astronomical Units, or 10,000 times further from the Sun than Earth is and thus getting a
10-millionth of the sunlight to reflect off itself and a 10-millionth of that is what reaches us so
it’s a not even a trillionth as bright as Mars. Correction: 10,000 squared = 100 Million, not 10 million.
and 100 million squared is 10 quadrillion. Thankfully, it will be emitting light of its
own, from its own internal heat, and that won’t be much and will be in the infrared but will be
significantly more and is in the spectrum we are looking for with infrared exoplanet or rogue
interstellar planet hunts. If we detected it 10,000 AU away, even if it was moving at a hundred
kilometers per second relative to us, we would have about 500 years advance warning. Now the
problem is what you can do with that much warning since it doesn’t have to hit us to seriously
screw up the solar system. Indeed, if it passes between the Earth and the Sun, in that volume, the
damage could be in the form of Earth being heavily and fatally perturbed from its orbit. The odds
of a direct impact are slim but utterly ruinous. Can you defend against that?
Yes, yes we could potentially send a mission there and with the intent of blowing
it off course or into a stable orbit in the outer solar system where it would pose no threat
other than possibly perturbing some comets and asteroids to migrate in-system, which is a much
more manageable situation. See our episode Planet Ships for a full discussion of how to either move
a planet so it doesn’t hit us or to make Earth able to survive such an ejection into deep space
itself or even move Earth out of the course of direct collision. As always, time is your ally,
the longer you have to act, the smaller a push the incoming rock needs to be deflected, and the
more time you have to assemble a stronger push. This can even work on an Ejected Black Hole
more massive than our own sun which might be making its way out of the galaxy and
at a few hundred kilometers per second. Thankfully black holes are not terribly
hard to see in spite of their reputation, especially one winging through the void perturbing
other stars and gathering interstellar gas into its accretion disc. We probably would not
see one well right now, but even within a century or two we should be able to comfortably
spot one even several centuries before arrival. This was the catastrophe premise in the prologue
of our episode Colonizing Alpha Centauri and is to this day the only natural catastrophe I’d say
represents a true threat to humanity’s existence beyond the next century or so, and even then, only
for a few centuries, as it would endanger not just Earth but all our other planets and asteroid
habitats and so on. In that episode we pointed out that the main risk would be it passing by
and causing perturbation to eject Earth or put us in a bad orbit, though it’s worth noting that
planetary orbits are not as stable and eternal as we tend to think and we could get ejected from
our solar system without any external astronomical disruption coming in from deep space. Of course
a black hole has far more mass to cause such a disruption and it could end up devouring our sun
explosively too, though more likely would pass through in a dangerously perturbative way to
orbits and possibly devour something smaller in a vicious blast of gamma radiation.
Now humanity would be in a good position to survive this if we already had a decent
supply of space habitats and asteroid colonies, and getting yourself in the orbital wake of such
a behemoth leaves you in a powerful position as we’ve discussed in other black hole episodes. A
stellar mass black hole is a rare and valuable object we are likely to actively seek out and
colonize around, but trying to save Earth from a close passage of one is a definite uphill fight
and the sort best done by a Kardashev-2 Scale or interstellar civilization with some practice at
stellar engineering and the resources implied, as you will need to be throwing the mass of whole
planets at such an object to move it much off course and it will be blowing that mass out
as ultra-high energy radiation as you do this, which is exactly what makes them so valuable if
you can do this in a controlled and long term fashion, as opposed to trying to starlift your
sun to provide a matter beam to hit it with or chucking planets at it or trying to build a
megastructure around it to create one of the stellar engines we discussed in Fleet of Stars
to make it a big spaceship under your control. This is exactly the sort of tasks self-replicating
machines like von Neumann Probes presumably excel at, along with making paper clips, but we
have to worry about them going crazy or encountering some alien Hegemonizing Swarm.
