On 1 May 2020 at 13:53, xxxxxx@gmail.com wrote:

> On Thu, Apr 30, 2020 at 9:07 PM 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).
>
> I recall someone once did an analysis of Babylon 5 station based on
> the mass quoted in the introduction and the dimensions of the station.
> The conclusion: Yes, this is in fact build of Unobtainium. It's way
> too light for its size by orders of magnitude.

That may have been *me* over on the babylon-5 usenet group.

As I pointed out to JMS, the *air* in the station would mass more
than the mass they gave for it.

It's a fairly common sort of innumeracy, caused by ignorance of the
square-cube law.

A one meter cube of water masses a metric ton. A one meter cube of
air masses a kilogram.

A one kilometer cube of water masses a *billion* metric tons. A one
kilometer cube of air masses a million metric tons.

If proportions remain the same, then a change in linear dimensions of
X, results in changes in area of X^2 and volume of X^3.

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com