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Closed Dyson sphere : is it really impossible ?


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Hi,

Here is my question, until now, I thought "of course, it's impossible". The matter will never be hard enough to resist, and the whole thing is in meta stable equilibrium anyway : any deviation would pull the closest sides of the sphere and break the whole thing. ("That's dumb !.")
Until I thought about this : what about solar wind and matter production from the star...? 
It seems to me now, that if you really close the star into a solid sphere, it will still produce a powerful solar wind, and temperature and pressure that would fill the solid sphere, until it increase enough to push the sphere away. 
So here is my question : is a "self pressured" Dyson sphere, where solar wind and matter pushes in every direction the sphere (and thwart gravity) totally impossible ? (it would then "only" require "pressure control", by venting enough Gaz to stabilize the sphere)
(I know the true answer would probably require serious modeling : has it been done ?)

Edited by Edgard Neuman
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Some scientific applications that are always going to prove difficult to obtain, if not impossible, at least for a hundred years or thereabouts.....space elevator: Terra-forming a Planet: Relativistic travel/speed and a Dyson sphere.

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5 hours ago, Edgard Neuman said:

(I know the true answer would probably require serious modeling : has it been done ?)

A primer of sorts was done some years back by Brandon Weigel

you should be able to just GOOGEL something like "    Dyson Spheres /  Brandon Weigel    "

 

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6 hours ago, beecee said:

Some scientific applications that are always going to prove difficult to obtain, if not impossible, at least for a hundred years or thereabouts.....space elevator: Terra-forming a Planet: Relativistic travel/speed and a Dyson sphere.

Just to elaborate and extend those thoughts more......

Terra-forming a Planet:

https://www.nasa.gov/press-release/goddard/2018/mars-terraforming

"Mars Terraforming Not Possible Using Present-Day Technology"

Relativistic travel/speed:

https://en.wikipedia.org/wiki/Relativistic_rocket

There is no known technology capable of accelerating a rocket to relativistic velocities. Relativistic rockets require enormous advances in spacecraft propulsion, energy storage, and engine efficiency which may or may not ever be possible. Nuclear pulse propulsion could theoretically achieve 0.1c using current known technologies, but would still require many engineering advances to achieve this.

Dyson Sphere:

https://en.wikipedia.org/wiki/Dyson_sphere#Feasibility

Although such megastructures are theoretically possible, building a stable Dyson sphere system is currently far beyond humanity's engineering capacity. The number of craft required to obtain, transmit, and maintain a complete Dyson sphere exceeds present-day industrial capabilities.

space elevator:

https://en.wikipedia.org/wiki/Space_elevator

Available materials are not strong enough to make an Earth space elevator practical.[4][5][6] Some sources have speculated that future advances in carbon nanotubes (CNTs) could lead to a practical design.[2][7][8] Other sources have concluded that CNTs will never be strong enough.

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Never say never, but at least not for quite a while! I will be happy if concrete evidence of life off this Earth is finally found, and we have boots on Mars before I kick the bucket. I can then die a happy little vegemite!😁

 

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8 hours ago, et pet said:

A primer of sorts was done some years back by Brandon Weigel

you should be able to just GOOGEL something like "    Dyson Spheres /  Brandon Weigel    "

 

https://medium.com/our-space/dyson-spheres-450146a7c13b
Thanks.. read this : no mention of pressure inside the Dyson sphere and its ability to thwart gravity.. so that don't answer my question.. 

I did google Dyson, and nowhere did I found any mention of pressure inside.. everybody assume the sphere is structurally stabilized by centrifugal force, like it's a structure in orbit. Here I ask about inner gas pressure actively supporting the sphere.. that's totally different. 

You can read that
https://en.wikipedia.org/wiki/Dyson_sphere#Feasibility
They talk about the gravity of the sphere, but they don't talk about the pressure generated by solar wind and inner gas pressure. 

Think about it. Suppose the totally closed sphere weight 1 ton by m² of surface (inside the sphere)... 1 ton by m² is already a heavy structure.  The sun gravity for 1 ton, is relatively low if the sphere is big enough.. we can then compute
the gas pressure inside the sphere necessary.
Let's assume Sun mass = 2×10^30 kg
Sphere ray = 57909050000 m (the orbit of mercury)
Gravity force for 1 m² = 1 ton of sphere = G * Sun mass * 1 ton /  r² 
I get a force of 39,8 Newton 
So 39,8 Pascal for 1 m² of sphere
And the bigger the sphere, the lower the pressure
It seems to me totally achievable if the sphere is filled with the gas from the star,  no ? 