These don’t have to be dumb but it’s usually assumed they are fairly locust-like and stupid
as you don’t give such things tons of brains unless you’re feeling especially reckless
and suicidal as a species. As such they represent a sort of in-between case straddling
natural catastrophes and intelligent enemies. They are the locust swarm or sledgehammer
hurricane that comes to your planet intent on turning it into more of themselves, or automated
killamajigs, or paperclips or whatever they wander space doing. We tend to assume their exploratory
probes or automated terraforming machines run amok and might be our own coming back to say hello
from an early space settlement effort. Which at least means you have some forewarning and an
instruction manual. See your favorite sci-fi show for handling the variations of these but I
would rate them as considerably more likely to trouble us and in a serious way than any of the
natural disasters we’ve discussed to this point. Your biggest ally here is that you do have brains
and you can even consider defenses like releasing other self-replicating machines that specializes
in killing these other ones or hijacking them, like immune systems or viruses do.
As I’ve mentioned on other occasions, while I don’t expect to find any intelligent
aliens in this galaxy or their left over toys or mistakes, if there had been other intelligent
civilizations out there that made it to space, I would have expect the reason for their
absence and our continued existence to be because a lot of these sorts of devices and
counter-agents had gotten deployed and left whole ecosystems of dumb machines and gray
goo infesting regions of the galaxy. See our Aliens vs AI episode and its discussion of
the aliens known as the Recluse and their crazy sector of space for more contemplation
of that. But in the end, brains beat muscle, especially when those brains can make machines
that can make more of themselves to give you more muscle at your disposal, because brains are
even better when armed with a giant space gun. Once you start putting brains and malice into
play, things get worse of course, and we have to consider not just aliens but intelligent
AI and options like angry interstellar space settlements of renegades or mutants deciding
they want to wipe us out. This is where RKMs, Relativistic Kill Missiles and Nicoll Dyson
Beams come into play, and the former are small and discrete hunks of metal with a little
bit of detection and guidance on them, moving at near light speed, while the latter is
basically a star converted into a giant laser. See our orbital defense platforms episode for a
full discussion of how to protect against these sorts of attack along with fleets and armadas,
but it tends to be like a lot of warfare, if your enemy is building it, you do too, and
you use smaller forms for protection and threats of mutually assured destruction. Diplomacy is
generally in play once other intelligence is involved too, albeit it might be very limited and
confined to nothing but threats of mutual murder. But if someone is throwing dumb matter at you at
super-high speeds, you defend by being ready to detect that far out and throw something dumb in
its path to destroy both. And you build response systems the enemy knows exist so that they know
if they attack your homeworld with some doomsday devices, some doomsday devices you’ve got on
alert in deep space or at another star system will launch on them, and you make sure you’ve
got lots of scattered colonies who can survive you or accept refugees, or get you some vengeance.
Of course, they may be the ones attacking you too, and that brings us to our final threats
for discussion today, a giant alien armada, because this is both more and less survivable than
it might at first seem. As we’ve discussed in our alien civilization series, there’s not much motive
to conquer Earth unless you subscribe to the idea that all the resources in the Universe must be
yours or that all other intelligence must be wiped out, in which case its very statistically
unlikely that in a galaxy billions of years older than our own planet such a species would just
happen to have never evolved until maybe the last million or so years and just now be reaching us.
They do not and never needed any signal from us to alert them we existed, because Earth is very
visible, and the galaxy is not a dark forest to them, because they either chopped it all down
for lumber or set the whole thing on fire to help them see and kill their prey. That means that odds
are if there are aliens nearby us who could send armadas, they are numerous in kind and type, with
many of them not being motivated to consume all or exterminate all. Thus anyone trying to do that
doesn’t just have us to worry about, which would be no worry at all right now, they would trash
us completely if they showed up tomorrow, but all those other neighbors, be they other aliens
or disparate colonies, and their own internal factions and feuds too, act as a check on them.
