Actually, it is not. I think that you are talking about the first law of thermodynamics which states that matter can neither be created nor destroyed. Have you taken any science courses at the university level? Maybe this analogy will help. Think of an atomic bomb warhead. It contains a shaped charge surrounding enriched plutonium (P-239). When the charge is triggered, it compresses the plutonium to a critical mass, which then causes the nuclear explosion. What happens to all the materials in that warhead? They're gone, right? Not exactly. Most of the material is converted into energy, therefore showing that the first law is valid.
As for the Universe, the Big Bang, and the first law:
"It really describes a very rapid expansion or stretching of space itself rather than an explosion in pre-existing space. Perhaps a better analogy sometimes used to describe the even expansion of galaxies throughout the universe is that of raisins baked in a cake becoming more distant from each other as the cake rises and expands, or alternatively of a balloon inflating.
"Neither does it attempt to explain what initiated the creation of the universe, or what came before the Big Bang, or even what lies outside the universe. All of this is generally considered to be outside the remit of physics, and more the concern of philosophy. Given that time and space as we understand it began with the Big Bang, the phase “before the Big Bang” is as meaningless as “north of the North Pole”.
"Therefore, to those who claim that the very idea of a Big Bang violates the First Law of Thermodynamics (also known as the Law of Conservation of Energy) that matter and energy cannot be created or destroyed, proponents respond that the Big Bang does not address the creation of the universe, only its evolution, and that, as the laws of science break down anyway as we approach the creation of the universe, there is no reason to believe that the First Law of Thermodynamics would apply."
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https://www.physicsoftheuniverse.com/topics_bigbang.html )
