On Aug 30, 12:57*pm, Art Unwin wrote:
Thus the exercise starts with Earth itself and then one determines the
next medium and so on until one reaches the outer Galaxy.

Visible energy/matter can occupy the same space as dark energy/matter,
much like solid salt and water can occupy the same space. Just as the
salt contributes to the mass contained in the water, visible mass
contributes to the mass occupied by dark matter.
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73, Cecil, w5dxp.com