I totally understand that the solar wind is 1–6 nPa ((1–6)×10−9 N/m2) at 1 AU
For a 1 UA sphere, the pressure necessary to support 1 ton / m² is 5.9641110164 Pa  
(since the solar wind pressure is also proportionnal to 1/D², the factor is always the same)

BUT : if we prevent the solar wind from escaping, the pressure should increase rapidly
I wouldn't be a "solid" sphere, but rather a space balloon, filled by the pressure of the star

Edited by Edgard Neuman
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19 hours ago, Edgard Neuman said:

So here is my question : is a "self pressured" Dyson sphere, where solar wind and matter pushes in every direction the sphere (and thwart gravity) totally impossible ? (it would then "only" require "pressure control", by venting enough Gaz to stabilize the sphere)

Solar wind is fairly weak in terrestrial terms (1 ATM being ~10^5 Pa)

"The wind exerts a pressure at AU typically in the range of 1–6 nPa ((1–6)×10−9 N/m2)"

https://en.wikipedia.org/wiki/Solar_wind

The differential pressure for a slightly off-center sphere would be much smaller. Not much "correction" would be happening

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2 hours ago, swansont said:

Solar wind is fairly weak in terrestrial terms (1 ATM being ~10^5 Pa)

"The wind exerts a pressure at AU typically in the range of 1–6 nPa ((1–6)×10−9 N/m2)"

https://en.wikipedia.org/wiki/Solar_wind

The differential pressure for a slightly off-center sphere would be much smaller. Not much "correction" would be happening

I totally understand that the solar wind is 1–6 nPa ((1–6)×10−9 N/m2) at 1 AU
For a 1 UA sphere, the pressure necessary to support 1 ton / m² is 5.9641110164 Pa  
(since the solar wind pressure is also proportional to 1/D², the factor is always the same)

BUT : if we prevent the solar wind from escaping, the pressure should increase rapidly inside the sphere. 
All we have to do is to put vents that only open when the pressure gets dangerously high (here that would be >6 Pa at 1 AU).. 

It's a "closed" sphere : the wind can't escape : it's a balloon, a sort of pressure cooker.

The sphere would be filled with gas from the star at least at the necessary pressure
(it would be incredibly difficult to construct before the pressure gets high enough) 

And the pressure gets greater when the surface get closer to the star : the correction is totally happening.  Also I suppose the scale would make it extremely hard to manage the constraints provoked by any variation of the pressure around the sphere, and solar storm would break everything.. it would need a very calm star, with highly symmetrical wind and pressure. 
 

Edited by Edgard Neuman
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The Dyson sphere is impossible for purely physical reasons, but its derivatives such as the Niven ring or the Dyson swarm may be possible at least theoretically, but it is extremely doubtful that humanity will be able to carry out construction of such a scale in the next few hundred years.
In addition, there are great doubts about the practical feasibility of such a construction, since the total area of the Niven ring with a thickness of 100 kilometers will be tens of thousands of times larger than the area of the Earth - in the foreseeable and even in the distant future, we simply do not need so much living space.

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14 hours ago, Edgard Neuman said:

For a 1 UA sphere, the pressure necessary to support 1 ton / m² is 5.9641110164 Pa

How do you arrive at this number?

Quote

if we prevent the solar wind from escaping, the pressure should increase rapidly inside the sphere. 

If the pressure is due to this, you lose the restorative force. There is no differential pressure from translation. It’s like balloon, which does not maintain a position from its internal pressure.

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11 hours ago, swansont said:

How do you arrive at this number?

If the pressure is due to this, you lose the restorative force. There is no differential pressure from translation. It’s like balloon, which does not maintain a position from its internal pressure.

For the number, I used the simple formula that I explained.. can you read all my messages ? (I compute gravity force (Newtonian) for 1m² of sphere where I assume 1 ton by m²), and then the pressure necessary for this force is trivial (since it's for 1m²)

The sun is inside the sphere.. it's not like a balloon movement, since the force from the sun come from inside.. 
Now I see that as always on this forum, you don't really think and don't bring me thoughtful answers. 
Bye.

 

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Ok you both seems to not understand my question. Please read carefully. 
This is not a ordinary Dyson Sphere : no, it's not a structure orbiting the star.  In that case, the sphere isn't even rotating (since rotation would break symmetry and create tension in the sphere). The star and the sphere would be perfectly symmetrical : nothing rotates. We don't use centrifugal force in any way here. 

