How to understand Vacuum: T=0K ?==.Physics (classical + quantum) lives under shadow of Vacuum.I want throw light on this Vacuum.Three theories explain the Vacuum T=0K :a) theory of ideal gas because its temperature is T=0K, b) QED theory because this theory explain interaction photon / electron not only with matter but with vacuum too, c) Euler’s equation: e^ i(pi) = - 1, because only in the negative vacuum T=0K can exist ‘ virtual imaginaries particles’ which Euler described by his formula: e^ i(pi) + 1= 0.d) The global conservation of energy is infinite .And this infinite energy belong to the vacuum because that more than 90% of mass ( dark mass/energy ) is hidden in the vacuum .How to understand vacuum's infinity ?Vacuum's infinity has only one physical parameter: T=0K.Without Vacuum T=0K it is impossible to understand quantum particles.The physical parameter T=0T is the key to understand the essence of Existence. Without Vacuum T=0K there isn’t Physics, there isn’t Philosophy of Physics.===.====.Best wishes. Israel Sadovnik Socratus.==============.