Dyson Sphere questions

[Solarbaby]

I have read up on Dyson spheres and know that it wasn't meant as a serious theory by Dyson, however the idea fascinates me. The practicality of building such a mammoth structure and time and resources make it seem impossible, But let's just assume it existed.

I am really interested in understanding how life would exist and evolve in the sphere. In TNG 'Relics' we learn the sphere has a surface volume equivalent to150 million earths. The inner surface has continents and oceans, the sun at the centre provides enough energy to sustain all the needs of any technologically developed societies.I have a few questions for a fan fiction I'm writing. I'd like to hear your thoughts please.

How would the sphere provide gravity? Would it use the same tech as on Starfleet ships or would the sphere revolve?

How would the people block out the sun if their biology required night and day? Let's imagine there was a planet in orbit of the sun inside the sphere. If the planet was the right size could it block out the light in certain hemispheres of the surface providing night time? Would it appear as an eclipse?Or would it gradually turn to night?

If there was no planet and it was just the sun what type of life forms would live on a world without any darkness?

Hoping for some interesting and different opinions. Thanks guys

 

[sojourner]

You haven't read much about dyson spheres if you still think it's an actual sphere.

Start here:
https://en.wikipedia.org/wiki/Dyson_sphere

 

[Solarbaby]

You haven't read much about dyson spheres if you still think it's an actual sphere.

Start here:
https://en.wikipedia.org/wiki/Dyson_sphere

I have read all this many times. I am thinking more about the Sphere in Relics. It was visually shown and described as a sphere. And you can see land masses in the episode.

 

[HIjol]

Maybe start with "Ringworld"! Though not an actual sphere, it will give you a perspective, a frame of reference for your writing, some answers to your questions, an one HELL of a read! Good Luck.

 

[Asbo Zaprudder]

I have read up on Dyson spheres and know that it wasn't meant as a serious theory by Dyson, however the idea fascinates me. The practicality of building such a mammoth structure and time and resources make it seem impossible, But let's just assume it existed.

I am really interested in understanding how life would exist and evolve in the sphere. In TNG 'Relics' we learn the sphere has a surface volume equivalent to150 million earths.

Greater than that assuming a sphere radius of 1AU around a identiaal start to the Sun for the same insolation .

Volume of a sphere = 4 * pi * r^3 /3
Area of a sphere = 4 * pi * r^2

Assume r = 1 AU = about 150 * 10^6 km or 23,455 Earth radii.

Assuming Earth a perfect sphere (near enough) gives:

Volume ratio = 12.9 trillion.
Area ratio = 550 million.

The inner surface has continents and oceans, the sun at the centre provides enough energy to sustain all the needs of any technologically developed societies.I have a few questions for a fan fiction I'm writing. I'd like to hear your thoughts please.

How would the sphere provide gravity? Would it use the same tech as on Starfleet ships or would the sphere revolve?

Rotation to simulate gravity requires ultrastrong materials, see Scrith in Larry Niven's Ringworld. It also less and less effective toward the poles, where the centripetal acceleration becomes zero -- hence Niven envisaging a ring rather than a sphere. Otherwise, you're best off inventing an engineering solution using made-up physics like Star Trek does.

How would the people block out the sun if their biology required night and day? Let's imagine there was a planet in orbit of the sun inside the sphere. If the planet was the right size could it block out the light in certain hemispheres of the surface providing night time? Would it appear as an eclipse?Or would it gradually turn to night?

Niven used an array of shadow squares to eclipse the star and block light. Simple as that. In Iain M Banks' Culture series, miniature ringworlds called orbitals spin to simulate gravity but orbit rather than encircle the star (which is dynamically unstable anyway). An orbital's spin can be arranged to give natural day-night cycles. Being smaller, the ring material wouldn't need to be as strong.

If there was no planet and it was just the sun what type of life forms would live on a world without any darkness?

But you said no planet. What do you mean by world? Anyway, plants would probably love it for the photosynthesis.

