What percentage of the universe's baryonic mass is constituted by hydrogen?

Answer

Approximately 75%

Hydrogen holds the dominant position in the elemental inventory of the cosmos, specifically regarding normal matter. When analyzing the baryonic mass of the universe—which encompasses all protons, neutrons, and electrons—hydrogen is calculated to account for roughly 75% of that total mass. This overwhelming proportion is a direct legacy of the conditions immediately following the Big Bang, where the rapid expansion limited the time available for fusion into heavier elements. Helium forms the next largest component at about 24%, leaving all other elements combined to constitute a mere 1% remainder. This distribution underscores the fact that hydrogen is the foundational material upon which all subsequent cosmic structure is built.

What percentage of the universe's baryonic mass is constituted by hydrogen?

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