
Dyson sphere - lelf
https://en.wikipedia.org/wiki/Dyson_sphere
======
lossolo
I learned what Dyson sphere is as by product of reading this by Bruce
Scheiner, really great read:

" One of the consequences of the second law of thermodynamics is that a
certain amount of energy is necessary to represent information. To record a
single bit by changing the state of a system requires an amount of energy no
less than kT, where T is the absolute temperature of the system and k is the
Boltzman constant. (Stick with me; the physics lesson is almost over.)

Given that k = 1.38×10-16 erg/°Kelvin, and that the ambient temperature of the
universe is 3.2°Kelvin, an ideal computer running at 3.2°K would consume
4.4×10-16 ergs every time it set or cleared a bit. To run a computer any
colder than the cosmic background radiation would require extra energy to run
a heat pump.

Now, the annual energy output of our sun is about 1.21×1041 ergs. This is
enough to power about 2.7×1056 single bit changes on our ideal computer;
enough state changes to put a 187-bit counter through all its values. If we
built a Dyson sphere around the sun and captured all its energy for 32 years,
without any loss, we could power a computer to count up to 2192. Of course, it
wouldn’t have the energy left over to perform any useful calculations with
this counter.

But that’s just one star, and a measly one at that. A typical supernova
releases something like 1051 ergs. (About a hundred times as much energy would
be released in the form of neutrinos, but let them go for now.) If all of this
energy could be channeled into a single orgy of computation, a 219-bit counter
could be cycled through all of its states.

These numbers have nothing to do with the technology of the devices; they are
the maximums that thermodynamics will allow. And they strongly imply that
brute-force attacks against 256-bit keys will be unfeasible until computers
are built from something other than matter and occupy something other than
space."

~~~
zump
Huh. I don't get it. A star powering a 219-bit counter? What?

~~~
rossy
It's about the feasibility of breaking 256-bit encryption keys with a naive
brute force attack. The simplest component of a computer that performs this
attack would be a 256-bit counter that iterates through all possible key
values, however Schneier is saying that according to our current understanding
of physics, even if you built the most efficient computer possible and powered
it with the energy output of a supernova, it would only have enough energy to
iterate through all the values of a 219-bit counter.

~~~
ams6110
On average you only need to iterate half the values.

~~~
AngrySkillzz
Yeah, that's still 255 bits worth.

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jcbeard
Wow, did nobody watch Star Trek TNG? I learned about them when I was about 10
watching the Relics episode
([https://en.wikipedia.org/wiki/Relics_(Star_Trek:_The_Next_Ge...](https://en.wikipedia.org/wiki/Relics_\(Star_Trek:_The_Next_Generation\)),
or amazon prime:
[https://www.amazon.com/Relics/dp/B00R143VHC/ref=sr_1_1?ie=UT...](https://www.amazon.com/Relics/dp/B00R143VHC/ref=sr_1_1?ie=UTF8&qid=1470789546&sr=8-1&keywords=star+trek%2C+tng%2C+relics)).
Very cool concept.

~~~
morganvachon
Yep, that was an awesome episode for what it was, and the novel that served as
a sequel was great as well.

Unfortunately the version of a Dyson sphere depicted in both is completely
untenable, according to Freeman Dyson himself. He reportedly enjoyed the
episode as "a piece of cinema" but denounced the science involved as 100%
fiction and not possible. As others have said, perhaps building something like
that around a dwarf star would be within the realm of possibility, but you
still have issues such as radiation, constant daylight, gravity, and drift
(the sphere would eventually drift into the star since it's not actually
orbiting and is much more massive than even a large planet).

Still, it's a really cool idea and a fun thought experiment.

