[MUSIC PLAYING] This episode is supported
by the Great Courses Plus. Space is big, maybe even too
big to be easily colonized by real, living aliens. But what about
almost-living machines? I mean spacecraft capable
of replicating themselves and exponentially spreading
across the galaxy. I'm talking about
Von Neumann probes. Our galaxy is depressingly
natural looking. Stars for the most part
act very star-like, their brightnesses
and colors slavishly following the equations
of stellar physics. Space stuff gravitates
around in slow, stately arcs that would make Newton proud. Even the unusual
denizens of the galaxy like pulsars and black
holes just do what they do. And Nature rules the sky. No one seems to be messing
around with stuff up there. As far as we've seen, humanity
is the only species ever to build anything
bigger than a beaver dam in the entire galaxy. And yet the Milky Way has
been around for long enough that any previous civilizations
with any inclination to expansion or
exploration should have been able to cross, even
colonize the entire galaxy. So we get back to the
famous Fermi Paradox. Some suggest that the
resolution to this paradox is that advanced
civilizations never make it to an interstellar
state, perhaps self-destructing before
building the great generation ships needed to seed
new star systems. Others suggest that interstellar
travel is just too hard, and that any sufficiently
advanced civilization will find better things to do with
its eternity, like turn inwards into complex virtual worlds. Today I want to argue that
even if these points are true, there are reasons to expect
a galaxy full of the evidence of past technological life. Why? Because of Von Neumann probes. Von what the? Self-replicating
robotic spacecraft-- that's right, completely
unmanned or unkerbled vessels capable of traveling
between star systems, and capable of extracting
resources at their destinations to build copies of themselves
to continue exploration of the galaxy. Well, that sure sounds
science fiction-y. However it's an idea
that a number of people who should know better
have taken and are taking quite seriously-- not
necessarily as something we should do, but as something
that someone, somewhere, surely would have done. We touched on the idea of
self-replicating machines recently when we talked
about the Dyson Swarm. It's time to generalize. Because these may be the
future of space development. Imagine-- a single
machine that can build a huge variety of other
machines, including itself. Not so hard to
conceive these days. Very soon, we'll
have 3-D printers that will be able to print
most of their own parts. But even in the late
'40s, John Von Neumann, Hungarian mathematician,
physicist, inventor, and general co-founder of the
modern technological world, laid down a
theoretical framework for a self-replicating
automaton. He called it a
"universal assembler." These days, we call it
a Von Neumann Machine. A number of luminaries
have proposed uses for such a device. Edward Moore conceived of
desert or ocean-dwelling self-replicators
whose only purpose was to build copies of
themselves, which humans would then harvest for parts. Freeman Dyson imagined several
types of Von Neumann machine, including a Martian terraformer
and the Astro-chicken. This is a tiny
spacecraft that will be powered by a solar
sail-fed ion drive that could harvest planetary resources
to build more of itself-- a self-replicating spacecraft,
a Von Neumann probe-- albeit one only capable of
exploring this Solar System. But with modern advances in
zero-g 3-D printing, material science, nanofabrication,
and automation software that verges on AI, we can
now realistically project much further into the future. We can imagine a Von
Neumann Machine much smaller than the infrastructure
it is able to build. This suddenly makes it
reasonable to use such machines for some pretty cosmic
scale endeavors. Let me outline how such
a device could populate the galaxy with robotic probes. Other applications,
like asteroid mining, Dyson swarm construction,
and terraforming-- really any large-scale automatable
space operation-- might be best handled with
self-replicating machines. This outline is inspired
by Robert Freitas' vision for a self-replicating
version of the Daedalus spacecraft. Although with modern
advances, it's now possible to be
even more ambitious. So a spacecraft is
launched from the home Solar System with an
engine capable of taking it to 10% or 20% lightspeed. Fusion engines might
be a good candidate, because the fuel is
abundant everywhere. The vessel contains a universal
assembler and minimal mining and/or processing machinery. After several decades,
it decelerates into a neighboring star
system, and parks in orbit, or lands on a nice, big
asteroid or gas giant moon. It deploys initial solar
panels and mining bots, and uses these resources
to build a factory. That factory includes
larger solar power plant, a strip-mining operation,
and perhaps more assemblers. It builds fuel
collectors-- maybe orbiters to harvest
deuterium or tritium from gas giant atmospheres. And it launches probes
to actually explore the planetary system, and
stream the data back home, or terraform the system,
or build a Dyson swarm, or annihilate all life--
whatever these aliens are into. At some point, the
assembler starts building new Von Neumann
