There is a balance in the universe, a law of conservation which governs both matter and energy.

"A variation on the law of conservation of energy and matter, or something like that."

From high school physics I remember something about the law of conservation of matter.

By the law of conservation of momentum it must be somewhere.

That would be rather too much to ask of the laws of conservation.

Such a device or system would be against the law of conservation of energy.

The author may also provide you with an experiment to test the law of conservation of mass.

Balancing is required by the law of conservation of matter.

It follows directly from the law of conservation of matter.

That is the law of conservation of matter as I understand it.