There are different explanations, but the original one (zero-point energy) is very heuristic, involving operations with infinity. There are more physical explan

There are different explanations, but the original one (zero-point energy) is very heuristic, involving operations with infinity. There are more physical explanations in terms of physical EM interactions (van der Waals forces), see https://arxiv.org/pdf/hep-th/0503158.pdf https://arxiv.org/pdf/hep-th/0503158.pdf