In that case, we want the pressure of the gas, coming from the star to build up, until it's enough to thwart the gravity of the sphere, keeping it from falling or breaking. The sphere needs to be closed (that's the reason I put the word "Closed" right in the title. If it's not closed, the pressure wont build up, and in that case, of course it wouldn't work.. I understand what Dyson spheres are thank you.. and please don't quote this writing "no you don't" .. that would be very idiotic. The fact that people come here not to really think but to spew cheap rhetoric is really annoying. ). 
It means inside the sphere, there's a high pressure of hot gas. There is a gradient of pressure inside the sphere, for 2 reason : 

- gravity (by itself, the gas wouldn't distribute equally since the star gravity is strong at the center). It would be some sort of dense hot gas atmosphere around the star.

- The continuous emission of gas from the star : there would still be a radial movement of matter. The sphere would need to vent some of the gas outside, because we want just the right pressure, so we want the gas to build up until the right pressure and then maintain this pressure.
And since it's still a radial movement of matter, the surface that each sphere of gas progressing from the center to the the outer is proportional to R², and the pressure proportional to 1/R² . So yes, definitively a gradient of pressure (just like there is for the solar wind, and everything that goes away from a sphere : gravity is 1 /D² .. every wave.. ).

Since there is a gradient of pressure, yes there is stabilization : if you move the sphere (let's say a length of x) , the pressure at the closest side would be 1/(R-x)² and the other side 1/(R+x)².
You can check that in every case (for d << R) :  
1/(R-x)² > 1/(R+x)²
So yes, if the star isn't at the center, there is a force appearing to correct that.  And yes I understand that gravity would work in the opposite way. So both forces would have to be precisely adjusted.

Now I understand, given the size of the thing, the real problem is how the forces would propagate through the sphere, and yes the sphere would have to support very large tensions (not necessarily be solid, but only tangential tensions to hold together enough)

Edited by Edgard Neuman
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14 hours ago, Edgard Neuman said:

The sun is inside the sphere.. it's not like a balloon movement, since the force from the sun come from inside.. 

But it's not from the sun (in direction), if the pressure is building up. Then it's just a gas contained inside a sphere. Solar wind gives a radial force that depends on distance from the origin. A gas in a container, by itself, does not give a force that depends on distance. 

13 hours ago, Edgard Neuman said:

There is a gradient of pressure inside the sphere, for 2 reason : 

- gravity (by itself, the gas wouldn't distribute equally since the star gravity is strong at the center). It would be some sort of dense hot gas atmosphere around the star.

 

Then you need to calculate how big this will be. It's the gradient that gives you a restoring force, not the pressure itself. There needs to be a different pressure on one side vs the other to give this force. 

14 hours ago, Edgard Neuman said:

For the number, I used the simple formula that I explained.. can you read all my messages ? (I compute gravity force (Newtonian) for 1m² of sphere where I assume 1 ton by m²), and then the pressure necessary for this force is trivial (since it's for 1m²)

I was responding to your first post. But why does the sphere need to be supported? That's a different effect than keeping it centered on the sun. 

 

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1 hour ago, swansont said:

But it's not from the sun (in direction), if the pressure is building up. Then it's just a gas contained inside a sphere. Solar wind gives a radial force that depends on distance from the origin. A gas in a container, by itself, does not give a force that depends on distance. 

A gradient of pressure should be inside the sphere for the reasons I gave. 

1 hour ago, swansont said:

Then you need to calculate how big this will be. It's the gradient that gives you a restoring force, not the pressure itself. There needs to be a different pressure on one side vs the other to give this force. 

I know, but i don't know how.. the result should be a combination of gas diffusion, gravity and solar wind..
 

1 hour ago, swansont said:

I was responding to your first post. But why does the sphere need to be supported? That's a different effect than keeping it centered on the sun. 

 

The mass of the sphere of course. Since I suppose the sphere is 1 ton / m² (the interior surface of the sphere),
The pressure inside needs to prevent the sphere to simply break and fall to the sun (the sphere doesn't need to be a rigid object).

I though about it, I suppose it's a more general question : what would happen if we could put a planet atmosphere (like Jupiter) into a giant balloon...Could the balloon be in a stable state ? Will the balloon fall ? For the balloon to fall, the atmosphere would need to change shape and not be spherical anymore, for the balloon to bend. I think it would be stable. 
For instance, some planets have a layer of liquid water : what prevent the inner core to move inside the water then ? You could say that the upper layer floats.. but then, in my case since the pressure inside the balloon should equal gravity of the material, it should be "as if" the sphere floats on the gas. 

