MATTHEW O'DOWD: This episode is
supported by "The Great Courses plus." The idea of Dyson spheres has
captured our imaginations. Vast mega structures, capable
of harvesting the power output of entire stars, the as
yet inexplicable Kepler Space Telescope observation of
swarms of somethings partially eclipsing a distant star has
led to some rampant speculation. Today we ask, are Dyson
spheres plausible? And are they inevitable? In 1960, astrophysicist
Freeman Dyson proposed that a sufficiently
advanced civilization would have such extreme real
estate and energy requirements that they might build
artificial habitats in the form of vast shells
surrounding their parent star. Such Dyson spheres would
be possible targets for our search for
extraterrestrial intelligence, appearing only as strange
points of infrared lights but otherwise black at
visible wavelengths. We don't really
know how the energy requirements of advanced
civilizations evolve. It may be that their most
natural progression does not require cosmic levels
of consumption. On the other hand,
securing access to an entire star's
energy output officially elevates
a civilization to type 2 on the
Kardashev scale. We're currently type 0. So obviously it would be nice
to unlock the achievement. Let's assume that access to
10 to the power of 26 watts is desirable. Are Dyson spheres the way to go? The plausibility
of a solid sphere the size of a planetary orbit
is not really in question. They are not plausible. The incredible stresses
on a solar structure that size are vastly
greater than could be sustained by any known
or yet imagined material. Even if a super advanced
material with enough strength was discovered, you'd need
impossibly large quantities, much more than there is
non-hydrogen or helium matter in all of the
planets in the solar system. The sphere would
not be habitable, having only a tiny gravitational
pull at its surface, and that would be
towards the sun. And finally, it would
be hopelessly unstable. Any small bump would cause
one side to fall into the sun. Some of these issues
could be dealt with. But in the end, it's
just not an efficient way to start your galactic empire. So do we ditch
Dyson's original idea in our quest to reach type 2? Not so fast. It's not feasible to build
a giant solar sphere. But collecting the entire
output of our home star may still be the smart choice. In fact, we can get around all
of the issues I just described with a simple adjustment. Instead of building
a Dyson sphere, build a Dyson swarm,
individual solar collectors that are only kilometers
or less in diameter and each with its own
independent stable orbit around the sun. Build enough of
these, and you can read the entire sun
in all directions, absorbing its entire
energy output. The crazy thing
about the Dyson swarm is that we could probably
start building one in the not too distant future. In fact, we could get started
on the first collector pretty much right away. The thing that makes it
seem a crazy prospect is the sheer scope. We'd have to disassemble entire
planets for the raw materials alone. But believe it or
not, there is a plan. It was proposed by Stuart
Armstrong, AI expert and futurist. The idea is to cannibalize
the planet Mercury. And that's just to
begin the swarm. Mercury is ideal, because
it has a gigantic solid iron core, comprising over
40% of the planet's mass. Combine that with the
abundant oxygen in its crust, and we can make hematite, a
naturally occurring, highly reflective iron oxide that
has been used for millennia as primitive mirrors. So each of the swarms
collectors would then be a giant polished hematite
mirror, perhaps a kilometer across, but as thin as tinfoil. It would reflect light
into a small solar power plant that would
then beam energy somewhere useful, perhaps
with a laser or a maser. The other nice
thing about Mercury is that its gravity
is low enough that launching mined
raw material into space for construction is
pretty efficient. Building the first collector
would be the slowest. We start with limited
mining, space launch, and orbital construction
facilities, all of it autonomous. Energy supply is the big
limiting factor at the start, so it takes about 10 years
to build the first collector. But once it's complete, we
have orders of magnitude more available power. We use it to power
replicator robots, building new mining and
manufacturing facilities, as well as replicatable
replicators. It's an exponential process. Every new collector
increases the energy available to build
more collectors. Within 70 years, we have
a partial Dyson swarm, and Mercury is nothing
more than a debris field. To fully encompass
the sun, we'd probably need to devour Venus, Mars,
and a good number of asteroids and outer solar
system moons, too, assuming we want to
leave Earth intact. Let's assume that. Sound over the top? It's totally nuts. But it's likely doable. Autonomy in manufacturing,
mining, and transportation are all progressing
exponentially. Engineers are in the
serious planning phases for all sorts of space-based
assembly projects, including 3D printing of
giant telescope mirrors. Real companies are gearing up to
do autonomous asteroid mining, perhaps within a
couple of decades. And all of this is
without considering nano robotics, which could
change the game entirely. Frankly, there's no
obvious deal breaker here. Once complete, the Dyson swarm
would harvest a good fraction of the sun's energy,
so trillions of times the current energy
output of the planet. What we then do with that
energy is another matter. But is the Dyson swarm really
the best path to type 2 status? Would other civilizations
have gone that route, casting very conspicuous
shadows on their home stars for us to detect? The advantage of using sunlight
is that the sun is already making it. However, in terms
of power efficiency, it's not all that great. Only 0.7% of the rest mass
of the ingoing hydrogen fuel at the sun's core
is converted to energy. Also, we need a mega
structure to harvest it, with a raw material
requirement close to that of all the terrestrial
planets in the solar system. Is there a better way? Maybe. What if instead of converting
0.7% of fuel rest mass into energy we could
achieve 100% efficiency? Anti-matter engines do this. But currently it
takes more energy to create the anti-matter
fuel than we get back out. Perhaps we can do better
there, but there are also other options, for example,
black hole engines. Energy can be harvested
from a black hole, either from the Hawking
