How Viable is a Dyson Sphere?

[Exarch]

For those unfamiliar, this what a dyson sphere is:



from an engineering/cosmological POV, how viable is the construction of a dyson sphere?

Discuss

[Medicus]

Give me 100,000 years, and I might be able to get back to you.

[Lord Rahl]

I really have no idea. I'd say impossible...I mean, just think of the engineering improbability of making it! In Star Trek there is one.

[Medicus]

I really have no idea. I'd say impossible...I mean, just think of the engineering improbability of making it! In Star Trek there is one.

I was waiting for you to bring that up, Rahl.

IIRC it was built within a region of space 200 LY wide, absent of any stars or planets. That gives you a little idea on how much matter is required to build one.

[Wild Bill Kelso]

So what happens when the Solar wind is stopped ead in its tracks? I guess it woul dbe contructed of some pretty resistant material to protect the inhabitants from deadly cosmic rays

[Exarch]

there's a great sequence in the game Freelancer where ur in a dyson sphere
give me a day or so and i can find the youtube link for it

[Spurius]

I'm not sure what the 3m stands for, I take it it's 3 miles thick, not three meters? The other scale is in km's though. 3 meters sounds ... disturbingly thin, even though even 3 miles on 150 million kms isn't 'thick'.

[Averroës]

Feasible today? Not at all, I think. It's a conjecture for some far future when Dyson proposed we'll be able to deal with the problems. As I understand it, the shell has to be thin to allow the inhabitants to pass through excess/unused energy, as shown in the diagram as infrared. I suppose Dyson's concept is that a civilization advanced enough to build the sphere would be advanced enough to deal with the solar energies. The whole point of the sphere is to capture and use as much of a star's energy as possible.

Larry Niven's sci-fi book Ringworld deals with an intermediate form of the concept as a ring instead of a full sphere.

[Ringeck]

A Dyson sphere is a near-impossibility unless we are talking god-like technologies. As the wiki article you nicked the picture from points out, material for sphere thicker than 20cm would likely require more mass than we have in our solar system. You'd have to cart it in from other systems, or convert gaseous materials to solid materials (making metals out of hydrogen and helium, the ultimate alchemist-science) on an absolutely garguantan scale to build a thicker sphere. If you can do that, harnessing solar energy might just be an old-fashioned way of gathering power...

[Ummon]

Besides, how would anyone tackle tidal forces?...

[Juvenal]

I think Dyson proposed it as a kind of thought-experiment.

He posited that civilizations as they became more advanced would use more and more of the available energy until they would eventually be capturing all of the energy from their star and using all of the materials of their solar system, perhaps using something like the Dyson sphere.

Bob Shaw wrote the science fiction trilogy Orbitsville, set in a Dyson sphere. In one passage he really captured for me the sheer unending nature of such a construct, describing intruding alien cultures that had entered the sphere and simply dissipated, unable to cope with or control its vastness.

[Spurius]

I think Dyson proposed it as a kind of thought-experiment.

...describing intruding alien cultures that had entered the sphere and simply dissipated, unable to cope with or control its vastness.

As in viable, not to us, maybe for noone. It's a thought-experiment, indeed.

I doubt any aliens would be so agoraphobic they could endure space then, first - whichi is a HECK of a lot bigger, still - makes no real sense.

'They melt before our grandeur' ahem...

[Medicus]

I doubt any aliens would be so agoraphobic they could endure space then, first - whichi is a HECK of a lot bigger, still - makes no real sense.

'They melt before our grandeur' ahem...

A spherical shell Dyson sphere in our solar system with a radius of one astronomical unit would have a surface area of at least 2.72x1017 km2, or around 600 million times the surface area of the Earth.

That's enough to drive anyone insane.

Still, if some civilization ever managed to build one - you could live there for millions, maybe even billions of years, and still have room. It's the ultimate solution to overpopulation.

[Harry Lime]

You could always start off with a Dyson Ring...

As used in Ringworld.

[Chaigidel]

the dyson sphere would be something that only a billion year old civilization could manage ( if the laws of physics even allow it) -- and by a billion years I mean exponential knowledge growth for a period of a billion years.

[Spurius]

Gosh the size head you must have after 1 billion years of exponential growth - you could get stuck, even in this one.

Seriously, if anyone could pull that type of extended civilisation off, don't you think all this would be rather childish prank stuff? I think they'd even think little of creating their private universe for a cozy pied-a-terre.

And lastly, all natural populations are pretty chaotic, economically and with wars and disasters. And the more civilized you get, the harder it hurts, too.

[Chaigidel]

yeah thats why I say thats how long it would take-- so to say as far as I understand things, I just dont see it being possible unless you learn how to make your own matter, or something-- its just beyond imagining, so to say; its impossible really , but if it did occur It would take a continous and powerful civilzation, or God.

( with co-processor/brain intergration I dont think the head will have to grow at all to attain exponential knowledge growth -- basically it would take a synthetic species, non organic to attain the Dyson sphere imo.