Edited by Edgard Neuman
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46 minutes ago, Edgard Neuman said:

I know, but i don't know how.. the result should be a combination of gas diffusion, gravity and solar wind..

The static contribution is less than the value of the pressure, to be sure.

It can at least be approximated by looking at the gravitational potential energy. The pressure should vary as pgh, where p is the density, g is the gravitational acceleration (which varies with r)

Quote

The mass of the sphere of course. Since I suppose the sphere is 1 ton / m² (the interior surface of the sphere),
The pressure inside needs to prevent the sphere to simply break and fall to the sun (the sphere doesn't need to be a rigid object).

It wasn't clear that this was the case. But to "break off" implies that there is some amount of rigidity involved. And this has nothing to do with correcting its position, i.e. the metastable equilibrium issue.

What you are describing here is closer to a Dyson bubble.

https://en.wikipedia.org/wiki/Dyson_sphere#Dyson_bubble

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On 1/27/2022 at 3:02 PM, swansont said:

What you are describing here is closer to a Dyson bubble.

https://en.wikipedia.org/wiki/Dyson_sphere#Dyson_bubble

uh.. no.. you would need the sphere to be hermetic for the gas inside to build up.
Free solar wind or radiation pressure alone would never be able to counteract the mass of the sphere. We established that solar wind pressure is thousands of time too weak. 
Here I suppose the gas inside the sphere exert pressure of several Pascals : the density of the gas inside is nothing close to density around a free star. The sphere would be filled with hydrogen / helium (i suppose). We can't tell the density since it depends of the temperature of the gas. 
It can't be made of several parts or the gas would escape. So no, it's not what they call a "Dyson bubble".. (why do they call it a bubble if it isn't hermetical ?)
The article doesn't seem to take into account that if you put the star inside a container, the space should start to fill up with atoms and gas.

Do you agree that if you put the star inside a hermetical container, the pressure would build up ?

Since we can (i suppose) build up the pressure this way, then a more massive sphere (not thin graphene, but any metal structure, thus more resistant to tensions) seems possible to maintains. The pressure inside have to be much greater than outside, greater that the normal distribution of gas around a free star. 
We can even control the pressure inside (by venting the gas accordingly), so we can control the amount of tension. We would aim to exactly compensate gravity with gas pressure. I totally understand how impossible it would be to build, my question is more about the stability of the thing once pressurized.

 

On 1/27/2022 at 3:02 PM, swansont said:

It can at least be approximated by looking at the gravitational potential energy. The pressure should vary as pgh, where p is the density, g is the gravitational acceleration (which varies with r)

I think it would be more complicated because of heat from the star.. I don't think the density of matter around a free star obey the pgh formula, because the star is emitting energy. It's not like a planet atmosphere. Honestly I think the only way to answer is to use simulations.

And since the pressure at 1 AU (for my example, I put the sphere at 1 AU but i have no ideas how big the sphere should be to optimize it).. is 6 Pa, that imply the volume of gas inside the sphere is enormous and so the mass of the whole system depends on the density of gas ; the mass of "atmosphere" of the star isn't negligible relative to the mass of the star itself. 
 

Edited by Edgard Neuman
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6 hours ago, Edgard Neuman said:

uh.. no.. you would need the sphere to be hermetic for the gas inside to build up.
Free solar wind or radiation pressure alone would never be able to counteract the mass of the sphere. We established that solar wind pressure is thousands of time too weak. 
Here I suppose the gas inside the sphere exert pressure of several Pascals : the density of the gas inside is nothing close to density around a free star. The sphere would be filled with hydrogen / helium (i suppose). We can't tell the density since it depends of the temperature of the gas. 
It can't be made of several parts or the gas would escape. So no, it's not what they call a "Dyson bubble".. (why do they call it a bubble if it isn't hermetical ?)
The article doesn't seem to take into account that if you put the star inside a container, the space should start to fill up with atoms and gas.

 

As you point out, it’s not sealed, so why would they take that into account?

But it’s the concept of why the components don’t fall into the sun; you’ve just added a new element.

 

6 hours ago, Edgard Neuman said:


I think it would be more complicated because of heat from the star.. I don't think the density of matter around a free star obey the pgh formula, because the star is emitting energy. It's not like a planet atmosphere. Honestly I think the only way to answer is to use simulations.

