How to pronounce “law of conservation of energy” in English

It almost has been 100 years since then, and precise observations conducted after the first discovery further validated the relationship between the distance and speed of galaxies.There are many evidences that prove the observations. Since the universe grew from small to big, Let us apply the law of conservation of mass and the law of conservation of energy, for example.The density drops when the volume increases while its mass remains the same.