/sci/ - Science & Math

I'd assume you would be able to see relatively clearly.

Most likely you wouldn't see the other side at daytime but at nighttime, perhaps.

>>1893944
> Dyson sphere
> Nighttime

lol

>>1893944
>>1893947

> Dyson sphere

> /sci/

>>1893973
Yeah, that sci-fi peddling hack Dyson...

Where else would it go? /cgl/? Besides, this is about visibility through atmospheres. As far as I recally, since the sun's always up, it'd be blue skies, but you'd have upcurve of the horizons.

d is about 92,000,000 miles and you're asking if your eyes could resolve objects at that distance? On the other side of a star, no less?

>>1893992
"Dyson sphere" is a misnomer and not fucking possible. Or, even IF possible, completely impractical and unsustainable for even a very short length of time. I.E., as it neared completion it would already be unsustainable in just its own orbit. You would need more energy than the star even produces just to keep it in place relative to the star.

My guess is that the radiance of the star would blur other objects.

It would also burn your retinas out when you tried to look at objects on the other side of a star.

>>1894023
Please explain this. Dyson Spheres are one of my favorite ideas.

>>1893937
If the perceived gravity in the sphere is equal to ours, and the atmospheric pressure is the same, then the atmosphere should have about the same width. So looking to the other side has double the usual distortion.

>>1894023
[citation needed]

>>1894031
how about the fucking wikipedia article?

You know, that place that spawned your little catchphrase?

Faggot.

http://en.wikipedia.org/wiki/Dyson_sphere

>>1894045
And to follow up, a quote
"In fictional accounts, the Dyson sphere concept is often interpreted as an artificial hollow sphere of matter around a star. This perception is a misinterpretation of Dyson's original concept. In response to letters prompted by his original paper, Dyson replied, "A solid shell or ring surrounding a star is mechanically impossible. The form of 'biosphere' which I envisaged consists of a loose collection or swarm of objects traveling on independent orbits around the star.""

>>1894045
>wikipedia
>citation

I'll have you know that wikipedia articles are not accepted as valid citations in the scientific world, as they are easily changed by people with less-than-honorable intentions.

>>1894031
>>1894028
A rigid shell cannot orbit. I think it was Huygens who knew that Saturn's Rings couldn't be solid, else they'd fall in. Same here; the sphere will not be stable in position. Whichever side is closer will be more attracted to the star - and fall towards it. It's a very heavy thing, so you'd have to use HUGE power to keep it from brushing against the star.

What's the gravitational acceleration exerted by the sun? Your shell of material has to exceed this just to keep your air and people from falling into the sun. Finally, there must be a wide band of vacuum between the atmosphere and the sun. If the atmosphere were near the sun, it'd have to orbit - revolving much more quickly than the shell. And then conduction becomes a factor ;)

>>1894049
Logical fallacy: "Information from a source is wrong because the source could be wrong." No, sir - you must address the claim, not the claimer. Science much?

>>1894049
I'll have you know that you're STILL an enormous faggot.

SOP: Check your source's sources.

http://www.sciencemag.org/cgi/reprint/132/3421/252-a

you DO have a membership, yes?

Oh wait no you're cocksmoking shitcunt who has no fucking clue that his pet soft sci-fi trope is completely full of shit.

>can't be a solid shell because it would collapse

Could we not build it strong enough to resist a star's gravity?

>>1894077
No.

>>1894079
To elaborate, if you built a shell strong enough to resist failure due to the sun's gravity alone, it would require enough mass that
A) it would be impossible to control. Surrounding, not orbiting, a star, it would have no force keep it from just drifting and colliding with the star.
B) It would collapse under it's OWN gravity. Assuming you could find enough usable matter in the first place...
C) It would have enough mass to perturb the sun itself into moving and colliding with the shell.

Solid shells are not fucking feasible.

>>1894053

> Whichever side is closer will be more attracted to the star - and fall towards it.

This is a common misconception. In reality, gravity inside a hollow sphere of constant thickness is zero for all points inside the sphere. With a perfectly constant thickness and no outside forces, the system will remain stable. Problem is, that idealized situation is fundamentally impossible.

The end result, however, is the same.

>>1894092
A: External jets to keep it in place?
B: A substance strong and light so that its strength always exceeds the force of its own gravity?
C: Would be corrected by jets?

A and C could result in a sphere that dances all over the place in order to keep from colliding. Would be funny to watch I guess.

Since a solid sphere is no good, maybe a system of satellites so complete that no energy escapes? Overlapping paths and all that?

Wait, I thought a Dyson sphere was like >>1894048
A bunch of objects orbiting a star in order to collect as much radiation from the star as possible.

Bitches don't know about my Fushigiboshi no Futago Hime
http://www.youtube.com/watch?v=qcE1r8ooCgo

>>1894111

>B: A substance strong and light so that its strength always exceeds the force of its own gravity?

I'm working on finding a value for this, but it's not looking promising.