 

[Ar-Pharazon]

Would the inside surface not get constantly bombarded by solar winds & other solar phenomena more than the Earth or other planets do?

 

[Kemaiku]

Would the inside surface not get constantly bombarded by solar winds & other solar phenomena more than the Earth or other planets do?

Yes, the entire inside of the sphere would be blasted clean by any solar activity/flare, absorb *all* the radiation and suffer for every gravitational imbalance the star experienced.

 

[Asbo Zaprudder]

I imagine a Kardashev type 1->2 civ would favour orbitals, which are more practical and much simpler to build and manage. It would also be easier to deal with solar comic rays, solar wind, and coronal mass ejections by a combination of shielding with suitable materials, atmosphere, magnetic field, and adjustment of the orientation of the structure.

 

[Silvercrest]

About 6-7 years back I had my own thread here about aspects of a Dyson Sphere (Shell). Mine was for a role-playing game and as such was able to handwave some of the realism concerns. But basically I postulated a habitat that
1) rotated to simulate gravity,
2) surrounded a variable star with a period of 1 year to simulate the seasons,
3) was "stairstepped" internally in increments about 100,000 miles across-- each "step" had its own atmosphere held in place by centripetal force and theoretically each could have its own environment/atmosphere/gravity,
4) had a set of technobabble energy fields which filtered light when they passed over each other, blocking out the star in various locations on a regular basis and simulating night (picture two rotating birdcages inside each other with translucent bars),
5) used the same energy fields to channel dangerous radiation off toward the poles,
and 6) was open at the poles to release all that excess. Essentially it had a jet of plasma being expelled at each end.

The RPG was set in the universe of Stargate SG-1. For that reason I didn't have to deal with large unwieldy hatches that can trap starships. You can dial in and out with a Stargate. (It's also proof against Goa'uld intrusions, too-- they can't fly their ships in.)

I didn't care for the idea of a single, titanic interior surface with continents and oceans. Those continents and oceans would have to be wider than Jupiter to be seen at the distance the Enterprise-D saw them. It makes travel a problem. Requiring several lifetimes of walking before you can reach the ocean does not make for a compelling narrative. Plus a single open surface with centripetal forces at work would result in the atmosphere pooling at the poles (or rushing out of them, in this case).

I came up with the "stairstep" inner surface to get around all that. At 100,000 miles across each "step" is still wider than the Earth, but it's not inconceivably large. And each step has its atmosphere pressed into place by centripetal force.

I also envisioned that the "steps" might not be solidly joined, but might allow slippage to reflect the difference in orbital speeds.

You could envision the whole thing as a gigantic bearing assembly in a spherical form-- made up of Ringworlds.

 

[Maurice]

From an old thread called What would a dyson sphere look like (link) here's something I made to illustrate how the inside of such a sphere would basically appear to be blank.

Looking straight up, with the sun shielded, you know what you'd see? Nothing. You'd see a featureless "sky". Even if there was no atmosphere, you couldn't see anything but an endless flat color.

I made the following image to crudely illustrate why this is:

CLICK TO SEE IN DETAIL
​

The math is crude, so dismiss it, but the point still stands.

As you can see, even at twice the distance to the Moon only the most gigantic details would be visble (continents), and by the time you cross into the millions of miles, all detail would vanish (to the naked eye). The next step beyond this illustration would be a field of view 80 million miles wide and from an distance of 40 million miles, at which distance, to be visible, features would have to be a minimum of hundreds of thousands of kilometers across...and that's still less than half an A.U.! The far side of the sphere would be almost five times that distance.

 

[Asbo Zaprudder]

If there were cloud cover, it might be more beige than grey or dark blue.

 

[Maurice]

At those distances it would all blur together unless those features were hundreds of thousands of kilometers wide. That's the point.

 

[MacLeod]

Would the inside surface not get constantly bombarded by solar winds & other solar phenomena more than the Earth or other planets do?

