The Practicality of a Supermassive Dyson Sphere

[infinix]

Alright, I did a little bit of calculation of my own using our sun and our earth as example. I'm not overly concerned about how long it might take to build this thing, but rather how many planets' worth of material it will take to build it. So my calculations are as follows.

Assumption 1. We will be using mostly titanium for building material.
Assumption 2. My Dyson's Sphere will be 1 AU in radius with an estimated material thickness of 20km.

1AU = 149,598,000km
Density of Titanium = 4.5*10^12 kg/km^3
Mass of Earth = 5.97*10^24kg

(in km)The surface area of my Dyson's Sphere is going to be 2.7*10^18, with a solid thickness of 20km, that means the volume of titanium required is 5.4*10^19.

Multiply that volume by the density of titanium we get 2.4*10^31, which is the total weight of the titanium required,

Titanium is fairly abundant in nature, comprised of 0.63% of Earth by mass, which means there is about 3.76*10^22 kg of titanium on earth.

So, to build a Dyson's Sphere with 1 AU radius, about 20km thick in pure material, entirely using titanium, we will need roughly 1,000,000,000 Earth's worth of titanium. If we take all of the planetary weight available to us in the solar system, which is about 4.0*10^26, also assuming 1% of the weight is titanium, we get about 4.0*10^24 in the amount of titanium. Which means instead of 1 billion earths, we will need 10 million solar systems worth of material.

Even if we can use the entire mass of the solar system (minus the sun), we are still looking at 100,000 solar system worth of material required. If we can use the sun's mass and convert that, then we only need about 100 suns. But this wouldn't be too logical since if a civilization can convert the energy of an entire sun to something else, they really don't have a reason to build a Dyson's Sphere. Unless they need the Dyson's Sphere to convert the energy. Chicken or the Egg. Have I lost anyone yet?

So at the end of the day, whoever wants to build this thing will have to devastate a good part of the galaxy by completely destroying a bunch of solar systems.

 

[Asbo Zaprudder]

Another big problem is how you're going to keep the star at the centre of the sphere. By Gauss' theorem, there's no net gravitational attraction between a symmetrical, spherical shell of matter and a body contained within it.

Not to mention the horrendous tension the structure would be under if you rotated it to simulate gravity on its inner surface (which would vanish at the poles anyhow).

Both problems were addressed for Larry Niven's Ringworld (rim jets, scrith) along with other matters.

 

[John O.]

I always thought imperial units were dumb. Why is there 360 degrees in a circle when 100 is far easier to calculate.

Real scientists use radians and steradians (solid angular units) -- 2 pi radians in a circle, 4 pi steradians in a sphere. Much more convenient.

I'm kind of one of these "real scientists" you speak of and I don't really consider the degrees/radians thing to be an Imperial/Metric distinction... it's just two different standards. My argument would be that there are many practical situations in which it's a lot easier to measure degrees than radians (since a full circle is 2pi radians which is an irrational number) and 360 is a number you can split 2, 3, 4, 6, 12 times in your head easily enough; whereas in mathematics, the sin and cos functions split more conveniently at half integer values of pi radians, so for computation we use that.

Maybe a 'degree' is 'an english unit' but it's a lot more common in real work than, say, slugs, or fortnights, or cubic inches.

I think using "Known Technology" as any basis to estimate building something that approaches the fantasy level for us is bound to result in absurd numbers. Remember, any technology that is sufficiently more advanced is indistinguishable from magic.

That's a valid argument, it's just not particularly useful to any discussion. The moment you say "is it practical to build a dyson sphere?" and then you say "why yes, because a futuristic race will be able to magically turn their magically harvested zero point energy into magically machined and cut and magically placed sheets of magically superthin material at exactly the right distance from the star" then you don't even have a discussion you have a premise, argument and conclusion about as long as this paragraph.

I always liked Larry Niven's explanation for the Ring world. The idea was that the Pak was an incredibly advanced race but never invented FTL. In any case I also thought it a bit strange to come up with an idea to come up with a Dyson sphere for a star that will inevitably go Supernova in a short time period.

Also a highly advanced race isn't going to build such a thing out of Steel. When we built the SR-71, did the planners think of using just steel? No, they went with an all titanium skin. Did we protect our pilots of the A-10 Warthog with steel? No, we used Titanium. Us poor backwards humans have been using more advanced things than just steel. That should mean that in the time it takes for a civilization to advance far enough to build a dyson sphere they would also come up with a different source of technology to to build such a device and cover it too.

Did you even read the entire post? It doesn't matter. The dependence on material is extremely limited. I even did a little example of 'what if you find a material a thousand times lighter than steel'. There's just too many zeroes for it to matter.

