rarefy
verb [ I or T ] (also rarify) uk/ˈreə.rɪ.faɪ/ us/ˈrer.ə.faɪ/
（使）变得稀薄;（使）变得稀疏
to become less solid or dense; to make something do this
The primordial cosmic soup is full of sound waves compressing and rarefying matter and light. 宇宙原始汤充满了声波，压缩并稀释着物质与光。