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Hi everyone.

I'm working on building my very own Dyson Sphere. I've started ordering the concrete for the foundation from my local hardware store. I plan to start construction this week.

Now, when I told my friends what I was planning, naturally they laughed. They scoffed, "Do you even know what a Dyson Sphere is?"

Of course I do. Picture a sphere with a radius the same distance as the Earth is to the sun (presumably when it's at its closest- I'm not in the mood to build an 'elliptical' sphere). Now imagine everyone living in the inside of the sphere, soaking up all the free sunlight. Click here for more info.

Anyway, the fact I knew this didn't stop their laughter. No sir. They replied, "Then what are you going to do for gravity? Sure, you could spin the 'Sphere around and live on the "equator", but what about the "poles"? There won't be any gravity there at all!"

Ah-ha, I responded, I've already thought this one out. The shell of the 'sphere will be as thick as the diameter of the Earth... whatever that is.

Let's say for the sake of an argument that the Earth is 100 000 kilometres in diameter (astronomical pendants, feel free to correct me as to its actual diameter). By making the shell of the 'sphere this thick, it will have enough density to provide all the gravity I need.

My friends are still laughing, though. They claim that the gravity of the sphere on the other side of the sun will cancel out the gravity beneath our feet. Please excuse my sloppy way of describing it, it may surprise you to learn I don't have much background in astronomy. But imagine a ping-pong ball in space made of super-dense material. Imagine an ant on the inside of the ball. Apparently the ant would float around the ping-pong ball!

"That's rubbish!" I thought. Surely, because gravity diminishes with distance you'd still get all the gravity you need! Can anyone help me explain this one to my friends.

First, some ground rules.

I am a kook. I will not tolerate any arguments that will destroy my dream of building a Dyson Sphere.

Anyone using reasoned, well-formulated arguments backed up with solid evidence will be subject to ad hominem attacks by myself.

I will not be required to provide any supporting evidence or math to substantiate my claims. Anyone disagreeing with me will require more evidence than any reasonable court of law in the world, or I will say they have no proof to support what they are saying.

Anyone trying to get me to see reason by asking questions in the Socratic style of debate, or even if anyone just asks me a question to clarify what the heck I'm talking about, will be subject to responses in the form of questions -from me- which have nothing to do with the topic whatsoever.

Presistant attempts to get me to see reason will be met with accusations that the person in question works for the government, or a multi-national company if the question is asked on a Thursday.

Ground rules to be changed by me without notice. Frequently.

PS- you can read my book "How Will Starshark's Dyson Sphere Affect YOU in 2004?" by sending a crossed cheque to:

Starshark's Dyson Project
PO Box 3141
Sydney NSW 2000
Australia

2. Newbie
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A non-Socratic response:

But wouldn't a set of overlapping ringworlds be a heck of a lot more awesome?

Do it right, and the outer ones would even have automatic day/night, thanks to the inner ones.

And from the outside, it'd look like a huge ball of rubber bands.

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No doubt you can build it, but consider this.

The martians will get rather angry when the sun is no longer shining on their planet. Make sure you have an outer coating that is resistant to {/dramatic music=on} MARTIAN RAY GUNS {/dramatic music=off}. This includes but is not limited to heat rays, shrink rays, magnetic rays, and static-cling rays.

Also, I heard a rumor that you were getting all of the building materials from out of Uranus. Is this true?

4. On 2003-01-02 06:39, just john wrote:
A non-Socratic response:
I want to help, to whom do I write the check out?

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The earth is only about 12,750 km in diameter, not 100,000 km. But to build a sphere that thick you'd need far more matter than we have in the solar system. And you still won't have gravity on the inside. The pull from each particle near you is much greater than the pull of each that is far from you, but there are a lot more of them far from you. They cancel out and leave you weightless.

A better way is to build a sphere closer to the sun and live on the outside. Build it at just the right distance so the sun's gravity is 1g. That would still give you a surface area of over 300,000 earths to live on. When you want power, drill a hole in the sphere and put a solar panel in front of it.

_________________
Life is like a box of chocolates. All of your choices are bad for you.

<font size=-1>[ This Message was edited by: Chuck on 2003-01-02 11:16 ]</font>

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Actually, you can't use thick concrete to simulate earth's gravity on the inside of a spherical shell.