[Spurius]

Star to neighbouring solar system: 'How you like my new TV setup'?

[Averroës]

Star to neighbouring solar system: 'How you like my new TV setup'?

A little to the left, you're blocking my reception.

[Simetrical]

So what happens when the Solar wind is stopped ead in its tracks? I guess it woul dbe contructed of some pretty resistant material to protect the inhabitants from deadly cosmic rays

Well, I don't think cosmic ray density would be very much greater than presently, with a 1-AU sphere. Some would reflect off the sphere, but many of those could be reflected back toward the sun (if the inner surface were sufficiently close to a perfect sphere). The remainder would probably lose a substantial amount of energy on striking the sphere, and so would grow ever weaker as they bounced back and forth.

Of course, it would likely be wasteful to build it at 1 AU, and more practical to build it as close as possible without damaging your machinery from the energy density. But the simple answer is, who says anything's going to be living inside the sphere? With the amount of power it would produce, we'd hardly need direct insolation.

As I understand it, the shell has to be thin to allow the inhabitants to pass through excess/unused energy, as shown in the diagram as infrared.

Well, energy can travel arbitrarily long distances with very little loss. Light will never diminish, no matter how far you fire it, unless it encounters some obstruction. So I'm not sure I get what you're saying.

Larry Niven's sci-fi book Ringworld deals with an intermediate form of the concept as a ring instead of a full sphere.

His concept of the ring spinning to produce gravity is, however, patently impossible. As he remarks in the introduction to the second book in the series, the tension in the ring would be on the order of the strong nuclear force.

Besides, how would anyone tackle tidal forces?...

Tidal forces are minor at distances comparable to 1 AU. Gravity at 150 million kilometers would differ from gravity at 151 million kilometers by only 0.01%, by the inverse-square law, and that's a difference of a million kilometers. Any Dyson shell would have to be much, much thinner. Although, of course, it would also have to be closer in.

Regardless, tidal forces wouldn't be anything to worry about, structurally. The sphere would presumably stay at a fixed position with respect to the sun, so each part of the sphere would be under constant gravitational pull and can be designed appropriately even if the interior is under much greater pull than the exterior.

the dyson sphere would be something that only a billion year old civilization could manage ( if the laws of physics even allow it) -- and by a billion years I mean exponential knowledge growth for a period of a billion years.

You don't appreciate the meaning of exponential growth. Exponential knowledge growth with any reasonable increase rate would, after a billion years, exceed the maximum amount of information that can exist in the universe by a massive margin. "Ultimate Physical Limits to Computation" estimates that one kilogram of matter confined to one liter of volume could contain a maximum of about 10³¹ bits. The mass of the observable universe is estimated at about 10⁵² kg according to the first Google hit (Cornell university website). Multiplying these together gives 10⁸³ bits if it's confined to 10⁵² liters; to account for uncertainty and dubious steps like confining its volume, call it 10¹⁰⁰⁰ bits (i.e., more than 900 orders of magnitude higher than the estimated figure).

Suppose knowledge progresses exponentially, according to I = I₀e^rt. Take I₀ (the initial amount of information known) as, say, a gigabyte, which is orders of magnitude below even today's digitized scientific knowledge, let alone all scientific knowledge. Then if we take t = 1,000,000,000 years for us to attain the desired level of knowledge, we have the equation

(10⁹ b)e^{(1,000,000,000 yr)r} = 10¹⁰⁰⁰ b,

which is readily solved to obtain

r = 9.91 × 10⁻⁷ ln(10) yr⁻¹ = 0.000002282 yr⁻¹,

i.e., an average rate of information increase of about 0.0002% per year. Which is hardly likely for the immediate future. And do keep in mind my ludicrously generous suppositions. (Although you can counter that the scientific premises of the fundamental limits might be wrong, which is possible.)

Anyway, the fact of the matter is, we aren't going to see exponential knowledge or technology increase forever, anywhere. There are fundamental limits we'll run up against. I doubt any exponential increase in knowledge or technology will last a thousand years before petering out to a trickle, let alone a billion. At some point we'll know all the science we'll ever be able to know. Remember that the scientific revolution has only really been the past two to four centuries, depending on how generous you are, and we already know a staggering amount about how the universe works. A billion years of comparable progress would imply a vastness of knowledge that isn't likely to even exist.

Edit (missed intervening post):

Nanotechnology could allow us to do something like the dyson ring, there was a scientific paper floating around that opined that the nano revolution was already on us and despite suppression of it in some ways and research in others it is going to explode like the computer did in the 80's and be a world changing phenomena in a matter of two decades.

At some point in the future we will be able to start thinking about building a second earth

The first problem you have to consider is the mass required, and the energy required to gather that mass. Nanotechnology doesn't help there any, and it's a fairly staggering obstacle for a proper Dyson sphere. Nanotech might help construct stronger materials and better solar cells, for instance, but I don't think those are the main issue here.