~~~
jcbeard
Exactly, most science fiction representations fail on the engineering test.
That' snot to say that some future change in our understanding of physics
might not change what is in fact possible. One reason I love scifi is that the
authors/readers/watchers are free to drop the need to be fully grounded and go
for something truly cool. I suspect what we view as totally impossible today,
might be within the realm of possible 2-3k years from now.

~~~
morganvachon
Yep, how does the saying go? Any sufficiently advanced technology will be
indistinguishable from magic when presented to a less advanced society.

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dexwiz
I was obsessed with the idea of dyson spheres when I was younger. The are the
alternate path of an advanced civilization besides exploring the stars.

You probably wouldn't want to build one around our Sun, since it will
eventually expand, and cook anything inside the sphere. Building the sphere
would likely take millennia, and there is no reason to invest in building
around a start that will eat it. Instead you would build it around a red or
white dwarf. These are stable for billions or trillions of years. Meaning you
could build a dyson sphere, and live on it until the end of the universe as we
know it (Stelliferous era).

Red dwarfs are much less massive than our star, so you could build a smaller
sphere (still relatively huge), and material property requirements would be
less. White dwarfs are a bit more massive on average, but will last much
longer.

Dyson spheres, bubbles, rings, whatever would not experience a day/night
cycle. So would either have to build it out of a material that passively
radiates excess energy out the other side, while maintaining habitable
temperature. Or you build a second set of smaller rings or disks that orbit
closer to the star at a different rate. The inner set casts shadows on the
outer set, simulating a day/night cycle.

Successfully building a dyson sphere would likely only be done to either power
a FTL gate of some sort or a giant computer. If you built a computer to
simulate a universe, and properly managed the inner star's output and
lifecycle, you could feasibly escape the end of the universe by simulating a
smaller one for yourself.

~~~
saalweachter
Freeman Dyson actually had another way to escape the heat death of the
universe: by taking advantage of it.

As the universe cools, the noise of the background radiation will diminish.
Dyson posits that this would allow us to build an analog computer which uses
less and less energy as time goes on-- it could run forever on a finite store
of energy.

So even if the universe "ends", we might be able to build a computer which
doesn't.

~~~
vollmond
Can you recommend any reading on this? Sounds interesting.

~~~
quakeguy
"The last 3 minutes" by Paul Davies[1] is a good popsci read on this topic.

[1] [https://www.amazon.com/Last-Three-Minutes-Conjectures-
Ultima...](https://www.amazon.com/Last-Three-Minutes-Conjectures-
Ultimate/dp/0465038514)

------
zombees
If all the dimming star headlines are piquing your interest, you must read
Pandora's Star and Judas Unchained by Alexander Hamilton. It's about the same
event being observed but a couple hundred years from now in a post FTL
society, so naturally they have to wander out and see what's up. The pair is
one of the best recent science fiction stories to come out in the past 15
years.

~~~
imron
Came here to suggest this.

Pandora's Star is an excellent (albeit long) read.

Note however, the author is Peter F. Hamilton.

~~~
13of40
Just bought it on Audible, and apparently it's 37 hours long...

~~~
kchoudhu
Yeah, Hamilton _really_ gets into world building. Often to the detriment of
actual storytelling -- which on its day, is actually quite good.

I'd still recommend these books though.

Edit to add: Hamilton also wrote _The Void Trilogy_ , set in the same universe
as _The Commonwealth Saga_. They're interesting, but less so than the
Commonwealth books.

------
triplesec
For an evolution of the Dyson sphere in fiction, read (Free online) Charles
Stross's Accelerando, a novel of 9 connected Singularity-oriented stories.
[http://www.antipope.org/charlie/blog-
static/fiction/accelera...](http://www.antipope.org/charlie/blog-
static/fiction/accelerando/accelerando-intro.html)

For those who don't know him, he used to be a professional programmer, and
he's a very smart writer, lives and his blog is here.
[http://www.antipope.org/charlie/](http://www.antipope.org/charlie/)

~~~
rbanffy
He's also seen here occasionally as cstross.

------
sehr
OT, but the Dyson Sphere was the first idea that gave me a deep sense of
sadness knowing I'll never see it.