Isaac Newton did the math some 300 years ago: inside a spherical shell, gravity from all directions cancels out.

So you're stuck with spinning the thing (a very small spin will produce 1G at the equator, and that will serve for a VERY broad band of habitable terrain!) As you approach higher latitudes, you'll also approach zero-g conditions.

As a matter of fact, why not take advantage of this, and only build a section of the sphere our of concrete? You could "dome over" the top and bottom with a much thinner material, solely for the purpose of capturing the sunlight for energy.

As a matter of fact, as all things are taken into considering, you'll come closer and closer to a Ringworld rather than a sphere: you save *so much* in construction costs, and, frankly, the benefits are pretty diminishing.

Of course, on a practical note, I have to ask if you've got your investors and underwriters lined up. Do you have a proven energy source for the maneuvering of large masses? Do you have a labor pool? Do you have the concrete required?

Perhaps you could start with a "feasibility" project, something smaller, like a small orbiting habitat at the L-5 position. That already has a lot of support (the L-5 Society) and could return a profit in only a decade.

Dream big...but maybe not *that* big!

Silas

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Oh, and more in keeping with your ground rules, "Away wi' yer blarney, ya spalpeen!" It'll never get off the ground! Have you thought about going at night, when it isn't so hot? Bwah hah hah hah!

(Friendly grin!)
Silas

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What is a "crossed cheque"? Can it be on a US bank?

Can we just send you some concrete instead? We'll pay for the materials if you pay for shipping.

By the way, will the energy required to build your sphere be more or less than that from the "free sunlight" you'll get in return?

9. Why not use those free AOL CD's (or its Australian equivalent)? There should be enough of them to collapse the Earth into a black hole by 2012, so you would actually be Saving the World by building your Dyson Sphere out of this all too ubiquitous material. [img]/phpBB/images/smiles/icon_smile.gif[/img]

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On 2003-01-02 11:21, Silas wrote:

Isaac Newton did the math some 300 years ago: inside a spherical shell, gravity from all directions cancels out.
Was it Isaac? I thought it was Laplace.

11. ^ Heh. [img]/phpBB/images/smiles/icon_biggrin.gif[/img]

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On 2003-01-02 16:20, GrapesOfWrath wrote:
I found this:
http://www.math.purdue.edu/~eremenko/newtpr.html
Thanks, Grapes. And sorry I doubted you, Silas.

Did y'all check out reason for the proof, the Gravity Train Project? Too bad he hasn't finished the Brachistochrone gravity train.

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Haven't checked thoroughly but that thing about that train was a physics problem I got a few years back... as a matter of fact last year, rofl!

And I think Bill is back, so everybody on your best behavior... I mean Phil. [img]/phpBB/images/smiles/icon_smile.gif[/img]

<font size=-1>[ This Message was edited by: Mr. X on 2003-01-02 18:31 ]</font>

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http://www.dyarstraights.com/msgundam/frontier.html#top

Just build yourself one of these. Now you will have to read throught it. (It's not all about Gundam, don't worry [img]/phpBB/images/smiles/icon_smile.gif[/img]. It's mostly about the design and problems dealing with this colony type). It is said that these colonies can hold anywhere from 3-20 million people, depending on the colony type. Just float in a few asteroids and all your material problems are solved.

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To quote from Martin Selbrede's article http://www.geocentricity.com/rebuttal.htm

Einstein taught that there is a force inside a sphere of matter that is in motion. He wrote plainly to Ernst Mach on June 25, 1913, "If one accelerates a heavy shell of matter S, then a mass enclosed by that shell experiences an accelerative force. If one rotates the shell relative to the fixed stars about an axis going through its center, a Coriolis force arises in the interior of the shell, that is, the plane of a Foucault pendulum is dragged around." Geocentrists have never denied the Gaussian proposition that there is no net force inside a stationary shell of matter * but
the distinguishing feature of geocentricity is the daily rotation of the universe around the earth.

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Hmm, it says the last poster here was me, and I haven't posted yet. Maybe the BB is psychic. Someone should tell Randi, could be worth a mil.

