If I understand correctly when the universe expands the matter in it is expanded as well but the "rest length" of the matter that gets stretched stays the same. So let's say I have a crystal in the ground state meaning all its atoms are at the ideal distance apart. When this crystal sits in an expanding spacetime does that mean that the atoms will be displaced from their ideal resting position resulting in the crystal gaining energy? Does this mean all the matter in the universe is always gaining a tiny amount of energy from the expansion of spacetime?