Alien "megastructure" mystery deepens, but probably isn't a Dyson sphere


#1

Originally published at: http://boingboing.net/2016/08/08/alien-megastructure-myster.html


#2

Or maybe very large space ships are sucking the star dry to fuel up.

Maybe, their listening post in our system has alerted these aliens to our gradual self-destruction, and they’ll be stopping by our oasis sooner rather than later.

Also, I don’t think robots will be exploring the universe; I think robots will do the flying, and us squishy life forms will be simply rebuilt on site.


#3

Nah, can’t be a Dyson Sphere, he hasn’t even finished the model yet, it’s still got a big hole in one side


#4

I can imagine really large structures in a defined orbit with calculatable and plannable external influences (gravity, sun wind etc). But is it even theoretically possible to build a mechanically sound space ship in the 100s or 1000s km size range?


#5

Coincidentally I recently felt a great disturbance in the Force.

But that’s interesting. I’m going to read more about that.


#6

Sure. You’re flying on one right now.


#7

Here’s hoping Morning Light Mountain was successfully trapped within the Dyson Sphere :slight_smile:


#8

Mass is more important than size.

As soon as you reach the mass of a planet, the spacecraft will collapse into a sphere, by definition (as a planet is an object with enough mass that it has collapsed into a spherical shape).

Constructing something that size without it massing enough to collapse in on itself is a materials science question that I can’t answer.


#9

I don’t think its that hard: you start with a ball of rock, bolt on your zeppelin pods, your wave-scifi-engine-thingie, your star-eating-array, travel.

I don’t even think you’d need all that much internal structure at all, just whats needed to correct the natural tectonic faults in such an object to produce a useful shifting under stress and maybe an automated maintenance system.

It’s really a question of how many people you’re moving.


#10

good point, but I want my own star ship. first step: buy some 1,9*1021 tonnes of iron to construct the core : )


#11

You can use dynamic stabilization. Enough mass, say a large stream of magnets, circling a track inside the structure, exerts a centrifugal force that will counteract the gravitational collapse. Nor would the track, and the supported structure, need to be circular, but that’s the easiest design after a simple hoop structure (just incline multiple hoops at angles to one another to hold up different latitudes and longitudes of the sphere’s interior), and a circular track is the most energy efficient. Kinky bends in the track will require additional energy to deflect the centrifugal mass.

Efficient, however, is a relative concept, and the energy requirements you’d be looking at are above a Type I civilization (leverages all energy of a planet) on the Kardashev scale (but below that of a Type II (leverages all energy of a star) at lest for a “ship” the size of, say, Jupiter). On the other hand, if you can build the ship in the first place, you’ve probably mastered self-replicating von Neumann probes to build it for you, and therefore have access to Type II energy levels. On the gripping hand, there’s the question of whether a Type II civilization would actually have any use that would make them decide to build it even though they could. We can build supersonic passenger airliners and maglev bullet trains, but we’ve allocated our resources elsewhere.

BTW, this is not my idea. The late British astronomer, engineer and author Paul Birch developed the concept as a way of building SupraJupiter, essentially a mediation on how to turn Jupiter into a hollow shell to live on top of, increasing the radius to where the gravity on the shell’s surface would be equivalent to Earth’s surface gravity. However, given the energy levels involved, slowly accelerating it for very patient space travel, or simply using the same idea to build colossal generation ships, is a logical extension of the engineering principles.

Nor would you have to make a fully hollow shell. A ship say the size of Earth could use dynamic stabilization to prevent the collapse of large internal caverns, or you could just make a SupraEarth. Regardless, you’re going to need a lot of them to build a magnet big enough to squeeze the mass out of a Sun-sized star, but once you have the magnetic elements in place, it’s simply a matter of using the star’s own energy against itself to deform its own mind-bogglingly large field geometry. Possible motives include getting even more mass to finish up a Dyson sphere and make the star smaller so it burns longer, or turning the magnetic poles into rockets to move the star.

Anyway, I digress. The cool thing about dynamically stabilized superstructures is that they don’t require superstrong materials, since you’re basically using momentum to counteract the forces that would tear the structure apart.

Side note: Because of the iron-clad laws of thermodynamics, the faster you try to build something, the hotter the environment gets. So building a Dyson sphere or Dyson swarm on anything less than a scale of thousands of Earth years is probably forbidden unless you’re okay with turning everything within an AU into plasma, which one imagines would be bad even for robotic construction equipment. You could or course use other masses on orbits through the heat island to carry heat into deep space (effectively a gigantic heat pump to climate control a solar system), but then you’d have to build that, so you still can’t escape thermodynamics.

TL;DR - Use the momentum of dynamic masses to counteract gravity and/or structural stress.


#12

Your response is a great example of why I read this forum religiously!

That, and the gifs.


#13

As proof of concept we have our very own Spaceship Moon, of course.


#14

BBS: Come for the gifs, stay for the delicious word salads :yum:


#15

It’s much easier than that. @renke said “theoretically possible,” not practical.

It’s theoretically possible to build a spaceship out of plane sections with zero mass and unlimited strength. The engine can be a point-source too. There’s room in that bad boy for two of every animal (seven of the clean ones) or just their genetic code on a thumb drive. Let’s go!


#16

Mathematically possible anyway. In physics though, even topological spacetime defects either have positive or negative mass-energy. I suppose if you could engineer negative mass (we know negative energy exists, so it’s not quite as far fetched as it sounds) you could use an equal negative mass-energy to achieve a net mass of zero with no net gravitational field. Sounds like something Bob Forward would have written about :slight_smile:


#17

Given your avatar, you’re obviously a fellow SF aficionado. You would probably enjoy Pushing Ice by Alastair Reynolds. The premise is that Saturn’s moon Janus is an alien spaceship/fishing lure…


#18

If we’re going to go for the thought experiments, give me a Watchmaker!


#19

seconded. Reynolds is generally a fine writer of SF


#20

No one give @William_Holz a map of known Alderson points, or we’re all doomed.