Now... where was I...

Ah, yes.

GODDAMMIT! THIS IS THE SECOND BB THAT'S TOLD ME YOU DON'T GET GRAVITY IN A NON-SPINNING DYSON SPHERE! CALL YOURSELVES SCIENTISTS?!? BECAUSE I DON'T!!!

And, no, I can't be reasonable and use the dome concept, or the smaller sphere concept, or the Larryniven'syesIlovedittoowhatabouthosepakprotecto rsfreakyorwhat Ringworld concept. IT'S THE FULL SPHERE OR BUST!

On the materials issue, I don't know why everyone harps on about there not being enough matter in the solar system to build it. I guess I should have known this was going to happen by asking an on-line forum of amateurs their amateur opinion. My local hardware store insists there'll be more than enough concrete, as long as I come up with the bucks, they'll come up with the concrete, and that's their guarantee.

(very friendly they are at the store, too. They have a great big smile right on their faces every time I come in with my chequebook or credit card. Never seen a happier bunch in my life).

Oh, and a crossed cheque has 'not negotiable' on it. It means it can't be given to someone else, only Starshark can cash it in Australia. I had a problem in the past with people trying to buy books that were non-existant... I mean... I hadn't gotten around to writing yet.

I know that the math has all been worked out by someone else, but I still can't believe there's no gravity in the inside of a sphere. Is everyone really, REALLY sure that we aren't talking about the centre of a sphere, not the edge of the inside?

17. I may be wrong but surely the gravity only cancels out in the exact centre of the sphere. If off centre then the side nearest you would exert a greater pull than the side furthest from you - inverse square law of gravity....

18. On 2003-01-03 02:18, Starshark wrote:
G*DD*MM*T! THIS IS THE SECOND BB THAT'S TOLD ME YOU DON'T GET GRAVITY IN A NON-SPINNING DYSON SPHERE!
Just who or what is it you are asking God to d*mn? Not the BABB, I hope! Nor us, I hope, too!

[Editted in stars, per GrapesOfWrath's reproof below!]

<font size=-1>[ This Message was edited by: nebularain on 2003-01-03 09:23 ]</font>

19. On 2003-01-03 02:18, Starshark wrote:
Hmm, it says the last poster here was me, and I haven't posted yet. Maybe the BB is psychic.
Maybe you read the wrong column. I do that all the time.
On 2003-01-03 07:39, Mainframes wrote:
I may be wrong but surely the gravity only cancels out in the exact centre of the sphere. If off centre then the side nearest you would exert a greater pull than the side furthest from you - inverse square law of gravity....
No, you're wrong, but don't tell Starshark--he'll start yelling profanities again. [img]/phpBB/images/smiles/icon_smile.gif[/img]
On 2003-01-03 08:38, nebularain wrote:
Just who or what is it you are asking G*sh to d*rn?
stars, neb, stars [img]/phpBB/images/smiles/icon_smile.gif[/img]

20. stars, neb, stars [img]/phpBB/images/smiles/icon_smile.gif[/img]
Oops! [img]/phpBB/images/smiles/icon_redface.gif[/img] You're right. I fixed it. [img]/phpBB/images/smiles/icon_smile.gif[/img]

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On 2003-01-03 07:39, Mainframes wrote:
I may be wrong but surely the gravity only cancels out in the exact centre of the sphere. If off centre then the side nearest you would exert a greater pull than the side furthest from you - inverse square law of gravity....
Nope; any point inside a uniform shell. Think of it this way: when you're very near one side...then nearly the entire mass of the shell is pulling you "away" from that side, and only a very small segment of the shell is pulling you toward it. The inverse square law just happens to coincide with the volume of a spherical shell to one side or the other of any point inside it.

See the proof: the point "A" can be anywhere inside the shell.

