Wirt Atmar <[log in to unmask]> wrote:
>
> I don't know if this is the physics that is used in "Ringworld," but if there
> are to be people in this "ringworld," they'd better be in a tube and be used
> to near zero-gravity conditions.

Here's a not-so-brief description, as best I can remember it, of the
"physics" used in the Ringworld novels:

The Ring is made of an imaginary substance called "scrith" that has
amazing tensile strength.  The whole structure rotates at a speed of 770
miles/sec to provide near-Earth-normal "gravity" through centrifugal
force.  The surface area inside the ring is equal to several million
Earth-sized planets.  There are thousand-mile-high walls at each
rim, sculpted to look like mountains, that hold in the atmosphere.
(The mountain peaks rise above the atmosphere.)  To the Ringworld's
inhabitants (many of whom are unaware they live on a ring) the surface
appears flat, with a huge arch that rises across the sky from opposite
horizons and passes behind the sun.

The outer surface is covered with a layer of spongy material -- foamed
scrith -- to absorb minor meteor impacts.  The inner surface is covered
with rock and soil landscaped to resemble a terrestrial world, and
stocked with plants and animals taken from many worlds to provide a
biosphere. There are two large oceans, on opposite sides of the inner
surface to balance one another, and many smaller lakes, rivers and
seas. Pumps on the ocean floors gather silt washed down in the rivers
and send it through pipes in the ring floor to points high on the rim
walls, where it is poured out down the walls to form "spill mountains."
The spill mountains gradually erode and the soil flows back down to the
surface in a soil-renewal process that takes many thousands of years
to complete.  (If not for this process all the Ringworld's topsoil would
eventually end up in the oceans.)

A day-and-night cycle is provided by "shadow squares," large flat black
scrith panels that are joined at the edges with thin (but superstrong)
cables and spun at a higher-than-Ringworld speed in a closer orbit around
the sun.  The shadow squares cast rectangular shadows thousands of miles
wide that move around the Ringworld and provide alternating periods of
day and night on the surface.  In times of heightened solar activity
the cables can be "reeled in" to pull the shadow squares closer together
and nearer the sun, reducing the amount of solar radiation reaching the
surface and providing protection from solar flares.  The shadow squares
also serve as power generators that can collect solar energy and beam
it to the surface, and as orbital telescope platforms that can beam
images of the Ringworld surface to observatories (called "map rooms")
located on the surface.

The scrith under the surface of the ring is crisscrossed with a network
of superconducting cables that allow immense magnetic fields to be
generated and precisely controlled.  These provide the second part of the
Ringworld's meteor defense.  Obviously a large meteor puncture in the
ring floor could allow the entire atmosphere to spew out the underside
of the ring into space.  Meteors or asteroids that are large enough to
pose a threat (especially those on a course that will take them over
the ring walls and cause an impact on the inhabited inner surface) are
handled by the secondary defense.  The magnetic field controlled by the
superconductor cables interacts with the sun to cause a solar flare to
form in the direction of the meteor.  After it reaches a few thousand
miles in length it lases in violet, producing an incredibly powerful
gas laser that destroys the threat.  This same mechanism can be used to
destroy invading fleets of spacecraft.  The system is entirely automated
and any craft approaching the Ringworld must either land on the spaceport
ledge outside, or, if it crosses the rim walls, must move slowly enough
to pose no threat to the inhabited surface or the meteor defense will
shoot it down.

The Ringworld would be longitudinally unstable if not for attitude
jets that keep it centered around its star.  These jets are actually
huge Bussard ramjets located on a ledge at the top of the rim walls.
They use magnetic fields to gather hydrogen from the solar wind, compress
it and fuse it to provide thrust that moves the Ringworld laterally.
These huge fusion motors are activated automatically to compensate for
events like meteor impacts or solar flares that might otherwise nudge
the ring off-center from its orbit and cause it to wobble around its sun.

And there's more than you ever wanted to know about the Ringworld.  :-)
I have no idea how much of this would really be feasible if a material
with scrith's properties actually existed, but Freeman Dyson is included
among those who have spoken favorably about it.

--
Wayne Brown  (HPCC #1104)  | "When your tail's in a crack, you improvise
[log in to unmask]      |  if you're good enough.  Otherwise you give
                           |  your pelt to the trapper."
"e^(i*pi) = -1"  -- Euler  |           -- John Myers Myers, "Silverlock"

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