>>1894136

Actually, on second thought, a hollow shell with constant thickness would have a mass scaling proportionally to the square of its total radius, whereas the cross-sectional area scales to the first power and the distance between points scales to the first power as well. Considering stress is equal to the force applied to the object divided by area, the gravitational force of the completed sphere would remain constant, provided it kept a constant thickness regardless of area, while the cross-section would keep increasing.

Apparently, a dyson shell would be completely stable under its own gravity, provided it was a hollow sphere with a very, very thin shell. This sounds like bullshit to me. I'm not very familiar with the necessary equations; could someone check my math?

>>1894169

Wait, no, forgot something, found my mistake. Wow, was that silly; I completely forgot about m2 in the gravity equation

It's looking like for a very thin shell, you'd need something like 47 million GPa compressive strength, although if it was a lightweight material you might be able to get away with only 59000 GPa

For reference, diamond has around 440 GPa. Carbon nanofiber, due to its structure, has very poor compressive strength compared to tensile strength.

>>1894049
Not him, but it is in fact valid for all internet discussions since the last alterations can be viewed on any article.
If you doubt the validity of the facts stated in the article, simply look at the references and the change log.

The reason we do not accept it in other venues is that Wikipedia is a secondary source and one would rather argue with primary sources.

>>1894203
Perhaps if there was some kind of internal support network, like strusses or something? Something like pic related?

>>1894023
Still don't see ANY support of why it would take so much energy to keep a solid sphere in place. I see that it will not be a stable structure, but if you keep the center of gravity of the sphere sufficiently close to the center of gravity of the sun, the force needed to make small adjustments (to stay at the right place) should be small. Incomparably so with the energy output of the sun.

>>1894475
Let's say you manage to build this shell without any mishaps, which is INCREDIBLY unlikely. But let's just say you pull it off.

As the sun moves around the galaxy, the shell WILL be moved relative to the sun. pick a reason. It will happen, guaranteed.

Perturbation by another body, or more likely uneven radiation from the sun itself exerting force on the interior of the shell in one direction more than another, or even MORE likely just that the sun itself is not completely homogeneous and exerts slightly more gravity in one location . The shell is now moving. Let's say at an extremely slow rate. 1 millimeter a "year".

How much force, or propellant, do you suppose would need to be expended to correct this small drift?

How often do you suppose this would need to be done?

Just ask yourself this...how feasible does it seem to make an adjustment to the earth's orbit?

This shell would be many, many times the amount of matter that composes just the earth.

It's completely infeasible to sustain such a structure.

But again, you would never even be able to construct it.

>>1894092
all of these arguments are ignoring every force and every factor except simple Newtonian mechanics?

What if you assume there are other forces in the universe -- magical forces like Energy, Magnetism, Light, etc.
Let's also suppose that the builders are working with some level of carpentry more advanced, since the questions presupposes that anyway.

>>1894549
more like advanced faggotry.

Okay. In a world of magic and faggoty sparkleponies you can have your dyson sphere. Happy?

Also in such a world I can blot your kind of retardation out of existence with a thought because hey, magic.

But you're still here.

>>1894353
That actually doesn't simplify any part of the discussion; what you are doing now is talking about the assembly method. You don't even have a material to assemble, a structure or architecture, parts, or methodology, and you're trying to assemble it.
Look at it this way: trusses and other kinds of support are a way to use a really hard material and take away as much as possible.
Or, you can look at it this way: you've taken an impossibly heavy and stiff object you can't control or move, and doubled the problem by adding a second layer, and then added millions of struts between them to really complicate it.

>>1894557
Good example of how sarcasm doesn't work online.
I was being sarcastic when I implied all of the other factors relevant are 'magical' -- obviously, rotation, giant magnetic fields, radiated energies and many others are relevant to such a structure.
Therefore, you can't defeat feasibility with Newtonian mechanics alone.
I wasn't one suggesting any of it is possible, nor did anyone deserve your ridiculous nastiness.

Okay, so over the past two hours I've worked out an equation for formulating the compressive stress in a solid dyson sphere made of a homogenous material with thickness t, radius r, and density ρ. Units are SI; meters, kilograms and so forth. G is the universal gravitational constant.
I apologize in advance for any weirdness in the equation; I've never used the math tags here before.
<span class="math"> σ=1.532*8*π*r*t*ρ^2*G [/spoiler]
Note the 1.532 is a geometric coefficient; I did this by taking two halves and calculating the gravitational force between them treating them as points; if this is a flawed method feel free to correct me.
So say you want to make it out of steel (ha ha ha). Steel has a ρ of 7800kg/m^3. If you wanted it to be, say, a meter thick and out to earth's orbit (150*10^9 meters), you'd get 23.4 gigapascals, which is 50 times more than steel can handle.
If you wanted to make it 2 centimeters thick, however, that would be doable. A better way would be to find a more lightweight material, however, which isn't *that* difficult. The real kicker would be in getting enough to equal a thousand earth masses, which is what the thing is going to end up being. There isn't enough material in the entire solar system for something of that size.
Note that this disregards the mass of the sun, which is going to be around three orders of magnitude more massive than the structure itself.