From: ldo@nz.invalid   
      
   On 4 Feb 2026 13:31:48 GMT, Stefan Ram wrote:   
      
   > Basically, all coordinate systems are on equal footing as long as   
   > you can link them with diffeomorphisms. So yeah, you can pick a   
   > system where Earth always has the coordinates (0,0,0), meaning it's   
   > "at rest", but you can't use one where Earth is flat, since there's   
   > no diffeomorphism that turns a sphere into a plane or a surface   
   > built from one.   
      
   You can do that for a sphere with a hole in it.   
      
   I’m sure the Earth has plenty of candidates for such a hole ...   
      
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