If those aliens are able to understand notions such as momentum, it would be because they can (in whatever way; sense or other) understand more fundamental notions which may be non-cosmic. Some good examples of such notions, from Eleatic philosophy (Parmenides, Zeno etc) are size, form, position, movement (change) and time. To a human, those ideas tie to something evident. An alien may not have them at all. An alien closely resembling humans may have them (as well as math).
If those aliens are able to understand notions such as momentum, it would be because they can (in whatever way; sense or other) understand more fundamental notions which may be non-cosmic. Some good examples of such notions, from Eleatic philosophy (Parmenides, Zeno etc) are size, form, position, movement (change) and time. To a human, those ideas tie to something evident. An alien may not have them at all. An alien closely resembling humans may have them (as well as math).