Time dependent zero-field-cooled magnetisation measurements have been performed in order to determine the temperature dependence of the free energy barriers, B(T), in the spin glass Cu(7 at% Mn). The results have been analysed using the temperature dependence of the free energy barriers predicted in the droplet model, B( T)∝Δ( T) Lψ where L is the size of the droplet. It is found that as T→0 K, Δ (T)→constant, yielding activated dynamics in agreement with the droplet model. As T→ Tg, Δ (T) decreases but stays finite at Tg. This result is in contrast to the current droplet model where Δ (T)→0 when T→ Tg.