How can you feel fulfilled laying the groundwork when things like this lay in
store? And I'm just a software developer, I can't imagine how people in more
relevant roles feel about it.

~~~
kbenson
The other option, which is what I generally feel, is a sense of purpose that
we need to make sure we shepherd the human race in the small way we can to the
eventual goal of something like this. That is, it's engendered a bit more
thoughtfulness about not just what policies yield the best current outcome,
but what if we took a path of advancement slightly less optimized for current
ease and happiness and more for future gain?

We are of course _very_ far from being able to correctly plan and carry out
anything like that if we really wanted to, given that our current advancement
is almost entirely directed by market forces and psychology that we are just
beginning to understand, but it's an interesting thought experiment.

Can you ethically deny X people currently for the betterment of n*x people in
the future, assuming population growth and expansion? If so, what's to keep us
from enslaving all the current people in pursuit of ultimate happiness of some
theoretical future? If not, why are we saving anything for future generations
rather than consuming it all for our benefit right now? The extremes are of
course easy to answer, but the variables that go into it make it interesting
to think about.

~~~
nickfromseattle
Interesting responses. If you haven't already, the Foundation trilogy is a
must read. Essentially a bunch of really smart folks create a new field of
science focused on predicting the geopolitical and technological advances of
the future universe to ensure the human race is successful.

~~~
kbenson
Yes, I'm very familiar, although it has been quite a while. :)

------
powertower
There are other more plausible options for these civilizations then building
absolutely gigantic structures around suns.

1\. Build devices/objects
([https://i.ytimg.com/vi/bQ7RaOMHb5I/maxresdefault.jpg](https://i.ytimg.com/vi/bQ7RaOMHb5I/maxresdefault.jpg))
that are able to get close to the stars, that would then absorb the emitted
energy from the various coronal ejections, magnetic fluxes, etc.

2\. There is more energy in the fabric of empty space-time than anywhere else.
An advanced civilization would likely be able to harvest this ZPE (zero point
energy or field) using rather small devices.

------
TheOtherHobbes
I can imagine a Dyson Swarm, although intuitively I wouldn't be surprised if
there's some kind of computational limit created by the fact that the bigger a
swarm gets, the more computation is needed to keep it gravitationally stable

But I think a Dyson Sphere - something as solid as a planet, but with a radius
the size of a planetary orbit - is physically impossible, even with unimagined
magic alien super-materials.

The physical configuration of a Dyson sphere is inherently unstable. It's the
astronomical equivalent of balancing a pencil on its tip. Any asymmetry at all
- including proper motion and radiational asymmetry from the star - would need
active correction. Without it, the entire structure will fall apart
catastrophically. (It might take a while, but there's not much point building
something that big unless it lasts.)

Active correction implies movement, which is not what you want on an
inhabitable surface, or even on a computing machine.

And it probably wouldn't be much use as a computing machine. The bigger the
system, the longer it takes information to propagate across it. A system with
propagation delays on the order of minutes isn't going to run nearly as fast
as its energy budget might suggest.

That's still true even if you imagine some kind of ultimate limit system where
the computation happens directly on a spherical spacetime shell instead of on
tangible hardware.

I suppose it's possible that if it turns out that KIC 8462852 is showing
evidence of alien action, the aliens are somehow dimming the star directly
instead of by building screens around it.

~~~
Aeolun
Seems to me that if you have the energy output of an entire star, you have
quite enough energy to keep your shell balanced around the center of it.

Even with those magic reaction-less engines they are working on now you could
keep the thing in place by just spacing engines on the outside at the correct
distance.

I imagine the movement would have to be insanely slow to prevent the entire
structure from collapsing though, and I wonder whether a solar flare wouldn't
put out so much energy/movement that you'd spent years correcting it.

~~~
XorNot
You don't need engines. You have a giant fusion reactor. You just need exhaust
vents you can open asymmetrically.

------
hedgehog
[https://en.wikipedia.org/wiki/Matrioshka_brain](https://en.wikipedia.org/wiki/Matrioshka_brain)

~~~
kbenson
Since this is apparently what we're doing now, here's my move. ;)

