Hi folks, There are many claims that vacuum energy has a physical relevance: in Casimir effect, in the Cosmological constant. But it seems, vacuum energy is a quantity we are not able to measure. It seems like a energy potential: the absolute value has no physical relevance, but the difference has a meaning: energy. In any theory (except supersymmetry) the absolute value of vacuum energy has no physical meaning. Why it should have a meaning in gravitation? The point is: vacuum energy is not a energy, it is a energy potential. Only differences of of the potential have a physical meaning, like in the Casimir effect: The effect do not measure the absolute vacuum energy, it measure die change of vacuum energy - a force. The value of vacuum energy is myriads to large for explaining the dark energy - the rational reaction would be: away with the vacuum energy and looking for a new source of dark energy. Why the majority of physists believe in vacuum energy - a quantity we can not measure and any quantum field theory is invariant against a renormalization of the vacuum energy which has a infinite value in the most cases?