No doubt it would be more complicated, but the point is that the pressure is not going to keep it centered, since there is a similar pressure at all points. You need a different pressure on opposite sides to give a restoring force in a given direction.

6 hours ago, Edgard Neuman said:

And since the pressure at 1 AU (for my example, I put the sphere at 1 AU but i have no ideas how big the sphere should be to optimize it).. is 6 Pa, that imply the volume of gas inside the sphere is enormous and so the mass of the whole system depends on the density of gas ; the mass of "atmosphere" of the star isn't negligible relative to the mass of the star itself. 
 

No, I don’t agree. The mass loss due to the solar wind is negligible. The sun would  have “evaporated” long ago if that were the case.

The pressure of the solar wind comes from the momentum of the particles. Their velocity is significant (many keV of KE) and some of this will be lost upon impact with the structure. So there aren’t a lot of atoms. It’s about 1.5 million tons (3 x 10^9kg) per second, as compared to the mass of 2 x 10^30 kg. 

https://slate.com/technology/2014/07/solar-wind-versus-fusion-how-does-the-sun-lose-mass.html

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If things worked as you assume, Edgar, you would not need 'vents' on the high pressure side to reduce pressure and restore position.
As the one side gets forced farther away by your imaginary high pressure, the opposite side would move closer, and as a result, experience higher pressure which would restore position.

But, of course, it doesn't happen that way in reality.

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I really don't understand what difficulties you have with the concept of a balloon filled with heated gas from the star. It's not a "free wind in space". It's a dense atmosphere  of several Pa heated by the star.. 
The pressure has to build up. The mass loss from the wind is negligible for the star, but since it's hermetical, the matter stays inside the balloon and over time, the density gets higher (Does "hermetical" means something else in english ?). No matter comes out. Since the star is creating heat, the pressure will inevitably build up inside. 
It is sealed. The title of my question is "CLOSED" dyson sphere. Sealed, Hermetical. I never said the opposite. I only said we should vent the sphere only because we don't want the pressure to get higher than necessary..At some point, since there a star inside, the pressure would get too high. 
It's exactly like a pressure cooker, with the heat source in the center. It is first sealed, but then there's a vent so the pressure doesn't get to high and blow the cooker. The vents are there ONLY to control the pressure. It is not related to the positioning of the sphere, I never said that. 
Gravity creates the gradient, and so the star keeps at the center.
A gradient of pressure means that yes, AT EQUILIBRIUM there the same pressure at all point, BUT if you move the sphere, the pressure on the closest side is higher. Can't you understand what a radial gradient of pressure is ? 

You say the pressure is "imaginary". So you put a star inside a hermetical container, a star the constantly emit energy, and the pressure wouldn't build up ? How does this work in you mind ? If it's not by means of matter, it's by mean of temperature. I talk about pressure. 
I'm curious. 

You don't even need the heat or the wind to keep the mass at the center.
Suppose you put a hermetical balloon around a cold gas planet, and suppose of course the material of the balloon is strong enough to support tangential forces.. How could the balloon fall into the planet ?? The balloon will stay around. You can imagine that a part of the balloon starts to sink into the planet. But since we assume the sphere is strong enough, it won't happen because the balloon isn't extensible. Now, if the pressure inside is equal to the gravity of the balloon, the whole thing can be stabilized with minimal tensions, even if the balloon is a thick material like tons of metal.

In the worst case, we can also simply control the position of the sphere by means of propulsion system around the sphere. 

Listen I'm going to not answer anymore.  My explanation are very simple I don't like to repeat everything multiple times because you are allergic to "new ideas". Here I'm only discussing your inability to understand what I explain and you inability to picture something that is not a star with a free wind, but a closed pressurized sphere. 
I come here very rarely because I always expect this kind of closed minds, and I'm never disappointed. 

 

Edited by Edgard Neuman
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I made a graphic :

 

dyson-pressure-cooker.thumb.png.f1eabb64cb84bca3e03de1e38ddda73b.png

Apparently the correct formula for gas pressure in gravity field is the barometric formula. The pressure is proportional to exp(-h).. 
So, ok, it will grow slower than gravity (when you get closer to the center).. and that's a problem for self stabilization. I do still believe that surface tension around the sphere would prevent it to bend into the gravity well.. because it would create more pressure in the other side.. (but then the sphere would need to be very strong in tension)
The question of a hermetic balloon around some atmosphere isn't simple.

 

Edited by Edgard Neuman
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