Law of the conservation of mass
The law of conservation of mass states that within a closed system, the total mass remains constant, regardless of the processes taking place in that system. Strictly speaking, this law only applies under certain circumstances, such as when dealing with chemical reactions. Nuclear reactions are exempt from this rule.
The law of Mass Conservation is a development of Lavoisier's experimental discovery that, when all substances were properly accounted for—specifically gases, during the process of combustion—the total weight of a closed system is not changed by a chemical reaction.
Over time, the understanding of this principle has developed. In the early twentieth century it became clear that radioactivity violated both the classic "law of conservation of elements" and the classic "law of conservation of weight." It was found that small changes in mass occur when elements undergo radioactive disintegration. As such, the classic form of the law holds only in situations where relativistic effects are so small as to be considered negligible. Conservation of energy still holds with relativistic effects if we consider mass an expression of energy (or vice versa).
As such, The Law of Mass Conservation is in conflict with traditional Christian teachings,  providing we understand the universe as a closed system, as is usual in science. If some form of interactive substance dualism can be shown to be true, then this assumption would be flawed, and the Law of Mass Conservation would not present a problem to Christian teachings.
- Matter being created by God in Genesis 1:1-31, and destroyed at the End of Days in Revelation 21:1