A hiker walks into a cave, and finds an old man, who has 9 identical looking cubes. The old man gives him a set of weighing scales and says; "8 cubes are made of copper, and 1 is made of gold. The gold cube is marginally heavier than the copper cubes. If you can tell me which is the gold cube, you may have it."

Find the minimum number of weighing(s) needed for the man guarantee he walks away with the gold cube.