Frodo Lives said:
All this talk about the galaxy having an 'up' and 'down' is a little strange, and seems to be based on the classic Earth-centric North and South directions, which would have no bearing on alien species.
What we consider up could just as easily be considered down to them.
How do we tell the difference between the 'top' of the galaxy and the 'bottom'? Is the 'bottom' the crummy part?
FalTorPan said:
Although the galaxy's shape and rotational axis might very well suggest a natural orientation for a rectangular, cylindrical or spherical coordinate system for the purpose of interstellar navigation, the galaxy's shape does not necessarily suggest a natural "upness" or "downness" for a spacecraft traveling within it.
But if you have an established navigational system based on the galaxy's obvious disk shape, which one might assume most starfaring peoples would, the ship will always be oriented to that system. It could be like an inertial nav system in a plane, set at takeoff with the starting coordinates and attitude, which the ship will remember and maintain orientation to. Or, like in the established case of starfleet, there could be a subspace nav buoy system continually feeding coordinates to the ship, by which it maintains its reference to galactic "up."
Only if some other folks' star system was 180° inverted from ours would they view our galactic "up" as their "down." And I suppose that's certainly possible.