radiation, from heat generated from infalling material, or
by extracting angular momentum from the black hole's spin. We talked about one
example, the Kugelblitz, in our previous episode on
possible starship engines. The show "Space" also
did a great episode on the Kugelblitz. Tapping the Hawking radiation
from an artificial black hole is appealing,
because once formed, we could perhaps sustain
it from evaporation by feeding it with new matter. This is really 100% efficient
conversion of mass into energy, assuming we can
find a way to pump new matter into the proton-sized
Kugelblitz against the tide of Hawking radiation. And we only need 1
billion Kugelblitzes to equal the sun's output. That's nothing,
compared to the hundreds of quadrillion solar collectors
in a full Dyson swarm. Added benefits. We get to keep Venus and Mars. And also Kugelblitz and other
100% efficient mass converters are indefinitely scalable. The Dyson sphere/swarm
can absorb at most the entire
energy output of the sun. However, there's enough
mass in the solar system to run a type 3
civilization's Kugelblitz swarm for many times the
current age of the universe. Of course, the trick is
making the black holes in the first place. To make an industry
standard, 600 million kilogram Kugelblitz,
it takes something like 10% of the sun's energy
output each second, focused into a single attometer
at a single instant. But wait. That's the power we get from
even a partial Dyson swarm. So there's something to do
with the swarm's energy. Burn through Mercury. Then use that partial
Dyson swarm's energy to build Kugelblitzes, in
orbit, say, around Jupiter. Type 3, here we come. Maybe this is why we
don't see Dyson swarms all through the galaxy. Aliens build partial swarms
to provide the energy to build more efficient
engines, which would be essentially undetectable. Or they try building
their first Kugelblitz, and it goes very, very badly. Either way, Fermi
paradox solved. Admittedly, the fading that
the Kepler Space Telescope observed in Tabby's
star is sort of consistent with a partial swarm. I guess it couldn't
hurt to point some radio telescopes, to look
for power leakage from the Kugelblitz swarm. But no. It's never aliens, unless every
other explanation is exhausted. And we don't go in for
that hokey stuff here on "Space Time." Thanks to "The
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or going to thegreatcoursesp lus.com/spacetime. Hey guys, quick announcement. We'll be taking a break week
next week while I travel and then coming back
the following week with the answer to the
quantum eraser lottery challenge and some
intriguing physics news. Also, I'm planning to
head to Austin for South by Southwest in September, to
do a panel that we're calling "We Are All Scientists." It will be with Joe Hanson,
from "It's OK To Be Smart" and Katie Mack, astrophysicist
and cosmic genius. But first, I want to
ask you guys to head to the South by
Southwest panel picker page, link in the description. You just need to make a quick
account and vote for our panel, please and thank you very much. A couple of weeks ago, we talked
about the mysterious delayed choice quantum eraser. There was some
heated discussion. A few of you pointed out
that an important bit of info was emitted from
the description. Now, we did this because we
wanted to expand on that point through last week's
challenge question. Now that we've done that, we
can talk a bit more about it. The point is that in order
to resolve the photon distributions at
the screen, you need to know which
detector was triggered by every one of those
photon's entangled twins. This is done with
coincidence electronics. If we see exactly
the right time offset between a hit on the screen and
a hit at one of the detectors, that means that those two
photons were an entangled pair. After the experiment is done,
we can pick out off the screen all of the photons that had
twins hitting, say, detector A. Those photons turn out to
show no interference pattern. But the photons
associated with C or D do have an interference pattern. However, there is
no way to figure out which photons correspond
to which detectors until the arrival
times at the screen are compared to the arrival
times at the other detectors. And that information
has to be sent at regular,
slower-than-light speeds. In a way, this is
even more crazy. Those locations are
recorded on the screen, and the interference patterns
are embedded in them. Those interference
patterns hold information about future events. But we can't extract
that information until those future
events have occurred, and we can compare notes between
the screen and detectors. We'll go into all of this in
more detail in the challenge question answer and also
when we come back to quantum entanglement. On a related note,
David Stagg would like to know what the
interference screen looks like before you know what the
data is at detectors A, B, C, and D. Well, the screen just
looks like a blur of photons. You see, it's not just that
the blur of photons connected to detectors A and B are
overlaid with an interference pattern from C and D, no. Even C and D produce
a blur until you compare coincidence data. As I mentioned in the
challenge question, the interference pattern
of C has the opposite phase to that of D. Its peaks line
up with D's valleys and vice versa. It's like adding a
sign in a cosine wave. It adds up to a
flat distribution, and it's only when you look
at the photons connected to C and D separately
that you see the bands. Jose Iturria would like to bring
up the topic of the Berenstain Bears. Good one. I actually got that.
Should we build it?
Yes.
9:25
How likely do you guy think this is?
Yes, and here is the man to do it.
WHAT DO WE WANT?
DYSON SPHERE!
WHEN DO WE WANT IT?
NOW!
But a question on a related note: what could we use to store whatever "excess" energy you generated?
EDIT
Read further. Thanks to the person who said "Kugelblitz black holes are batteries." Yay :D
Yes.
Remind me in 10.000 years.
Cool. I'd like to see Isaac's response to this Fermi Paradox solution.
Like anything, it depends on whether we need the power. You don't really need the full Dyson Swarm to do fast interstellar travel with lasers, although if you're running some enormously big set of computations you could use the power (but getting rid of the waste heat from massive amounts of redirected solar energy would be a nightmare).
I'd prefer you guys invest that time and energy into designing and building my next model Waifu 9000.