Silas

22. On 2003-01-03 08:38, nebularain wrote:
Editted in stars, per GrapesOfWrath
Just trying to keep us on topic!

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On 2003-01-03 02:18, Starshark wrote:

G*DD*MMIT! THIS IS THE SECOND BB THAT'S TOLD ME YOU DON'T GET GRAVITY IN A NON-SPINNING DYSON SPHERE! CALL YOURSELVES SCIENTISTS?!? BECAUSE I DON'T!!!
Now don't shoot the messenger. We're trying to save you time and money. It'll be much easier to build a Dyson sphere with artificial gravity, if you build it with artificial gravity in mind. I suspect trying to add artificial gravity to an already built Dyson sphere would by nigh impossible.

I know that the math has all been worked out by someone else, but I still can't believe there's no gravity in the inside of a sphere. Is everyone really, REALLY sure that we aren't talking about the centre of a sphere, not the edge of the inside?
Actually there is gravity inside a Dyson sphere. Remember that star we're surrounding; well it's pulling us to the center. But the sphere itself has no effect gravitational effect anywhere inside the sphere. So you will need some sort of artificial gravity to keep people from falling into the Sun.

I know of at least three different proofs of this: direct integration, Newton's, and Gauss's Law. They all say the same thing: the gravity inside a uniform spherical shell is not affected by the shell. Sorry.

<font size=-1>[ This Message was edited by: Wiley on 2003-01-03 13:46 ]</font>

24. Simple answer would be to use enough of that hardware store concrete to equal 1600 solar masses--you'd probably need just about that much anyway. Let's see, 1600 solar masses is 3 x 10^33 kg...so that's about 10^30 cubic meters of concrete. The distance to the Sun is 1.5 x 10^11 m, so the area of the shell would be 4pi(1.5 x 10^11m)^2, or 3. x 10^23 square meters. It'd be only 3. x 10^6 meters thick, a fourth the diameter of the Earth. Did I do that right?

That way, folks on the outside of the sphere would experience about one g, towards the Sun. Sunlight could be piped to their side--the "outside"--and, if they wanted to, they could drop down to the inside where yes they could fly.

Hey, wait, that's a hundred times more massive than Betelguese!? How you gonna pay for all that?

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concrete ? outfashioned. forget it.
consider QM.
u can do anything u want with QM. starting from nothing. no cheques. nothing to buy.
the whole universe was created from a QM point, that expanded ...
let alone u spheric shell. the only thing u have to care about is "decoherence". YES sir !!
otherwise the sphere shall remain in a undtermined or superposed QM states, that means nothing in real world, u can't see it.
don't undersyand ? well u have to be a QM addict ... [img]/phpBB/images/smiles/icon_biggrin.gif[/img] [img]/phpBB/images/smiles/icon_biggrin.gif[/img]

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On 2003-01-03 14:07, GrapesOfWrath wrote:
Simple answer would be to use enough of that hardware store concrete to equal 1600 solar masses--you'd probably need just about that much anyway. Let's see, 1600 solar masses is 3 x 10^33 kg...so that's about 10^30 cubic meters of concrete. The distance to the Sun is 1.5 x 10^11 m, so the area of the shell would be 4pi(1.5 x 10^11m)^2, or 3. x 10^23 square meters. It'd be only 3. x 10^6 meters thick, a fourth the diameter of the Earth. Did I do that right?
Assuming the price of concrete is \$50/cubic meter, that's \$5e31. I gonna recommend buying a concrete manufacturing company. I think this will save you a lot money in the long run.

27. On 2003-01-03 14:22, cable wrote:
concrete ? outfashioned. forget it.
Not my decision. Starshark has a deal with the local hardware store. Hard to beat, that.

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On 2003-01-03 13:46, Wiley wrote:

Actually there is gravity inside a Dyson sphere. Remember that star we're surrounding; well it's pulling us to the center. But the sphere itself has no effect gravitational effect anywhere inside the sphere. So you will need some sort of artificial gravity to keep people from falling into the Sun.
Well he did mention he is from down under, and you know Aussies are quite skilled in the art of falling up.

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On 2003-01-03 14:26, Wiley wrote:
Assuming the price of concrete is \$50/cubic meter, that's \$5e31. I gonna recommend buying a concrete manufacturing company. I think this will save you a lot money in the long run.
First of all, this should come in handy:

http://www.csgnetwork.com/concreteccalc.html

Secondly, I think you could get a big volume discount --- bringing that price down to I dunno, \$3x10^30.

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