Holism as the significance of gauge symmetries

Understand

Not all symmetries are on a par.

• For instance, within Newtonian mechanics, we seem to have a good grasp on the empirical significance of boosts, by applying it to subsystems.
• This is exemplified by the thought experiment known as Galileo's ship: the inertial state of motion of a ship is immaterial to how events unfold in the cabin, but is registered in the values of relational quantities such as the distance and velocity of the ship relative to the shore.
• But the significance of gauge symmetries seems less clear.