This question already has an answer here:
The phrase of 'expansion of universe' , as we are led to believe, is mostly referring to an expansion in space. But is space expanding in the sense that the space between two particles is increasing or in the sense that the particles themselves are somehow getting bigger because of this expansion? If its the first one, woudn't that be inconsistent with conservation of energy? For example, say we have two oppositely charged particles placed next to each other. If the space between them suddenly expands, then potential energy is generated out of nowhere. Is it not?