3 ms·

I was literally repeating to myself “The Ringworld Is Unstable” as I read the article, glad to see the last section where he mentions Niven’s book.

lmilcin 8y ago
The Ringworld was kept stable artificially if I remember. Also it rotated extremely quickly which prevented it from getting squashed like the steel ring in the article. The rotation was so high that it created artificial gravity and so was also high enough to counteract star's gravity. In effect, the ringworld was in constant tension. Since it was made from some pretty exotic stuff it is difficult to say anything about the tensile strength of the material.
- sliken 8y ago
  I believe this is pretty impractical, the required velocity was relativistic and created too much tension for any plausible material.
  - ColinWright 8y ago
    For reference, using the Earth as a measure, we are about 150 x 10^9 metres from the Sun, acceleration due to gravity is about 10 m/s^2, and a=v^2/R. So the speed required is about sqrt( 10 x 150 x 10^9 ) which is about 1.22 x 10^6 m/s. Light speed is about 3 x 10^8, so this is about 0.4% of c. So yes, we're coming into the realm of relativity.
ColinWright 8y ago
As you say, the Ringworld is unstable. This was always something I had known, and accepted, but never really knew why. This article came from the problem Bill presented, and then in understanding that better, and making the connection with the Shell Theorem, meant that I can see why it's morally true, and not just a result of "doing the sums." As lmilcin[0] says[1], the Ringworld was kept stable by artificial means, and that's the major plot point/device in the sequel. [0] https://news.ycombinator.com/user?id=lmilcin https://news.ycombinator.com/user?id=lmilcin [1] https://news.ycombinator.com/item?id=19165894 https://news.ycombinator.com/item?id=19165894

lmilcin 8y ago

The Ringworld was kept stable artificially if I remember. Also it rotated extremely quickly which prevented it from getting squashed like the steel ring in the article. The rotation was so high that it created artificial gravity and so was also high enough to counteract star's gravity. In effect, the ringworld was in constant tension. Since it was made from some pretty exotic stuff it is difficult to say anything about the tensile strength of the material.

sliken 8y ago
I believe this is pretty impractical, the required velocity was relativistic and created too much tension for any plausible material.
- ColinWright 8y ago
  For reference, using the Earth as a measure, we are about 150 x 10^9 metres from the Sun, acceleration due to gravity is about 10 m/s^2, and a=v^2/R. So the speed required is about sqrt( 10 x 150 x 10^9 ) which is about 1.22 x 10^6 m/s. Light speed is about 3 x 10^8, so this is about 0.4% of c. So yes, we're coming into the realm of relativity.

ColinWright 8y ago

As you say, the Ringworld is unstable. This was always something I had known, and accepted, but never really knew why. This article came from the problem Bill presented, and then in understanding that better, and making the connection with the Shell Theorem, meant that I can see why it's morally true, and not just a result of "doing the sums." As lmilcin[0] says[1], the Ringworld was kept stable by artificial means, and that's the major plot point/device in the sequel. [0] https://news.ycombinator.com/user?id=lmilcin https://news.ycombinator.com/user?id=lmilcin [1] https://news.ycombinator.com/item?id=19165894 https://news.ycombinator.com/item?id=19165894