Sent_en: 2zh Various measurements give a good estimate of the mass-density of baryons - the neutrons and protons that make up the nuclei of atoms and ions - in the Universe 10 billion years ago.
Sent_yy: 各种测量方法可以很好地估计重子的质量密度。在100亿年前的宇宙中，重子是构成宇宙中原子和离子原子核的中子和质子。