  A controversial issue in spin glass theory is whether mean field correctly
describes 3-dimensional spin glasses. If it does, how can replica symmetry
breaking arise in terms of spin clusters in Euclidean space? Here we argue that
there exist system-size low energy excitations that are sponge-like, generating
multiple valleys separated by diverging energy barriers. The droplet model
should be valid for length scales smaller than the size of the system (theta >
0), but nevertheless there can be system-size excitations of constant energy
without destroying the spin glass phase. The picture we propose then combines
droplet-like behavior at finite length scales with a potentially mean field
behavior at the system-size scale.