Again, see our Alien Civilization and Fermi Paradox series for more discussion of those sorts
of scenarios, Earth might get destroyed for some seemingly weird reasons by aliens like uploading
our minds to a virtual sub-verse or sending the Vogons in to demolish Earth to make way for
a hyperspace bypass. At the moment at least, they seem to either not exist anywhere
near us or not be interested in conquering, absorbing, or obliterating us.
Ultimately, I wouldn’t want us to rely on that good fortune of having friendly and
non-expansionist neighbors. The best way to defend Earth is to develop space and technologies to
help us detect threats earlier and prepare robust measures. And the best way to defend humanity is
to explore and develop space and make sure not all of humanity is located on this one beautiful,
precious, but terribly vulnerable, Pale Blue Dot. Odds are if you’re watching this show you’re
a big fan of science, and probably like me enjoy scifi too, be it books, TV, video games, or
good old tabletop RPGs. I’ve been rolling dice, making characters, running games, and building
settings for almost thirty years now and as you’d probably guess, I tend to be noted
for the depth of worldbuilding I tend to do, and if you’re running a tabletop, or writing a
novel or designing a game, the audience always appreciates those extra touches that help with
immersion and adding depth to the setting. That’s where World Anvil can be an amazing tool
for organizing your campaigns or stories, and also for helping craft content and share it. World
Anvil, the award-winning Worldbuilding Toolset is an amazing suite of software for gaming and
worldbuilding that lets you use all the awesome modern computerized options while still enjoying
the versatility of pencil and paper gaming, or fantasy and sci fi novel writing for that matter.
Create customized articles and entries, interactive maps, wiki-style presentations,
character chronicles, event timelines, genealogies of characters, and many other awesome
features to help you craft your world. World Anvil is also amazing for helping you run your game,
with a Digital GM screen & campaign manager with support for over 45 tabletop RPG systems,
including a robust library of character sheets and stat blocks. Not to mention wonderful
tutorial videos exploring features to make it easy for you and your players to use, and
giving great worldbuilding and storycrafting ideas to help you on your Hero’s journey.
World Anvil has all the tools you need, to try it out, just click the link in this episode’s
description and start forging new worlds, today! So as I mentioned this episode is one the
foundational topics of the National Space Society, as is last week's episode on Clean Energy
from Space, and I wanted to thank John Dagle, Dale Skran, and Rod Pyle from the NSS for lending
their expertise to writing these episodes. Every year we host the International Space Development
Conference, where experts in the field, be they from NASA to commercial space leaders
like Elon Musk and Jeff Bezos have given talks, and where you can meet with astronauts and
best-selling sci-fi authors. This year’s conference is in Los Angeles at the Sheraton
Gateway, May 23rd to 26th, and will be hosted by Melissa Navia, helmsman Ortegas from Star
Trek Strange New Worlds. We also give out awards and two folks coming by to receive them
this year will be my good friend Brian McManus, from the amazing show Real Engineering, and
the legendary William Shatner. Come join us as we boldly explore strange new worlds.
Speaking of scifi, this weekend it will be time again for Sci Fi Sunday here on
SFIA, where we’ll be looking at the idea of Stargates and parallel devices for bridging
between worlds and ask if there’s any theories bridging between science and scifi there. Then
we’ll take a look at a different type of tunnel, the immense lava tubes on the Moon, and what life
in those might be like for lunar settlers. Then we’ll finish out the month with a pair of episodes
looking at colonizing white dwarf star systems, bringing new life to those dead stars,
and binary star systems, and their unique challenges with habitable zones and stability.
If you’d like to get alerts when those and other episodes come out, make sure to hit the like,
subscribe, and notification buttons. You can also help support the show on Patreon, and if
you’d like to donate or help in other ways, you can see those options by visiting
our website, IsaacArthur.net. You can also catch all of SFIA’s episodes early
and ad free on our streaming service, Nebula, along with hours of bonus content like
Galactic Beacons, at go.nebula.tv/isaacarthur. As always, thanks for watching,
and have a Great Week!
