From Aristotle’s Physics
(the context is disproving the need for a void for contraction and expansion of objects specifically and for movement in general)
@217a26-31: The same matter also serves for both a large and a small body. This is evident; for when air is produced from water, the same matter has become something different, not by acquiring an addition to it, but has become actually what it was potentially, and, again, water is produced from air in the same way, the change being sometimes from smallness to greatness, and sometimes from greatness to smallness.
Similarly, therefore, if air which is large in extent comes to have a smaller volume, or becomes greater from being smaller, it is the matter which is potentially both that comes to be each of the two.
St. Thomas’ commentary says:
@ 554: Therefore condensation does not take place by certain parts moving into others, or rarefaction by inhering parts being extracted, as those thought who posited a void within bodies. Rather it is because the matter of the same parts now has greater, now lesser, quantity: hence, to become rare is nothing other than for matter to receive greater dimensions by being reduced from potency to act; and the opposite for becoming dense. For just as matter is in potency to definite forms, so it is in potency to definite quantity. Hence rarefaction and condensation do not proceed ad infinitum in natural
Basically, I gather from this that the matter, the more or less it is in act can be seen between states of energy and matter as scientists understand them today. (Of course, Fr. William Wallace, O.P.’s book, The Modeling of Nature, was very helpful in seeing things such as this). But I am working through St. Thomas’ commentary on myown right now and this seemed to really show how philosophy had this figured out pretty accurately well before our modern scientists.
Modern science not only more and more sees that there probably is no true void, no true vacuum (with ether and dark matter and everything else that seems to come along), and also “discovered” the law of conservation of matter and energy.