Cooling, physical scales and the vacuum structure of Y-M theories.

We present a cooling method controlled by a physical cooling radius that de fines a scale below which fluctuations are smoothed out while leaving physi cs unchanged at all larger scales. This method can be generally used as a g auge invariant low pass filter to extract the physics from noisy MC configu rations. Here we apply this method to study topological properties of latti ce gauge theories where it allows to retain instanton-anti-instanton pairs.