What pray tell, is the definitive proof? I ask this question upon reading a recent article regarding data from the WMAP probe suggesting that the Cosmos is flat. Now it did not specify whether this implies that the Cosmos is locally Euclidean or has a Euclidean spacial metric and zero mean curvature. If the latter is such, then this would most likely imply the shape of the Universe is best described by a non-compact manifold which implies that it is indeed infinite in size. If there is enough evidence to demonstrate that the Universe has finite size, I'd like to see some of it if you wouldn't mind.