On 30 Apr 2020 at 18:48, Cian Witherspoon wrote:

> On Thu, Apr 30, 2020 at 18:06 shadow at shadowgard.com (via tml list)
> <xxxxxx@simplelists.com> wrote:
>     Ringworlds require unreasonably strong materials. Dyson spheres
>     are worse.
>
>     But Alderson discs take the prize. they need some sort of
>     reinforcing to prevent them collapsing radially into a sphere.
>     Worse, the amount of material required would use up all the matter
>     in quite a few solar systems. Like hundreds or thousands. Probably
>     more than that (I don't feel like doing the math right now).
>
> Yes, but when the flat earthers are willing to be right no matter
> what...

Cute. But Alderson discs are weird even if you ignore the unobtanium
and sheer amount of material needed.

The *sun* "orbits" the disc. Not in a circle, but in a linear path at
right angles to the surface. It basically "bobs" up and down thru the
center hole. (and the day length gets kinda long if you have the sun
get reasonably far above the horizon. Like 96 hours from sun-high to
sun-high)

This adds another magitech requirement as the resulting tides would
be enormous. And very much "sideways". Lakes and ocens would try to
climb the sunward side of their basins.

Climate gets interesting too. Ignoring coriolis forces, the shady
side of mountains and hills versus the sunny sides will lead to
interesting effects.

Adding in coriolis forces, I'd expect cyclonic systems that were
bigger than Earth.

And, of course, you get the temperature variations as you move ove
the several AU from the Rim to the edge of the hole (which will have
a ringwall bigger than on Ringworld to stop atmospheric losses.

In the Traveller universe(s) the Jump limit would be real fun too.
The 10 and 100 diamtere limits are apt to be in terms of the *disc*
diameter. So 50 and 500 AU for a disc with a diameter of 5 AU.

And you'll be fighting a 1 g field for at least an AU above the
surface.

Yikes. That means meteor strikes are *bad*. Fortunately, anybody
building an alderson disc will have cleareed things out for a *long*
ways.

Any holes from one side to the other are gonna be fun too. The
gravity in them will probably drop linearly from 1 g at either end to
zero g in the middle.

The air pressure on the other hand... I'd not be surprised to see
rocks "floating" in the hyper-compressed air long before you hit the
zero gee point.

Be one hell of a place to misjump to. and require a lot more than the
36 parsec max in the standard misjump tables.
As I've noted before, an evil GM could have the "destroyed" result on
the misjump tables instead to the ships to someplace too far away to
make contact with home.

One of the Magellenic Cluds? One of the globular clusters orbiting
the galaxy (that's actually not a good place as there stars are
likely to old to have usuable planets).

But just imagine the PCs reactions when their ship misjumps and comes
out 500 AU or more above an alderson disc.
--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com