5 ms·

Actually we've defined a boundary at 100km https://en.m.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line https://en.m.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line

• mikeash 10y ago
  Yep, just because there's no clear physical boundary doesn't mean there isn't a clear line separating "in space" from "not in space."
  • amelius 10y ago
    It is a surface, not a line :) And it isn't very clear either, since the sea level isn't very well defined as it changes all the time :)
    • mikeash 10y ago
      Heh, you're doing it again! The actual water level is constantly changing, but "sea level" is typically defined to some fixed level. Although there is more than one definition to pick from.
      • amelius 10y ago
        Yes, and I can continue until you run out of definitions to cling to :) Sea level is (presumably) defined in terms of the center-of-mass of the Earth. This center of mass is constantly changing (even as a side-effect of the rocket moving).
        • mikeash 10y ago
          Changes smaller than your ability to measure them don't really matter. Especially when we're talking about being ~30km below the definition's altitude.
          • amelius 10y ago
            And here I thought this was a nitpicking subthread.
            • mikeash 10y ago
              Ah yes! But at this point it only works if you're nitpicking over the definition of "clear," since the "in space" bit is now settled. Right? Maybe I missed a nit!