probes which, one by one, launch to new, more
distant star systems. This whole process
takes a while. Assume an average
10% light speed, 10 light year jumps
for each probe, and up to 500 years
for production of the first daughter
probe at each jump. It might take
several million years to cross the galaxy this way. But the exponential
nature of the process means that the
entire galaxy would be covered in these things
in that amount of time. This brings us back
to the Fermi paradox. I think it's fair to say
that A, Von Neumann probes are possible to build. In fact, I think we could build
one in a few 100 years at most. And B, once a successful
probe is built, the galaxy will be swarming with
them in 10 million years, max. Given B, we should see
replication factories in our own solar system. So we have to conclude that
either no civilizations ever choose to build these
things, or there were very few
technological civilizations 10 million years ago. Both options are
difficult to buy. Let's talk about
numbers before we get into the intricacies
of alien psychology. There are, at a minimum,
tens of billions of terrestrial planets with
liquid water in our galaxy. The Kepler Space
Telescope showed us this. The random events that
led to technological life dominating the Earth could
have happened at least tens, but perhaps hundreds of
millions of years earlier on our own planet. So if complex life
is even remotely common-- say it evolves in one
in 1,000 habitable planets-- and another one in 1,000 of
these evolve technological species, that still
means tens of thousands of planets in our galaxy
get tech at some point. Even if Earth is in the
earliest 10% of these, that's thousands of
civilizations before us, many of which may have had
thousands of generations to do lots of crazy stuff. OK, so alien psychology--
the exclusivity argument, that civilizations will
never do certain things, is fatally flawed. We know very well from
our own recent history that it only takes an
individual, sometimes with questionable motives,
to drive some pretty crazy and large-scale programs. So thousands of generations
of thousands of civilizations, which means potentially
quadrillions of individuals,
and not one of them builds a single
self-replicating spacecraft? Something we could
do pretty soon? No. The only reasonable
conclusion is that those numbers are wrong. They are wildly wrong. There have been so
few civilizations capable of doing this that
it hasn't been done-- yet. This doesn't mean that there are
no advanced civilizations out there. It just means that
they are probably few and far between-- few enough
that the numbers game doesn't guarantee that one will
commit this single, relatively easy act-- building
one Von Neumann probe. So how are we here if
technological life is so rare? Well, sort of luck,
but not really. Perhaps a variation of
the Anthropic Principle needs to be invoked. In any universe that
produces intelligence, someone, somewhere, at
some point has to ask, why are we alone? Perhaps that's us, preparing
to explore the young and still untamed reaches
of this space-time. Thanks to the Great Courses Plus
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in the description, or going to thegreatcoursesp
lus.com/spacetime. In a recent episode, we asked
whether it's even possible, or a good idea, to build
a Dyson swarm to capture all of our sun's energy. You guys had a lot
of good questions. Paul Baba asks whether
such a Dyson swarm would cause the Earth to freeze. Well, a full Dyson swarm
interior to Earth's orbit would, indeed, block sunlight
and freeze our planet. There's no way to make a
consistent hole in the swarm if you have full
spherical coverage. However, it is
conceivable that you could cause the solar
collectors to fill up as they transited the sun,
leaving a gap for sunlight. A couple of you pointed out
that the Dyson swarm proposal is both ridiculous
and nowhere near close to being logistically
possible yet. And for that reason, we
shouldn't even talk about it. Look-- if we only ever
talked about things that are immediately doable
and not slightly ridiculous, then we wouldn't have
Segways, or sporks, or Joss Whedon's "Firefly." Cobra60six would
maybe like us to talk about more doable energy
solutions like thorium power stations. Yeah, good point. Dyson swarms will not solve
the current energy crisis. But there are several solutions,
and safer nuclear power-- maybe thorium-- could be an answer. But even solar power
stations at Earth's surface will soon be a viable solution
for most of our current energy needs. The issue is, of
course, political. Mr. Mercury is a
little uncomfortable with building a power source
that has the potential to destroy our solar system. Nice try, Mercury. I'm afraid you have
outlived your usefulness. Shawn Tripp imagines
how cool would be if we started
exploring the Kuiper Belt, only to find out that it is the
remnants of an ancient Dyson sphere. Huh. Hey, Joss-- hey, yeah,
I got this idea for you. Yeah, I came up with it myself. [MUSIC PLAYING]
You just found me an interesting channel to watch , thanks ! :D
Thanks for sharing. Very informative.
Yep. That is my guess as well.
Origin of sentinels ta
I always thought the sentinels attacked us for mining materials (or animals) because they wanted the materials for replicating themselves. "MINE!"
tl;dr? (tl;dw rather? lol)