Galaxies are different than particles - they consist of more particles. Interparticle interaction makes them behave the way they (galaxies) do. So, how can we use, say SO(3) symmetry of rotations in 3 dimensions (which is good for elementary particle because we assume that the particle is symmetric in all directions) for a galaxy? Galaxies are different - some indeed are spherically symmetric, but most not. We may ASSUME that they are all spherically symmetric or are cylindrically symmetric, and get some number out of this assumption, but this number will match the reality only as good as our original assumption does.

So, I do not know what exactly you mean by asking why can't we use method 2 for galaxies. We can. But what are original "axioms" to start with?

• Do you agree that... - harvey1 - January 17, 2002 - 23:13 UTC
  • Galaxies are not identical, like particles. - alexander - January 18, 2002 - 00:15 UTC
• That's not the point, though - harvey1 - January 18, 2002 - 17:25 UTC
  • Harvey, you are again incorrect. - alexander - January 20, 2002 - 22:07 UTC
• What a single principle gives you - harvey1 - January 21, 2002 - 14:37 UTC
  • Correction.Least action principle follows from f=ma,not vicevers - alexander - January 21, 2002 - 18:20 UTC
• re: least action principle - harvey1 - January 21, 2002 - 22:33 UTC
  • Please, define energy (or action) without dp/dt. - alexander - January 24, 2002 - 06:35 UTC