3 ms·

...as long as nothing hits the system, right? I don't know much about astrophysics, but this sounds logical: https://news.ycombinator.com/item?id=14767295 http

• keymone 9y ago
  2+2 is also not 4 when you change the base assumptions drastically. obviously if another star smashes into planetary system - it won't survive, at least not in original form.
  • ithinkso 9y ago
    The point is, if you perturb it by a small enough epsilon will it go back to the initial configuration or fall apart? Pencil standing on its tip kind of a deal.
    • keymone 9y ago
      in nbody terms - that is an additional condition so the problem would have to be solved separately. ask the author, i'm just a lurker here.
  • mabbo 9y ago
    I think the problem gets into some chaos theory, the kind you see in weather prediction. When the forecast says "60% chance of showers tomorrow", what he really means is that they ran a few billion simulations of the environment with very tiny perturbations of the initial conditions and in 60% of those simulations, it rained. In 40%, it didn't. Tiny little changes in any variable in a chaotic system will, in the long run, lead to huge variations in outcomes. This system with it's 416 planets has one outcome- perfect orbits constantly. But if you add a single 1 kg asteroid to the system, that would perturb everything ever so slightly. That slight change could result in the entire system chaotically coming apart from stability.
    • keymone 9y ago
      "stable" always comes with conditions, even if implicit. there's no need to add any asteroids - if any of those planets has tectonic activity, that will already introduce perturbations into gravity fields and cause a collapse eventually.
    • maskedinvader 9y ago
      going off on a tangent here, since you mentioned weather prediction, chance of rain % or probability of precipitation (pop) are computed not only for probability of rain in a given area but also for area of location that will receive the rain if any at all, ie 60% here expresses combination of degree of confidence that rain will occur in an area and geographic coverage of that rain. more details on the wiki entry here - https://en.wikipedia.org/wiki/Probability_of_precipitation https://en.wikipedia.org/wiki/Probability_of_precipitation
  • beobab 9y ago
    Yeah, my dad was always quick to remind me that 2 + 2 = 5 for large values of 2. He said he came across that particular problem in a system which handled rounding numbers in a very suspect manner.
• VMG 9y ago
  he said stable, not robust