[https://en.wikipedia.org/wiki/Computronium](https://en.wikipedia.org/wiki/Computronium)

~~~
hedgehog
Nice. I named our company after the Matrioshka brain in a roundabout way
([http://1026labs.com](http://1026labs.com), 10^26 being the wattage of our
sun) but we haven't called anything computronium yet.

Edit: We're on the way...
[http://www.theregister.co.uk/2016/07/25/semiconductor_indust...](http://www.theregister.co.uk/2016/07/25/semiconductor_industry_association_international_technology_roadmap_for_semiconductors/)

------
rbanffy
One issue of ring worlds is traction (and Dyson spheres are much more
complicated than that). Nothing we can imagine and certainly nothing we can
build can take it but what if instead of rotating it above orbital speed to
create gravity inside the ring we rotate it below orbital speed, create
gravity on the outer surface and rely on materials that can withstand the
compression?

Sunlight could still be reflected by a fleet of orbiting mirrors that wouldn't
orbit the star in sync with the ring and thus would not be subjected to the
structural forces of the ring. In case the ring is built around a smaller star
with a spectral emission very different from the one preferred by the ring
builders, the mirrors could adjust that too.

~~~
powmonk
> create gravity on the outer surface

That's a tricky one. Do you mean make the ring thick enough that it has enough
mass to have its own gravity?

~~~
rbanffy
No.

When the ring rotates at orbital speed, there is no perceived gravity on
either side. If the ring rotates faster than that, one would perceive a force
pulling them away from the central star. If, however, the ring rotates below
orbital speed its mass would be pulled toward the central star (along with
anyone standing on its outer surface). The forces pulling it towards the star
would compress its structure (the opposite of the traction forces a faster
ring with positive gravity on the inner surface would experience).

I think (I haven't checked the numbers) the ring's mass can't be neglected,
but, because of the shape, it'd act as an extra mass within the central star.
The ring is, in fact, in its own orbit.

~~~
rbanffy
Good and bad news. A stationary ring around a star with one solar mass would
be very close, about a tenth of the distance Mercury orbits the sun, to make
its inhabitants experience one Earth gravity on its outer surface. The good
news is the ring would be much smaller than 1AU and it'd be easier to do it
around a large white dwarf and still get a lot of energy from it. Not sure how
much pressure solar wind would be, but, if the star is active enough, we could
use it to partly sustain the ring structure.

------
SubiculumCode
dysonspheres are cool, real cool, but how does the dyson sphere wikipedia page
get to the front page of hacker news?

~~~
kevin_thibedeau
People are speculating about alien megastructures around Tabby's star. That's
why.

------
jlebrech
A variation on this and the first rung of he Dyson swarm would be a space
station that follows the earth's orbit rather than orbits it. you could call
it a dyson tile or fly or something like that.

------
dysob
Why not a Dyson-like moon coverage which allows us to regulate the night and
day illumination provided by our celestial satellite?

Solar operated mirrors whose focus and intensity can be regulated remotely.

------
foobarbecue
[https://www.youtube.com/watch?v=AS_fiyKkAno](https://www.youtube.com/watch?v=AS_fiyKkAno)

------
SubiculumCode
isnt a dyson ring good enough?

~~~
thatswrong0
Good enough for what?

If we're talking about providing for the energy needs of the Earth, that'd be
way way overkill too. See how much solar we'd need on Earth to power our
needs: [http://www.techinsider.io/map-shows-solar-panels-to-power-
th...](http://www.techinsider.io/map-shows-solar-panels-to-power-the-
earth-2015-9)

If we're talking about powering some future hypothetical civilization.. Yeah
it'd have to be ginormous and have huge energy requirements to warrant that
much energy. Maybe if they wanted to channel that energy and blow up a few
planets it could be useful..

~~~
veli_joza
Building the ring would be interesting engineering challenge. Once you build
it with sun in its center of mass, it's in unstable equilibrium, so you only
need to compensate for the drift. But until it is built, your components have
to orbit the sun. So the finished ring would also keep this momentum and it
would be rotating around its center.

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grabcocque
Unlike other speheres it's made from transparent plastic and doesn't lose
suction.

~~~
jessaustin
...and it costs $500.

------
pascal1usa
Can someone please build one of these around SF. We desperately need it. ;)

