MATTHEW O'DOWD: This episode is supported by "The Great Courses
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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."
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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.