Yes, the entire inside of the sphere would be blasted clean by any solar activity/flare, absorb *all* the radiation and suffer for every gravitational imbalance the star experienced.

If you could engineer a Dyson Sphere as depicted in "Relics", then I guess you wouldn't have problem engineering something that works like a planets Magnetosphere. Or perhaps you had a way to affet the star as to how much solar radiation/winds etc. that it emitted

 

[Asbo Zaprudder]

At those distances it would all blur together unless those features were hundreds of thousands of kilometers wide. That's the point.

Yeah, I was being facetious.

 

[Solarbaby]

Thanks peeps, that's given me food for thought.

I wonder how much thinking went into the origin of the sphere in Relics. The concept is cool scifi, however its more fantastical than realistic.
Sometimes Star Trek takes a lot of liberty and artistic license with basic scifi premises.

 

[Solarbaby]

I like the idea of the stairstep sections. I've been thinking a lot about in universe physics. From the perspective of the teams that would have studied the sphere shown in Relics rather than a real life ring world. Does this sound absurd or workable in the TNG universe; The sphere is made up of 2 hemispheres with a solid shell that revolve in opposite directions providing some artificial gravity. Whilst advance gravity equipment and forcefields keep everthing ground based and an atmosphere around the stairstep areas. I'm not sure how long it would take to revolve, maybe decades. The civilisations living closest to the 'equator' would gradually pass each other. The 'poles' would be unihabitable and contain most of the mechanisms to control the sphere. A powerful forcefield 1000s of miles above the atmosphere would protect against radiation and even block out the sun to provide night time.

I am talking specifically about the sphere in Relics which is already rather a fantastical invention than something you could consider realistic.

 

[Asbo Zaprudder]

Ringworlds and sphereworlds are not stable with regard to the central star. For a ringworld, there is no net gravitational attraction between the structure and the star in the plane of the ring; only on the axis. For a sphereworld, there is no net gravitational attraction between the sphere and the star (Gauss's Law) so active station keeping would be required.

Orbitals -- smaller ringworlds that orbit , not encompass, the primary star, and require less exotic materials technology -- are a much more practical solution.

ETA: Someone asked about using rotation to simulate gravity. The acceleration experienced is r * w^2, where r is that radius of rotation and w is the angular velocity (radians per second). In SI units, to simulate Earth sea-level gravitational acceleration of 1g = 9.81 m/s^2, the value for r is therefore:

r = 9.81/w^2 = 9.81/(pi * rpm/30)^2

or roughly 900/ rpm^2.

If r = 1 AU = 1.5 * 10^11 m, rpm = 3 * sqrt (1/1.5*10^9) or 1 revolution every 215 hours. The velocity = r*w = 1225 km/s.

The tensional stress in the structure due to its rotation is S = g * r * d, where d is the density of the substrate. Given the values above, this yields a stress of 1.5 * d TPa, which would require a material with a tensile strength on the order of the strong force in atomic nuclei.

https://forums.spacebattles.com/threads/ringworld-physics.108243/

That page explains why this would likely not be practical using actual nuclear material such as neutronium mentioned in Star Trek.

Using carbon nanotubes (max tensile strenghth 300 GPa), someone worked out the maximum diameter of an artificial megastructure spun to 1g would be 46,000 km.

 

[publiusr]

A Dyson swarm is perhaps the easiest

Some recent tech that might influence how these things look
http://nextbigfuture.com/2015/10/thermal-energy-harvesting-antennas-by.html

Also per that site--92% of Earthlike worlds have yet to be born--so it may come to us to have to build them.

 

[Asbo Zaprudder]

Rectenna sounds like someone with a TV aerial stuck up their arse. Anyway, the heat's got to come out somewhere, sometime -- so say the laws of Thermodynamics.

 

[SPCTRE]

I imagine a Kardashev type 1->2 civ would favour orbitals

*commences Gregorian chanting*