  This can be best understood by looking at the very analogy used by Boltzmann: the gravitational account of up and down. What do we mean by the downward direction at a spatial location? All of the phenomena by which we intuitively identify the downward direction (as the direction in which rocks fall, for example) receive an explanation in terms of the spatial direction of the local gravitational force. Even our immediate awareness of which direction is down is explainable in terms of the effect of gravity on the fluid in our semi-circular canals. It comes as no shock to us at all that “down” for Australia is in the opposite direction as “down” for Chicago. Nor are we dismayed to be told that in outer space, far from a large gravitating object such as the Earth, there is no such thing as the up-down distinction and no direction of space which is the downward direction.