Besides, if you use something synthetic - and supposing you're actually having a realistic discussion about manufacturing and processing and all that - then you don't even have to rely on the harvest time being astronomical - because purification and processing will take just as long or longer. Ever wonder why we don't have 400 SR-71's cruising the skies? or why the B-2 isn't being built anymore? Or the F-22? Because the skin is RIDICULOUSLY EXPENSIVE.

But I agree in principle there are better ways to achieve the goal of a Dyson sphere, I just don't think there are any that would be manageable engineering feats of a "normal" technological society - i.e., one with biological, social and political barriers to, oh say, harvesting entire planets at a time for raw materials and ferrying said materials across hundreds of lightyears, for millions of years, the way we ship crude oil from Saudi to Texas to be refined. Another idea I've always liked was quarterspheres with hemispherical channels for transit in/out/around.

 

[infinix]

Yeah, I understand that we should never simply say "don't worry about technology since someone will be sufficiently advanced to get something done magically."

I think both of us agree that if a race is advanced enough to turn energy into matter and matter into energy efficiently on a very large scale, that race could probably build a Dyson's Sphere within a reasonable time. But there would be no logical reason why such a race would need a Dyson's Sphere, ever.

My calculations are pretty much identical to your, the only difference is that I ignore time and focused only on material. Indeed because of the fact that we are dealing with such great volume, a few orders of magnitude difference in mass density doesn't really effect anything.

Any race with the desire to build something like this will exhaust the resources of millions upon millions of solar systems. With the only known benefit of the Dyson's Sphere being able to harness 100% of the energy output of a sun, one really has to wonder if its really worth all the trouble.

 

[infinix]

We do have an example from the Trek Lit "Star Trek TNG: Q-Zone" where there was a Tkon Empire that actually build a transporter network around two different suns and were about to successfully switch the two. If I recall, the only reasons Tkon did it were 1. To prove that they can as if to surpass a test, and 2. Because they didn't want to abandon the old world.

All indications point to that the race had already expanded into multiple solar systems thus sacrificing one isn't a huge issue. Yet they went and did it anyway. If I recall correctly, they build the two transport networks in a span of about a century. It wasn't the practical thing to do, but they did it anyway. So we never know...

 

[Robert Maxwell]

To even enclose a red dwarf like Gliese 581 with a sphere set off 1000km from the surface of the star, you'd need a sphere with a surface area equivalent to about 1.6 quintillion Earths. Just doing the math is kind of mind-boggling.

 

[BolianAuthor]

Yeah, I understand that we should never simply say "don't worry about technology since someone will be sufficiently advanced to get something done magically."

I think both of us agree that if a race is advanced enough to turn energy into matter and matter into energy efficiently on a very large scale, that race could probably build a Dyson's Sphere within a reasonable time. But there would be no logical reason why such a race would need a Dyson's Sphere, ever.

My calculations are pretty much identical to your, the only difference is that I ignore time and focused only on material. Indeed because of the fact that we are dealing with such great volume, a few orders of magnitude difference in mass density doesn't really effect anything.

Any race with the desire to build something like this will exhaust the resources of millions upon millions of solar systems. With the only known benefit of the Dyson's Sphere being able to harness 100% of the energy output of a sun, one really has to wonder if its really worth all the trouble.

I just think it'd be hysterical if some uber-race built something that incomprehensibly and obscenely massive just on a whim, as if it were built for some alien equivalent of the World Fair.

 

[Asbo Zaprudder]

As I've hypothesised elsewhere they're more likely to be jerking off on a holodeck while their sun explodes.

 

[infinix]

You know, our discussion makes the robots from this Japanese Animation that much more ridiculous.

Tengen Toppa Gurren Lagann

See this picture? see the galaxies behind that robot? IT IS TO SCALE. The fraking robot is BIGGER THAN A GALAXY. Anyone care to calculate if there is enough material in all of the known universe to build something that size?

 

[Robert Maxwell]

Heavy elements (as in metals) do not exist in sufficient quantity in the entire universe to build a robot that size. I don't think we even have to try to calculate that. Gut feeling will do.

 

[Asbo Zaprudder]

Plus the fact that the robot would move extremely slowly from our perspective due to the finite speed of light. It would also collapse into a singularity due to its enormous mass.

 

[infinix]

Plus the fact that the robot would move extremely slowly from our perspective due to the finite speed of light. It would also collapse into a singularity due to its enormous mass.

LoL.... imagine the dialogue.

"Look, those two robots are going to fight." "One of them looks like it is about to throw a punch."

a couple of million years later...

"Wow, that punch landed perfectly"

 

[publiusr]

I don't know about Dyson spheres, but was thinking about placing explosives (or steam as Dandridge Cole spoke about) to inflate a molten asteroid that passes near a star, so as to inflate a bubble.

http://en.wikipedia.org/wiki/Bubbleworld#Bubbleworld

Spacecraft to visit it perhaps
http://dvice.com/archives/2011/02/nautilus-x-coul.php

That's about as good as it gets...